furnace install

[MarkR]

So I'm finally installing my Furnace - Suburban w/ the Stainless Steel Cover/Cap/Trim that goes on the exterior (for the combustion air intake and the combusted air exhaust). Because of the sloping exterior wall, especially down near the floor, the furnace has to be set at an angle so the outside trim/cap will slide in tight against the skin.

I didn't find anything in the literature saying the furnace must be level to operate but I wanted to find out if anyone knows for sure. And are your floor mounted furnaces installed level? Or are they angled?

Thanks.

Also, the literature points at the top "lip" of the exterior trim piece and says, "provide sealant" . . . I'm assuming this trim piece will get fairly hot - can I use Trempro/Vulcom Or do I have to find something designed for "heat"?

Thanks.

[dbj216]

I've put three Suburban furnaces in my two trailers. All three were mounted parallel to the floor. I had to elevate the furnace on a platform in the Trade Wind to align with the existing exterior opening. I sealed the exterior piece with vulkum.

It seems like there is some slop in the way the exterior trim fits on the tubes. Maybe there is enough to have the trim sit flush with the skins.

Interesting idea to tilt the furnace a bit to match the exterior skin. I've not seen it but I can't think of a reason it couldn't be done. I did tilt my water heater a bit to match the exterior skins.

David

[Minno]

We installed our new Suburban furnace on a platform also to conform with the holes already there. Sealed with vulkum also, and it is level.

Kay

[ventport]

I also set the furnace on a platform to line up with the old outside vent holes. Furnace is level with the floor, the vent fits the sloped wall in my 77 Argosy just fine. There is enough adjustment in the outside trim to fit the slope of the outside wall.

[perryg114]

There is enough wiggle in the outlet flanges to handle a few degrees off normal for the outside wall plate. My furnace sits on the floor. The wall is pretty close to 90 degrees where it meets the floor. It is certainly close enough. Sheet metal is very forgiving.

Perry

[MarkR]

thanks for the replies.

i am installing directly on the floor and in a new location. my '60 is pretty sloped at the base of the exterior walls (see attached pdf). when i tried slipping the outer sleeves over the furnace pipes, and pushing towards skin, they did not want to "slant" very much at all, and just end up "binding". if i put the furnace on a platform and got it far enough up, then the wall starts to head towards being "plumb" (or close to it), but i really want it down on the floor . . . and also because of being near the skin to track rivet line, the aluminum does not want to "forgive", not enough anyway.

if i tilt the furnace up an 1-1/2" or so then i can slide the outer trim piece all the way on . . . but then i'm worried that the furnace will not function properly . . .

thanks for your help w/ this.

markr

[perryg114]

What you need is a wedge shaped frame to go under the outlet flange. This should be made of solid aluminum with holes a little bigger than the vent tubes. What is the angle of the wall? Looks like maybe 15-20 degrees if your drawing is accurate. Knowing the dimensions and the gap at the bottom would work as well. It won't be flush with the skin but that is the drawback of putting it on a slanted wall. You might can Suburban and see if they have a different outlet flange. I don't think the furnace will care if it is slanted 15-20 degrees if you go that route. I am sure there are some purist that will have a fit but they will get over it. The thing is forced convection which means it will work in any position. If you were to take this to extreme, things like the sail switch might not work properly.

Perry

[64airstream]

Thanks for the timely thread. Last week I was measuring and contemplating how to install a new furnace in our 68 Overlander, using the existing inlet and exhaust holes.

Without intent of highjacking the thread...For those that built a platform, what material did you use? And did you include a plenum/ductwork below to support existing underfloor ducting?

Thanks,

Roy

[dbj216]

64 Airstream, we are highjacking MarkR thread! But your question is similar to one I had last year.

As you know, the ducting Airstream used in mid-sixties trailers was for cold air return. Warm air exhausted out the front of the furnace.

I decided to use under floor ducting for warm air and have the return air in the front of the furnace as usual.

I built a wood platform to mount the furnace. I purchased the bottom ducting kit for the Suburban furnace, and built a galvanized sheet plenum below the furnace with three 4" ducts routed to the front, to the waste water tank compartment, and to the rear bath.

Here is a couple of pictures. PM me if you have further questions.

Now back to MarkRs thread.

David

[MarkR]

hijack away, i'm honored . . .

[64airstream]

dbj,

In an effort to continue this thread highjacking at MarkR's request... Thanks for the response and photos. This is similar to what I'm contemplating. I'm thinking about using the existing cold air under floor duct, back to the bath, and putting the plenum under the platform floor and above the coach floor, with one vent forward and a 4" duct aft to the twin area. It's great to know it's worked for someone, before you build it. By the way, since you're heating a 24 ft in the northern tier, can I ask what size furnace did you install? Have you used it in cold weather? Were you satisfied with the heat output and operation?

MarkR,

Thanks for allowing the intrusion. I think Perry's suggestion of a wedge is probably your most direct option. If you oversize the aluminum wedge (wider and longer than the vent plate), you could add a nice bevel along the edges and it would look good and function well. To me this seems a lot easier than trying to inset the top of the vent. I read in the Suburban instruction manual, they don't want you to modify the connectors (shorten the lower one). That would be the other option, but there's probably a good reason (likely backed by court action) Suburban doesn't like the idea.

Roy

[perryg114]

The vents are located such that the top vent is the exhaust which is quiet hot and the lower vent which is the fresh air intake for the burner. You would be wise to order some screens to go over the vents to keep wasps and dirt daubers out. Anything that is in front of the exhaust will be melted or heat damaged.

Perry

[dbj216]

Hello 64, I purchased a Nt30 furnace. I did so as they are a very common size, and I elected to use under floor ducting so I am likely to loose heat to the "basement" before it gets to the bathroom. I am also dumping a 4" duct to the waste water tank compartment with a cold air return duct back. I have too much heat there, but I thought some of it will keep the bath floor a bit warmer. My system will be a propane hog.

The original plenum under the floor in my Trade Wind was rather rotted. But the main thing is the material was cheap wood. That would work for cold air, but not 190 degree heated furnace air. So I tore it out and replaced it with a galvanized plenum box with three 4" holes in it. The sheet metal can take the heat. I put about 1/4 inch air gap between the plenum and the subfloor.

I positioned the furnace over the old hole in the subfloor. I had to make the hole a bit bigger to fit the ductwork. I had to select a furnace height that fit the 90 degree duct protruding through the floor. I used D&K RV flex duct and plastic floor vents, which is an industry standard.

I have not used the trailer in cold weather yet. All I can confirm is I have decent air flow out of the in floor ducts in the bath and front of the gaucho.

David

[MarkR]

I like the "wedge" idea as well . . . although it means I'll need a metal break - right? Or have it machined from a solid chunk of aluminum, I'm sure that won't cost much :-)

[64airstream]

MarkR,

I was thinking machining it out of a solid chunk of aluminum. Your sketch is great, but I'm not sure how thick the lower edge would need to be for the exhaust plate to be flush. I took a quick look on aircraftspruce.com for aluminum bar stock. They have ½ inch thick X 6 inch wide bar of 2024 T3 (same as sheet on pre 1969 trailers) for about $35 per foot. That could end up being a pretty expensive wedge, but the machining would be pretty straightforward.

dbj,

I'm leaning toward the NT30 also. Seems like plenty of heat output for a 26 ft. I plan to put the plenum above the floor and under the new support I build. I'll use the single cold air return as a hot air duct and add the other vents from the plenum. I like your idea of leaving a ¼ inch gap, although, I may add ¼ inch insulation board. I need to raise the new furnace 6 inches, so with ¼ inch top and bottom and ¾ inch for the support, I'll still have enough duct height to easily handle a 4 inch duct. Thanks for you insights and experience.

Roy

[perryg114]

I could probably make some of these things if we had some folks interested.

Perry