Hi,

I need some thoughtful thoughts about blower speeds.

First the facts: I have a Sears 105,000 BTU / 84,630 BTU natural gas
furnace in a 1,900 sq ft 2 story house.

The thermostat is a Honeywell programmable with "fuzzy logic".

The blower speed is currently set at "Med-Lo" which is about 1,100
cuft/min or 70% of maximum (1,500 cuft/min) volume.


Question: Would the furnace be more efficient at a higher blower speed?

If so, is there a benefit from adding an outdoor temperature sensor to
trigger the higher blower speed when the outdoor temperature falls
below, say 45 degrees F.?

Any thoughts will be appreciated.

Tom

"T.G. Lambach" wrote in message
...
Hi,

I need some thoughtful thoughts about blower speeds.

First the facts: I have a Sears 105,000 BTU / 84,630 BTU natural gas
furnace in a 1,900 sq ft 2 story house.

The thermostat is a Honeywell programmable with "fuzzy logic".

The blower speed is currently set at "Med-Lo" which is about 1,100
cuft/min or 70% of maximum (1,500 cuft/min) volume.


Question: Would the furnace be more efficient at a higher blower speed?

If so, is there a benefit from adding an outdoor temperature sensor to
trigger the higher blower speed when the outdoor temperature falls below,
say 45 degrees F.?

Any thoughts will be appreciated.

Tom

Don't **** with it. You might blow yourself up.

"Oscar_Lives" wrote in message
news:Lsvif.583390$_o.490100@attbi_s71...

"T.G. Lambach" wrote in message
...
Hi,

I need some thoughtful thoughts about blower speeds.

First the facts: I have a Sears 105,000 BTU / 84,630 BTU natural gas
furnace in a 1,900 sq ft 2 story house.

The thermostat is a Honeywell programmable with "fuzzy logic".

The blower speed is currently set at "Med-Lo" which is about 1,100
cuft/min or 70% of maximum (1,500 cuft/min) volume.


Question: Would the furnace be more efficient at a higher blower speed?

If so, is there a benefit from adding an outdoor temperature sensor to
trigger the higher blower speed when the outdoor temperature falls
below,
say 45 degrees F.?

Any thoughts will be appreciated.

Tom

Don't **** with it. You might blow yourself up.

Stay with alt.hvac where your comments and wiseass remarks are the norm.
This forum is for helping out not competing with the rest of the gang trying
to show just how dumb you are. BTW, have you ever shown your family the
type of trash you spew out at people?

"T.G. Lambach" wrote in message
...
Hi,

I need some thoughtful thoughts about blower speeds.

First the facts: I have a Sears 105,000 BTU / 84,630 BTU natural gas
furnace in a 1,900 sq ft 2 story house.

The thermostat is a Honeywell programmable with "fuzzy logic".

The blower speed is currently set at "Med-Lo" which is about 1,100
cuft/min or 70% of maximum (1,500 cuft/min) volume.


Question: Would the furnace be more efficient at a higher blower speed?

If so, is there a benefit from adding an outdoor temperature sensor to
trigger the higher blower speed when the outdoor temperature falls below,
say 45 degrees F.?

Any thoughts will be appreciated.

Tom

Leave it alone...higher for cooler...slower for warmer...oh..whats the
static pressure for that unit, and whats the heat rise set to?

Blower Range settings: ON 125 and OFF 90

Don't know the actual static pressure, manual gives .2 to .5 range

I'm not looking for trouble, it works well, just ruminating if it could
work better - more efficiently.

"T.G. Lambach" wrote in message
...
Blower Range settings: ON 125 and OFF 90

Don't know the actual static pressure, manual gives .2 to .5 range

I'm not looking for trouble, it works well, just ruminating if it could
work better - more efficiently.

Don't **** with it unless you are a trained technician.

the thermostat that calls for heat is best thought of as an on-off
switch where the demand for heat is requested. could the factor of the
house's heat loss might be better handled with a variable speed blower?
remembering the comfort of your home in winter requires a balance of
temperature and humidity and sufficient oxygen from air changes.
if you blow the heat out of the plenum too fast into the house you will
not enjoy even heating of a close temperature differential of one
degree.
if you blow it out too slow the house will drop below the desired
temperature. get a digital thermometer with high low memory and monitor
the temperature at the thermostat to see how your range varies, and
determine a course of action to zone your home so no room gets excess
heat.

Thanks for your thoughts.

This is Turtle.

What you need to do is get a Service tech out there and set your heat
Rise to about 50 degree F and find out at what speed it should be at.
heat Rise is the difference between the air going into it and the air
coming out.

Now speaking off the hand and no facts to stand on. Set it up higher
and see how it does but you will have to try to measure the heat rise
to not get it too low. 29 degree F or less would be too low and nothing
over 65 degrees F. differencial or heat rise.

Now speaking off hand here , if you can increase the blower speed it
will get the heat out to the rooms faster and then cut off faster. So
it would help a little to speed the blowers.

Now the out door thermostats is for another post here after you get
this right.

TURTLE

Thanks TURTLE, I'll chew on these ideas.
Tom

Now the fun part, measure blower amp draw where it is at, and at your
desired setting, , calculate run time , at present and new setting, run
your Kwh costs to reflect your increase in kwh and decrease in run time
if any. You just lost in electricity costs. For most of the US Kwh are
more expensive than NG so you are a net looser there. Oh did you
increase efficiency of the Ng side, , im sure not enought to matter or
offset the higher Kwh to run the blower. Say your blower takes 375 watts
and runs 8 hrs a day avg and cost is .125kwh, mine is, your present avg
cost is 9 kwh a day or $33.75 a month.

m Ransley errs again:

Now the fun part, measure blower amp draw where it is at, and at your
desired setting, , calculate run time , at present and new setting, run
your Kwh costs to reflect your increase in kwh and decrease in run time
if any. You just lost in electricity costs. For most of the US Kwh are
more expensive than NG so you are a net looser there. Oh did you
increase efficiency of the Ng side...

The heat exchanger will probably be more efficient at the higher airspeed.

Say your blower takes 375 watts and runs 8 hrs a day avg and cost is
.125kwh, mine is, your present avg cost is 9 kwh a day or $33.75 a month.

....8hx375W = 3 kWh, ie 3x$0.125/kWh = $0.375/day or $11.25/mo.

If you increase the airflow from 1100 to 1500 cfm, the blower may use
(1500/1100)^3x375 = 951 vs 375 watts, according to the fan laws. At
1100/1500x8 = 5.9 hours per day, it might use 5.9x951 = 5.6 kWh/day
or 5.6x0.125x30 = $20.92/mo.

Nick

If you only had a clue...

wrote in message
...
m Ransley errs again:

Now the fun part, measure blower amp draw where it is at, and at your
desired setting, , calculate run time , at present and new setting, run
your Kwh costs to reflect your increase in kwh and decrease in run time
if any. You just lost in electricity costs. For most of the US Kwh are
more expensive than NG so you are a net looser there. Oh did you
increase efficiency of the Ng side...

The heat exchanger will probably be more efficient at the higher airspeed.

More efficient? Maybe not.

Say your blower takes 375 watts and runs 8 hrs a day avg and cost is
.125kwh, mine is, your present avg cost is 9 kwh a day or $33.75 a month.

...8hx375W = 3 kWh, ie 3x$0.125/kWh = $0.375/day or $11.25/mo.

If you increase the airflow from 1100 to 1500 cfm, the blower may use
(1500/1100)^3x375 = 951 vs 375 watts, according to the fan laws. At
1100/1500x8 = 5.9 hours per day, it might use 5.9x951 = 5.6 kWh/day
or 5.6x0.125x30 = $20.92/mo.


You are obviously overeducated.

The manufacturers specify a temperature rise for each line (and size) of
furnace. Go out of these lines, you void any warranty. Period. These temp
rise numbers are to get the most heat and longest life out of the heat
exchangers.

Get a life.

"m Ransley" wrote in message
...
Now the fun part, measure blower amp draw where it is at, and at your
desired setting, , calculate run time , at present and new setting, run
your Kwh costs to reflect your increase in kwh and decrease in run time
if any. You just lost in electricity costs. For most of the US Kwh are
more expensive than NG so you are a net looser there. Oh did you
increase efficiency of the Ng side, , im sure not enought to matter or
offset the higher Kwh to run the blower. Say your blower takes 375 watts
and runs 8 hrs a day avg and cost is .125kwh, mine is, your present avg
cost is 9 kwh a day or $33.75 a month.


Don't spew this **** in this group. Take it to alt.hvac where it belongs.
We only want fantasy fairy tale advice in alt.homo.repair.

Oscar_Lives wrote:

"m Ransley" wrote in message
...

Now the fun part, measure blower amp draw where it is at, and at your
desired setting, , calculate run time , at present and new setting, run
your Kwh costs to reflect your increase in kwh and decrease in run time
if any. You just lost in electricity costs. For most of the US Kwh are
more expensive than NG so you are a net looser there. Oh did you
increase efficiency of the Ng side, , im sure not enought to matter or
offset the higher Kwh to run the blower. Say your blower takes 375 watts
and runs 8 hrs a day avg and cost is .125kwh, mine is, your present avg
cost is 9 kwh a day or $33.75 a month.



Don't spew this **** in this group. Take it to alt.hvac where it belongs.
We only want fantasy fairy tale advice in alt.homo.repair.


Let us know when you attain puberty, ok?

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Tom,

1) What is your temperature rise? Should be 40 to 60 degrees. If you
increase air flow, your gas efficiency will go up a little as you
remove more heat from the heat exchanger. Your flue temperature will
go down slightly, increasing combustion efficiency slightly. The
electric efficiency will go down a little as you will use more
electricity to move a little more heat. With a lower temperature rise,
your supply air temperature will go down, which may reduce your
comfort. Now your furnace supply air will feel like that from a heat
pump.

2) How did you measure the air flow? What instruments did you use?


There are tradeoffs to everything you do.

Stretch

He probably actually read that info off the wiring diagram.

"Stretch" wrote in message
oups.com...
Tom,

1) What is your temperature rise? Should be 40 to 60 degrees. If you
increase air flow, your gas efficiency will go up a little as you
remove more heat from the heat exchanger. Your flue temperature will
go down slightly, increasing combustion efficiency slightly. The
electric efficiency will go down a little as you will use more
electricity to move a little more heat. With a lower temperature rise,
your supply air temperature will go down, which may reduce your
comfort. Now your furnace supply air will feel like that from a heat
pump.

2) How did you measure the air flow? What instruments did you use?


There are tradeoffs to everything you do.

Stretch

yep...

measure the hot air temp near the furnace.....

stick a thermometer in the duct somehow...

if it is much over 120 deg F after the furnace has reached full temp...
then a faster blower may be a good thing for you.

But if you don't REALLY know how to re-wire it, you can create
problems...

make sure the saftey function still works,, if the furnace overheats,
the furnace must turn off and the blower turn on...


Mark

"Mark" wrote in message
ps.com...
yep...

measure the hot air temp near the furnace.....

stick a thermometer in the duct somehow...

if it is much over 120 deg F after the furnace has reached full temp...
then a faster blower may be a good thing for you.

Now...if its got an older model, you know the blower wont even start to
about 160 give or take a couple of degrees...right?


But if you don't REALLY know how to re-wire it, you can create
problems...



make sure the saftey function still works,, if the furnace overheats,
the furnace must turn off and the blower turn on...


Not on all models..


Mark

Heatman, you're right, I read the heat rise off the furnace manual, not
a thermometer. This Sears FAG furnace (105,000BTU / 84,630 BTU) was
installed 1987, prior to the AFUE rating system. No changes have been
made from the (125 degree ON and 90 degree OFF) factory settings and
none are contemplated - they're fine.

The blower is now set to run Med. Lo. (1,100 +/- cu ft/min).

The original question was if any BTU efficiency would be gained if the
blower speed were raised to say, Med. Hi. (1,315 cu ft/min).

Our No. Calif. utility is charging $1.79375 / Therm (above a Baseline
quantity) for NG so the monthly bill is focusing my attention on this
subject. Last winter we used about 1,020 Therms.

Tom

"T.G. Lambach" wrote in message
...
Heatman, you're right, I read the heat rise off the furnace manual, not
a thermometer. This Sears FAG furnace (105,000BTU / 84,630 BTU) was
installed 1987, prior to the AFUE rating system. No changes have been
made from the (125 degree ON and 90 degree OFF) factory settings and
none are contemplated - they're fine.


Some of us won't use the term "FAG." Nothing personal, mind you....

Oh, your furnace was rated, but the AFUE rating wasn't that well known.


The blower is now set to run Med. Lo. (1,100 +/- cu ft/min).

The original question was if any BTU efficiency would be gained if the
blower speed were raised to say, Med. Hi. (1,315 cu ft/min).

Check your Delta T and see if it can be changed.

Heatman - Tell me - Delta T????

Tom,

Measure the return air temperature near the furnace with an accurate
thermometer. Your thermometer should read degrees and tenths of
degrees. Take at least 2 readings and get the average. Write it down.

Measure the supply air temperature near the furnace the same way, Take
at least 4 readings and get the average. Make sure all readings are
out of direct sight of the heat exchanger. Write that temperature
down.

Subtract the return air temperature from the supply air temperature.
That is the Temperature Rise or Temperature Difference (TD). Write it
down. Get theBTU per hour OUTPUT rating from the furnace data plate.
Write it down. Put these numbers in the following formula:

BTUs Output / (1.08 * TD) = CFM

This is the ACTUAL CFM of air flow. Note that each fan speed has a
range of air flows. This is called a fan curve. It is usually shown
as a graph or a table. For every pressure difference across the
furnace, there will be a different air flow even though the blower
speed connection has not changet. Each speed connection has a different
fan curve. If you use all the fan speed connections and measure the
air flows as shown above and plot them over the fan curves, you will
get the system curve. The air flow will always be where the system
curve crosses the current fan curve. A duct system with a higher
resistance will result in a lower air flow. When you increase the
resistance, the blower amps will go down! Try measuring the blower
amps and partly covering the return with cardboard to demonstrate that.

If you cannot make the measurements and tests I outlined above, DO NOT
try changing the blower speed connections. You should be able to
measure the results of your efforts if you are going to make any
changes.

Hope this helps.

Stretch

Thanks Stretch!