measuring temperature rise on gas furnace

[bblexus]

I have a 20 year old 90% gas furnace. I decided to save some electricity so I had a AO Smith CSL1056 ECM motor installed in my furnace to replace the existing PSC motor. The tech installs the motor and sets up the speed taps for my heat and A/C. For the heat mode he measures the temperature rise on the return side, records it, measures the supply side three inches at the turn where two main ducts branch from the vertical plenum above the furnace. I ask him why there (apparently the guy is snippy cause I'm standing next to him) and he says to keep the probe away from the radiant heat of the heat exchanger, Ok. Checks the static pressure and says good bye. Overnite I'm not liking the blower noise so I call the company back the next day. A different tech comes and measures temp rise on the supply side just above the A coil above the furnace (about 24 inches above furnace), resets heat speed tap lower and leaves. OK, can someone tell me where is the best place to measure that supply side temp rise? Two different techs with two different locations
Please do not make multiple threads/posts on same topic.

[big sky hvac]

I have a 20 year old 90% gas furnace. I decided to save some electricity so I had a AO Smith CSL1056 ECM motor installed in my furnace to replace the existing PSC motor. The tech installs the motor and sets up the speed taps for my heat and A/C. For the heat mode he measures the temperature rise on the return side, records it, measures the supply side three inches at the turn where two main ducts branch from the vertical plenum above the furnace. I ask him why there (apparently the guy is snippy cause I'm standing next to him) and he says to keep the probe away from the radiant heat of the heat exchanger, Ok. Checks the static pressure and says good bye. Overnite I'm not liking the blower noise so I call the company back the next day. A different tech comes and measures temp rise on the supply side just above the A coil above the furnace (about 24 inches above furnace), resets heat speed tap lower and leaves. OK, can someone tell me where is the best place to measure that supply side temp rise? Two different techs with two different locations

For me personally, I check the temp. rise the same way as the first tech did. I try not go directly above the evap. coil if at all possible. What confuses me a little bit though is why would you invest the money in a new blower motor instead of replacing a 20 year old furnace. Life expectancy of a furnace is 15 - 20 years. Your money would have been much better spent on investing in a new furnace rather than putting it into a 20 year old unit, IMO.

[bblexus]

Money was the issue. The furnace is in good shape, been checked out and cleaned every year. The tech said the motor is one of the first things to go out, so thought I would try out the new style motor.

[big sky hvac]

Money was the issue. The furnace is in good shape, been checked out and cleaned every year. The tech said the motor is one of the first things to go out, so thought I would try out the new style motor.

I think you would have been better off saving that money and then installing a new furnace at a later date. Those motors aren't cheap. You spent more money on that motor than what your furnace is worth. Hopefully you don't have any major issues with your furnace and it will last until you do have the funds to replace it. Good luck. Let us know how this new motor affects your electricity bill, it should make a difference. I'm just curious how much. Maybe it'll pay for itself and make the investment worth it.

[firecontrol]

The first guy measured right. The second guy was probably sent out by the company to "resolve" the complaint of too much noise and to make sure you were happy. Only way to do that with just the motor.......... reduce the speed it runs at.

If they adjusted it down but kept the temperature rise within the manufacturers specs....... great! If not, least you're not complaining about the noise anymore and any further calls they can charge for again. IMO

[bblexus]

The first tech's temp rise was about 60-65 degrees where measured and the second tech's was about 70 degrees. The furnace specs calls for 55-85 degree temp rise.

[big sky hvac]

The first tech's temp rise was about 60-65 degrees where measured and the second tech's was about 70 degrees. The furnace specs calls for 55-85 degree temp rise.

Based on what the furnace's temp. rise rating is, 70* would be ideal. This must be an older furnace, I don't know too many new units that have a temp. rise rated that high.

[bblexus]

I went and bought a digital thermometer, turned up the heat, and put the thermometer at the same point above the furnace after 10 minutes warm up.
It measured 142 degrees, and at the turn point (from the first tech's measured location) it measured 128. At the return it was 68 degrees. First location temp rise is 74 degrees and second point temp rise is 60 degrees. Both within the furnace spec's of 55-85. Leave it alone and call it a day? Or call the company?
I don't know what's safe or should I worry? Sure is quieter though as far as blower noise running slower.

[blownfuse99]

Is there a problem with it not heating or something??

[genduct]

It measured 142 degrees, and at the turn point (from the first tech's measured location) it measured 128.
So the coil was "absorbing" some of the heat before it is distributed? OR did the first location "see" some of that radiant heat? 14 degrees in such a short distance is pretty interesting.

[bblexus]

The 142 degrees is measured just above the coil. About 18 inches or so from there where the branch ducts come off the main vertical plenum, right at the turn, about six inches, measured 128 degrees. The first tech said it was away from the radiant heat of the heat exchanger (out of line of sight), which is under the A coil. I just measured where they did.

[blownfuse99]

:det: if it is working good I don't see anything to worry about...

[Piedmont user]

I went and bought a digital thermometer, turned up the heat, and put the thermometer at the same point above the furnace after 10 minutes warm up.
It measured 142 degrees, and at the turn point (from the first tech's measured location) it measured 128. At the return it was 68 degrees. First location temp rise is 74 degrees and second point temp rise is 60 degrees. Both within the furnace spec's of 55-85. Leave it alone and call it a day? Or call the company?
I don't know what's safe or should I worry? Sure is quieter though as far as blower noise running slower.

I'd be interested in hearing what the temperature is above the coil with a radiant heat shield. And to follow-up with what someone else said, you don't really expect that the air temperature dropped 14 °F in a few feet, do you?

[REP]

The first tech did it right,the second tech did it wrong.
As long as the temp rise is in line with the required temp rise you are fine.If the temp rise is too much you will hurt the furnace and add to the premature failure of that furnace.

[bblexus]

The difference of 14 degrees I would imagine being the 142 degrees is 'looking at the heat exchanger' (evaporator coil in between exchanger and gauge) and the test point at the turn (about 3-6 inches where one of the main horizontal ducts connects to the vertical main plenum) in the main duct being 128 degrees not looking at the heat exchanger(out of the radiant heat).
Anyway, I'm going with the first tech's measurements and slower blower speed. Job finished, I think. Thanks guys for all your input.

[bblexus]

Now that my temperature rise is satisfying, I have a question to ask before I call my heating contractor back.
I noticed when the guy was replacing the blower motor, the ECM motor mounted on the blower housing was on the return air filter side of the furnace. I mean the main blower opening was on the opposite side of the filter. Shouldn't that be just the opposite so more air movement comes from the main opening facing the filter? I hope you guys know what I mean.