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Old 11-04-2009, 06:23 PM   #1
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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?
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Old 11-05-2009, 04:22 AM   #2
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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
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Old 11-05-2009, 05:38 AM   #3
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Quote:
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"
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Old 11-05-2009, 05:44 AM   #4
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You might try relocating your temperature sensing probe vertically higher in the trailer. Just a thought.
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Old 11-12-2009, 01:32 AM   #5
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Name: Dana
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Quote:
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:


Click image for larger version

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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.
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P1090062a.JPG   P1090066a.JPG  

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Old 11-12-2009, 01:39 AM   #6
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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:


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Whaddya know, it worked!
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Old 11-12-2009, 02:04 AM   #7
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Name: Dana
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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....
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Old 11-12-2009, 03:10 PM   #8
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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.
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Old 11-18-2009, 02:06 PM   #9
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Duo Therm 65810-2


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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.
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Old 11-18-2009, 04:45 PM   #10
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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
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Old 12-07-2011, 06:02 PM   #11
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Quote:
Originally Posted by Raya View Post
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.
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Old 12-09-2011, 05:41 AM   #12
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Originally Posted by David Tilston View Post
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.
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Old 12-09-2011, 09:21 AM   #13
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Quote:
Originally Posted by Dana T View Post
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:
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Old 12-09-2011, 05:53 PM   #14
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Smile

Quote:
Originally Posted by Dana T View Post
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 friendsí 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 canít 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
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Old 01-02-2012, 02:56 PM   #15
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Spent the first night in the trailer

I wanted to test out the Duo-Therm gravity furnace in my Trillium 4500. So on new years eve, I set up the bed and got the 1500W ceramic heater if required. No, I was not in the dog house, but my wife declined the invite to join me.

It was -13 deg C, (9 deg F)

The furnace lit just fine, I cranked the output temp, but after an hour, it was warmer, but still not comfortable. more heat seemed to be cumming out the exhaust then into the trailer. I set the ceramic heater on the 900W setting. This, and the Duo-Therm kept it comfortable all night.

I am a bit disappointed with the furnace. Any one know how to increase the heat output of a Duo-Therm 65211? Maybe a fan?
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Old 01-08-2012, 04:52 PM   #16
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Originally Posted by David Tilston View Post
I wanted to test out the Duo-Therm gravity furnace in my Trillium 4500. So on new years eve, I set up the bed and got the 1500W ceramic heater if required. No, I was not in the dog house, but my wife declined the invite to join me.

It was -13 deg C, (9 deg F)

The furnace lit just fine, I cranked the output temp, but after an hour, it was warmer, but still not comfortable. more heat seemed to be cumming out the exhaust then into the trailer. I set the ceramic heater on the 900W setting. This, and the Duo-Therm kept it comfortable all night.

I am a bit disappointed with the furnace. Any one know how to increase the heat output of a Duo-Therm 65211? Maybe a fan?
Hi David,
The DuoTherm you have only produces 7000 BTU.

Because intake and exhaust of combustion is outside, you don't need more ventilation than normal human oxygen use. The critical aspect is to keep the top vent SHUT, otherwise all heat is sucked up and you can't really benefit from the furnace heat. This is OK if all you want is to get rid of dampness inside, but if outside temperature is getting close to freezing point, opening the top vent is definitely a bad idea. Opening a side window a bit is far more efficient for basic ventilation with maximal heating efficiency.

Such old fashion gravity furnace use a lot of gas for the amount of heat they produce, but they are much safer to use than catalytic type in a small volume RV when ventilation is not sufficient. I carry a small portable catalytic Blackcat (3000BTU) Coleman Canada as backup unit in case I have a problem with my 30 year old DuoTherm. I added a second propane tank on the front so I have little chances of running out of gas with heating on.
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Old 01-08-2012, 05:57 PM   #17
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Originally Posted by lamimartin View Post
Hi David,
The DuoTherm you have only produces 7000 BTU.

Because intake and exhaust of combustion is outside, you don't need more ventilation than normal human oxygen use. The critical aspect is to keep the top vent SHUT, otherwise all heat is sucked up and you can't really benefit from the furnace heat. This is OK if all you want is to get rid of dampness inside, but if outside temperature is getting close to freezing point, opening the top vent is definitely a bad idea. Opening a side window a bit is far more efficient for basic ventilation with maximal heating efficiency.

Such old fashion gravity furnace use a lot of gas for the amount of heat they produce, but they are much safer to use than catalytic type in a small volume RV when ventilation is not sufficient. I carry a small portable catalytic Blackcat (3000BTU) Coleman Canada as backup unit in case I have a problem with my 30 year old DuoTherm. I added a second propane tank on the front so I have little chances of running out of gas with heating on.
IIMSS....Warm is nice, dry is nice, Warm and dry is even nicer! Crack the vent.
Love that furnace, no wasted battery and no real noise!
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Old 01-09-2012, 12:13 PM   #18
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I plan to remove the furnace and clean it. I did some basic dis-assembly of the furnace. I removed the grill, and the inspection hatch on the heat exchanger. The heat exchanger is just a large box with a horizontal depression pressed into the exposed face of the box and an exhaust port on the back at the top. I think the box aluminum, since there is no rust on it. I put my camera into the inspection port. It is clean, (no rust) all the way to the top, inside and out. The burner inside however is very rusty. there is a collection of rust dust at the bottom of the box. I am hoping that once I get the furnace out, I will be able to source a replacement burner. Other then the burner, the rest of what I can see is good.

In removing the inspection hatch, I sheared off two of the six studs that hold it on. The studs that are obviously steel. After running my hand over the part of the stud that is on the inside of the heat exchanger, I realize that it is actually an L shape, as if they just bent a stud and pounded the inside part flat. The inside part binds up against the lip of the inspection port. I hope this will not be difficult to replace.The burner, thermocouple and temperature sensor all enter the heat exchanger from the side on a similar flanged access port. I sheared one of the four bolts off that one as well.

I hope to have the whole thing out and in my house this week.

Anyone know where I should start looking for a new burner?
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Old 01-09-2012, 04:33 PM   #19
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Question

I think you would very be lucky to find a burner to exactly replace it. However, I have often wondered why a standard barbeque burner could not be used. They work exactly the same way, the only issue would be finding one that fits into the available space. Of the four furnaces I have worked on, my own and a couple of friendsí, each one had a radically different burner design that all did the same thing. Since barbeque burners are also designed to do the same thing and seem to be just as heavy duty steel as the furnace burners I have seen, I would think that one could be used without any problems. I would also think that you could modify a barbeque burner to make it fit by cutting and crimping a too-large piece if necessary. Since the combustion box of the furnace is basically a big empty box and the gas already shoots out from the nozzle to be combined with the sealed intake air before entering the burner itself (also just like a barbeque), there is no issue with air contamination or such problems. Since the amount of gas from the nozzle will be the same regardless of what shape the burner is, it really should not matter what shape it is as long as it does not get too close to the sides of the furnace box. Disclaimer: I am not a furnace tech, I just havenít been able to think of any reason (over the past year I have been thinking about it) why it would not work.

In my previous post on this thread (see above) I posted pictures of two furnace burners. You can see they are radically different, but both are simply bolted on over the gas nozzle, with an air space before it gets into the burner tube (just like a barbeque). So, I canít think of any reason why not to try it.

However, I see you are in Alberta. You could try Murphyís RV parts at (780) 992-1830 in Josephburg, north of Edmonton. They might have a used furnace or parts.

Have fun.
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Old 01-10-2012, 05:47 PM   #20
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Thanks for the input Rick. As usual, upon further inspection, the burner, while covered in a thin layer of surface rust, looks OK. I will pull it out and clean it, but I don't think it needs to be replaced.

The heat exchanger that I thought looked like aluminum, sounds like very nicely galvanized steel.

The studs that held on the inspection port cover do not want to punch out, so I conclude that they are welded to the inside of the exchanger. I will have to come up with a way to replace the ones that I sheared off.

The rust pile at the bottom of the exchanger seems to have come from the exhaust pipe. I am having trouble removing the furnace because the vent pipe, (exhaust) is rusted to the furnace.

Does anyone have a suggestion about how to separate concentric tinned steel tubes that have rusted together? Lots of WD40? CLR, (diluted HCl)? I would really like to keep the damage to a minimum.
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