Furnace return vent - Montana Owners Club

twindman · 12-03-2016, 10:57 AM

On the subject of covering the return vent under the stairs in the Montana, am I missing something? Some say they just put a magnetic cover over them or something like that. On my unit, the vent is just wood with slots in it. Do you fashion some sort of hole and install a metal register vent?
Thanks.

**DQDick** · 12-03-2016, 11:12 AM

I just cut black poster board to fit and screwed the covers back on. Add it in the spring when I put the register vents that cloose in for the summer and take them back out when I put the open register vents back in in the fall. just the thought of blocking the return air and running the furnace gets the furnace manufacturer reps all excited at the Rally.

bigskyjimmy · 12-03-2016, 03:22 PM

I always wondered why that would be a problem as there is tons of fresh air in the basement and the partition in the basement does not even go to the top of basement letting even more air into there,I have closed my stairs off on my 2012 and 2015 all year round and for sure the Winter where lots of cold air comes in with no ill effects

Quote:

quote:Originally posted by DQDick

I just cut black poster board to fit and screwed the covers back on. Add it in the spring when I put the register vents that cloose in for the summer and take them back out when I put the open register vents back in in the fall. just the thought of blocking the return air and running the furnace gets the furnace manufacturer reps all excited at the Rally.

1retired06 · 12-03-2016, 03:23 PM

We use a runner on the stairs, easy on and off

**DQDick** · 12-03-2016, 04:38 PM

Ours actually is fully sealed from the basement otherwise I wouldn't worry about it.

bigskyjimmy · 12-03-2016, 05:16 PM

Both my 2012 and my 2015 never had the Partition go to the top in the basement and I wish it did and maybe I would not have to block off the stairs

PapaBeav · 12-04-2016, 04:04 AM

I cut 1" soft foam to fit the registers, they also act as a filter.

Irlpguy · 12-04-2016, 05:43 AM

Folks need to think differently on how the return air gets to your furnace in your 5er than your home. In your home the cold air return ducts are connected to the furnace and that is the only place they get their air supply so you cannot block them without affecting the supply of air to the furnace.
In your RV particularly most if not all Montana's the furnace draws air from all around the area where the furnace is located, that includes the length of the unit and the entire space above the covering under the tanks which encloses the entire bottom of the RV. On most units there is also an opening between the area where the furnace is mounted and the storage space (basement).
While it may be desirable to draw cold air from inside the living area of the RV, in reality there is minimal air being drawn from that area through the vents under the stairs.
Ideally the RV furnace would draw all of its cold (return) cold air from within the RV in which case you would be circulating the slightly cooler air from near the floor through the furnace again to reheat it. That however is not reality.
I have closed mine off both in the summer to assist in cooling and in winter to stop the cold drafts from entering the RV from under the stairs. That has had no affect on the performance of the furnace.

I know others on this forum will disagree with me on this subject, so if you want to know exactly how and where your furnace gets it's air, open up the wall of the storage compartment and look at the furnace and judge for yourself.

Close the steps off completely, put filter material in there if you wish as some have done, BUT do not believe you are starving your furnace for air, it simply is not the case.

dieselguy · 12-05-2016, 03:50 AM

I fully agree about the return registers being just a suggestion as to function. Here's proof at least on the dropped frame models dating back to @ 2010. prior to my mod, I could have permanently blocked my under step register and the furnace would still get plenty of return air from all over. http://www.montanaowners.com/forums/...rms=Insulation

psomers · 12-05-2016, 04:04 AM

While I don't disagree 100% with Iripguy, I wouldn't run my furnace with stair vent closed off. If you do make sure your carbon monoxide detector is working.
If your furnace is blowing 1000 CFM it has to be sucking 1000 CFM. With vent closed off it has to be sucking air in around basement doors and any other place it can get air.
My first 5th wheel had the furnace in living area under the refrigerator. It only had a vent hose running to tanks. Much more efficient.
On my Montana I have taken some rigid foam board and closed off my storage from the furnace area.
When your thermostat calls for heat the fan runs for several seconds before the burner lights and then a few more seconds before the heat exchange gets hot enough to produce warm air. Until that time cold air from under your camper is being mixed with cabin air.
My home furnace has two blowers. One for combustion and one for heat circulation. Much more efficient.

dieselguy · 12-05-2016, 07:27 AM

You're not replacing 1000 cfm of air ... you are drawing supply air from inside the camper, warming it, and then just blowing it right back inside. The combustion air is totally separate on the outside of your camper. What my link shows is that the back wall of your front storage compartment does not completely seal off the area your furnace draws from. There is open space between each floor joist and open space straight down into the belly pan which is by no means 100% sealed tight from the outside air.

psomers · 12-06-2016, 01:14 AM

Quote:

quote:Originally posted by dieselguy

You're not replacing 1000 cfm of air ... you are drawing supply air from inside the camper, warming it, and then just blowing it right back inside. The combustion air is totally separate on the outside of your camper. What my link shows is that the back wall of your front storage compartment does not completely seal off the area your furnace draws from. There is open space between each floor joist and open space straight down into the belly pan which is by no means 100% sealed tight from the outside air.

It's obviously you know what you're talking about. I just don't see how with your vents under the steps sealed off you are drawing air from inside the camper. What am I missing.
I have taken rigid insulation board and with duct tape tried to seal between floor joists. Not 100% sealed but I think better.
I value your comments as I have read many.

dieselguy · 12-06-2016, 03:42 AM

I wasn't really saying seal off the step vents ... I was just agreeing with Irlpguy that on many models, the vents are more of a suggestion than function. On most any Montana there is way more places connected to your living area for the return air to draw from "If" the step vents were sealed off. Think of the area that your furnace sits in as a big irregular box that is no means air tight. It's about the width of your fiver encompassing an area from the rear wall of your front storage compartment to say a couple of feet rearward and as tall as from the main floor to the bedroom floor. The furnace just sits in this irregular area ... there is no ducting directly from the intake of the furnace to the step vents. On my 3150 for instance ... there is a huge grill under the fridge that the furnace can pull air through. This alone makes the step vents just a suggestion. In some of the Montanas I've been in, there is a couple of inches gap between the stair risers and the walls leading up to the bedroom. The furnace can draw from this opening right next to the vents. On any dropped frame Montana, if you remove the rear wall of the main pass thru storage area ... where the main flooring ends you can look right down between the wall studs for the storage compartment rear wall into the belly. The furnace can draw from this opening as it's part of the "box". The plastic wall in the pass thru that covers the plumbing behind the convenience center is not sealed and doesn't extend between the bedroom floor joists. If you were to remove that plastic panel, you can see the furnace right behind the water heater. This area can supply air to the furnace as well as it's part of the big "box" I was talking of. So ... the way I see it on most models ... the stair vents are just a suggestion of supply air. The link I inserted in my first reply shows what I did to plug up some of the "box" as on a windy summers day if I opened a main storage door, hot air blew into my living area like crazy making the A/C work OT.

Irlpguy · 12-06-2016, 06:23 AM

I have posted this picture before I believe but here it is again. You can see the back of my furnace and see that the furnace draws air into the squirrel cage fan in two spots, the slot along the right side and the top of the fan cage, I have put two red dots to identify these area's.

The area from which my furnace can draw air to these two spots includes the entire space under the bathroom, all of the tank holding area, all of the underbelly and the storage compartment. I cannot say that no air is drawn from under the stairs, but it is minimal because of the large void where the furnace is located.
It would be great if the supply came only from the stair openings as it would then be recirculating partially warmed air from within the RV, unfortunately that is not the case.

psomers · 12-06-2016, 08:06 AM

OK. I can see I'm dealing with a couple of smart fellows. My little pea brain thinks if you blown air into (heated space) living area and that area was completely sealed, that area would be somewhat pressurized. Yea, I know a lot of leaks but the air would want to leak at point of least resistance. Underneath storage would be at a slight vacuum to me would be least resistance.
Living in Alabama don't know why I even think about it. In the four years of owning this camper and my previous nine campers I rarely use furnace. We go to Gulf Shores right after Christmas for two months and electric space heater is more than enough.

jcurtis934 · 12-06-2016, 12:53 PM

Paul, the slides in your montana are by no means air tight...plenty of air can leak out there and many other places you wouldn't even think about. You couldn't pressurize a montana if your life depended upon it and it's okay because it is just a trailer or rv, etc.

psomers · 12-07-2016, 12:10 AM

My comments are taken too literally. Every one knows a piece of swiss cheese could be more easily pressurized. Having worked with manometers a manometer would show a pressure.

bowlesj · 12-07-2016, 02:05 AM

FWIW Paul, I see your point very well, and as an aircraft maintenance technician I feel I have a pretty good understanding of pressurized compartments.

I know the coach has lots of leaks but there are pressure changes based on windows, doors, etc open or closed.

One just has to run a Maxxair fan on speed 3 or 4 and open and close a window to hear a pitch change which is indicative of a pressure and flow change.

Personally, I can see the advantage to the air exchange you are concerned about.

I'm also sure the furnace will survive just fine with the "return air" blocked as well.

John

jameswbarton · 12-11-2016, 03:48 AM

I am almost complete with isolating the basement from the furnace area. Having had many other RV's I saw no reason to use precious warm air from the furnace to heat the basement and outdoors, nor did I see any reason for the AC units to draw in outside air through the basement trying to cool the warm air in summer. I am using two marine heaters with Freeze functions to keep the basement and convenience center from freezing. Eventually for extreme cold useage I may need to install tank heaters as my HC does not have them. I am also adding extra insulation in the basement. The AC unit and Furnace works so much better without the huge amount of outside air they were drawing.

Bad Moon · 12-13-2016, 05:10 PM

I don't want to hijack this thread, but I have a question about how my furnace operates. When i set the t-stat to "furnace", the upper (air conditioner) air circulation fan comes on too. The furnace cycles on and off with the heat duct fan, but the upper fan NEVER shuts off. This is really annoying, because it is blowing cold air around, and freezes our butts off until the furnace cycles back on. Is this how it's supposed to work? Is there any way to shut off the AC fan so that only the furnace/fan will work?

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