Cold Air Intake

[sandpirate]

OK, when you pressurize that area and air is leaking to the out side, where do you get air to make up what you have blown out side?? It has to come from somewhere. Lets say your living area is air tight, you would create a vacuum in the living area, once the furnace shuts down, you would suck cold air in any hole you would leak air out of until your inside would equalize with the outside. Once you build up the pressure in an area and equals the output of the source of the pressure, you will not get any more air in there than what leaks out any holes. You will have the area pressurized before you get any heat since the blower will start circulating air before it gets warm. Your output of the blower is greater than any leak you may have or not, you would get very little warm air in that area before the thermostat in the living area is satisfied and shuts down the furnace.

In these rv's we are concerned about keeping the heat in the conditioned space since we aren't dealing with a 6500cfm motor in these furnaces. A little positive pressure inside will not create this backlash of cold air being sucked back into the coach if it's properly sealed from the outside air; as a matter of fact it will do just the opposite. Either way, I'm not going to pay to heat an uninsulated trailer underbelly that is only being protected by plastic sheeting that is no thicker than a cheap cardboard box.

 

[Bob&Patty]

Sandpirate, there always has to be some fresh (new) air available in any heating or A/C system. If this does not happen all the oxygen will be used up help the heater burn the propane. Even automobiles always have some fresh air entering the passenger compartment....even on the recirculate mode. It has to or you would run out of oxygen to breath.

Now you may have an excessive holes in the floor by your heating unit and in the underbelly. I would seal them if you like but leave a little bit of space for some fresh air. Either that or crack a window. You can't have your unit air tight....bad things can happen.

 

[mountainlovers76]

Sandpirate, there always has to be some fresh (new) air available in any heating or A/C system. If this does not happen all the oxygen will be used up help the heater burn the propane. Even automobiles always have some fresh air entering the passenger compartment....even on the recirculate mode. It has to or you would run out of oxygen to breath.

Now you may have an excessive holes in the floor by your heating unit and in the underbelly. I would seal them if you like but leave a little bit of space for some fresh air. Either that or crack a window. You can't have your unit air tight....bad things can happen.

The air for the furnace to mix with and burn the propane in a central heating system does not come from the inside of the RV (or even in your sticks and bricks for that matter) it comes from the outside. In the central furnace system in your RV there is an inlet and an outlet on the furnace on the outside of your coach. The inlet draws in the fresh air to burn the propane and the outlet discharges the hot exhaust. The interior is simply circulating the heated air, NOT providing fresh air to the furnace. Just like a central system in your house draws air from the attic, below from a crawl space , etc. depending on type of construction. Fireplaces, gas logs, free standing gas heaters, etc. do pull air from inside the living space and thus need a fresh air source in that space. Central systems typically do not but as always there can be exceptions.

The key concern from many, as well as myself, is the fact that in our coaches, warm air is pumped into the unsealed underbelly and ultimately finds its way outside and then is replaced with the outside cold air returning back into the living area. That is the very reason that shortly after taking delivery of my coach, I dropped the belly and added 3 1/2" fiberglass insulation to the entire length of my Bighorn between the I-Beams and then a poly vapor barrier under that. I sealed every hole in the frame I could find from the inside, then I then re-attached the foil insulation and the corrugated bottom Then sealed EVERY hole and seam I could find on the outside of the I-Beam frame as well. It did make a HUGE difference. While in the Smoky mountains during all the cold and snow during the Christmas holidays, I heated my Bighorn with only two 1500 watt heaters and occasional use of the fireplace. My son complained about it being to hot inside even then. Was there 10 days and the propane furnace ran maybe once or twice at night for about five minutes each time with it set to 70 degrees. There is enough heat from the small heaters filtering down below through all the holes for ductwork and plumbing to help keep the tanks from freezing since I added the insulation below them. I have had my coach three years now and have camped quite a bit during the fall, winter and early spring and just two weeks ago used only my 3rd 30lb tank of propane.

 

[TomMar]

The air for the furnace to mix with and burn the propane in a central heating system does not come from the inside of the RV (or even in your sticks and bricks for that matter) it comes from the outside. In the central furnace system in your RV there is an inlet and an outlet on the furnace on the outside of your coach. The inlet draws in the fresh air to burn the propane and the outlet discharges the hot exhaust. The interior is simply circulating the heated air, NOT providing fresh air to the furnace. Just like a central system in your house draws air from the attic, below from a crawl space , etc. depending on type of construction. Fireplaces, gas logs, free standing gas heaters, etc. do pull air from inside the living space and thus need a fresh air source in that space. Central systems typically do not but as always there can be exceptions.

The key concern from many, as well as myself, is the fact that in our coaches, warm air is pumped into the unsealed underbelly and ultimately finds its way outside and then is replaced with the outside cold air returning back into the living area. That is the very reason that shortly after taking delivery of my coach, I dropped the belly and added 3 1/2" fiberglass insulation to the entire length of my Bighorn between the I-Beams and then a poly vapor barrier under that. I sealed every hole in the frame I could find from the inside, then I then re-attached the foil insulation and the corrugated bottom Then sealed EVERY hole and seam I could find on the outside of the I-Beam frame as well. It did make a HUGE difference. While in the Smoky mountains during all the cold and snow during the Christmas holidays, I heated my Bighorn with only two 1500 watt heaters and occasional use of the fireplace. My son complained about it being to hot inside even then. Was there 10 days and the propane furnace ran maybe once or twice at night for about five minutes each time with it set to 70 degrees. There is enough heat from the small heaters filtering down below through all the holes for ductwork and plumbing to help keep the tanks from freezing since I added the insulation below them. I have had my coach three years now and have camped quite a bit during the fall, winter and early spring and just two weeks ago used only my 3rd 30lb tank of propane.

Rick - I like your mod ! ! I am going to look at doing that to my 3600RE

 

[TedS]

I'd be concerned about the vapor barrier being on the cold side of the insulation. It will condense moisture. The vapor barrier should be on the warm side of the insulation.

 

[mesteve]

I think the term vapor barrier is misleading, more like a standing water barrier from road-bourne water I think.