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Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 20749
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have a LF24-45-4 garage furnace that seems to function normally

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I have a LF24-45-4 garage furnace that seems to function normally but doesn't produce any heat. I bought this house a year ago and when the original owner left he had the propane tank taken back. I just purchased a 100lb tank, had it filled and I hooked it up to the existing gas line that the old owner had used. Now the furnace fires up and I can see the blue flames going into the heat exchangers, but the output of heat isn't there. I also can see the circuit board light flashing rapidly which indicates normal operation. Any help would be appreciated. Joe

Rick :

Welcome, my name is XXXXX XXXXX I will do my best to help you with your issue.

Does the fan come on?

Customer:

Yes, it almost seems like it's blowing to fast and not allowing heat transfer from the heat exchanger.

Rick :

I don't see any provision for adjusting the fan speed which leaves me to think the main burners aren't firing high enough which could be due to low gas pressure

Rick :

The gas pressure could be low at the burner manifold or possibly the supply pressure could be low

Customer:

Is the 100lb tank adequate for a 45000 btu furnace? For the amount I'll be using the garage (weekends) I didn't want to invest in a huge tank.

Rick :

It's not a question of the tank's volume it's a matter of the regulator pressure setting. This really should be checked with a low pressure gauge that reads in inches WC (water column). Your tank is probably big enough for your purposes

Customer:

Is there anything I can do to check this? Are you referring to the regulator in the furnace? There isn't a regulator at the tank, so I'm assuming it's in the furnace.

Rick :

There should be a regulator between the tank and the unit otherwise you can have pressures that are way too high and could damage the gas control valve. The gas supply pressure should be ~11" wc and the manifold pressure 9.5" WC. You could buy a gauge and check it yourself but you also need to install a regulator at the tank

Rick :

These gauges can be a bit pricey with costs around $50 not uncommon

Customer:

Could that be what's causing the no heat problem, to much pressure? Can this regulator be bought at an RV center? They heat those with propane, right?

Rick :

The high pressure might have damaged the gas control valve and that might be the cause. You need to go to a plumbing supply house and get a regulator that can be adjusted and a gauge if you want to do this. I don't go to RV centers so I don't know if they carry adjustable regulators, they might. If after you install the regulator and set/check your pressures if you still have a problem it could be due to damage to the gas valve.
Here is a link to the manual for your unit. You might find it useful

http://www.lennox.com/pdfs/installation_maintenance/Lennox_LF24_IOM.pdf

Customer:

I just ran across this while I was waiting and it flows 11 wc. What do you think, might possibly work?

Rick :

Yes that's a decent option. I don't like that it's not adjustable but it doesn't really need to be

Customer:

Thanks for your help, I think I'm in the right direction now.

Rick :

You're welcome!

Customer:

I went out and bought a dual stage regulator that was pre set to 11wc. Problem solved, furnace is performing as it should.

Rick :

I glad I could help.

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