Furnace

It needs substantial return air. I suggest you google for the installation manual for your model for the requirements.

Typically a furnace with ducted outlets in an RV has a metal louvered plate mounted on the cabinet facing somewhere near the furnace. This allows the free flow of air back to the furnace intake. There is no direct air duct back to the furnace like in a house. There is no filter to change either. Being under the couch like yours there is probably enough air flow getting back to the furnace inlet. If you box it in you will need to leave an opening in the box and add a grill to the opening. The grill and opening will need to be sized to ensure enough air is getting to the furnace intake.

There's no ventilation for ours. There's a futon over the ducted system with a wood base. Believe all the air/gas fun stuff happens outside the RV...in that vent.

We're thinking of doing the same, we'll measure the pieces taken out (with no vents) and replace with the same dimensions.

In the end, contact your manufacturer and they'll likely guide you.

The room air that is to be heated must get to the furnace. As mobeewan said furnaces mounted under couches get their return air from spaces that are left open under and around the couch. If you box the furnace area the size of the opening for return air will be depend on the furnace capacity.

The air inlet should have the same, or larger cross sectional area as the outlet duct.

I have an Atwood Hydro Flame it is in a 2003 Four Winds 29F. Dutchman.
It has floor vents.

Barry

MUST have a return air inlet of a min. size spec'd by the furnace manufacturer. Also must have min. clearances to sides and top, also as per specs.

Combustion air is drawn in from outside, and exhaust gases go outside. But the furnace requires return air from inside the living space.

I would get the model number and go to BryantRV and download the manual. It should tell you the minimum spec for the return air.
Bryant RV

Ride S40T wrote:
There's no ventilation for ours. There's a futon over the ducted system with a wood base. Believe all the air/gas fun stuff happens outside the RV...in that vent.

We're thinking of doing the same, we'll measure the pieces taken out (with no vents) and replace with the same dimensions.

In the end, contact your manufacturer and they'll likely guide you.

No, the combustion air (where the fire us burning) is all done outside.

But, for the furnace to work it has to draw air from inside the RV (or home) then heat it and then return it to the RV or home. Some how your furnace is getting air from inside the RV.

It's just sucking it around cracks and fabric around the Futon.

Your furnace might actually work better if you allowed it to have more air movement.