Trane XL 90 Question

I have a Trane XL 90 Propane fired furnace. Does anybody have a clue what the output temp should be at the plenum? The problem is my heating bills, I am spending over $1000.00 a month on propane (over 300 Gl) to be chilly all the time. I peformed a test yesterday. The t-stat was @ 65 I turned it up to 68. The burner kicked on and then the fan within 1 minute at 80 degrees. The plenum output temp heated up to a top temp of 99 degrees. My input temp @ the blower is between 62-67. The air at the vents is lukewarm at best. It took about 45-1hr to bring the house up 3 degrees. The heater seems to constantly run for long periods at a time. It would seem to me that the air should be hotter coming out of the furnace for faster warm up and less running time.

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99F is quite low...quite, quite low. BUT, the proper place to check for the supply air temperature (to be fair to the furnace) is at the supply plenum...in other words, at the beginning of the supply trunk, right after the evaporator coil (if you have central A.C., else, right after the furnace on the supply side)

You should be looking at 120-to-130F or so right by the supply plenum.

But if your ducts are bare metal (no inside nor outside insulation) and run through an unconditioned space (such as an attic or unfinished basement), expect a drastic drop in the temperature of the circulating air inside the ducts as it moves thru trunks and branches towards the various registers.

 

Thats what I thought about 120-130. The furnace is where a took the reading, right at the unit itself about 8" above the unit where the supply exits. All the ducts are well insulated throughout the house. (intake & supply)

 

One thing I could think of is that perhaps the selected speed is too high...use a lower speed.

Is this a retrofitted unit? was it perhaps purchased and set from factory for natural-gas operation and not propane? A changeover is possible but a retrofit kit will have to be ordered and installed.

 

The unit is approx. 5 yrs old and I do beleive it was retrofitted, but I will check the paperwork when I get home today to make certain. Is it normal for the blower to kick on so quickly (about 30 seconds after burner) at such a low temp(80) on a cold furnace?

 

These newer furnaces typically have many operating functions governed by its control-board, so it is quite likely that in your case the delay for the blower is time not temperature controlled. The service manual of the unit will tell you if you can adjust the Delay-ON feature of the blower.

 

Thanks for you response. I'm going to check to see if all the burners are operating and put call in to the tech who installed it. Maybe it just needs a tune-up. I will re-post if I find anything out.