Luxaire gas orifice change

Jim Davis_7

If your furnace is over-fired it also could be very dangerous. Did you do a combustion test? What is your plenum temperature?? I would probably lower gas pressure but not without a combustion analyzer. That is like lighting a stick of dynamite blindfolded.

Riverrat35

Luxaire gas orifice change

I have a Luxaire gas furnace 80% model GM8S130D20UH11B.The furnace shuts down fter a few minutes on over temperature.The btu value is very high , 1167 btu's per scf dry.The installed burner orifice is #45.Can I cut down the heat output with smaller orifices,or cut gas pressure to burner.Luxaire says to change orifices but won't tell me what size because I'm not a certified installer with them.I have my own HVACR Business (20 years).My theory is this unit was simply oversized

Steve Ebels_3

Had to read that twice

Where in the blazes are they pumping gas with 1167btu/Ft?

First thing I'd look at is the duct system. You mentioned oversizing and you can look at that two ways with F/A. The furnace can be oversized for the house and still not trip the high limit. BUT! if it's oversized for the duct system, now you have a problem. As long as you're getting enough airflow to keep the thing operating at required temps all you'll have is short cycling. I'd suspect that you'd have to reduce the input so far that it wouldn't be practical if the duct system is undersized. You can only cut your primary air so much to compensate for the reduced fuel supply.

Before you adjust fuel pressure or volume, see what the CFM of the system is. From the model number it looks like the furnace has a 5T blower which means that even in heating mode you should still be getting 1,400-1,600CFM.


You could try the gas pressure route but check your flue temp and gases with an analyzer to see if all parameters remain as they should.

Riverrat35

This furnace is in Pa lots of gas wells in area.customer had gas analized professionally.Has methane ethane and a host of other anes (lol)in it.I havent seen system yet.Im guessing duct system is not getting the heat out of the furnace as you sugested

flange

you should be able to get this system in line using an analyzer. setting the gas to 3.5 isn't the answer. this is a starting point only and needs to be checked. even luxaire will tell you that if you ask. they assume that you already did that.

Riverrat35

Thanks for the help. I think I,ll leave this one to someone else.this has the potential to become a ten year headache.

Techman

LuxAire

Or you could become the hero!!!!

jw734

wife

where is orifice located on luzaire furnace