Adding "Some" Underbelly Heat

[GolfingDave]

After being informed that I did not have underbelly heat(thought the small hose going to the rear bathroom was underbelly heat), I thought I might add some. Just want to keep it above freezing in extreme temps which I hope not to see too often.

I have three heat vents going to the main living area and I had already capped the one off directly below the thermostat. Still plenty of air flow to cycle on the thermostat and not duct limit.

I was able to use that four inch duct to do it. Luckily there was an opening nearby between my drawers and the duct outlet with wires running through to the underbelly. I did have to enlarge it a bit using a drill and dremel tool.

Final setup was buying some six foot bilge hose, cutting them in half and taping them all together at one end. They then fit nicely in the four inch duct. Insert them, tape it all up with aluminum foil tape and slip the other ends down through the floor.

I had originally only used one bilge hose with two sections through the opening but when I only had a high of 25 for the day my underbelly temp crept down to 28 that night. My hot water line froze below my sink. Wind was blowing pretty good too and the underbelly cover is only screwed in every so often. Maybe will put some tape the length of the seam on both sides?

The next day I added a third hose through the opening. Just capped off the end of the fourth hose. Turned the heat on and during the couple of minutes it ran to bring the cabin temp up a couple of degrees the underbelly temp went up one degree.
That night my underbelly was down to around 33 degrees with just the fireplace running. Gave it another try and after a short run of one cycle it came up a degree also. My thermometer is located closer to the rear bathroom maybe five feet away from the opening. I can feel air being pushed up through the opening for the shower drain when I remove the shower base access cover, much better with three sections of hose than just two(guess that would be 50% more volume).

The bilge hose is good for 140 degrees. Depending on where I take the temp reading on the bilge hose right at the end of the duct it is reading 140-150. Should be ok there. It only runs for a few minutes and there was no deformity on the two hoses I had already used.

Don't think I would just cut an opening if not one there already. Not without removing the underbelly cover and seeing what is in the area.

It is kind of trial and error though on getting the fireplace and propane heat to act together. The fireplace is right above all the ductwork so it warms up whenever the propane heat is on. I even block off below the fireplace but enough heat radiates up and shuts off the fireplace. Or the fireplace heat if set too high will drift up to the thermostat and not let the propane heat kick on.







Hoping trimming the panels down in height will help with keeping my water line valves from freezing. They was only maybe four inch gap at the top. Had my hot water line freeze.

[Crutter]

RVs are extremely air leak prone. I guarantee that the air that you are feeding to your underbelly is leaking out causing the insignificant rise in temps. The air is probably leaking from the joints in the frame and where the underbelly material is laid in the frame channel. I wonder how much of a temp rise you would get with a little sealant?

[GolfingDave]

Originally Posted by Crutter

RVs are extremely air leak prone. I guarantee that the air that you are feeding to your underbelly is leaking out causing the insignificant rise in temps. The air is probably leaking from the joints in the frame and where the underbelly material is laid in the frame channel. I wonder how much of a temp rise you would get with a little sealant?

"insignificant rise in temps" If you are referring to the 1 degree rise I noticed after adding the third hose that was just a test for 1 cycle of the heater. Always took several cycles prior to that.

Further on I stated I removed the cover at the shower base and had a lot more air movement. With the temp rise and more airflow I was more confident in not having anything freeze at lower temps. Not that anything had except for the lower point drain hose and that is on the outside of the frame. It is teed off the bathroom sink is how I noticed that.

I don't recall if I ever did another test overnight with the heater running. Cold weather is gone for now, have to wait until next winter.

I am planning on putting seam tape along the whole underbelly cover to frame this summer.

[tdjmain]

You could get the foam wraps for your pex lines just slide on and self sealing

[GolfingDave]

Originally Posted by tdjmain

You could get the foam wraps for your pex lines just slide on and self sealing

Had/still have some on. Even plugged the opening at the bottom. Got fairly cold again a few weeks later for a couple nights when I got in the mountains a bit so I put a trouble light in the area and it kind of enclosed with some Reflectix for some added protection for a couple of nights.

I think cutting the board back and better airflow did the trick though for that small area. Thinking the added heat will definitely help keep the shower and kitchen sink lines warmer.

[GolfingDave]

Pleasantly surprised.

I have been able to work with this a bit now since I added the heat. Initially I tried to set my thermostat and fireplace close to one another so they would kind of flip flop between which one would run. Kind of worked.

So now I have figured out that just setting the fireplace to a higher temp and the propane heat to what temp I prefer to be comfortable at works best(when I have to use the propane heat). My fireplace can keep up until the temps get below thirty and no sun. My fireplace is close to my pantry area so it picks up some cooler air from that area. But the underbelly heat I added is directly below the fireplace so it picks up that heat when I have the propane heat on. I even added a floor under the fireplace but heat still migrates up.

I ran into a couple of days last year in the upper teens at night and the underbelly was still getting pretty cold, right at freezing. Now with adjusting the heat as mentioned above and sealng my underbelly perimeter here

https://www.forestriverforums.com/fo...ml#post2920332

I now feel comfortable with the temps getting to the mid teens and things not getting frozen.

At least until power goes out. I do carry a generator.