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#1
Posted to alt.home.repair
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Furnace Air Filter Questions
My 95.5% Gas furnace came with a fiberglass air filter
with little restriction and no filtering action. I substituted a Filtrete allergy reduction filter and went about my business. Been running that way for 2 years. In my filter search today, I found a gauge that tells you when to change the filter by monitoring negative pressure near the blower inlet. It says it can be calibrated for 0-.4"WC. I did some measurements on my system. With the filter removed and the filter door open, I measured -0.1"WC. I measured with my Filtrete installed and with a lesser MERV9, I think, filter then a washable permanent electrostatic filter. All measured -.55"WC. With the filter access door closed, it goes up to -0.6"WC. That's outside the calibration range of the filter monitor gauge, so it got me thinking. I don't have a fiberglass filter to compare. I also measured some temperatures. With indoor temperature at 65F, the air coming out of the closest vent stabilizes at 119F. It's about 12' from the furnace and the ducts are insulated, so it should be somewhere near the furnace output temperature. Looks like I'm getting 60F rise across the furnace. That's near the max claimed in the spec. Another thing is that I don't heat part of the house. Three registers are closed. Last time I did the experiment, heating the whole house cost me almost 50% more in gas. So, I don't want to heat the whole house. I need the better air filters. Should I worry about overheating the furnace? Is there anything simple I can to about it? Like turn up the blower speed? I do have an electronic filter that's designed to replace the 1" paper filter. I'd have to cut it down to fit. Looks like it has about as much material as the original fiberglass filter, so should have lower pressure drop. Is that a viable alternative? It's not clear how they compare at removing pollen. It's hard to decide based on the vague marketing hype. Thanks mike. |
#2
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Furnace Air Filter Questions
mike wrote: My 95.5% Gas furnace came with a fiberglass air filter with little restriction and no filtering action. I substituted a Filtrete allergy reduction filter and went about my business. Been running that way for 2 years. In my filter search today, I found a gauge that tells you when to change the filter by monitoring negative pressure near the blower inlet. It says it can be calibrated for 0-.4"WC. I did some measurements on my system. With the filter removed and the filter door open, I measured -0.1"WC. I measured with my Filtrete installed and with a lesser MERV9, I think, filter then a washable permanent electrostatic filter. All measured -.55"WC. With the filter access door closed, it goes up to -0.6"WC. That's outside the calibration range of the filter monitor gauge, so it got me thinking. I don't have a fiberglass filter to compare. I also measured some temperatures. With indoor temperature at 65F, the air coming out of the closest vent stabilizes at 119F. It's about 12' from the furnace and the ducts are insulated, so it should be somewhere near the furnace output temperature. Looks like I'm getting 60F rise across the furnace. That's near the max claimed in the spec. Another thing is that I don't heat part of the house. Three registers are closed. Last time I did the experiment, heating the whole house cost me almost 50% more in gas. So, I don't want to heat the whole house. I need the better air filters. Should I worry about overheating the furnace? Is there anything simple I can to about it? Like turn up the blower speed? I do have an electronic filter that's designed to replace the 1" paper filter. I'd have to cut it down to fit. Looks like it has about as much material as the original fiberglass filter, so should have lower pressure drop. Is that a viable alternative? It's not clear how they compare at removing pollen. It's hard to decide based on the vague marketing hype. Thanks mike. Hi, I think you should do the measurement with all the registers open. I use EAC only on our furnace. I clean the elements twice a year. |
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#5
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Furnace Air Filter Questions
On 2/10/2012 11:31 AM, radiotom wrote:
Tony Hwang;2799305 Wrote: mike wrote:- My 95.5% Gas furnace came with a fiberglass air filter with little restriction and no filtering action. I substituted a Filtrete allergy reduction filter and went about my business. Been running that way for 2 years. In my filter search today, I found a gauge that tells you when to change the filter by monitoring negative pressure near the blower inlet. It says it can be calibrated for 0-.4"WC. I did some measurements on my system. With the filter removed and the filter door open, I measured -0.1"WC. I measured with my Filtrete installed and with a lesser MERV9, I think, filter then a washable permanent electrostatic filter. All measured -.55"WC. With the filter access door closed, it goes up to -0.6"WC. That's outside the calibration range of the filter monitor gauge, so it got me thinking. I don't have a fiberglass filter to compare. I also measured some temperatures. With indoor temperature at 65F, the air coming out of the closest vent stabilizes at 119F. It's about 12' from the furnace and the ducts are insulated, so it should be somewhere near the furnace output temperature. Looks like I'm getting 60F rise across the furnace. That's near the max claimed in the spec. Another thing is that I don't heat part of the house. Three registers are closed. Last time I did the experiment, heating the whole house cost me almost 50% more in gas. So, I don't want to heat the whole house. I need the better air filters. Should I worry about overheating the furnace? Is there anything simple I can to about it? Like turn up the blower speed? I do have an electronic filter that's designed to replace the 1" paper filter. I'd have to cut it down to fit. Looks like it has about as much material as the original fiberglass filter, so should have lower pressure drop. Is that a viable alternative? It's not clear how they compare at removing pollen. It's hard to decide based on the vague marketing hype. Thanks mike.- Hi, I think you should do the measurement with all the registers open. I use EAC only on our furnace. I clean the elements twice a year. I can't really comment on your questions but you've got me thinking. I too use Filtrete filters. I think maybe I should get one of those gauges. Never even occurred to me. Wonder how much I'm wasting. Those gauges can be useful for people who don't have a calendar and a pencil. You can do the same measurement with some plastic tubing and water. Google "manometer". Once you figure out how long a filter lasts in your situation, just mark the calendar to change it. While there's no question that moving air costs money and friction adds to that, I've never seen any apples-to apples numbers that support how much. In any given situation, you have the ratio of the BTU's in the gas supply to the BTU's that end up as heat in the dwelling. For small changes in back pressure, I don't expect that ratio to change much. The blower may use more power...I'd like to hear some real numbers on that. Next time I have the cabinet open, I'm gonna stick a current meter on the blower power and try it with and without the air filter installed. Just gotta figure out how to read the meter through the metal door. The vendors for low restriction filters and gauges use all sorts of marketing speak and misdirection to induce you to buy their stuff. They throw the apples and oranges into the mix and claim it's proof. Here's what I think I know about filters. I'm sure people won't be shy about correcting my misconceptions. For a simple, passive filter, the size of the particles that can be trapped is determined by the pore size of the filter. As the pores get smaller, you can put more pores in the same space. But the filter material has some minimum fiber dimension. At some point, you're down to one fiber width between pores and you can't fit any more in. And there are significant friction effects as the pores get smaller. Pressure goes up for smaller pores, so you have to have more surface area. Pleating is the first thing to do, but even that has it's limits. You can make the filter as large as will fit in the cabinet, but that has limits too. Smaller pores plug up faster. Making the media thicker doesn't help. To reduce pressure, you'd have to make the pores even bigger and not be able to trap the small stuff. Thicker filters can accommodate bigger pleats of the thin media resulting in larger surface area. The solution to this diminishing returns situation is to use technology that traps particles in a way unrelated to their size. Electronic filters use an electric field to force particles to displace out of the air stream and collect on a plate. The electric field has little effect on the air stream, so pressure rise is minimal. This also has tradeoffs, so you usually end up with a passive filter for the big stuff and the electric field for the stuff that gets thru. Now, back to the question that I started in another thread. There is a technology that uses an electric field that does not require external power. I thought the field was created by the triboelectric effect of air passing through insulating media. The only response to that was the rude statement that, "my education was faulty," but no real useful help was provided. The other theory presented was that the electric field was permanently installed at the time of manufacture. That was debunked. I've looked at my sample and can't find any evidence of an electric field. I stuck one on my HRV, but can't tell if it's better than an ordinary filter. That led me to another quest for a particle counter to measure actual results. People who sell passive electrostatic filters say they're terrific. Technical people seem to think they're snake oil. Jury is still out on that one. Are we having fun yet? mike |
#6
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Furnace Air Filter Questions
On Fri, 10 Feb 2012 13:41:57 -0800, mike wrote:
On 2/10/2012 11:31 AM, radiotom wrote: Tony Hwang;2799305 Wrote: mike wrote:- My 95.5% Gas furnace came with a fiberglass air filter with little restriction and no filtering action. I substituted a Filtrete allergy reduction filter and went about my business. Been running that way for 2 years. In my filter search today, I found a gauge that tells you when to change the filter by monitoring negative pressure near the blower inlet. It says it can be calibrated for 0-.4"WC. I did some measurements on my system. With the filter removed and the filter door open, I measured -0.1"WC. I measured with my Filtrete installed and with a lesser MERV9, I think, filter then a washable permanent electrostatic filter. All measured -.55"WC. With the filter access door closed, it goes up to -0.6"WC. That's outside the calibration range of the filter monitor gauge, so it got me thinking. I don't have a fiberglass filter to compare. I also measured some temperatures. With indoor temperature at 65F, the air coming out of the closest vent stabilizes at 119F. It's about 12' from the furnace and the ducts are insulated, so it should be somewhere near the furnace output temperature. Looks like I'm getting 60F rise across the furnace. That's near the max claimed in the spec. Another thing is that I don't heat part of the house. Three registers are closed. Last time I did the experiment, heating the whole house cost me almost 50% more in gas. So, I don't want to heat the whole house. I need the better air filters. Should I worry about overheating the furnace? Is there anything simple I can to about it? Like turn up the blower speed? I do have an electronic filter that's designed to replace the 1" paper filter. I'd have to cut it down to fit. Looks like it has about as much material as the original fiberglass filter, so should have lower pressure drop. Is that a viable alternative? It's not clear how they compare at removing pollen. It's hard to decide based on the vague marketing hype. Thanks mike.- Hi, I think you should do the measurement with all the registers open. I use EAC only on our furnace. I clean the elements twice a year. I can't really comment on your questions but you've got me thinking. I too use Filtrete filters. I think maybe I should get one of those gauges. Never even occurred to me. Wonder how much I'm wasting. Those gauges can be useful for people who don't have a calendar and a pencil. You can do the same measurement with some plastic tubing and water. Google "manometer". Once you figure out how long a filter lasts in your situation, just mark the calendar to change it. While there's no question that moving air costs money and friction adds to that, I've never seen any apples-to apples numbers that support how much. In any given situation, you have the ratio of the BTU's in the gas supply to the BTU's that end up as heat in the dwelling. For small changes in back pressure, I don't expect that ratio to change much. The blower may use more power...I'd like to hear some real numbers on that. Next time I have the cabinet open, I'm gonna stick a current meter on the blower power and try it with and without the air filter installed. Just gotta figure out how to read the meter through the metal door. The vendors for low restriction filters and gauges use all sorts of marketing speak and misdirection to induce you to buy their stuff. They throw the apples and oranges into the mix and claim it's proof. Here's what I think I know about filters. I'm sure people won't be shy about correcting my misconceptions. For a simple, passive filter, the size of the particles that can be trapped is determined by the pore size of the filter. As the pores get smaller, you can put more pores in the same space. But the filter material has some minimum fiber dimension. At some point, you're down to one fiber width between pores and you can't fit any more in. And there are significant friction effects as the pores get smaller. Pressure goes up for smaller pores, so you have to have more surface area. Pleating is the first thing to do, but even that has it's limits. You can make the filter as large as will fit in the cabinet, but that has limits too. Smaller pores plug up faster. Making the media thicker doesn't help. To reduce pressure, you'd have to make the pores even bigger and not be able to trap the small stuff. Thicker filters can accommodate bigger pleats of the thin media resulting in larger surface area. The solution to this diminishing returns situation is to use technology that traps particles in a way unrelated to their size. Electronic filters use an electric field to force particles to displace out of the air stream and collect on a plate. The electric field has little effect on the air stream, so pressure rise is minimal. This also has tradeoffs, so you usually end up with a passive filter for the big stuff and the electric field for the stuff that gets thru. Now, back to the question that I started in another thread. There is a technology that uses an electric field that does not require external power. I thought the field was created by the triboelectric effect of air passing through insulating media. The only response to that was the rude statement that, "my education was faulty," but no real useful help was provided. The other theory presented was that the electric field was permanently installed at the time of manufacture. That was debunked. They are called ELECTROSTATIC filters. They are not electronic - and they DO work on the electrostatic charge built up by the air flowing through them.. Don't know if triboelectric is the correct term or not - but the darn things work pretty well and are quite low resistance. And they fit directly in place of the 1 inch cheap folded paper or the even cheaper tangled string filters. I've looked at my sample and can't find any evidence of an electric field. I stuck one on my HRV, but can't tell if it's better than an ordinary filter. That led me to another quest for a particle counter to measure actual results. People who sell passive electrostatic filters say they're terrific. Technical people seem to think they're snake oil. I don't sell them, and I've used the real electronic "dust zappers" as well as pleated and fiber filters - The electrostatics are MUCH more effective than the fiber or paper, perhaps not quite as good as the expensive electronic units. I've also found "treated" fiber filters work pretty good. I used to have a can of spray that made the fiber ones act like an electrostatic. But the darn stuff wasn't cheap, and you could not wash and re-use the filters like you can the electrostatic. Jury is still out on that one. Are we having fun yet? mike |
#7
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Furnace Air Filter Questions
On 2/10/2012 6:23 PM, wrote:
On Fri, 10 Feb 2012 13:41:57 -0800, wrote: On 2/10/2012 11:31 AM, radiotom wrote: Tony Hwang;2799305 Wrote: mike wrote:- My 95.5% Gas furnace came with a fiberglass air filter with little restriction and no filtering action. I substituted a Filtrete allergy reduction filter and went about my business. Been running that way for 2 years. In my filter search today, I found a gauge that tells you when to change the filter by monitoring negative pressure near the blower inlet. It says it can be calibrated for 0-.4"WC. I did some measurements on my system. With the filter removed and the filter door open, I measured -0.1"WC. I measured with my Filtrete installed and with a lesser MERV9, I think, filter then a washable permanent electrostatic filter. All measured -.55"WC. With the filter access door closed, it goes up to -0.6"WC. That's outside the calibration range of the filter monitor gauge, so it got me thinking. I don't have a fiberglass filter to compare. I also measured some temperatures. With indoor temperature at 65F, the air coming out of the closest vent stabilizes at 119F. It's about 12' from the furnace and the ducts are insulated, so it should be somewhere near the furnace output temperature. Looks like I'm getting 60F rise across the furnace. That's near the max claimed in the spec. Another thing is that I don't heat part of the house. Three registers are closed. Last time I did the experiment, heating the whole house cost me almost 50% more in gas. So, I don't want to heat the whole house. I need the better air filters. Should I worry about overheating the furnace? Is there anything simple I can to about it? Like turn up the blower speed? I do have an electronic filter that's designed to replace the 1" paper filter. I'd have to cut it down to fit. Looks like it has about as much material as the original fiberglass filter, so should have lower pressure drop. Is that a viable alternative? It's not clear how they compare at removing pollen. It's hard to decide based on the vague marketing hype. Thanks mike.- Hi, I think you should do the measurement with all the registers open. I use EAC only on our furnace. I clean the elements twice a year. I can't really comment on your questions but you've got me thinking. I too use Filtrete filters. I think maybe I should get one of those gauges. Never even occurred to me. Wonder how much I'm wasting. Those gauges can be useful for people who don't have a calendar and a pencil. You can do the same measurement with some plastic tubing and water. Google "manometer". Once you figure out how long a filter lasts in your situation, just mark the calendar to change it. While there's no question that moving air costs money and friction adds to that, I've never seen any apples-to apples numbers that support how much. In any given situation, you have the ratio of the BTU's in the gas supply to the BTU's that end up as heat in the dwelling. For small changes in back pressure, I don't expect that ratio to change much. The blower may use more power...I'd like to hear some real numbers on that. Next time I have the cabinet open, I'm gonna stick a current meter on the blower power and try it with and without the air filter installed. Just gotta figure out how to read the meter through the metal door. The vendors for low restriction filters and gauges use all sorts of marketing speak and misdirection to induce you to buy their stuff. They throw the apples and oranges into the mix and claim it's proof. Here's what I think I know about filters. I'm sure people won't be shy about correcting my misconceptions. For a simple, passive filter, the size of the particles that can be trapped is determined by the pore size of the filter. As the pores get smaller, you can put more pores in the same space. But the filter material has some minimum fiber dimension. At some point, you're down to one fiber width between pores and you can't fit any more in. And there are significant friction effects as the pores get smaller. Pressure goes up for smaller pores, so you have to have more surface area. Pleating is the first thing to do, but even that has it's limits. You can make the filter as large as will fit in the cabinet, but that has limits too. Smaller pores plug up faster. Making the media thicker doesn't help. To reduce pressure, you'd have to make the pores even bigger and not be able to trap the small stuff. Thicker filters can accommodate bigger pleats of the thin media resulting in larger surface area. The solution to this diminishing returns situation is to use technology that traps particles in a way unrelated to their size. Electronic filters use an electric field to force particles to displace out of the air stream and collect on a plate. The electric field has little effect on the air stream, so pressure rise is minimal. This also has tradeoffs, so you usually end up with a passive filter for the big stuff and the electric field for the stuff that gets thru. Now, back to the question that I started in another thread. There is a technology that uses an electric field that does not require external power. I thought the field was created by the triboelectric effect of air passing through insulating media. The only response to that was the rude statement that, "my education was faulty," but no real useful help was provided. The other theory presented was that the electric field was permanently installed at the time of manufacture. That was debunked. They are called ELECTROSTATIC filters. They are not electronic - and they DO work on the electrostatic charge built up by the air flowing through them.. Don't know if triboelectric is the correct term or not - but the darn things work pretty well and are quite low resistance. And they fit directly in place of the 1 inch cheap folded paper or the even cheaper tangled string filters. What measurement techniques did you use to determine that "they work pretty well"? I'm interested in pollen capture. I cut one down to 64 square inches and stuck it on an experimental Heat recovery ventilator. Put about 20 CFM through it. Velocity is pretty low, so I'd like some info on performance vs air velocity that's creating the electrostatic field. Also wonder how humidity affects it. If you have any links to actual, unbiased engineering tests, I'd like them. If there's an electric field in there, I should be able to detect it. So far, I've not been able to do that. Exactly where is the field supposed to be? A particle counter ought to be able to verify performance instantly. If that could show that they work, you'd think the vendors would publish that video alongside their flashy videos of marketing speak. We've been having rain lately, so the pollen count has gone down. I have no idea whether the filter is doing its job in my application. I've looked at my sample and can't find any evidence of an electric field. I stuck one on my HRV, but can't tell if it's better than an ordinary filter. That led me to another quest for a particle counter to measure actual results. People who sell passive electrostatic filters say they're terrific. Technical people seem to think they're snake oil. I don't sell them, and I've used the real electronic "dust zappers" as well as pleated and fiber filters - The electrostatics are MUCH more effective than the fiber or paper, perhaps not quite as good as the expensive electronic units. The people who sell 'em make wild claims that their electronics are WAY superior to anything else. https://www.toxbox.ca/why-toxbox/ I've also found "treated" fiber filters work pretty good. I used to have a can of spray that made the fiber ones act like an electrostatic. But the darn stuff wasn't cheap, and you could not wash and re-use the filters like you can the electrostatic. Jury is still out on that one. Are we having fun yet? mike |
#8
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Furnace Air Filter Questions
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#9
Posted to alt.home.repair
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Furnace Air Filter Questions
On Feb 10, 2:41*pm, mike wrote:
...snip... Now, back to the question that I started in another thread. There is a technology that uses an electric field that does not require external power. I thought the field was created by the triboelectric effect of air passing through insulating media. *The only response to that was the rude statement that, "my education was faulty," but no real useful help was provided. The other theory presented was that the electric field was permanently installed at the time of manufacture. *That was debunked. I've looked at my sample and can't find any evidence of an electric field.. I stuck one on my HRV, but can't tell if it's better than an ordinary filter. That led me to another quest for a particle counter to measure actual results. People who sell passive electrostatic filters say they're terrific. Technical people seem to think they're snake oil. Jury is still out on that one. Are we having fun yet? mike Yes, term is electrostatic. Triboelectric is the garranteed charge distribution that is caused by forcibly separating dissimilar materials with different electron work functions. Examples are wool to rubber, hair to comb, almost everything some more than others. Electrostatic filters REQUIRE air movement to work. Yes, they work. ...and I'm technical. To be equivalent to electronic air cleaners requires a bit of volume in comparison. From memory, I thought it possible/plausible to create a 'built-in' field during manufacturing, but know that charges would quickly accumulate to null the fields out. You say it was debunked. Was the 'ability' to "...install..." the charge debunked? Or, rather whether it was done by electrostatic filter manufacturers at all? |
#10
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Furnace Air Filter Questions
On 2/11/2012 5:17 AM, Robert Macy wrote:
On Feb 10, 2:41 pm, wrote: ...snip... Now, back to the question that I started in another thread. There is a technology that uses an electric field that does not require external power. I thought the field was created by the triboelectric effect of air passing through insulating media. The only response to that was the rude statement that, "my education was faulty," but no real useful help was provided. The other theory presented was that the electric field was permanently installed at the time of manufacture. That was debunked. I've looked at my sample and can't find any evidence of an electric field. I stuck one on my HRV, but can't tell if it's better than an ordinary filter. That led me to another quest for a particle counter to measure actual results. People who sell passive electrostatic filters say they're terrific. Technical people seem to think they're snake oil. Jury is still out on that one. Are we having fun yet? mike Yes, term is electrostatic. Triboelectric is the garranteed charge distribution that is caused by forcibly separating dissimilar materials with different electron work functions. Examples are wool to rubber, hair to comb, almost everything some more than others. Electrostatic filters REQUIRE air movement to work. Yes, they work. ...and I'm technical. To be equivalent to electronic air cleaners requires a bit of volume in comparison. From memory, I thought it possible/plausible to create a 'built-in' field during manufacturing, but know that charges would quickly accumulate to null the fields out. You say it was debunked. Was the 'ability' to "...install..." the charge debunked? Or, rather whether it was done by electrostatic filter manufacturers at all? The electronic filter creates several kilovolts across about a centimeter or so. I believe you can create a fixed electrostatic field by solidifying a polar polymer in the presence of a strong electric field. Since the distance is tiny, you might even convince yourself that you have similar kilovolts/cm. But does that do any good in a filter application. Wouldn't a dust particle have to actually bang into that molecule to experience any field at all? So, if the electrostatic had any permanent electric field, where is it in the material stack and how would one measure it? I don't have much air volume, so the electrostatic may not work for me even if it does work in a furnace. Might as well build another electronic one and be done with it. A particle counter would settle the question rather easily. I considered buying one of the $10 Sharp optical counter modules, but it looks like what I want to measure would be down in the noise level for that module. The projects built on that module have lots of glitz, but no real numbers. Anybody can detect a cloud of smoke. Optically detecting small amounts of pollen is quite another matter. |
#11
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Furnace Air Filter Questions
On Feb 6, 7:29*am, mike wrote:
My 95.5% Gas furnace came with a fiberglass air filter with little restriction and no filtering action. I substituted a Filtrete allergy reduction filter and went about my business. *Been running that way for 2 years. In my filter search today, I found a gauge that tells you when to change the filter by monitoring negative pressure near the blower inlet. *It says it can be calibrated for 0-.4"WC. I did some measurements on my system. With the filter removed and the filter door open, I measured -0.1"WC. I measured with my Filtrete installed and with a lesser MERV9, I think, filter then a washable permanent electrostatic filter. All measured -.55"WC. With the filter access door closed, it goes up to -0.6"WC. That's outside the calibration range of the filter monitor gauge, so it got me thinking. I don't have a fiberglass filter to compare. I also measured some temperatures. With indoor temperature at 65F, the air coming out of the closest vent stabilizes at 119F. *It's about 12' from the furnace and the ducts are insulated, so it should be somewhere near the furnace output temperature. Looks like I'm getting 60F rise across the furnace. That's near the max claimed in the spec. Another thing is that I don't heat part of the house. Three registers are closed. *Last time I did the experiment, heating the whole house cost me almost 50% more in gas. So, I don't want to heat the whole house. I need the better air filters. Should I worry about overheating the furnace? Is there anything simple I can to about it? Like turn up the blower speed? I do have an electronic filter that's designed to replace the 1" paper filter. *I'd have to cut it down to fit. Looks like it has about as much material as the original fiberglass filter, so should have lower pressure drop. Is that a viable alternative? It's not clear how they compare at removing pollen. It's hard to decide based on the vague marketing hype. Thanks mike. I spray my fiberglass filters with WD40 then set them in the sun to dry so I dont get wd40 in my coils. You just won't believe how ell this works until you try it. Jimmie |
#12
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Furnace Air Filter Questions
On Feb 6, 7:29*am, mike wrote:
My 95.5% Gas furnace came with a fiberglass air filter with little restriction and no filtering action. I substituted a Filtrete allergy reduction filter and went about my business. *Been running that way for 2 years. In my filter search today, I found a gauge that tells you when to change the filter by monitoring negative pressure near the blower inlet. *It says it can be calibrated for 0-.4"WC. I did some measurements on my system. With the filter removed and the filter door open, I measured -0.1"WC. I measured with my Filtrete installed and with a lesser MERV9, I think, filter then a washable permanent electrostatic filter. All measured -.55"WC. With the filter access door closed, it goes up to -0.6"WC. That's outside the calibration range of the filter monitor gauge, so it got me thinking. I don't have a fiberglass filter to compare. I also measured some temperatures. With indoor temperature at 65F, the air coming out of the closest vent stabilizes at 119F. *It's about 12' from the furnace and the ducts are insulated, so it should be somewhere near the furnace output temperature. Looks like I'm getting 60F rise across the furnace. That's near the max claimed in the spec. Another thing is that I don't heat part of the house. Three registers are closed. *Last time I did the experiment, heating the whole house cost me almost 50% more in gas. So, I don't want to heat the whole house. I need the better air filters. Should I worry about overheating the furnace? Is there anything simple I can to about it? Like turn up the blower speed? I do have an electronic filter that's designed to replace the 1" paper filter. *I'd have to cut it down to fit. Looks like it has about as much material as the original fiberglass filter, so should have lower pressure drop. Is that a viable alternative? It's not clear how they compare at removing pollen. It's hard to decide based on the vague marketing hype. Thanks mike. Use the filter the manufacturer recommended for your furnace. Spray it with WD40 before installing, preferably a day before installing so the volatile parts can evaporate. What will be left on the filter is a sticky wax that greatly improve the ability of the filter to do its job. Works unbelievably great. Alternatively you can buy a can of filter coat, much more expensive and in my opinion doesn't work as well. Jimmie |
#13
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Furnace Air Filter Questions
mike wrote:
On 2/10/2012 11:31 AM, radiotom wrote: Tony Hwang;2799305 Wrote: mike wrote:- My 95.5% Gas furnace came with a fiberglass air filter with little restriction and no filtering action. I substituted a Filtrete allergy reduction filter and went about my business. Been running that way for 2 years. In my filter search today, I found a gauge that tells you when to change the filter by monitoring negative pressure near the blower inlet. It says it can be calibrated for 0-.4"WC. I did some measurements on my system. With the filter removed and the filter door open, I measured -0.1"WC. I measured with my Filtrete installed and with a lesser MERV9, I think, filter then a washable permanent electrostatic filter. All measured -.55"WC. With the filter access door closed, it goes up to -0.6"WC. That's outside the calibration range of the filter monitor gauge, so it got me thinking. I don't have a fiberglass filter to compare. I also measured some temperatures. With indoor temperature at 65F, the air coming out of the closest vent stabilizes at 119F. It's about 12' from the furnace and the ducts are insulated, so it should be somewhere near the furnace output temperature. Looks like I'm getting 60F rise across the furnace. That's near the max claimed in the spec. Another thing is that I don't heat part of the house. Three registers are closed. Last time I did the experiment, heating the whole house cost me almost 50% more in gas. So, I don't want to heat the whole house. I need the better air filters. Should I worry about overheating the furnace? Is there anything simple I can to about it? Like turn up the blower speed? I do have an electronic filter that's designed to replace the 1" paper filter. I'd have to cut it down to fit. Looks like it has about as much material as the original fiberglass filter, so should have lower pressure drop. Is that a viable alternative? It's not clear how they compare at removing pollen. It's hard to decide based on the vague marketing hype. Thanks mike.- Hi, I think you should do the measurement with all the registers open. I use EAC only on our furnace. I clean the elements twice a year. I can't really comment on your questions but you've got me thinking. I too use Filtrete filters. I think maybe I should get one of those gauges. Never even occurred to me. Wonder how much I'm wasting. Those gauges can be useful for people who don't have a calendar and a pencil. You can do the same measurement with some plastic tubing and water. Google "manometer". Once you figure out how long a filter lasts in your situation, just mark the calendar to change it. While there's no question that moving air costs money and friction adds to that, I've never seen any apples-to apples numbers that support how much. In any given situation, you have the ratio of the BTU's in the gas supply to the BTU's that end up as heat in the dwelling. For small changes in back pressure, I don't expect that ratio to change much. The blower may use more power...I'd like to hear some real numbers on that. Next time I have the cabinet open, I'm gonna stick a current meter on the blower power and try it with and without the air filter installed. Just gotta figure out how to read the meter through the metal door. The blower being restricted will start to use less power. It will tend to speed up because the air just tumbles. I was wondering if my furnace had a air speed sensor, which could detect flow, being a variable rate fan. Greg The vendors for low restriction filters and gauges use all sorts of marketing speak and misdirection to induce you to buy their stuff. They throw the apples and oranges into the mix and claim it's proof. Here's what I think I know about filters. I'm sure people won't be shy about correcting my misconceptions. For a simple, passive filter, the size of the particles that can be trapped is determined by the pore size of the filter. As the pores get smaller, you can put more pores in the same space. But the filter material has some minimum fiber dimension. At some point, you're down to one fiber width between pores and you can't fit any more in. And there are significant friction effects as the pores get smaller. Pressure goes up for smaller pores, so you have to have more surface area. Pleating is the first thing to do, but even that has it's limits. You can make the filter as large as will fit in the cabinet, but that has limits too. Smaller pores plug up faster. Making the media thicker doesn't help. To reduce pressure, you'd have to make the pores even bigger and not be able to trap the small stuff. Thicker filters can accommodate bigger pleats of the thin media resulting in larger surface area. The solution to this diminishing returns situation is to use technology that traps particles in a way unrelated to their size. Electronic filters use an electric field to force particles to displace out of the air stream and collect on a plate. The electric field has little effect on the air stream, so pressure rise is minimal. This also has tradeoffs, so you usually end up with a passive filter for the big stuff and the electric field for the stuff that gets thru. Now, back to the question that I started in another thread. There is a technology that uses an electric field that does not require external power. I thought the field was created by the triboelectric effect of air passing through insulating media. The only response to that was the rude statement that, "my education was faulty," but no real useful help was provided. The other theory presented was that the electric field was permanently installed at the time of manufacture. That was debunked. I've looked at my sample and can't find any evidence of an electric field. I stuck one on my HRV, but can't tell if it's better than an ordinary filter. That led me to another quest for a particle counter to measure actual results. People who sell passive electrostatic filters say they're terrific. Technical people seem to think they're snake oil. Jury is still out on that one. Are we having fun yet? mike |
#14
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Furnace Air Filter Questions
On 2/11/2012 10:44 AM, gregz wrote:
wrote: The blower being restricted will start to use less power. It will tend to speed up because the air just tumbles. I was wondering if my furnace had a air speed sensor, which could detect flow, being a variable rate fan. Greg You're absolutely right. I had it in my head that the power went up, then headed down as the airfoil stalled. Not so. Just measured an axial fan and a squirrel cage blower. Both powers headed down immediately with restriction. |
#15
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I'm guessing when you say it's been running like that for two years that you've replaced the filter since then? I use the Filtrete allergen filters because I have dust allergies. If you close off the registers in certain rooms, you may want to think about getting baffles to close off the vent runs to make it even more efficient.
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