Atwood 8531-IV-DCLP Combustion Box Insulation?

Dinosaur does make an Extend-A-Life kit which relocates the circuit board external to the furnace- it was designed for the Suburban NT/Hydroflame DC82 type furnaces, where the board is right next to the combustion chamber. Should work on any model that doesn't use a fan control board, though.Fan control boards could be made to work- just need a few more wires.

Thanks again for the feedback. Pictures would better inform this topic in terms of openings (the intake is 20" x 10"), clearances, air intake path, CCA location, CDX riser and such, but I think we're decided; I'll not attempt to insulate the box.

Chris, I think you pegged it. The installer put the furnace on a three inch open-ended CDX box with a short piece of ducting between the top of the box and the trailer heating duct. The furnace, with its decrepit foam seal, sits on top of this short duct. The other side of the duct was at one time joined to the trailer duct with metal tape, but the tape no longer sticks. The result was that a lot of hot air was leaking from the furnace output back into the enclosure space. Replacing the metal tape with some heavy duty aluminum foil and a little bit of high-temp RTV seemed to make a difference in enclosure temperature. It's still hot, but not as hot.

I'll put a spare Ignition Board in the cupboard.

Thanks again for your thoughts.

These things are basically zero clearance though, it's 1/2 inch to the case, but zero to the spacers which are built in. The board should not get hot at all, it is located right in the return. If it is getting hot, you have a return problem, and hot air is recirculating.

Hferguson writes “The reason I'm pursuing this in the first place is that the blower wasn't coming on when the thermostat told it to. It appears that there is a sealed relay on the Ignition Board CCA that routes power to the blower prior to furnace ignition. That relay appears to be sticking. It's working now, but that CCA and everything else in the enclosure gets really warm. Can't be good for electronics.”

Per Atwood installation manual
HERE

Please read the following text from the manual above.. Pay special attention the text I bolded!

"*When furnaces are installed to minimum clearances, an additional 16in2 of return air must be provided to blower side of furnace, or a 2 ?
clearance the full length and height on blower side must be
maintained.

Return air is supplied through openings in furnace casing. All return air passages must be kept clear for furnace to function properly.

Refer to
MINIMUM CLEARANCE TO FLOORBOARDS, WALLS & SIMILAR COMBUSTIBLE BUILDING
MATERIAL. The total unobstructed return air opening size(s) must NOT BE LESS than specified in
SPECIFICATIONS- MINIMUM RETURN AIR. Failure to meet minimum return air requirements nullifies furnace warranty.


•It is not recommended to install furnace on material that restricts
return air, such as directly on carpet, or soft material (like vinyl).
•If you must install furnace on carpet or soft material, install fur-
nace on cleats, or on a wood or metal panel extending the full
width and depth of furnace plus minimum clearances to combustibles

CRITICAL INSTALLATION WARNINGS
•DO NOT install furnace on material that restricts return air, like carpet or any soft material such as vinyl.
•DO NOT install furnace where clearance to combustibles cannot be maintained.
•DO NOT modify furnace in any way."


Replace the ignition board..

Relays go bad due to pitting/wearing of the contacts, has nothing to do with the overall heat of the relay or the control board.

Putting an insulating “blanket” around the furnace case will actually INCREASE the internal temperature of the furnace and hence increase the temperature that the control board will endure..

INCREASE RETURN AIR OPENING. This will allow more air to flow around the furnace lowering the overall temp of the furnace closet..

The MIN return air opening is 65 square inches (something like 6.5"x10"), the RECOMMENDED is 80 square inches (something like 8"x10")..There is nothing wrong with MORE than 80 square inches if you have the wall space to add an extra opening..

But as I mentioned the temperature has nothing to do with your problem..

Now we understand what you want to do. BAD IDEA.
1. The furnace boards have been designed to take the heat and have been for almost 25 years. It is rare for a furnace board to fail
2. That "housing", if you look at it has numerous vents and cut outs. That is for the furnace to PULL the interior air over the combustion chamber, heat that air and throw it out the furnace ducts. If you try to insulate, it will not only stop that cold to hot circulation, it will also OVERHEAT the area around and the combustion chamber. Then your furnace will short cycle(hi limit kicking in and out) the combustion chamber and take forever to heat the RV. Doug

Thanks for replies!

My apologies for poor terminology GDE; I'm referring to the exterior box that houses the heat exchanger. I don't want to tinker with the innards of the thing; am looking at a potential installation mod rather than trying to upgrade the furnace manufacturer's design. That said, a design that requires the box to shed heat to the surrounding air moving *over* it rather than the air moving *through* it (and then out to the distribution duct) is rather curious, especially since this now pre-heated air is what is drawn into the box.

Dutch, thanks for the vent idea. That would help with residual heat after the furnace turns off.

The reason I'm pursuing this in the first place is that the blower wasn't coming on when the thermostat told it to. It appears that there is a sealed relay on the Ignition Board CCA that routes power to the blower prior to furnace ignition. That relay appears to be sticking. It's working now, but that CCA and everything else in the enclosure gets really warm. Can't be good for electronics.

Failing the jacket on the furnace box idea, perhaps a cool air snorkel for the CCA.

Thanks again for the replies!

One of our two furnaces is located in a kitchen cabinet and the interior would get quite toasty when the furnace ran a lot in colder weather. To let some of the heat escape the cabinet, I added a register vent near the top of a blank side. The interior stays much cooler now, and the heat does not go to waste since it exits to the coach interior.

Bad idea, if it WAS a "good idea" the MANUFACTURER WOULD HAVE PUT INSULATION THERE!

I don't know what you are calling a "combustion box" but there is NO combustion box in these furnaces..

The flame is BLOWN through a labyrinth of piping called the "heat exchanger", the heat exchanger keeps the flame and combustion products sealed from the inside air. The outside of the heat exchanger gives off the heat into the inside air blower..

The outside CASE portion of the furnace is COOLED by the INSIDE RETURN AIR supply. Cover the furnace CASE up with insulation will result in your furnace burner constantly tripping off due to the fan not being able to move enough air (IE you would have to increase fan CFM which means faster fan motor which will affect the burner fan)..

You CAN NOT "IMPROVE" the furnace efficiency without causing OTHER problems, please for your own safety don't be a cheapskate and worry about fuel usage..