Return Air

[Secondwind962]

2017 3820.... I’ve had a cold draft coming in the the trailer via the “grates” in the steps up to the kitchen. Looking back behind the slotted panels, it appeared to be a utility chase, so I blocked it off with some insulation board. I no sooner got the last piece in and panels re-installed, the thought occurred that I might have just blocked off the return air for the gas heater. Did I? Where would this cold breeze be coming from ??

[jsb5717]

Yes, you did block the air return. Maybe someone has a good solution for fixing that. In the heat of last summer we had the opposite issue of very hot air coming in through those vents.

I've thought about buying some rigid insulation and trying to make some kind of baffles that would allow air to move for the furnace but slow down air movement when the furnace isn't on.

[Daryles]

Here is my list of "Air Gaps" to date.

Air gaps:
Look under your frame. There are lots of holes and gaps. This allows cold (or hot, summer time) air into your underbelly and can freeze your pipes.
Use gorilla tape to close off any small openings (hydraulic lines, slide cylinder).
Use aluminum sheeting and cut to fit around the hydraulic jacks. Leave the opening around the propane tanks. They must have ventilation.
Take down your basement walls, crawl in and close the doors. You will see daylight coming in through all the gaps along the frame.
I have a 3130re. There is a panel under the bottom shelf in the pantry. Behind the panel is the water heater. Again you can see daylight coming in around the edges. This requires fire retardant insulation around the water heater to block out the air gaps.
Under your kitchen island there is a panel covering your plumbing. Take it out and there is a big Triangle gap in the corner. Cut and fit styrofoam to fill the gap tight. Use gorilla tape to seal it in place.
Remove the drawers closest to the fridge. At the back where the propane and electric wiring come through to the oven, there is a gap in the wall by the fridge. Remember the back of the fridge is vented to the outside. Cold air comes in through this gap. Mine is an RV fridge so I have to be careful because on the other side of that wall is the chimney for the fridge heater. I have to use flame retardant insulation here.
Make sure your inside and outside slide seals are good.

[Secondwind962]

It’s down in the high teens this morning and the water hasn’t frozen so I’m good there. I heat the rv with the electric fireplace and a couple small electric heaters as much as possible, but I’d still like to be able to use the gas furnace to knock the chill off when needed. It’s a sizable draft before I covered it up. It would certainly blow a match out I believe. I climbed in the basement ( pretty small on this unit) and didn’t really feel it in there. It’s has a heat vent in it as well. The very top where the floor joists are is the only opening in there. Doors are tight. Under belly looks pretty tight. The refrigerator ( residential size) is up on the elevated platform as is the water heater so I don’t think they’re related.
Is there any way that I could be getting a back draft through the furnace exhaust? I would think I’d be having a CO2 issue when it’s running if that were the case. It has me baffled ( no pun intended) but I’m getting cold natured in my old age and I need to do something with it.
I’m thinking about making some shutters out of aluminum flashing and 1/4” rod, similar to the shutter in the range exhaust hood. I just hope the furnace has enough suction to open them

[ChuckS]

Blocking off those two furnace returns will not impede the operation of that furnace nor will you encounter any overtemp conditions.. Ive been running mine for eight years with those furnace returns blocked off..

You can feel a cold draft coming thru them when the furnace isn't running.. regarding protection of the furnace it has a limit switch mounted on its frame that is NC (normally closed) and completes the electrical circuit to let the furnace run... IF the furnace were to get too hot this limit switch OPENS UP thus breaking the electrical circuit and immediately shuts down the furnace...

That furnace is getting plenty of ambient air from other holes throughout

[Daryles]

The propane furnace has separate combustion chamber from the cabin air. It has its own blower to forcibly vent the combustion gas from the exhaust tube.
The cabin air is circulated through the heat exchanger by a different blower (mounted on the other end of the same motor).

[Secondwind962]

That’s was my thought this morning. However, if I have them blocked, and there’s cold air in the return from the source of the draft, am I trying to heat 19 degree ( outside) air now rather than heating the inside ambient air? And with the returned blocked, why aren’t I feeling the draft up through the vents when the furnace isn’t running ?? Or am I, but because they’re spread out, I’m feeling it less??
I thinking a thermo scanner is in the future.

[dieselguy]

Although some may not, I totally agree with ChuckS. There are so many openings for the furnace to source return air in any Montana model besides the "grills" beneath the steps that it almost makes the "grills" more of a suggestion than a function. Daryl mentioned several of those openings. On my 3150RL, there is a huge grill right under the fridge that makes my step "grills" more of a trim option than a return air source. Our RV furnaces are notoriously inefficient to start with. Also, unlike our stick houses, there is no dedicated ducting to supply return air ... the furnace just sits in an available location per floor plan drawing cabin return air at will. Like mentioned earlier ... the combustion air is totally separate with combustion supply and exhaust air sourced via the grill on the outside of your RV. Doing all the plugging of holes like Daryl mentioned will cut down on drafts, but the propane furnace will easily run safely either way.

Secondwind ... yes with any Montana floor plan you are heating "some" outside air due to the dozens of opportunities for air leaks as Daryl pointed out. We all are ... like you, many use supplemental ceramic heaters.

[jsb5717]

I would love to hear from an HVAC expert on this. There has to be some engineered purpose in the vents in the steps otherwise why would they have been spec'd into the design? They would serve no other purpose. A combustion furnace is designed to recycle air. If the return vents are covered then the air isn't recycling. Yes, the furnace will still work but then efficiency comes into question which translates into propane use.

I'm NOT an HVAC expert...just wondering the pros and cons of covering up the return vents and negating their designed purpose.

[dieselguy]

Jeff ... I'm no HVAC guru, but I have been in the underbelly, inside cabinets, and behind the pass thru storage areas of several different Montana and Forest River products. You can't compare a stick house HVAC system in total to any RV. Like I mentioned ... there is no dedicated return air duct in our Montanas ... the furnace just sits in an open space that is not sealed by any means. There are 3 to 4 runs of supply ducts coming off a plenum, but no dedicated run of a return duct.

[Kyle and Lisa]

I believe the purpose of the step vents are to allow air circulation for inside the rig as well as the basement to keep things from freezing. I used to close mine off with cardboard in the summer, but not anymore it did not to seem to make that much difference with 4+ years on the road. I also read that when using propane to heat your rig you need good ventilation because of the moisture content it puts out so you do not start having mold issues. We did 6 months research before we ever bought our rig and hit the road full time.

[Secondwind962]

A good point on most, I’d say, but my basement is heated. In fact, there a 30 degree difference in the air in basement and the air coming in the return vents. ( basement being warmer) When I had propane heat in the house, it was dry air that we fought so we were going to use a humidifier in the trailer. Not a good idea?

[R.S.O'Donnell]

Originally Posted by Daryles

Here is my list of "Air Gaps" to date.

Air gaps:
Look under your frame. There are lots of holes and gaps. This allows cold (or hot, summer time) air into your underbelly and can freeze your pipes.
Use gorilla tape to close off any small openings (hydraulic lines, slide cylinder).
Use aluminum sheeting and cut to fit around the hydraulic jacks. Leave the opening around the propane tanks. They must have ventilation.
Take down your basement walls, crawl in and close the doors. You will see daylight coming in through all the gaps along the frame.
I have a 3130re. There is a panel under the bottom shelf in the pantry. Behind the panel is the water heater. Again you can see daylight coming in around the edges. This requires fire retardant insulation around the water heater to block out the air gaps.
Under your kitchen island there is a panel covering your plumbing. Take it out and there is a big Triangle gap in the corner. Cut and fit styrofoam to fill the gap tight. Use gorilla tape to seal it in place.
Remove the drawers closest to the fridge. At the back where the propane and electric wiring come through to the oven, there is a gap in the wall by the fridge. Remember the back of the fridge is vented to the outside. Cold air comes in through this gap. Mine is an RV fridge so I have to be careful because on the other side of that wall is the chimney for the fridge heater. I have to use flame retardant insulation here.
Make sure your inside and outside slide seals are good.

Ours was exactly the same. I've got it pretty tight now. My big one was behind the J channel beside the convenience center. I had an entire panel missing. You could actually see the middle jack from inside the basement.

[scuba dude]

When I have to camp in cold weather I put a small electric heater in basement and set thermostat where it will cycle on and off and not get too warm in basement. The heat will move over the wall that seperates basement from underbelly portion of camper. It will make a huge difference in temperature inside camper. Keep water from freezing where it hooks to camper in wet bay. Fireplace and one or two heaters inside has keep thing nice down into teens or lower.

[WeBeFulltime]

Originally Posted by jsb5717

Yes, you did block the air return. Maybe someone has a good solution for fixing that. In the heat of last summer we had the opposite issue of very hot air coming in through those vents.

I've thought about buying some rigid insulation and trying to make some kind of baffles that would allow air to move for the furnace but slow down air movement when the furnace isn't on.

How about modifying a standard 1" thick paper disposable HVAC filter to proper size and install on the back side of the slatted piece? Should allow some air movement but stop drafts.

[Daryles]

I made stair covers for the summer to trap cold A/C air inside. We remove them for winter. The furnace return air goes through here and helps keep the pipes from freezing in the basement.
I read of one person installing plastic sheets behind the stair vents. This allows return air to be drawn through but blocks drafts from coming into the cabin.

[lewy64]

I use those magnetic register covers, over that area under the steps. The ones i bought have 4 small magnetic strips. This covers the whole area, takes 3 of them. The strips just get self adhesive and covers the edges of the openings. I got these off amazon. The small strips are black and dont show up on my dark brown coloring.



https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[MARK A]

I haven't read all the posts entirely, so if this is repetitive I apologize.
An enclosed area needs a place for air pressure to escape if there is no 'real' cold air return. Conceivably the furnace could pressurize the space and hamper the fan's ability to force air into the trailer.
I would think a 'flapper' on the stairs on the BACK side of the stair vent might work. Personally we always have a window or a vent open anyway.



Mark

[DutchmenSport]

The cold draft coming through return vent under the steps is caused because air is blowing inside the underbelly. The chloroplast needs to be sealed. This is where the air is blowing in under the floor and thus, blowing in the return vent in the steps.

The return vent in my camper is not ducked at all. It's designed to pull air from the inside of the living area and also pull the air from the inside of underbelly, as the underbelly is heated also, and the furnace return pulls from all directions. It's not vented anywhere. It all open.

The return on your furnace will circulate what the furnace actually blows out. And when the furnace is running, this works well.

However, when the furnace is not running, any air leaks from the outside of the camper will blow through that same space, and across the floor of the lower living area.

The best way to stop the drafts is to seal up the chloroplast underbelly with a BUNCH of caulking and/or sealers. Close up any holes with expanding foam "Stuff" too. Close off all the holes, leaks and openings where the chlorplast is connected to the various frames, it's joints, and open, cut locations, and that WILL stop the drafts from coming through the furnace return vent under the steps.

I was (somewhat) scolded on a different forum when I stated this and the conversation led to the camper needing those drafts to run the ceiling fan vents. Poppy-cock!

If the underbelly is sealed tight, and you need to run the ceiling vent fans, crack a window. That will let the air flow and suck out any moisture and keep your camper warmer as all that air is not being pulled from under the camper, across the floor, and out the roof vent fan.

Furnaces returns will pull only the same amount they blow out. Gaps in the underbelly allow the furnace to pull cold air in, and also keep the air being blown into the living space to be not as warm.

[dieselguy]

Mark ... there is no cabin pressurization by the furnace as Dutchmensport said, it will only blow what it can suck in. What we both are trying to get across to everyone is ... there is no dedicated return duct in any of out RV's. The furnace just sits in a space provided per floorplan and draws air from that space which is by design also connected to the underbelly and pass thru storage. Loose the idea that the vents under the steps are the sole point of intake air for the furnace's air recirculation.