New furnace install

[Newbob]

Hi All, For reasons that I will spare you from (unless you INSIST :-) I am installing a 16k Atwood RV furnace in a box mounted on the receiver hitch of my BB bus and using flexible duct work to run it into the bus from the rear of the box into the back wall of the bus - (6" or less). The box also houses, in a separate compartment, a gas bottle, a small generator and probably a small wheelchair battery to run the furnace (or I may just wire it to the house batteries)

So my question is this: - the furnace is installed in the top left section of the box - vent facing the drivers side of the box and heat ducted out the rear - So what would be the best place to get the "make up" air from? If I pulled it from the top or front (which is actually the rear- facing part of the box?) would that be okay? Usually it is pulled from inside the RV - I'm guessing because it is slightly warmer than the frigid outside air?

Any other considerations? - I understand the general issues of gas and spark/ flame and batteries in proximity etc but feel free to express your concerns :-)

[eagle19952]

will you be using this while driving ?

[lvmci]

Collision alert Bob! Lvmci...

[OneLapper]

 

Let me make some popcorn.......

[Stormcloud]

That set-up won't provide much heat at all. With no return air to draw the cooler air to the furnace, the warmed air won't be able to move efficiently into the bus.

[TomC]

16k btu is not a very large furnace-like 3 electric heaters. Propane furnaces are made to be mounted inside since they have sealed combustion out the side. This will allow air from the inside to be recirculated and heated rather than trying to heat out door cold air.
I am mounting my furnace (Suburban NT40, since they have just a small intake/exhaust vent outside wall mounted) in the basement. It will be in a sealed cabinet with air being drawn from the inside of the living space and distributed by 4-4" ducts. Good Luck, TomC

[scanzel]

It may work but you won't like it when the fresh air being heated and fed into the rv picks up some sort of odd smell near by and pumps it into your rv. Stray diesel fumes, gas fumes from cars and who nose what other fume/smell it may pick up when the wind blows. Attempting to heat air that may be 20 to 30 degrees with 16k will only give you marginal heat.

[bevans6]

There are a number of reasons a cold air return pulls the air from the heated space, one is heating pre-heated air, and the second is not allowing the heated space to become pressurized and resist intake of heated air, plus the heated air needs to be encouraged to circulate inside the space.  16K is well on the small side for a bus, 30K to 40K is more appropriate.  A small wheel-chair battery won't run a furnace long, they are real current hogs when the fan is on.

Brian

[Lin]

As others have pointed out, drawing the air from outside is an issue.  Any force air heater only has the capacity to raise the temperature of the intake air by a limited number of degrees.  Just suppose that your heater can discharge air that is 40 degrees hotter than the intake air (this figure is just for example sake).  If the intake air was 20 degrees, the discharge would be only 60 degrees.  Now if the the intake air comes from the interior space, it is gradually heated up, so when it reaches 30 degrees the discharge will be 70 degrees.  When it reaches 40 degrees, the discharge will be 80 degrees, etc.  Therefore your heater will gradually bring the inside temp up to your thermostat set point of say 70 degrees and shut off.  If you are only processing cold outside air, your heater, depending on capacity, may never be able to reach the temp you want.

[chessie4905]

    First, . Now that that's out of the way, mounting in back like that might pull engine exhaust fumes into it. Unless you aren't planning on driving it. You may get too much bouncing on the unit over rough roads.

[bevans6]

I forgot about the exhaust and the bouncing.  BB Transit FE is a front engine, short wheelbase (front axle behind the door) flat nosed schoolie with a long rear overhang, the back of that thing is going to ride as rough as an 8 year old kid would want.  It's going to be a problem, without a doubt, you could probably launch stuff off the back of that bus...  Exhaust would normally be right under this box, and the rear low pressure area will trap it there and try to push it inside the bus.

Brian

[Geoff]

I am always open to new ideas, but a heater on the outside of the bus (especially with 14-17 BTU's) is totally unworkable.  Previous posts have indicated problems with using new cold air to heat the interior-- what you want is the previous warm air to feed the heater so it gets that much warmer.

I installed a Webasto diesel fired heater that incorporates the already existing heating system to warm the bus.

--Geoff

[dbldragon]

Geoff I would like the details of the unit you used as I am thinking that way myself but getting very little help from people up here.Webasto  head tec called me and then said get a aquahot they use our burners and hung up.

[Debo]

It sounds like you have a reason for not installing it as it's intended, and it may be a very valid one. If it were me though, I'd certainly give installing it as the manufacturer intended some more thought - even if it meant relocating something else. Heat, for me at least, would be a pretty high priority.

[lvmci]

Hi Bob, there are addons for overhead AC units, heat strips, under counter or under sofa, as an example, that are electric, if propane flames are an issue, actually they are pretty simple to install, lvmci...