Duo Therm Furnace Settings

[Chris McVeigh]

Our Duo Therm - gravity type - furnace does not seem to have any range of temperature settings. Furnace starts well enough, pilot stays on, but when the gas comes on even on the lowest setting it gets too hot after just a few minutes.
Turning the knob does not seem to change the amount of flame as far as I can see.
Any ideas?

[Joe MacDonald]

Do you mean the trailer gets too hot, or the furnace?
in my 1300, i used the furnace to get the trailer warm, then generally left it on pilot till it got too cold, then repeated

[Chris McVeigh]

Do you mean the trailer gets too hot, or the furnace?
in my 1300, i used the furnace to get the trailer warm, then generally left it on pilot till it got too cold, then repeated

Yes the trailer gets too warm. I am trying to find a setting between "pilot" and "min"

[DonDeutsch]

You might try relocating your temperature sensing probe vertically higher in the trailer. Just a thought.

[Dana T]

Our Duo Therm - gravity type - furnace does not seem to have any range of temperature settings. Furnace starts well enough, pilot stays on, but when the gas comes on even on the lowest setting it gets too hot after just a few minutes.
Turning the knob does not seem to change the amount of flame as far as I can see.
Any ideas?

Funny you should ask this question because I was going to ask a very similar one!

I also have a Glen-Aire Duo-Therm gravity furnace -- mine was probably made in 1973. Anyway, like yours it has no thermostat and also has no proportional control -- it's either running full blast or it's just the pilot.

So my question is whether it is reasonable to replace the current control with a thermostatically governed one.

The current control says "General Controls" on the back.

Here are some pictures for mavens like Harry Young and others to look at and comment on:





BTW, I have carefully checked the firebox and made sure it is still airtight -- I don't want to be asphyxiated in my sleep with combustion products.

[Dana T]

There's something wrong with the image insertion function -- I uploaded 4 pictures but one image refuses to display (all I get is the image referance number), and the last image is displaying in an entirely different part of my post than where I placed it. I finally gave up and deleted the image that wouldn't display.

When I try to edit the post it shows the placement is just what I specified, but when the post is displayed "for real" the image is displayed at the end of the post instead of with the other two.

Fiddlesticks!! Now the closeup image of the control isn't displaying properly!

Yet another try at showing the builder's plate:





Whaddya know, it worked!

[Dana T]

Well now that I can see the model number of my furnace so easily, I Googled the following
"duo-therm" "65211-1"
and came up with the following link:
http://www.ntpdistribution.com/PDF/Via/41-...qkchart1of2.pdf

I downloaded the PDF file and I see that furnace 65211-1 uses gas control 41-0640 and has no wall thermostat, but furnace 65211-3 has a wall thermostat and uses gas control 41-0475.

In general, all of the furnaces listed on that page either use gas control 41-0640 and have no wall thermostat, or use 41-0475 and do have a wall thermostat.

Searching for
"41-0475" control
leads me to http://www.rvshop.com/Furnaces_c_1462-7-0.html where I see they have the control for a mere $214.29.

To that we need to add the price of a new thermocouple (this control uses a different one than the current control does) and a wall thermostat.

Several weeks ago in the "Hydro Flame for Trillium 1300" thread Harry Young mentioned Johnstone Supply, which is a chain of HVAC supply stores. Maybe their prices are better than RVShop's.

Sure wish I could find a picture of the 41-0475 control to see if it would fit without too much effort. I'm getting pretty adept at yanking that furnace out and putting it back in....

[Dana T]

The controls I am looking at now are

Honeywell VS820A1336 $125
http://www.pexsupply.com/Honeywell-VS820A1...-NPT-13864000-p

Robertshaw 700-501 $130
http://www.pexsupply.com/Robertshaw-700-50...s-Valve-100-000

Robertshaw 705-501 $58
This one adds thermostatic control to the existing control instead of replacing it entirely.
http://www.southsidecontrol.com/acatalog/P...5_501_1759.html

Remember, each of these controls still requires a wall thermostat (about $25) and a millivolt thermopile (about $35).

The question is whether it is worth sinking $200 into this old furnace or buy something new. What I really like about the old furnace is that it is dead quiet and consumes no battery power.

[Chris McVeigh]

Duo Therm 65810-2





Looking at some old manuals I found that some models had a regulator adjustment screw under the temp control knob - no such luck with mine. Maybe the problem lies with the thermometer not telling the gas to switch off when it gets hot enough. Had a temp of 75 at floor level inside the trailer the other day and the heat was still pouring out.

Does anyone else have better luck with their gravity type furnace.
I must admit we have had the trailer in the family for over 30 years and we have never been able to just let the furnace run.

[Raya]

Chris,

I'm thinking from your last post that you do have the operating instructions for your furnace. But if not, I have a copy of them in front of me and could perhaps answer a question. What I have is "Duo-Therm Owners Operation Instructions for Direct Vent Heaters" [Form No. 19-424-7]

It looks like even the model(s) with no thermostat do have temperature control via the black dial shown in your photo.

Raya

[David Tilston]

Originally Posted by Raya

Chris,

I'm thinking from your last post that you do have the operating instructions for your furnace. But if not, I have a copy of them in front of me and could perhaps answer a question. What I have is "Duo-Therm Owners Operation Instructions for Direct Vent Heaters" [Form No. 19-424-7]

It looks like even the model(s) with no thermostat do have temperature control via the black dial shown in your photo.

Raya

Raya,

Could you please post the instructions that you have? My trailer did not come with any instructions.

[Donna D.]

Originally Posted by David Tilston

Raya,

Could you please post the instructions that you have? My trailer did not come with any instructions.

David, just so you don't think you're being ignored, it's possible we won't hear anything from Raya... she had Last Activity: 03-07-2011 12:38 PM on FiberglassRV. We miss her.

[David Tilston]

Originally Posted by Dana T

Sure wish I could find a picture of the 41-0475 control to see if it would fit without too much effort. I'm getting pretty adept at yanking that furnace out and putting it back in....

Actually, here are pictures of each from the web site that you linked to. The first one is a 41-0475:

[Rick G]

Originally Posted by Dana T

The controls I am looking at now are

Honeywell VS820A1336 $125
http://www.pexsupply.com/Honeywell-VS820A1...-NPT-13864000-p

Robertshaw 700-501 $130
http://www.pexsupply.com/Robertshaw-700-50...s-Valve-100-000

Robertshaw 705-501 $58
This one adds thermostatic control to the existing control instead of replacing it entirely.
http://www.southsidecontrol.com/acatalog/P...5_501_1759.html

Remember, each of these controls still requires a wall thermostat (about $25) and a millivolt thermopile (about $35).

The question is whether it is worth sinking $200 into this old furnace or buy something new. What I really like about the old furnace is that it is dead quiet and consumes no battery power.

Hi Dana,
To respond to your last question first, in my opinion it is definitely worth saving the furnace and putting in a new control device. These gravity feed furnaces are great for not using battery power when boon docking, so that all you need is gas to run them. Very reliable, last a long time.

As for the replacement, you have the most basic type of control, simple off/on with no temperature control. You can also get one where you set the temperature manually and a bulb sensor regulates the heat according to the manual setting. You can also get the cream of the crop, a control that responds to a millivolt thermostat mounted elsewhere in the trailer.

I have worked on some of my furnaces in different trailers, and friends’ as well. It seems to me that they are very basic in the controls, and also very forgiving. Since the furnace is basically an empty box with an orifice and burner controlled by a gas module, you should be able to put a similar type gas controller in it without any problems, if it can be made to physically fit in the space available.

For example, in my prior Boler, my original Wagonmaster furnace controls were replaced in 2004 by a new Mertik Maxitrol GV-30 series controller (see picture). That controller is still currently sold, so obviously it was not designed for my 1974 Boler, but it worked well.

In my current 1980 trailer, I have a Duo-Therm 65512-006 furnace, which has a control that responds to a thermostat on the wall. It does not require any outside electricity, as the heat from the pilot light generates the current required to run the thermostat. As you can see from the picture of the control attached to the burner when I removed it for cleaning last year, it is still very simple. I can’t see any reason why this or a similar control unit could not be made to fit into your furnace. It is only attached to the burner by the gas pipes, so they can probably be made to fit for many brands and styles of control unit.

Good luck,
Rick G