Huge source of air leakage and infiltration

[cmikal]

My 377RLBH has air vents under each step inside the rig that open into the underbelly of the RV. There is also a shoe garage under the bottom step. It has a piece of wood at the back of the step, but when you reach into that area, the piece of wood only partially covers the opening into the underbelly. These openings are a huge source of air infiltration into the rig. Right now, there is a constant cold air draft coming from the steps. The heat kicks on a LOT.

Yes, I understand that in the winter maybe those openings help keep the tanks warm, but they also help keep my living space cold.

I'm not sure where the propane furnace gets its combustion air, but if it comes from the underbelly, there is still a lot of air leakage from other areas, so I doubt getting enough combustion air would be an issue if those stair openings were sealed off, or is it? Also, when it's above freezing outside, I don't even run the furnace. I run the heat pump and/or fireplace. Frozen tanks aren't even an issue at those temperatures.

Is there any reason that I shouldn't block these openings so outside air stays outside and inside air stays inside?

[GHen]

Those vents are the cold air return for your furnace and are required for it to work properly. (Combustion comes from outside air on most furnaces)

If you’re not going to be using the furnace you could cover them.

Your tanks are actually under the 5th wheel between the frames and have no connection to those vents. You do have plumbing, hot water tank and the water pump in the pass through area that could use some heat if it’s below freezing.

[RoadrunnerII]

We boxed in the step in the basement area and cut a 4 inch hole in the hardboard then connected a 4 inch flex heat vent tube from that to the cold air intake on the furnace.
Furnace works fine. No more cold air draft on the floor by the steps.
On our eagle there is a two inch flex line for heat pointed at the water valves and water pump. Furnace pushes enough hot air in basement with that to keep those from freezing. Furnace itself radiates heat into the area as well. We don't winter camp but have been caught in freezing temps during a couple trips. We insulated from basement to rear bumper 4 inch fiberglass batts plus a layer of reflectix between coroplast and fiberglass. In cool temps once furnace has warmed it up the floor is much warmer.
Bonus is it helps the AC as well. Knocks down outside noise as well.

YMMV

RoadrunnerII

[cmikal]

Originally Posted by GHen

Those vents are the cold air return for your furnace and are required for it to work properly. (Combustion comes from outside air on most furnaces)

If you’re not going to be using the furnace you could cover them.

Your tanks are actually under the 5th wheel between the frames and have no connection to those vents. You do have plumbing, hot water tank and the water pump in the pass through area that could use some heat if it’s below freezing.

I had the underbelly covering pulled off as well as the basement interior walls while working on another problem so I could see all of the wiring, plumbing, heating, water pump, water heater, and tanks. Thats how I found out the stair vents were an air passage between the interior and the storage area and tank area. It's all one big open area. I can see the tops of the tanks from the storage compartment when the wall is removed. The storage floor does not cover them completely.

I would think that there is so much air leakage coming from under the trailer, that there would be plenty of fresh air for combustion. If not, then what would be the downside of boxing in the fresh air input to the furnace and ducting it to the outside air under the trailer. The furnace would get 100% of the air it need from underneath, and if I closed off the stair vents, it would stop the cold/warm air migration between the 2 areas of the RV?

[cmikal]

Originally Posted by RoadrunnerII

We boxed in the step in the basement area and cut a 4 inch hole in the hardboard then connected a 4 inch flex heat vent tube from that to the cold air intake on the furnace.
Furnace works fine. No more cold air draft on the floor by the steps.
On our eagle there is a two inch flex line for heat pointed at the water valves and water pump. Furnace pushes enough hot air in basement with that to keep those from freezing. Furnace itself radiates heat into the area as well. We don't winter camp but have been caught in freezing temps during a couple trips. We insulated from basement to rear bumper 4 inch fiberglass batts plus a layer of reflectix between coroplast and fiberglass. In cool temps once furnace has warmed it up the floor is much warmer.
Bonus is it helps the AC as well. Knocks down outside noise as well.

YMMV

RoadrunnerII

In another reply, I mentioned having the underbelly covering and interior basement wall removed, so yes, I saw where there were flex lines pushing air into the basement and around the tanks.

I'm confused though about where you connected the flex hose for the furnace inlet air. Did you go out the bottom of the RV or did you run the flex to the stairs so there was still an air path from inside the rv to the furnace?

[RoadrunnerII]

On our furnace the cold air intake was on the front side of the furnace. Had to remove two hot air ducts to get at it. It's just a grille in the side of the furnace case.
I used a stick on style duct fitting from big box store. Then connected the cold air flex ducting I added from the stairwell. 10 foot length worked fine.
Then hooked up the 2 heat ducts again. Ours you just turned the fittings Had two tabs in them that you match up to remove or install on furnace. Worst part was reaching it as the furnace is against the wall and the plumbing and 12 volt pump are all in the way. Cabling heat ducts it was a rats nest. Laying on my side in basement reaching around that stuff. I was able to clean it up a bit.
You want to tumble exchange the air inside the heated space like in a stick and brick. Helps with humidity control. Using outside air into the furnace only it is going to make furnace work harder as the air inside trailer is warmer. Furnace in these things is horrible on effiency. Huge amount of heat exiting the exhaust with the exhaust fumes.
Just my thinking

RoadrunnerII

[GHen]

The cold air return needs to pull air from inside the rv, it’s much more efficient to warm 60 to 70 than to pull 30 outside air and warm it to 70.

With no inside cold air return you also pressurize the inside and get less air flow out of the furnace in the rv. It’s the same way a house forced air system works.

I like the idea of boxing in the area and running a true return air duct to the inside, great idea!

[RoadrunnerII]

Originally Posted by GHen

The cold air return needs to pull air from inside the rv, it’s much more efficient to warm 60 to 70 than to pull 30 outside air and warm it to 70.

With no inside cold air return you also pressurize the inside and get less air flow out of the furnace in the rv. It’s the same way a house forced air system works.

I like the idea of boxing in the area and running a true return air duct to the inside, great idea!

Furnace doesn't seem to cycle near as often. I have thought about adding a furnace filter behind the stair step grates. Manufacture specifically says no furnace filter. Must be an airflow issue for sail switch. I'm not a HVAC guy but logic said cold air return duct made sense. Also helps stop bugs getting in the living area.. fly's, mosquitoes.... Our basement rear wall is open between floor joists

RoadrunnerII

[cmikal]

Originally Posted by RoadrunnerII

On our furnace the cold air intake was on the front side of the furnace. Had to remove two hot air ducts to get at it. It's just a grille in the side of the furnace case.
I used a stick on style duct fitting from big box store. Then connected the cold air flex ducting I added from the stairwell. 10 foot length worked fine.
Then hooked up the 2 heat ducts again. Ours you just turned the fittings Had two tabs in them that you match up to remove or install on furnace. Worst part was reaching it as the furnace is against the wall and the plumbing and 12 volt pump are all in the way. Cabling heat ducts it was a rats nest. Laying on my side in basement reaching around that stuff. I was able to clean it up a bit.
You want to tumble exchange the air inside the heated space like in a stick and brick. Helps with humidity control. Using outside air into the furnace only it is going to make furnace work harder as the air inside trailer is warmer. Furnace in these things is horrible on effiency. Huge amount of heat exiting the exhaust with the exhaust fumes.
Just my thinking

RoadrunnerII

Thank you. I never thought about the indoor air exchange aspect of it, but it makes sense that pulling interior air is better than pulling exterior air. Right now, it's doing a little of both (interior and exterior) and doing it in a way that causes a breeze at the stairs.

The furnace is definitely inefficient. I don't understand why, with today's technology that they can't make them more efficient. They probably can, but don't.

Anyway, in the near future, I'll remove the storage wall again (its just a few screws that hold it in place) and run an intake duct from the stairs to the furnace and seal the steps except for the new intake hole.

thanks again

[Lowmiler]

As others have stated, this is the return path for the inside air so it can be reheated by the furnace, so you don’t want to close it off.

That being said, there should be no drafts into the underbelly of your rig to begin with. You’re best served to get under the rig and close up any and all gaps, such as with expanding foam, to make interior heating and cooling as efficient as possible (and to block rodent infiltration, too).

[kirkelli]

You need those in the Winter when running heater for return air to the furnace. I replaced mine with vented grates that you can manually close with a screw driver, which you want to do in the Summer to retain the AC. I found them on Ebay, and are perfect fit and look a lot better than that wood..

[ShotgunZ71]

My return is below the desk in the mid bunk. I have a piece of window screen over it to stop debris and bugs, but also put a piece of Reflectix over it in the warmer months to keep the cooler air inside the camper. Warm air will absolutely flow through there, especially with an exhaust fan on.

[RogerR]

Regarding air filtration. I would not suggest a good filter due to the lousy safety switch. You could try vent filters and catch some of the dust as it comes out of the vents. Start with maybe half the vents and work up to see if it will trigger the safety shutoff.
About $10 at Walmart of any Lowes, Home, Menards of similar for a 24 pack. Just a thin layer of polyester but should stop some gravel dust, pet hair and such. I replaced my useless foam ones on my AC with them and they work better than the foam filters but have to be replaced more often.