Cold air return redux

[Rivernerd]

19 hours ago, DavePhelps said:

Finally, and just to be clear, those vents at the top and bottom of the closet door are not return air vents.

Agreed.  That is why I also installed a vent on the aisle side of the front dinette seat, to allow more return air from the front of the main cabin back through the underbelly area to the furnace.  See photo below.

[Rivernerd]

19 hours ago, DavePhelps said:

Personally, I would still think about closing the main return vent next to the furnace and add other returns strategically placed (like where Routlaw mentioned earlier) to create better below deck ventilation/heating.

One caution for Truma Varioheat owners:  The Truma Varioheat air intake is right behind the return air vent.   I tried adding  a furnace filter over that air intake, but it generated error messages.  Closing off all or part of that return air vent right in front of the Truma Varioheat air intake could create more problems that it solves.

See my April 25, 2023 post in this thread:

 

[Rivernerd]

16 hours ago, routlaw said:

Are these 4 inch vents commonly available?

Yes.  See, e.g.:

https://www.amazon.com/Vent-Cover-Built-Ventilation-Plastic/dp/B0822VXRNQ?th=1

 

[rich.dev]

30 minutes ago, Rivernerd said:

That is why I also installed a vent on the aisle side of the front dinette seat, to allow more return air from the front of the main cabin back through the underbelly area to the furnace. 

Did you leave the rectangle stock vent under the curb side open? This, and moving the one furnace exhaust vent from under the curb side bed to under the street side bed are on my to do list. 

[Rivernerd]

1 hour ago, rich.dev said:

Did you leave the rectangle stock vent under the curb side open?

Yes, because I believe that closing it off would cause our Truma Varioheat furnace to throw error codes.  See my post above on this thread about the furnace filter affecting performance of the Varioheat furnace.

[Snackchaser]

Does anyone happen to have a picture of a return air vent in the bathroom?  Is there is a corresponding vent under the dinette seat, or does it return the air through the underbelly?   I'm unclear if this was something that Oliver was now doing, and/or, if it's only for Truma units?

Adding a return vent in the bathroom seems like a worthwhile modification, although it also seems like it could create a draft when the heat is not on.   

[routlaw]

A couple more thoughts on this. Good thread though.

To my way of thinking there is yet another mod to do if you decide to install a vent under the seat cavities. There is a barrier made from 1/4 inch plastic just behind the furnace and hot water heater that would eliminate any air flowing back through the basement as a fresh air return. This sheet is sort of a janky affair that is most likely meant to protect the furnace and hot water heater should stored items go flying around in the rear compartment under the bed. I suppose one could devise a heavy duty net that might accomplish the same thing but otherwise a vent hole needs to be cut into this barrier sheet. No idea if this is installed with those people who have the Truma units.

I have taken mine out a couple of times to service the hateful Suburban furnace and it is a PITA to get it out then back in. 

[routlaw]

7 hours ago, topgun2 said:

 

I'd bet too that the Thinsulate will also help decrease noise levels.

Bill

p.s.  Ace, WalMart, Lowes etc. all have this foam pipe insulation.

While looking around the internet for this material I came across a number of RV Van modification companies that use this stuff extensively and also sell it on the open market. It is used mostly for sound insulation more than thermal insulation though. Apparently the R value of the thinsulite is 5.2 better than nothing and pretty good for something this thin. 

Yep, seen the pipe wrap by the box load in the home centers and hardware stores. 

[routlaw]

20 hours ago, rich.dev said:

Here are the links for the 3M Thinsulate 600L and 3M 90 Spray adhesive, you might even find it cheaper, just google it. You can buy the 1/2" pipe insulation in 3' or 6' lengths from Home Depot 

Thanks that was one of the companies I had found while searching for this product. Knew about the pipe wrap though. All good info.

[Snackchaser]

29 minutes ago, routlaw said:

I suppose one could devise a heavy duty net that might accomplish the same thing but otherwise a vent hole needs to be cut into this barrier sheet.

FYI  On my LEII there is an underfloor pass through from street side to curb side just aft of the fresh water tank, and forward of the rear jacks.  Plenty of air can pass though there.

[rich.dev]

2 hours ago, Snackchaser said:

FYI  On my LEII there is an underfloor pass through from street side to curb side just aft of the fresh water tank, and forward of the rear jacks.  Plenty of air can pass though there.

Same on my 2023 with the Truma furnace and water heater, it’s a pretty big pass through. Here’s a picture of it, I believe taken from the curb side (where the fresh water drain is) to the street side behind the Inverter. Plenty space for air to pass through. 

[routlaw]

Hadn't thought about that passageway, but that clears up a lot. Not sure how much of the return air would hit the outside shower pipes though, maybe some.

[DavePhelps]

11 hours ago, topgun2 said:

As I have pointed out in other threads, an added benefit of the pipe insulation is that it will help quiet the water pump. 

I will definitely try this! Now if I could just keep the furnace quieter! That would be a big plus for the new Truma heater as our Suburban is like a rocket going off. Keeps the place warm though!

I've been absorbing all the good ideas presented. Thanks to all. We are expecting another cold front soon so I will do some more testing. I'll also take floor temperature readings next time, could be interesting. Looks like all you LE2 folks will have to do your own due diligence figuring out return air flow but I see the gears are turning! I think it is a worthwhile endeavor. Cheers.

Dave

 

 

[Rivernerd]

18 hours ago, Snackchaser said:

Does anyone happen to have a picture of a return air vent in the bathroom?

Below is a photo the return air vent in the bath installed by Oliver in our 2022 Elite II Hull #1291.  The photo is taken looking down; our standard Dometic toilet is visible in the upper right corner of the frame.

This 3" vent allows hot air pushed into the bath by the Truma Varioheat furnace to return through the underbelly to the furnace.  It does not create a draft.

Below is a photo of the other side of the bath return air vent, taken from underneath the front dinette seat.

In addition to this factory 3" return air vent, I added a 4" vent on the aisle side of the front dinette seat.  A photo of that "owner-installed" vent appears above in this thread.  The additional 4" vent further improved the flow of return air through the underbelly of the trailer.  That allows us to camp in colder ambient temps without putting the plumbing in the underbelly at risk.

Edited March 4 by Rivernerd

[Ronbrink]

21 hours ago, Rivernerd said:

Below is a photo of the other side of the bath return air vent, taken from underneath the front dinette seat.

Any concerns of moisture being drawn from the wet bath through said bath return vent into the underbelly? I know when running the ceiling exhaust fan while showering that the wet bath has negative pressure and air is subsequently drawn in through the warm air duct whether the furnace is running or not. Post shower, if the fan is turned off before the wet bath throughly dries it seems any excess moisture could pose an issue, especially if the furnace is on. Personally, I squeegee the bath interior as best possible and keep the door closed with the fan running until completely dry to lessen the chance of raising the humidity level in the cabin proper. 

[Rivernerd]

12 hours ago, Ronbrink said:

Any concerns of moisture being drawn from the wet bath through said bath return vent into the underbelly?

No.  We have the Oliver-installed shower curtain, which keeps the toilet area, including the return air vent location, fairly dry during showers.  And, like you, we squeegee the shower walls to speed up drying of the wet bath.

Given the amount of air flow whenever the furnace is running, we have experienced no moisture issues in the underbelly.  I believe the more abundant source of any moisture in that area comes from condensation when outside ambient temps are low and humidity is high.  The flow of return air through the underbelly, which is enabled by the return air vent in the shower, actually helps dry out this condensation.

Edited March 6 by Rivernerd

[DavePhelps]

Thought I'd wrap up this discussion with some more test data. It's been around freezing here the past few nights so I wanted to verify past results and include a baseline test with the original OEM setup with just the return by the furnace.

Pretty much all original results (OEM return blocked, and two 6" returns added at the rear of trailer) were confirmed, with some minor variances, with curbside rear temps increasing on average 15 degrees, street side rear temps increasing on average 20 degrees, and the under sink area increasing on average 12 degrees. Floor temps at the rear of the trailer increased 14 degrees. These increases were from a cold start in the morning. To start, all under floor areas were about 5-6 degrees warmer than the outside temps, and 11+ degrees colder than the inside temps (I keep a small space heater running in the trailer in the winter).

Interestingly, when I put the heating system back in its OEM configuration, and closed off my 6" test returns, this showed only 3 degree temperature increases in the rear curb and street side areas. So not so great there! Under the sink, however, had similar gains (12 degrees). So I think some return air must travel in through the spaces between the cabinet drawers and back to the area under the sink. In my 2015 E1, the cabinet box is open in the back so return air can pass through to that area.

All this may not apply to some of the newer trailers, but there are a lot of older ones out there that could benefit from this mod if you travel when it's cold out. Just how cold one can go I can't say yet, but this mod will certainly help a lot and is very simple to implement. The E1 will be different than the E2 as the furnace locations are different among other things. The same principles will apply however, with high pressure (cabin) moving to low pressure (under floor), and the returns will just be located in different areas. Preferably, but not always, as far away from the furnace and supply outlets as is practical (depending what path you want the return air to travel). Thanks. Now I have some big holes to drill out...yikes! 🤯

Dave

[johnwen]

2 hours ago, DavePhelps said:

Now I have some big holes to drill out...yikes!

Good luck with the drilling, Dave :)

John

[ADKCamper]

Thanks, Dave! Appreciate all of the research/experiments with your Elite... its earlier and slightly different from ours, but much more similar heating-wise than the Elite II's discussed in other "keep the plumbing warm" threads!

Camp on 😎