furnace

[Hube]

Fire Guy; The fan control usually has 2 indicators, one for fan on set at approx 95, and one for fan off set at approx 125. It would appear by your description,(gauge) your High Limit is probably a "fixed" one, but, if it is adjustable it could be set at approx 180-200.MAXIMUM. Check it out.BTW, how's the temp in the house doing.? Hope your not freezing, Hube

[fire guy]

Hube Thanks for all the info, you have been a big help.P S The temp is still not to bad around 16 (c) The good news is its only minus 18 (c) outside. Iam going to change both high limit and fan control units. Fire Guy

[Joel]

New limit may do the same if there is a nother problem first dettermine why it goes off on limit a dirty filter will cause this even

[Altrade]

Not enough heat.

Lukewarm heat coming from duct? The duct is barely warm?
I had the same problem with my Rheem High efficiency furnace.
we called the Gas Company. He tested the gas coming into the house and then to the furnace. He disovered that the gas pressure was not proper.

They calibrated the gas and as more gas pressure was applied to the flames got bigger in the furnace and heat was immediate.

The cause was a flexible copper pipe was installed beween the black gas pipe and the furnace. Some gunk was in this pipe. the gas pressure up to the house was ok. It was in the house that the pipe was 50% plugged with putty like substance.

i hope this helps.

Altrade

[imeduc]

I have to ask here is the filter clean and new. I dont think you have a AC coil there but if so is it clean . The blower wheel is it clean????? The small cup blades in it get dirt build up .That makes them flat and they dont blow the air .you can go off on high limit.
then is the anticipator set right on the tstat. Also if its LP pressure should be set 11" W/C You have lots of ifs ifs here.

ED

My mistakes dont define me they inform me.

[opposablethumb]

Hi Altrade,

Thanks for this post.

I was looking on HomeRepairForum.com for 'exactly' the same problem you posted. When you say that your duct was 'barely warm' - how warm is 'barely'? I have exactly the same problem; if I put my hand on the duct after the furnace has been running for a while the warmth of the metal is almost unnoticable. The vent from my clothes dryer when it's running is much warmer than the uninsulated heating duct coming drectly out of my furnace. The house takes a very long time to heat up, and the 'warm' air coming out of the registers has a slight 'cooling' effect.

The furnace is Rheem 90 Plus high efficency furnace that was installed in October 2001. I purchased the house in December 2004. I called the company that installed the furnace to inspect the problem and when they arrived they told me that high efficency furnaces are cooler - that's what makes them more 'efficient'. They did not test the furnace or the gas supply. The looked at the filter, and turned 'up' the termostat setting and left me a bill for $75.

Then I got my first gas bill and there was nothing about the furnace that would indicate its efficency. The gas bill was as high as my previous house with a 25 year old furnace and single pane windows (I now have a smaller house with thermal windows).

I guess my question is, does anyone know if high efficency furnaces run cooler, and if so, how much cooler? And when the furnace is running, how warm should the ducts be (specifically the ducts closest to the furnace)? If the gas pressure is too low, would that potentially make the furnace so inefficient that I would have a high gas bill?

Thanks for your time.

Daniel Armstrong

quote:Originally posted by Altrade

Not enough heat.

Lukewarm heat coming from duct? The duct is barely warm?
I had the same problem with my Rheem High efficiency furnace....

... calibrated the gas and as more gas pressure was applied to the flames got bigger in the furnace and heat was immediate.

Altrade

[Hube]

Opossablethumb; Generally, a high efficient (90+) furnace will not perform any different temperature-wise than a mid efficient (80). The main difference is the high efficient will normmally consume LESS fuel.
When a T stat calls for heat, the burner will start, and when the air temperature in the unit gets to approx 120 the blower fan will also start. The burner will continue to run until the T stat is satisfied and shuts the burner off. The blower fan will continue to run until the air in the unit is cooled off to approx 95.
If any overheating of the furnace occurs during the burner cycle,(caused by restrictions, dirty filter,dirty ac coil,etc the High limit will shut the burner down (safety)
Some units have pre-set controls, some units have adjustable controls.
Generally a heat cycle goes like this; ,air temperature in the warm air plenum will be in the 125-150 range. The fan should kick in at approx 120 -125 and continue to run until all warm air is expelled from the unit, usually around 95.
A high limit will usually kick out at 180 or so ,depending on the unit,etc.
Any air temp less than, say 90 or so will feel cool at the supply registers.
If you have a probe type thermometer $ 10. check out the temps at the plenum with burner(and running for at least 5 min) on ,and at the closest and furthest supply register .
Post back with these results and we can advise you further.
Also, check to see if you have 'adjustable' fan/on/off and High limit controls. If they are not the adjustable type, record the printed settings on the control.

[imeduc]

opposablethumb If the gas pressure is too low, would that potentially make the furnace so inefficient that I would have a high gas bill?
You bet it makes a lot of differents. The W/C pressure of the gas should be checked all the time.

Also no one said if the filter was clean when the furnace went on and off and didnt get up to temp there.

ED

My mistakes dont define me they inform me.

[Hube]

Yes ,I too do agree that the gas pressure should be checked out.

And it was suggested that the problem could be because of a dirty filter, but if that was true the furnace's air would be quite warm because the High limit would cut the burner off, but only when the temperature is up in the 160 or higher range.