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seangoodwin 01-13-2012 11:12 AM

Bryant Plus 90 398AAV -- Not Enough Heat
 
My furnace isn't producing enough heat. Here is what I mean. When I take the temperate at the registers, I get an average of 85 degrees on the main level and 95 degress on the 2nd story. These readings were taken after the furnace had been running for about 8 minutes. I've timed the cycle as follows:
Flame kicks on and burns 1.5 minutes. Then the Blower kicks on and runs for a total of 10-12 minutes.
The flame kicks off after 9 minutes.
Thermostat is set at 72 degrees.

The furnace appears to be clean. The filter is changed every couple months and is currently clean.

Any ideas on (1) why heat isn't very hot and (2) how to correct this?

REP 01-13-2012 11:41 AM

First, flame on times mean nothing.That will change with the tempature of the outside air.
The most important measurement you did not make and that is the tempature rise through the furnace.
Im don't understand the 10 degree differance between floors unless your basement is cold and your main floor runs need to be insulated.
You also didn't say why you went through all this work.Is the house not coming up to the set tempature??
If the furnace comes on and shuts down several times before set temp is achived then that would be somewhat of a problem,otherwise it would be running fine.

seangoodwin 01-13-2012 12:44 PM

Thanks for the quick reply. I mentioned the burn time because I read on other posts that their system was short cycling (flame on for 2 minutes or so). Temperature Rise = 31 degrees. I measured the temp about 3 feet up on the output side. It is 100. On the return side it is 69. I have the thermostat (digital) set at 72. The temperature in that room does get to 72. It is in the dining room where the vent temperature measures 100. Adjacent rooms get to 69 degrees (vent temperature measures 85 degress). The furnace runs for 10-12 minutes and then usually kicks back on in about 5 or 10 minutes. Outside air temp is 19.

I've cranked the thermostat up to 75 and let the furnace run for a while. I took the temperature again at the vents. Some are blowing out 100 degree air and others are 85 degrees. The 85 degree ones are on the main level (1st floor), except for the dining room where the thermostat is...that vent is 100 degrees. The 100 degree vents are on the 2nd level and in the basement (where the furnace is).

The problem is that the heat coming out of the vents is not really warm at all so the furnace is running a lot more than it used to. Could dirty or misadjusted burners cause this?

REP 01-13-2012 04:50 PM

Is this a new unit?Is it an old unit that worked differantly last year?
I would normally look for a higher temp rise but I don't know the furnace.Without knowing the suggested temp rise I'd just be guessing.
Lacking that I guess I would check gas pressure and blower speed.A slower blower would produce a warmer supply air.
The differance in outlet temps is a result of duct design and not the furnace.

seangoodwin 01-13-2012 05:33 PM

The house was built in 1994. I assume the furnace is original. There aren't any LED code lights or anything so I think it is the original furnace. I'll check the gas pressure -- I was wondering about that.

Doc Holliday 01-13-2012 05:45 PM

I'm confused. A tempereature rise should be taken at the return plenum (or grill) and ONLY at the furnace supply plenum. The difference in those two temperatures is the rise. Outside of that when you measure the temperature of the air coming out of each vent, let's say the one's showing 85 degree air, then that is temperature loss and that would be duct issue.

31 degrees is not a good enough rise. Blower, if not on lowest speed, could be lowered to increase air temp and thus temperature rise but regarldess, it appears that you have ducts leaking or not insulated or something with the ducts happening.

You can expect to lose 1 to maybe 2 degrees at best, not 15.

Doc Holliday 01-13-2012 05:50 PM

And what are you using to determine the temperature? If one of those light guns that refract light than none of your numbers are any good. You need an actual thermometer that you stick in the air flow.

how 01-13-2012 06:07 PM

Maybe I'm missing something but the main complaint that I'm hearing is that the dining room (where the furnace thermostat is located) is reaching the desired temp before some other rooms. This is usually a air distribution issue where one would adjust the heating outlets down in the thermostat room to give other rooms a greater proportion of the furnaces heat before the dining room's asked for temp is reached.
As for the "new" cooler temp out the heating registers. Have you recently switched from an allergy filter to a plain Jane economy filter? The slower the air flow through the heating registers because of a more restrictive air filter, the warmer it will feel for anyone feeling that flow. The faster the air flow because of a cheap filter, the cooler that same air temp will feel.
Anything that slows down that air flow will make the air feel warmer but will also make your furnace less fuel efficient.

seangoodwin 01-13-2012 06:57 PM

Based on Doc Holiday's post, I'm going to borrow a temperature probe tomorrow and get more accurate readings so I can measure the temperature rise. I don't feel like the temperature rise is enough. Or more specifically I feel like the furnace is blowing lukewarm air. I have shut the vent in the dining room so it will no longer affect the thermostat. The temperature feels a bit more evenly distributed but now the furnace runs for even longer to get up to 72 degrees. It is important to note that this was not the case last year. Something has changed. I'm using the same furnace filters (3M pleated) and I change them every 2 months. I haven't messed with any dampers.

It seems like the furnace isn't producing as much heat as it used to. Is that possible?

REP 01-13-2012 07:11 PM

Don't know if this is part of your problem,but thought you should know.
http://hipspro.com/pubs/Furnace-clas...led_notice.pdf

Doc Holliday 01-13-2012 07:12 PM

Quote:

Originally Posted by seangoodwin (Post 821762)
Based on Doc Holiday's post, I'm going to borrow a temperature probe tomorrow and get more accurate readings so I can measure the temperature rise. I don't feel like the temperature rise is enough. Or more specifically I feel like the furnace is blowing lukewarm air. I have shut the vent in the dining room so it will no longer affect the thermostat. The temperature feels a bit more evenly distributed but now the furnace runs for even longer to get up to 72 degrees. It is important to note that this was not the case last year. Something has changed. I'm using the same furnace filters (3M pleated) and I change them every 2 months. I haven't messed with any dampers.

It seems like the furnace isn't producing as much heat as it used to. Is that possible?


I was just searching for the manual for your unit and came across a class action lawsuit which involves your high efficiency furnace. Something you might want to look in to. Possibly the cause of your problem..??

http://www.hipspro.com/pubs/Furnace-...led_notice.pdf

Doc Holliday 01-13-2012 07:14 PM

Quote:

Originally Posted by REP (Post 821774)
Don't know if this is part of your problem,but thought you should know.
http://hipspro.com/pubs/Furnace-clas...led_notice.pdf


I just posted a thread on it. :laughing: dang, what in the heck is going on? I'm glad we don't push those furnaces.

Seattle Inspect 03-07-2012 06:17 PM

Quote:

Originally Posted by Doc Holliday (Post 821778)
I just posted a thread on it. :laughing: dang, what in the heck is going on? I'm glad we don't push those furnaces.

Any update on the furnace recall? I just had a client with same furnace.

and Doc....I'm your Huckleberry. Tombstone on BlueRay, nothing better!


Thanks-
Seattle Inspector


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