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#1
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how quickly can a furnace raise house temp 20F?
Just had the blower motor replaced on our York furnace this morning.
Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? |
#2
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how quickly can a furnace raise house temp 20F?
KLS wrote:
Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? 2(+/-) F/hr unless _WAY_ oversized would be pretty typical....you're about right sounds like. -- |
#3
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how quickly can a furnace raise house temp 20F?
On Jan 25, 7:53*pm, dpb wrote:
KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. *The new motor was assigned the task of warming the house from 45F to 65F. *This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? * 2(+/-) F/hr unless _WAY_ oversized would be pretty typical....you're about right sounds like. -- I guess mine is way oversize, i can pick up easily 10 degrees per 1/2 hour. I have the unoccupied downstairs set to 55 over night, & brought up to 68 at 6:30 am. I've never seen it not make 68 by 7:00 even when it is in the 20s outside. |
#4
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how quickly can a furnace raise house temp 20F?
On Sun, 25 Jan 2009 19:30:24 -0800 (PST), Eric in North TX
wrote: On Jan 25, 7:53*pm, dpb wrote: KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. *The new motor was assigned the task of warming the house from 45F to 65F. *This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? * 2(+/-) F/hr unless _WAY_ oversized would be pretty typical....you're about right sounds like. -- I guess mine is way oversize, i can pick up easily 10 degrees per 1/2 hour. I have the unoccupied downstairs set to 55 over night, & brought up to 68 at 6:30 am. I've never seen it not make 68 by 7:00 even when it is in the 20s outside. The length of time the temp was low makes a difference. The thermal mass of the structure and contents make a diference that becomes greater if it has all chilled to match the lower temps. That stuff takes a long time to heat back up. |
#5
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how quickly can a furnace raise house temp 20F?
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#7
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how quickly can a furnace raise house temp 20F?
Eric in North TX wrote:
On Jan 25, 7:53 pm, dpb wrote: KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? 2(+/-) F/hr unless _WAY_ oversized would be pretty typical....you're about right sounds like. -- I guess mine is way oversize, i can pick up easily 10 degrees per 1/2 hour. I have the unoccupied downstairs set to 55 over night, & brought up to 68 at 6:30 am. I've never seen it not make 68 by 7:00 even when it is in the 20s outside. Hmm, Oversized furnace won't be very efficient. |
#8
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how quickly can a furnace raise house temp 20F?
On Tue, 27 Jan 2009 21:14:32 -0700, Tony Hwang
wrote: Eric in North TX wrote: -snip- I guess mine is way oversize, i can pick up easily 10 degrees per 1/2 hour. I have the unoccupied downstairs set to 55 over night, & brought up to 68 at 6:30 am. I've never seen it not make 68 by 7:00 even when it is in the 20s outside. Hmm, Oversized furnace won't be very efficient. No- but if it gets to 30 below then the furnace is designed for a 100 degree temp difference. By design, when it is 20 out the furnace is double the size it needs to be. But most of us have just one furnace. [and those of us with 30 yr old furnaces probably only have one fan speed] Jim [and to save anyone the trouble of posting 'you should replace that old beast' - Maybe I will someday, but it tests at 85%, I know all of its *very simple* parts intimately & I only burn 400 gallons of oil a yr so I'm not in a rush] |
#9
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how quickly can a furnace raise house temp 20F?
a better question is why would one want to raise temperature 20
degrees? if your leaving the home cool to save energy thats good. the OP could add some extra heating like a couple gas wall heaters on a master timer switch to help reheat when you arrive home fast.turn knob trips on extra heat for 30 minutes to help with re heat new furnaces are sized for efficency and lack the BTUs to raise the home fast. adding a wall heater or other gas heater solves that and is a nice back up if your main heating plant fails |
#10
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how quickly can a furnace raise house temp 20F?
On Wed, 28 Jan 2009 08:51:03 -0500, Jim Elbrecht
wrote: On Tue, 27 Jan 2009 21:14:32 -0700, Tony Hwang wrote: Eric in North TX wrote: -snip- I guess mine is way oversize, i can pick up easily 10 degrees per 1/2 hour. I have the unoccupied downstairs set to 55 over night, & brought up to 68 at 6:30 am. I've never seen it not make 68 by 7:00 even when it is in the 20s outside. Hmm, Oversized furnace won't be very efficient. No- but if it gets to 30 below then the furnace is designed for a 100 degree temp difference. By design, when it is 20 out the furnace is double the size it needs to be. But most of us have just one furnace. [and those of us with 30 yr old furnaces probably only have one fan speed] Jim [and to save anyone the trouble of posting 'you should replace that old beast' - Maybe I will someday, but it tests at 85%, I know all of its *very simple* parts intimately & I only burn 400 gallons of oil a yr so I'm not in a rush] That's why I installed a 2 stage furnace. So far it has not been cold enough long enough to require the furnace to run on the high BTU setting (only had it 6? years now) |
#11
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how quickly can a furnace raise house temp 20F?
On Jan 27, 10:14*pm, Tony Hwang wrote:
Eric in North TX wrote: On Jan 25, 7:53 pm, dpb wrote: KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. *The new motor was assigned the task of warming the house from 45F to 65F. *This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? * 2(+/-) F/hr unless _WAY_ oversized would be pretty typical....you're about right sounds like. -- I guess mine is way oversize, i can pick up easily 10 degrees per 1/2 hour. I have the unoccupied downstairs set to 55 over night, & brought up to 68 at 6:30 am. I've never seen it not make 68 by 7:00 even when it is in the 20s outside. Hmm, Oversized furnace won't be very efficient. Depends, Mine is a 96% efficient model, computer controlled. The exhaust is so cool they use PVC to plumb it. I can't see how an undersized one running 24-7 at max capacity could top mine cycling as intended. I've got a 5 ton heating and cooling about 2k fairly well insulated sq ft. My only complaint is; it is a bit noisy on the intake side. |
#12
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how quickly can a furnace raise house temp 20F?
On Jan 25, 7:53*pm, dpb wrote:
KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. *The new motor was assigned the task of warming the house from 45F to 65F. *This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? * 2(+/-) F/hr unless _WAY_ oversized would be pretty typical....you're about right sounds like. -- A minor quibble: 20 degrees in 7 hours is (much closer to) 3 degrees per hour. -- H |
#13
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how quickly can a furnace raise house temp 20F?
On Sun, 25 Jan 2009 20:47:15 -0500, KLS wrote:
Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? You're joking, right? You expect somebody to give you a figure without knowing the size of your furnace or the size of house? Hint: a twenty million BTU furnace is going to warm a dollhouse a bit faster than a bic lighter will warm up the taj mahal. |
#14
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how quickly can a furnace raise house temp 20F?
KLS wrote:
Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? It depends. steve |
#15
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how quickly can a furnace raise house temp 20F?
KLS wrote:
Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? FWIW, I have my programmable thermostat set to let the house cool about 5 degrees during the day when I'm not here, and I think it takes about an hour to bring it back up to temp, so I would say 4-5 degrees per hour isn't unreasonable. Your experience seems to be in the ballpark, particularly given the cold outdoor temperature. As the other posters have pointed out, there are many variables involved -- furnace size, house size, insulation effectiveness, outdoor temperature, etc. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
#16
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how quickly can a furnace raise house temp 20F?
"KLS" wrote in message ... Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? There are many factors. Size of furnace, insulation, number of windows, day or night, opening of the door, amount and type of furnishings, etc. No one can say for sure without a lot of calculations, but that does not seem unreasonable. There was a lot of sensible heat lost that has to be replaced and that takes a lot of time.. |
#17
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how quickly can a furnace raise house temp 20F?
"KLS" wrote in message
... Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? I turn my heat off at nights and when we are not home. If it is 60 in the house, it takes about an hour to warm it up to 72. If it takes 7 hours to warm your house that much, I would wonder if your insulation is particularly poor or if your furnace is undersized. |
#18
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how quickly can a furnace raise house temp 20F?
If this is gas or propane fuel, windows are excellent and insulation
is right, then that is a long time. However, if you have a heat pump, that sounds about right. Activate the emergency heat option which will use the resistive heat strips and watch your electric meter whirl. On Sun, 25 Jan 2009 20:47:15 -0500, KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? |
#19
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how quickly can a furnace raise house temp 20F?
"Tom Kendrick" wrote in message ... If this is gas or propane fuel, windows are excellent and insulation is right, then that is a long time. However, if you have a heat pump, that sounds about right. Activate the emergency heat option which will use the resistive heat strips and watch your electric meter whirl. Usually the heat strips come on anytime you are more than about 3 or 4 deg low. If the heat pump is turned up about 2 deg at a time they will not come on , but if it is moved from 45 to 65 deg then they probably will. Also at 20 deg the heatpump is not too efficiant and it might as well be using the heat strips. |
#20
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how quickly can a furnace raise house temp 20F?
On Jan 25, 5:47*pm, KLS wrote:
Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. *The new motor was assigned the task of warming the house from 45F to 65F. *This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? Funny that you ask this question.....I have to have done the expereiment on three houses Two in Orange COunty, Ca. One is a 1 1/2 story 1930 ....no wall insulation but ~R30 in the attics.....on cold (for SoCal) winter day of about 50F outside, about 5 or 6F degs per hour Second on is a one story ranch iwth blown in cellulose attic insulation......about the same performance the last home is an eastern sierra two story lots of wall & ceiling insulation, propane heat...takes about 3 or 4 hours to go from 55F to 70F your temp rise of 2F deg per hours seems a bit on the low end in my experience but not hugely unreasonable...a furnace needs to be able to maintain the house at a reasonable temperature......how quickly it gets there isn't really all that important. what is the out side temp (I'm guessing in the 20's?) an important thing to check would be the temp rise across the furnace But I'm sure Bubba will jumping right in with a helpful addition (along with his typical serving of insults) to this thread being the furnace expert that he is cheers Bob |
#21
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how quickly can a furnace raise house temp 20F?
On Sun, 25 Jan 2009 20:47:15 -0500, KLS wrote:
Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? If I turned my furnace off & let the house get to 45- then turned it on [while it was 20 with wind] I imagine it would take 1 -1 1/2 hours of running to bring the house up to 65. But my furnace was designed to keep the house at 70 when it was 30below outside- and that was with old, drafty windows & no insulation. If 20 is about as cold as it gets where you live- and if it was 45 for some time so all the mass had to be re-heated- and if you've got room for improvement in your windows and insulation- then don't worry about your furnace. Work on the insulation. You say you "had the blower motor replaced". That implies that some guy who knows a whole lot more about your setup was in your house. What did he/she say? Jim |
#22
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how quickly can a furnace raise house temp 20F?
On Jan 26, 7:48*am, Jim Elbrecht wrote:
On Sun, 25 Jan 2009 20:47:15 -0500, KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. *The new motor was assigned the task of warming the house from 45F to 65F. *This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? If I turned my furnace off & let the house get to 45- then turned it on [while it was 20 with wind] *I imagine it would take 1 -1 1/2 hours of running to bring the house up to 65. But my furnace was designed to keep the house at 70 when it was 30below outside- and that was with old, drafty windows & no insulation. If 20 is about as cold as it gets where you live- and if it was 45 for some time so all the mass had to be re-heated- and if you've got room for improvement in your windows and insulation- then don't worry about your furnace. * Work on the insulation. You say you "had the blower motor replaced". *That implies that some guy who knows a whole lot more about your setup was in your house. What did he/she say? Jim With the house thoroughly chilled to around 50, with an outside temp in the 30s, I'd say my forced air will do about 4 or 5 deg an hour. So, I'd agree that 2 deg an hour sounds on the low side. |
#23
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how quickly can a furnace raise house temp 20F?
On Mon, 26 Jan 2009 07:48:40 -0500, Jim Elbrecht
wrote: On Sun, 25 Jan 2009 20:47:15 -0500, KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? [cut] If 20 is about as cold as it gets where you live- and if it was 45 for some time so all the mass had to be re-heated- and if you've got room for improvement in your windows and insulation- then don't worry about your furnace. Work on the insulation. Yes: when I find time, I'm going to be calling for a polyurethane closed cell insulation install quote for the box band of the house, which should be fairly easy/inexpensive, all factors considered. You say you "had the blower motor replaced". That implies that some guy who knows a whole lot more about your setup was in your house. What did he/she say? The HVAC company that installed the furnace has been here four times in just over 2 weeks. The first time was when the inducer blower died on a Friday night; Saturday morning the tech checked a bunch of things, decided the motor wasn't dead, and propped up the long horizontal PVC exhaust pipes to correct a sag that apparently was preventing gases from exhausting properly. That got the motor going for another two weeks until this past Saturday night when it died again. A second tech came over, checked the system, determined the motor was dead, but was able to get it going again. He told me to call again if it didn't keep working. It died overnight, so I called Sunday morning (yesterday) and told him we really needed to replace the motor, per his diagnosis. He was able to get one and came over to install it, and all was more or less well, except that the house took 7 hours to warm up when it had taken about 3 with the previous motor the previous episode. This morning a third tech came over and replaced the condensate pump (gratis as he broke off something on it) plus the vinyl condensate discharge tubing (which I asked for, as ours was pretty gunked up after almost 6 years in service). We agreed to do this after he found several kinks that I'd asked the first tech about, which that tech dismissed. Anyway, all seems well now; I will be watching tomorrow morning to see how quickly the furnace brings the house to the called-for temp (it took almost 2 hours to bring the house up 5 degrees F this morning and used to take one hour with the old motor). Tonight will be low teens, tomorrow mid teens, so pray for us all! |
#24
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how quickly can a furnace raise house temp 20F?
On Mon, 26 Jan 2009 21:22:47 -0500, KLS wrote:
On Mon, 26 Jan 2009 07:48:40 -0500, Jim Elbrecht wrote: On Sun, 25 Jan 2009 20:47:15 -0500, KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? [cut] If 20 is about as cold as it gets where you live- and if it was 45 for some time so all the mass had to be re-heated- and if you've got room for improvement in your windows and insulation- then don't worry about your furnace. Work on the insulation. Yes: when I find time, I'm going to be calling for a polyurethane closed cell insulation install quote for the box band of the house, which should be fairly easy/inexpensive, all factors considered. You say you "had the blower motor replaced". That implies that some guy who knows a whole lot more about your setup was in your house. What did he/she say? The HVAC company that installed the furnace has been here four times in just over 2 weeks. The first time was when the inducer blower died on a Friday night; Saturday morning the tech checked a bunch of things, decided the motor wasn't dead, and propped up the long horizontal PVC exhaust pipes to correct a sag that apparently was preventing gases from exhausting properly. That got the motor going for another two weeks until this past Saturday night when it died again. A second tech came over, checked the system, determined the motor was dead, but was able to get it going again. He told me to call again if it didn't keep working. It died overnight, so I called Sunday morning (yesterday) and told him we really needed to replace the motor, per his diagnosis. He was able to get one and came over to install it, and all was more or less well, except that the house took 7 hours to warm up when it had taken about 3 with the previous motor the previous episode. This morning a third tech came over and replaced the condensate pump (gratis as he broke off something on it) plus the vinyl condensate discharge tubing (which I asked for, as ours was pretty gunked up after almost 6 years in service). We agreed to do this after he found several kinks that I'd asked the first tech about, which that tech dismissed. Anyway, all seems well now; I will be watching tomorrow morning to see how quickly the furnace brings the house to the called-for temp (it took almost 2 hours to bring the house up 5 degrees F this morning and used to take one hour with the old motor). Tonight will be low teens, tomorrow mid teens, so pray for us all! So it is not the "blower motor" that was replaced but the "eductor fan" or "combustion purge fan" |
#25
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how quickly can a furnace raise house temp 20F?
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#26
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how quickly can a furnace raise house temp 20F?
On Sun, 25 Jan 2009 20:47:15 -0500, KLS wrote:
Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house from 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? Depends how many BTUs the furnace output is, as well as how much heat loss the house has. Also depends how much thermal mass. If it needs to heat up a lot of masonry it will take longer than heating up a lot of stud-framed walls with good insulation. |
#27
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how quickly can a furnace raise house temp 20F?
"Bubba" wrote in message ... On Sun, 25 Jan 2009 20:47:15 -0500, KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? You do know you have asked a trick question? With the information you have given, it cant be answered. Here let me give you and example or two so you might understand. Where I live, we design furnaces to maintain an indoor temp of 70 at a 0 degree outdoor design temp. What that means is: If my furnace is sized properly and my indoor temperature is 70 and the outdoor temp is 0, then my furnace will run 24/7 until the outdoor temp begins to raise. If the outdoor temp continues to drop to -10 or -20 below 0 then my house will begin to get colder and colder and I will need to add some type of supplemental heat. On the other hand, with that same furnace, if it is 50 degrees outside and 60 degrees in my home and I want to raise it to 70 I would probably take much less than an hour. What you are interested in is if the motor replacement you just got is set properly. It should be set so that you get the proper "temperature rise through your furnace as stated on the furnace equipment label. Usually a temp in the range of 35 - 70 degrees. More blower speed will lower this temp range. Less blower speed will raise this temp range. Bubba Why would more blower speed lower this temp range? It seems to me that the faster the air, the cooler the air blowing across elements/heat exchanger will be, and the more heat is getting transferred in. |
#28
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how quickly can a furnace raise house temp 20F?
"Zootal" wrote in message More blower speed will lower this temp range. Less blower speed will raise this temp range. Bubba Why would more blower speed lower this temp range? It seems to me that the faster the air, the cooler the air blowing across elements/heat exchanger will be, and the more heat is getting transferred in. Heat a pan on the stove. Quickly smack it with your hand. Now hold you hand for 2 seconds. Now hold your hand on it for 10 seconds. Did the fastest speed give you the most heat? Same with the air blowing across the heat exchanger. There is only a given amount of heat available and the longer the residence time, the hotter it will get and it can them move the heat to another location. Cool air then replaces the heated air. Check this out with your car heater as it warms up on a cold day. Run the blower speed up and down and see how the temperature changes. You may have other issues with your furnace too. You mentioned a sagging PVC pipe, kinks in the condensate drain, other parts were replaced. First, it sounds like a hack did the original install. Some of these little errors may be causing the heat exchanger to cycle off and on too frequently or it is not reaching temperature. While it is nice that the tech can resurrect motors from the dead, I think perhaps, you need a new service company. |
#29
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how quickly can a furnace raise house temp 20F?
On Mon, 26 Jan 2009 22:02:22 -0500, "Ed Pawlowski"
wrote: You may have other issues with your furnace too. You mentioned a sagging PVC pipe, kinks in the condensate drain, other parts were replaced. First, it sounds like a hack did the original install. Some of these little errors may be causing the heat exchanger to cycle off and on too frequently or it is not reaching temperature. While it is nice that the tech can resurrect motors from the dead, I think perhaps, you need a new service company. Well, the furnace was installed in April 2003, and that run of PVC pipe is 20 feet long, so five years of gravity apparently became persuasive. |
#30
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how quickly can a furnace raise house temp 20F?
On Mon, 26 Jan 2009 17:09:24 -0800, "Zootal"
wrote: "Bubba" wrote in message .. . On Sun, 25 Jan 2009 20:47:15 -0500, KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? You do know you have asked a trick question? With the information you have given, it cant be answered. Here let me give you and example or two so you might understand. Where I live, we design furnaces to maintain an indoor temp of 70 at a 0 degree outdoor design temp. What that means is: If my furnace is sized properly and my indoor temperature is 70 and the outdoor temp is 0, then my furnace will run 24/7 until the outdoor temp begins to raise. If the outdoor temp continues to drop to -10 or -20 below 0 then my house will begin to get colder and colder and I will need to add some type of supplemental heat. On the other hand, with that same furnace, if it is 50 degrees outside and 60 degrees in my home and I want to raise it to 70 I would probably take much less than an hour. What you are interested in is if the motor replacement you just got is set properly. It should be set so that you get the proper "temperature rise through your furnace as stated on the furnace equipment label. Usually a temp in the range of 35 - 70 degrees. More blower speed will lower this temp range. Less blower speed will raise this temp range. Bubba Why would more blower speed lower this temp range? It seems to me that the faster the air, the cooler the air blowing across elements/heat exchanger will be, and the more heat is getting transferred in. Something called delta T |
#31
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how quickly can a furnace raise house temp 20F?
Why would more blower speed lower this temp range? It seems to me that the faster the air, the cooler the air blowing across elements/heat exchanger will be, and the more heat is getting transferred in. Something called delta T Delta T is highest when the air flowing over the hot surface is coldest. Max delta T = max heat transferred. This happens when the airflow is fastest because if the air flow is slower, it gets hotter because it is in contact with the heated surface longer. Reduced delta T means less heat transferred from hot surface to air and then to house. Which make me think that you want higher air flow, not lower. |
#32
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how quickly can a furnace raise house temp 20F?
Bubba wrote:
On Mon, 26 Jan 2009 17:09:24 -0800, "Zootal" wrote: "Bubba" wrote in message ... On Sun, 25 Jan 2009 20:47:15 -0500, KLS wrote: Just had the blower motor replaced on our York furnace this morning. Outside temps were 20F today with some wind. The new motor was assigned the task of warming the house 45F to 65F. This took it 7 hours, which seems like a long time. How many degrees per hour is a usual rate of temperature rise for gas forced-air furnace? You do know you have asked a trick question? With the information you have given, it cant be answered. Here let me give you and example or two so you might understand. Where I live, we design furnaces to maintain an indoor temp of 70 at a 0 degree outdoor design temp. What that means is: If my furnace is sized properly and my indoor temperature is 70 and the outdoor temp is 0, then my furnace will run 24/7 until the outdoor temp begins to raise. If the outdoor temp continues to drop to -10 or -20 below 0 then my house will begin to get colder and colder and I will need to add some type of supplemental heat. On the other hand, with that same furnace, if it is 50 degrees outside and 60 degrees in my home and I want to raise it to 70 I would probably take much less than an hour. What you are interested in is if the motor replacement you just got is set properly. It should be set so that you get the proper "temperature rise through your furnace as stated on the furnace equipment label. Usually a temp in the range of 35 - 70 degrees. More blower speed will lower this temp range. Less blower speed will raise this temp range. Bubba Why would more blower speed lower this temp range? It seems to me that the faster the air, the cooler the air blowing across elements/heat exchanger will be, and the more heat is getting transferred in. Hey Zoot. Think of it this way: Lets take a 100,000 btu furnace and pull the blower and motor out of it. Now install a bathroom fart fan in its place. Turn it all on. What happens? You get an extremely high temperature with almost no air movement. Now, lets take that same furnace and install a 4 foot wide 4 blade fan with a 50 hp motor turning at 30,000 rpm. Now tell me how much heat you feel on the outlet side of that furnace. Answer: None It all needs to be done within a range. Thats why motors have 3 and 4 blower speeds. Its so you can set the heating blower speed and cooling blower speed to fall within a temperature rise or drop across the heat exchanger or cooling coil. Clear as mud now or are you one of those guys with an EE degree? Bubba Exactly correct. That info applies in automobiles also . You'll always get colder air from your air conditioner if you drop the blower a notch or two. We (as mechanics) would always measure the temp of an air conditioner with the blower on medium, and the mode on recirc. (max) steve |
#33
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how quickly can a furnace raise house temp 20F?
Exactly correct. That info applies in automobiles also . You'll always
get colder air from your air conditioner if you drop the blower a notch or two. We (as mechanics) would always measure the temp of an air conditioner with the blower on medium, and the mode on recirc. (max) steve Are you going to tell me next that if you take your thermostat out of your car's cooling system that the engine will overheat? |
#34
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how quickly can a furnace raise house temp 20F?
On Jan 27, 9:24*pm, "Zootal" wrote:
Exactly correct. *That info applies in automobiles also . *You'll always get colder air from your air conditioner if you drop the blower a notch or two. *We (as mechanics) would always measure the temp of an air conditioner with the blower on medium, and the mode on recirc. (max) steve Are you going to tell me next that if you take your thermostat out of your car's cooling system that the engine will overheat? No it will run cold and under perform due to not maintaining proper operating temperature at least in the winter. You can overheat one by upping the flow of water to the point that it passes through too quickly to absorb the heat. |
#35
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how quickly can a furnace raise house temp 20F?
x-no-archive:
Are you going to tell me next that if you take your thermostat out of your car's cooling system that the engine will overheat? No it will run cold and under perform due to not maintaining proper operating temperature at least in the winter. CORRECT You can overheat one by upping the flow of water to the point that it passes through too quickly to absorb the heat. NOT CORRECT Mark |
#36
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how quickly can a furnace raise house temp 20F?
Zootal wrote:
Exactly correct. That info applies in automobiles also . You'll always get colder air from your air conditioner if you drop the blower a notch or two. We (as mechanics) would always measure the temp of an air conditioner with the blower on medium, and the mode on recirc. (max) steve Are you going to tell me next that if you take your thermostat out of your car's cooling system that the engine will overheat? I guess i just assumed that anyone with any mechanical knowledge knew that. The water actually runs cooler, but the metal parts run hotter. Especially in the back of the heads on a v-8. The thermostat actually provides a necessary restriction even when wide open that is required to make the proper flow to the back end of the block. If you insist on running no 'stat, the it's best to just take the innards from one and install the outer ring. steve |
#37
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how quickly can a furnace raise house temp 20F?
On Tue, 27 Jan 2009 19:24:06 -0800, "Zootal"
wrote: Exactly correct. That info applies in automobiles also . You'll always get colder air from your air conditioner if you drop the blower a notch or two. We (as mechanics) would always measure the temp of an air conditioner with the blower on medium, and the mode on recirc. (max) steve Are you going to tell me next that if you take your thermostat out of your car's cooling system that the engine will overheat? On SOME cars, they actually WILL. |
#38
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how quickly can a furnace raise house temp 20F?
Exactly correct. That info applies in automobiles also . You'll always
get colder air from your air conditioner if you drop the blower a notch or two. We (as mechanics) would always measure the temp of an air conditioner with the blower on medium, and the mode on recirc. (max) steve So, me make sure I understand. According to what others are saying, the rate at which heat will transfer from a solid to a fluid is not just dependant on the difference in temp between the solid and fluid (delta T), but is also dependant on the speed at which the fluid flows past the solid? IOW, if the liquid is moving, heat transfers slower, and the faster the fluid moves, the slower the heat transfers, even if it means the fluid is coolder then it would be if it was moving slower. Therefore, the solid will be hotter and fluid colder if the fluid is moving? Is this decrease in efficiency linear on the speed of the fluid? |
#39
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how quickly can a furnace raise house temp 20F?
x-no-archive:
So, me make sure I understand. According to what others are saying, the rate at which heat will transfer from a solid to a fluid is not just dependant on the difference in temp between the solid and fluid (delta T), but is also dependant on the speed at which the fluid flows past the solid? IOW, if the liquid is moving, heat transfers slower, and the faster the fluid moves, the slower the heat transfers, even if it means the fluid is coolder then it would be if it was moving slower. Therefore, the solid will be hotter and fluid colder if the fluid is moving? Is this decrease in efficiency linear on the speed of the fluid? Zoot, I think the basic fact that you are missing is that HEAT and TEMPERATURE are not the same thing. Consider a candle flame has a very high temperature but not a lot of heat. A ton of water at 90 deg F has a low temperature compared to the candle flame but the water has a lot more heat. If you slow the airflow down through a furnace, the TEMPERATURE of the air will go up but the total amount of heat will go down a little. If you speed up the airflow the temperature will go down, but the total amount of heat will go up. Heat and temeprature are not the same thing. Bubba, yes I'm an EE. Mark |
#40
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how quickly can a furnace raise house temp 20F?
wrote in message ... x-no-archive: So, me make sure I understand. According to what others are saying, the rate at which heat will transfer from a solid to a fluid is not just dependant on the difference in temp between the solid and fluid (delta T), but is also dependant on the speed at which the fluid flows past the solid? IOW, if the liquid is moving, heat transfers slower, and the faster the fluid moves, the slower the heat transfers, even if it means the fluid is coolder then it would be if it was moving slower. Therefore, the solid will be hotter and fluid colder if the fluid is moving? Is this decrease in efficiency linear on the speed of the fluid? Zoot, I think the basic fact that you are missing is that HEAT and TEMPERATURE are not the same thing. Oh, no, I'm not missing it at all. Let's consider a simple example. Say we have a heating element with some heat source applied to one side of it (gas flame), and air flowing over the other end of this element. The question is, how can I get the maximal amount of energy to pass from the element to the air? The assumption is that the temperature of the house is dependant on 1) how much energy is passing from flame through element into air flowing past it and 2) how much energy is escaping through doors, windows, walls, etc. What we are interested is how much energy we are putting into the house, not how efficient the house is. Let's first look at the side of the element in proximity to the flame. Assume that the gas flame is constant so that a constant amount of energy is available. How much of this energy is going into the element, and how much is going up the chimney? Simple physics tells us that the amount of energy that goes into the element is dependant on the difference between the temperature of the flame and the temperature of the element. If they are both the exact same temp, then all of the energy from the gas flame is going to go up the chimney and get vented outside. If the temp of the element is 10 degress lower then the flame, the a certain constant amount of energy is passing into the element. If it is 20 degrees colder, even more energy is passing into it and again this is a constant amount(we'll get to what is going on at the other end of the element in a bit). The assumptions are that 1) The amount of energy going into the element is dependent on the difference between the temperature of the elemen and the temperature of the flame and 2) the energy going into the element is being dissapated at the other end and is going into the house. Does it stand to reason therefore, that the lower the temperature of the element, the more energy is going from flame into the element, and therefore the more energy goes from the element into the house, and that the difference between the temp of the flame, which we assume for now is constant, and the temperature of the element, is a measure of the amount of energy going into the house? I need agreement on this before I can go any further, otherwise I'm wasting my time and yours |
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