Furnace return vent

[Art-n-Marge]

Bad Moon, in my rig, it is impossible to run the A/C at the same time as the Furnace, since my climate control's mode switch options are Fan Only, Cool (A/C) and Furnace meaning the mode can only be one at a time.

When in Fan Only, the furnace fan circulates air from the furnace without heat or cold. Cool means the overhead A/C unit can operate and operates independently of the furnace, then finally when mode is set to Furnace, means the furnace fan can run and turns on the furnace heat as needed. There are other selector buttons for selecting other parameters such as automatic/low/medium/high fan in Cool mode depending in what mode you have selected.

I suggest you post all the selector buttons on your unit, then we might be able to help you decipher how it works. I, for one am already confused with your setup if you are able to have the A/C AND the furnace running at the same time. that doesn't seen right unless you have a truly automatic system that turns on the Furnace or the A/C depending on your settings. I lived in a house that worked this way and while it was nice and automatic, once furnace or A/C worked but never both.

[Carl n Susan]

This is a common question by from owners of newer rigs. Here is one of many discussions which describes the problem and solution (Hint: fan on Auto) http://www.montanaowners.com/forums/...ad.php?t=63365

You really should have posted this questions as a new topic. This questions gets lost in a multi-page unrelated topic and will be difficult for others with the issue to find it. Plus use the "Search" tool in the upper right corner of the page. Most Montana problems have been asked and answered already.

As for Art-n-Marge, technology has passed you by. Your 10 year old rig has a completely different thermostat and technology.

[Bad Moon]

Thanks Carl-n-Susan. Actually found my answer on Youtube:

https://www.youtube.com/watch?v=tYD5FN6SmjQ

[John5five]

I agree with you completely. Having HVAC in my blood and having a 2020 4811ms Montana, there should be a return duct and filter grill at the stairs for complete HVAC recirculation. This would be more energy saving and efficient imo.
The area around the furnace is around 45deg f and that's the air being circulated over the heat exchanger. With a 50 temp rise that's 95 deg supply air temp out the registers. It's not circulating room temp it's circulating basement area temp. Now if it were circulating room temp at say 70 deg F with a 50deg TR, ( my unit has a 50deg f temp rise) that would give you a 120 supply air temp out the registers. 120 very 95. See how much quicker you will maintain and hold a 70deg set point. If I could fit in there I would install a return duct to the stairs and restrict return air flow not needed. But that's me. I winter camp and propane and electric has become a factor. 😁✌️ Happy Camping

[John5five]

I simply removed the wood covers, double duct tape from the back, and reinstalled them lol. Works for me plus we still have the wood look. 😁

[Rykki]

Set the fan on the upper air con thermostat to Auto. Everything will function fine. As an added precaution you can always shut off the 120v 15 Amp breaker suppling the air con for the winter.

[DutchmenSport]

I did not read all the posts here. But reading posts about the return vent in the past, makes me believe different models are set up kind of different. On mine, this is how it works.

First, the furnace ducts run both inside the camper coach and under the floor. I opened the back wall, and there are lines actually running in the gigantic open spaces under the floor and the ends of the ducts are open.

What that tells me is, in order for there to be proper air flow (yes, like in your home), the air has to circulate INTO the furnace and then blow OUT of the furnace. In order for each room to heat properly, the warm air has to be able to enter the room, and there has to be some kind of suction of the air to pull the cold air out. Otherwise, it's like blowing air into a bottle. It simply won't circulate anywhere.

Now, if the air flow is obstructed anywhere, either the "in" or the "out" flow you simply do not get heat.

Considering my vents are both inside the coach and under the floor, it's important that the furnace have the right air return. Blocking the steps will stop the return from the coach. Sealing off the underbelly and isolating the furnace will result in frozen pipes in the winter. No ... that return vent (ON MINE) cannot be covered if I want the furnace to run right.

Also, I have read on these forums in the past, that obstructing the furnace, closing off air ducts and such will cause the furnace to over-heat and eventually fail and cause problems. (I don't know about that, it's never happened to me).

So, blocking the return vent under the steps IS NOT ON OPTION on my Montana. But, what about all those drafts that come through there when the furnace is not running. Yes, it's cold. Well .... it WAS cold.

Simple solution, but does does take some work and bit of money. Simply open the back wall of your pass through front bay, look inside and anywhere you see light coming through the underbelly, seal it up. This will eliminate ALL the cold drafts.

I used about 15 tubers of caulking, sealers, foam insulation in a spray can, Liquid Nails, and extra screws, a bit of drilling for the screws, and about 3 days of work crawling under the camper to seal up all those holes, cracks, and places were the underbelly Coloplast had gaps. The end result ... no drafts any more across the lower level floor any more.

It not only makes the furnace more efficient now, I use a lot less propane to run the furnace to produce a more comfortable heat. No drafts when furnace is not running. No cold air is being sucked in from the outside through the underbelly, and truly, the furnace is cycling air in and air out without obstruction.

In addition, sealing up all the underbelly holes and cracks made the air conditioner run more efficient too. The air conditioner is not pulling warm air in the hot months through the underbelly any more now either. The camper is actually cooler.

It took some time to seal all those holes and cracks up with half a dozen different types of sealing caulks and such. And if I ever have to remove the underbelly Coloplast I may regret it, having sealed everything so permanent. I was fully aware of this when I did the work. But, I also figured ... I'll just deal with that (if and when) the time comes. Well, it's been over 3 years now and so far, so good!

If you want to eliminate those drafts, cold spots, and make your furnace run more efficient, then take the time and seal up all those holes and cracks UNDER the entire trailer. This is the best thing you can do.

Additional edit: There was a problem I encountered after sealing up all those holes. I noted the ceiling air vent in the bathroom, when the fan was running, pulled more "stink" from the toilet when flushing. I also noticed, the washing machine dryer seemed to be struggling to pull air air to properly dry clothes in the dryer. End result ... when running a ceiling/roof vent fan I have to crack a window somewhere. When running the washing machine/dryer, a window has to be cracked, or the roof vent open with no fan running so it gets air circulation.

Of course in the Summer when the doors are open, running the dryer is no problem. But when weather gets colder and things are shut, we have to leave a window cracked or one of the ceiling vents open. But, we've adapted to that pretty well.

[Todd & Mary]

I agree with some of the comments here. I have a 3761FL so there are 2 large vents in the stairs, In the winter there are cold drafts and summer I can feel the cool air passing into the basement, because the basement is cold! I have packed bubble wrap behind these vents in the summer but leave them open in the heating season because it is easy to install and remove. And here is my reasoning for opening the vent in the winter. The kitchen is the lowest (coldest) part of the rig. Therefore, I want the furnace to draw the cold air out of the kitchen and replace it with warm air. I was trying to design a lightweight one-way damper that would open if the furnace was drawing air, but I have too many leaks in the basement to try that just yet. We just started full time and I have not had time to seal the basement yet, but it's on the list of things to do. Monster tape along the sides to seal the belly and expanding foam and caulk for other larger gaps. I have to be careful because I have installed most of my solar system and inverter in the space the furnace is in also, so I need to ensure air moving thru there if needed to cool all that equipment. I still like the idea of a light piece of plastic plate attached at the top which would open when running the furnace, kind of like a swing gate attached to the top of each vent. That way you wouldn't have to worry about it.