... the heat output is low.


Centurion Furnace, 75,000 btu., with AC
Thermostat works correctly, starts/stops correctly.
Furnace starts correctly, blue flame shooting ~5-6 inches into the heat exchanger
Wind blows from all vents as expected, and the same as when working.
Air temp is very low, a few degrees above intake air.
Furnace worked correctly for entire season, as above, except with warmer air and able to achieve 75 degree home temp in 28 degree weather, from cold to warm in ~1-2 hours.


PROBLEM: Now furnace can run non-stop and not achieve a 70 degree house temp increase in 50 degree weather. Takes hours of running to get about 68 and will keep running to maintain that temp.

Note:


Changed filter
See that the fan that draws heat through heat exchanger working
Feel warm exchanger exhaust pipe tht goes through roof
Removed entire heat exchanger and noted mildly dusty with no rust (4% humidity here in the high desert) and slight oxidation.
Washed heat exchanger inside and out, and removed oxidation with green scotchbrite pad.
Vacuumed out heavy coat of dust/buildup on AC condensor in Furnace. (This cause air output to increase marginally (5-10%) and zero affect on air temp heat out.
AC works perfectly.
All vents air temperature is the same, low level.
All vents air speed is proportionate to the vent/duct size


I have no idea how air can blow by a clean and apparently hot heat exchanger but reach the interior at ~75 degrees. I would call someone out to help but I can see me paying for a service call and having a dundering chowderhead try to sell me a furnace because he cannot figure out the problem. I am no Rocket Surgeon but a furnace looks pretty straight forward to me, SO ANY HELP WOULD BE GREATLY APPRECIATED!

Thanks Folks,

Karl

First thing that needs to be done is a gas pressure test to see if the furnace is firing at the correct rate. This requires a gas pressure testing tool. The furnace label will tell what the inches of water column should be. If this is off the furnace will not heat to its capacity.

A simpler test below

Take a thermometer and measure the air going into the return air. Then measure the temperature coming out of the heat vents. Post those numbers and also look on the furnace tag for a temp rise figure and post that also.

First thing that needs to be done is a gas pressure test to see if the furnace is firing at the correct rate. This requires a gas pressure testing tool. The furnace label will tell what the inches of water column should be. If this is off the furnace will not heat to its capacity.

A simpler test below

Take a thermometer and measure the air going into the return air. Then measure the temperature coming out of the heat vents. Post those numbers and also look on the furnace tag for a temp rise figure and post that also.


Thanks for the quick reply! Ok, I will get a gas pressure testing meter. Do I measure this on the propane tank side of the furnace gas valve or the output (burner) side?

Propane, eh? If this problem developed suddenly, there may be a problem with the regulator on the LP tank.

Measure at the gas valve. It has a small fitting. Do the thermometer test first and post results.

Propane, eh? If this problem developed suddenly, there may be a problem with the regulator on the LP tank.

Thank you for the help. First reply steered me to low gas input possibility, from there the above got me thinking about the regulator at the outdoor propane tank.

Dead on Target. Propane Regulator at tank was exchanged with an old one from the neighbor (much older than the known 20 year old neighbors), propane flame output now 3x previous output level.

Heat output now reaches level as remembered from before. Then about 10 seconds later...

Now (and OMG!) nice blue smoke immediately and lightly drifts from all vents, likely from a crack that was not detected due to the previously vastly reduced flame (1.25"x 6" x 3 burners versus 2.5" x 7"+ x 3 burners) . Furnace shut down and removed from gas supply, then the heat exchanger was removed again and a tiny crack detected (1 " long directly above flame at middle of three burners was now seen and was most likely there undetected during the previous removal and cleaning.)

So Now I need a new heat exchanger.

If anyone can steer me to a site that sells these that would rock :D

Thanks for all the help!

Blue smoke? What's the problem, blue is a nice color... you may get your hands on a replacement h/x more quickly if you can find a distributor nearby.

Centurion is York is Coleman is UPG is Source One for some parts etc. In other words the no exact model number furnace you have might be able to be serviced by many different part numbers since most of the furnaces made by the different companys listed above are the same furnace with just a different name. There was also a warranty on the heat exchanger for 10 to 20 years depending upon the model number.

Here is where you might run into a problem. Since you are not a HVAC contractor it might be very difficult for you to obtain a heat exchanger. Usually that part and others will not be sold to a home owner but you never know for sure till you ask them.

Centurion is York is Coleman is UPG is Source One for some parts etc. In other words the no exact model number furnace you have might be able to be serviced by many different part numbers since most of the furnaces made by the different companys listed above are the same furnace with just a different name. There was also a warrenty on the heat exchanger for 10 to 20 years depending upon the model number.

Here is where you might run into a problem. Since you are not a HVAC contractor it might be very difficult for you to obtain a heat exchanger. Usually that part and others will not be sold to a home owner but you never know for sure till you ask them.

Hehe, OK thanks for the help with the cross branding information, I will see how interested the local heating and AC place is about making a sale during the current economy. My nieghbor knows a guy that would get the thing for me if I run into the usual "all home owners will blow themselves up" parts guy.

Will update results after received and installed :D Thanks Folks!

It is more of a liability issue than anything else. A friend of mine owns a parts house and his liability policy limits him from selling to non trade individuals. He says the risk to sell retail is too great so he never sells unless the HVAC company has a vendors number and provides a copy of the vendors card listing that the contractor is in the HVAC biz. For each account he has on his books there is a file with a copy of the vendor certificate. Ten years ago the wife of the husband that injured himself working on a furnace sued the manufacturer and the supplier of the gas valve that since it was hooked up wrong dang near blew his head off. It was a nasty case and I was called in as a PW (professional witness). By the time it was over with lawyer fees and settlement/award from court the total cost was near 1.5 million dollars. This is the reason non trade people have a hard time getting parts. A heat exchanger installed wrong without the proper tools (CO tester etc.) can kill you so you can see why they might be hesitant to sell it.

I hope you get one way or the other you seem to be on the ball and you should not have a problem with the install. Just make sure to use new factory gaskets or in some cases very good quality RTV to seal that unit up.

It is more of a liability issue than anything else. A friend of mine owns a parts house and his liability policy limits him from selling to non trade individuals. He says the risk to sell retail is too great so he never sells unless the HVAC company has a vendors number and provides a copy of the vendors card listing that the contractor is in the HVAC biz. For each account he has on his books there is a file with a copy of the vendor certificate. Ten years ago the wife of the husband that injured himself working on a furnace sued the manufacturer and the supplier of the gas valve that since it was hooked up wrong dang near blew his head off. It was a nasty case and I was called in as a PW (professional witness). By the time it was over with lawyer fees and settlement/award from court the total cost was near 1.5 million dollars. This is the reason non trade people have a hard time getting parts. A heat exchanger installed wrong without the proper tools (CO tester etc.) can kill you so you can see why they might be hesitant to sell it.

I hope you get one way or the other you seem to be on the ball and you should not have a problem with the install. Just make sure to use new factory gaskets or in some cases very good quality RTV to seal that unit up.

Hehe I hear you on the liability issue, I'd have no problem signing away my rights. Yep my heat exchanger had but one micromillimeter gasket at that h/e exhaust fan perimeter and another press type fiberglass foil gasket at the cover but none around the input tubes to the h/e, which has me wondering if the new "superflame" was slipping around the input tubes and going straight into the box. I mean the blue smoke filled the house but the crack was tiny.

That could be a possibility

Xxx