What would it take?

K

Ken B

Well-known member
Oct 9, 2002
16,834
279
83
Is there any practical way to run an Duo-therm furnace in a 1978 GMC on natural gas rather than on propane?

If the answer is yes, then is there a practical way to run the furnace on both. Using natural gas when parked and propane on the road?
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
> Is there any practical way to run an Duo-therm furnace in a 1978 GMC on natural gas rather than on propane?
>
> If the answer is yes, then is there a practical way to run the furnace on both. Using natural gas when parked and propane on the road?

Ken,

I have converted more than a few things (not all were great successes) between the two for a number of reasons. Most often there is little more than
a change of the main gas jet and a similar change to the pilot or what ever. If it has no pilot, then that is a non-issue. But, to make the change
fast and simple might be impractical. Someone of our people here was a service guy for Duotherm - I sent him a bunch of parts from the salvage coach
here (Erv Troyer?) - and he may be able to give you a much better answer.

You could always convert the coach's gas system to CNG and then the changeover disappears.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
While most household appliances can be configured to run on either one I doubt you will find any sort of kit for that.

I have converted gas fireplaces and ranges by modifying the orifice size and burner. LP and propane run at different pressures.

I would not want to even try that in an RN furnace. The plumbing alone would be a nightmare. Also, a NG would be even more dangerous than LP. Seen
plenty of RV propane fires but never seen one detonate like our neighbors house did back when I was a kid.

Im guessing you want to use NG for winters at home? If its just for storage? Maybe electric oil radiant heaters?
--
76 Glenbrook
 
Besides orifice sizing you would need some sort of switch gear that would make backfeeding impossible.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Matt C./Ken B:
Matt - The Duotherm service guy you are thinking of is probably Lyle Rigdon - a GMC 6 Wheeler who lives in/near Joliet, IL.
Yes - he would be very helpful regards this discussion.
Mike/The Corvair a holic

Sent from my iPhone

>

>> Is there any practical way to run an Duo-therm furnace in a 1978 GMC on natural gas rather than on propane?
>>
>> If the answer is yes, then is there a practical way to run the furnace on both. Using natural gas when parked and propane on the road?
>
> Ken,
>
> I have converted more than a few things (not all were great successes) between the two for a number of reasons. Most often there is little more than
> a change of the main gas jet and a similar change to the pilot or what ever. If it has no pilot, then that is a non-issue. But, to make the change
> fast and simple might be impractical. Someone of our people here was a service guy for Duotherm - I sent him a bunch of parts from the salvage coach
> here (Erv Troyer?) - and he may be able to give you a much better answer.
>
> You could always convert the coach's gas system to CNG and then the changeover disappears.
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
While it seems many of us have changed back and forth in house and shop heaters and logs, all I ever changed was jet size due to propane delivering more BTUs (per gallon or per cubic foot) than natural gas. It burns less volume per hour than natural gas by a factor of two-to-one. now how to do that in your unit would almost require two separate fire chambers, etc. so as to be able to burn one or the other. without tear down and conversion. probably better to just carry a ng heater and a hookup or fagedaboutit.

jofarr
soddy daisy tn

----- Original Message -----
From: Mike Kelley
Reply-To:
To:
Sent: 11/21/2018 11:29:09 AM
Subject: Re: [GMCnet] What would it take?
________________________________________________________________________________

Matt C./Ken B:
Matt - The Duotherm service guy you are thinking of is probably Lyle Rigdon - a GMC 6 Wheeler who lives in/near Joliet, IL.
Yes - he would be very helpful regards this discussion.
Mike/The Corvair a holic

Sent from my iPhone

>

>> Is there any practical way to run an Duo-therm furnace in a 1978 GMC on natural gas rather than on propane?
>>
>> If the answer is yes, then is there a practical way to run the furnace on both. Using natural gas when parked and propane on the road?
>
> Ken,
>
> I have converted more than a few things (not all were great successes) between the two for a number of reasons. Most often there is little more than
> a change of the main gas jet and a similar change to the pilot or what ever. If it has no pilot, then that is a non-issue. But, to make the change
> fast and simple might be impractical. Someone of our people here was a service guy for Duotherm - I sent him a bunch of parts from the salvage coach
> here (Erv Troyer?) - and he may be able to give you a much better answer.
>
> You could always convert the coach's gas system to CNG and then the changeover disappears.
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
 
When I converted my propane barbicue to natural gas there was an online formula for the correct jet size going by the btu of the device. Natural gas
requires a larger jet size.
--
Roy Keen
Minden,NV
76 X Glenbrook
 
Natural gas (mostly methane) has a lower energy per unit volume than propane which means a larger burner orifice will let the furnace at least work on
natural gas. It may not produce quite as much heat. Remember, methane is lighter than air and will mix with it. While propane will mix, it's
heavier than air and will fall out of the openings in the bottom of the tank cubby in case of a leak. I forget the percentage of natural gas which is
best for a bang, I believe it's under ten percent. The only reason I can see for running natural gas in a coach is if you're homesteading someplace.
In that case, I'd plumb a separate natural gas space heater of the catalyst type and leave the propane to the stove.

--johnny

--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
You have the situation exactly. I want to run the furnace for the next few months on NG. Someone (not me) will be living 4 days a week in the coach.
I do not need the quick changeover but I need to know how to change it to NG. It gets real cold up here at times. Frequently below zero. I would
like to run using the furnace and not some more dangerous portable propane system.

How or where do I find out about changing jet(s)s and possibly the required pressure?
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Ken

I am unfamiliar with a duo therm furnace. Having said that I am VERY familiar with household furnaces. I have installed and worked on hundreds of
furnaces and if this were my project I would locate another gas valve and burner assembly from an identical furnace. I would set one up for propane
and one for NG. Here are some stats for your math work. NG has 1050 btus per cubic foot (from my supplier) propane has 2500 btus per cubic foot. NG
is supplied at 3.50 water column inches and propane is supplied at 11 water column inches. These numbers are assuming that the regulators are set as
such. If you are not dealing with altitude over 2000 feet you can ignore any necessary derating of the orifices. Get a good CO detector and be sure
to check the CO after the furnace is set up and running. Should be 0 at the inside and I like it to be in the 20s to teens at the vent. Then it is
the simple (you will get good at it if you do it often) job of disconnecting the gas flex and changing the burner assembly to switch from one fuel
source to the other. Many propane connectors are left threaded and I would use them to prevent a mix up.

HTH

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
 
What would those who are in the know think about using something like the ace hardware small, ventless combination heater?

https://tinyurl.com/yde5rpof

jofarr, soddy tn

----- Original Message -----
From:
Reply-To:
To:
Sent: 11/25/2018 11:47:17 AM
Subject: Re: [GMCnet] What would it take?
________________________________________________________________________________

Ken

I am unfamiliar with a duo therm furnace. Having said that I am VERY familiar with household furnaces. I have installed and worked on hundreds of
furnaces and if this were my project I would locate another gas valve and burner assembly from an identical furnace. I would set one up for propane
and one for NG. Here are some stats for your math work. NG has 1050 btus per cubic foot (from my supplier) propane has 2500 btus per cubic foot. NG
is supplied at 3.50 water column inches and propane is supplied at 11 water column inches. These numbers are assuming that the regulators are set as
such. If you are not dealing with altitude over 2000 feet you can ignore any necessary derating of the orifices. Get a good CO detector and be sure
to check the CO after the furnace is set up and running. Should be 0 at the inside and I like it to be in the 20s to teens at the vent. Then it is
the simple (you will get good at it if you do it often) job of disconnecting the gas flex and changing the burner assembly to switch from one fuel
source to the other. Many propane connectors are left threaded and I would use them to prevent a mix up.

HTH

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
 
> Ken
>
> I am unfamiliar with a duo therm furnace. Having said that I am VERY familiar with household furnaces. I have installed and worked on hundreds
> of furnaces and if this were my project I would locate another gas valve and burner assembly from an identical furnace. I would set one up for
> propane and one for NG. Here are some stats for your math work. NG has 1050 btus per cubic foot (from my supplier) propane has 2500 btus per cubic
> foot. NG is supplied at 3.50 water column inches and propane is supplied at 11 water column inches. These numbers are assuming that the regulators
> are set as such. If you are not dealing with altitude over 2000 feet you can ignore any necessary derating of the orifices. Get a good CO detector
> and be sure to check the CO after the furnace is set up and running. Should be 0 at the inside and I like it to be in the 20s to teens at the vent.
> Then it is the simple (you will get good at it if you do it often) job of disconnecting the gas flex and changing the burner assembly to switch
> from one fuel source to the other. Many propane connectors are left threaded and I would use them to prevent a mix up.
>
> HTH
>
> Melbo

I guess I understand. I have the furnace apart right not for replacement to the igniter electrode and flame sensing assembly. I am waiting for it to
arrive in the mail.

Are you saying that the gas valve needs to be replaced / changed to accomplish the conversion to NG.

BTW, I was working on an overhead infrared radiant heater just yesterday. The label said the pressure was 14 WC running on NG.

Where do I find it about these calculations.

On the application for gas service the gas company asks if you want 6.5WC, or 2PSIG, or 5PSIG, or 10PSIG.

What is all of this and what parts to I need to order to convert the current furnace to NG.

If I am asking dumb questions, let me know. We are into something I know absolutely nothing about.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Ken

There is a kit to change a gas valve from propane to ng. They are valve specific. There is a meter that is connected to the gas valve to measure the
gas valve output pressure (ie water column inches). Neither of these items are expensive. There should be an orifice on the furnace and it will have a
number on it. That will tell you the size of the opening (the larger the number the smaller the hole). There is a chart that tells how many cubic
feet of gas will pass through the orifice at a specific pressure. If there is more than one orifice you need to divide by that number. A four burner
furnace that is rated at 100,000 btus will only put 25,000 btu's per burner and the orifice needs to be sized accordingly. A 35,000 btu natural gas
furnace with four orifices should only put out 8.33 cubic ft of ng (1050 btu's per cubic ft) or 8,750 btus per orifice. Be sure to check the CO when
you finish and start things up. Orifices openings can be made larger or smaller as necessary.

If you seek the help of a furnace guy be sure he has some grey hair for this kind of thing. If I was closer I would be glad to help BUT I am allergic
to snow. ;)

HTH

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
 
Thanks, I am starting to understand.

There is not that much snow here. First snow of the year was yesterday morning with 1" to 2" on the ground. You can still see the grass in my front
yard and the roads are clean. My southern dog from Alabama loves the snow in the winter time. I always invite Colonel Ken to visit here when it
snows. He never does.

http://www.gmcmhphotos.com/photos/member-galleries/p52861-snow.html

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Better you come HERE!

Ken H.

> Thanks, I am starting to understand.
>
> There is not that much snow here. First snow of the year was yesterday
> morning with 1" to 2" on the ground. You can still see the grass in my
> front
> yard and the roads are clean. My southern dog from Alabama loves the snow
> in the winter time. I always invite Colonel Ken to visit here when it
> snows. He never does.
>
> http://www.gmcmhphotos.com/photos/member-galleries/p52861-snow.html
>
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
When do the hurricane and bug seasons start?
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
You must log in or register to reply here.
GMCMI Fall 2026 Rally
Get your shine on at www.cruzingear.co

Share this page

Share this page
Top Bottom
Back