Lennox G40 Furnace - Convert to LP?

**TyWebb** · 07-06-2007, 09:48 AM

I picked up a nearly new Lennox G40 Furnance from a remodeler friend who had no use for the unit. I've been through the Lennox website and user manuals and cannot find anything about converting this unit to LP (propoane). Can it be done? Is a kit needed?

**PNWbrit** · 07-06-2007, 10:19 AM

Think it's normally just a smaller gas orifice for LP?

The furnace we put in our cabin had them included in the parts baggie.

**Pow4Brains** · 07-07-2007, 01:13 AM

Originally Posted by PNWbrit

Think it's normally just a smaller gas orifice for LP?

The furnace we put in our cabin had them included in the parts baggie.

And usually a lower gas pressure regulator. Natty gas runs at about 3.5” of water column vs. 7-11ish for propane. Give Lennox a call, I’m sure they make a retrofit kit.

**Snow Dog** · 07-07-2007, 10:15 AM

Originally Posted by Pow4Brains

And usually a lower gas pressure regulator.

True but the regulator is usually provided by the gas supplier -- i.e. it's attached to my gas meter.

While browsing around I did find this CozyParts Lennox forum which probably has more expertise about your conversion. I did find out there's more to it than changing some jets -- there's "combustion shutters" to control the air flow and extra safety switches (like low pressure). Lennox furnaces are shipped as NG and converted to LP in the field. The kits aren't available to the general public; only licensed installers.

**Pow4Brains** · 07-07-2007, 10:55 AM

Originally Posted by Snow Dog

True but the regulator is usually provided by the gas supplier -- i.e. it's attached to my gas meter.

You are right about having a regulator at your meter. This regulator usually brings the city/utility pressure from 2# down to 11-15”. As stated above, normal running pressure for a natural gas appliance is roughly 3.5”. Most newer furnaces have the regulator located in a “combination gas valve” (because it's also the device that opens and closes the gas flow on a call for heat.) Sometimes they are adjustable, sometimes you can change the spring in the regulator and sometimes you gotta replace the whole thing. Eitherway, make sure after you do the conversion to clock the gas meter with the furnace running on high to verify the input. 1 Cft of natty gas is 1000 BTUs. Good luck!

**TyWebb** · 07-09-2007, 01:29 PM

Thanks for the info - through that forum I found a dealer close to me willing to sell the conversation kit. I called around to Lennox dealers, but they all insisted on doing the install themselves. That one shop sold it outright for $50. We're in business!