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Old 01-11-2016, 07:09 PM   #1
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Underbelly heater mod

A temporary mod to help keep the underbelly warm in below freezing temps. So far I have recorded a 20 degree jump in the temps. Today it was above freezing 39-40 degrees, so it is untested in really cold temps. As recorded today, the underbelly running off furnace heat only was only 10 degrees above the outside temp, now I am seeing 30 degrees above the outside temp in the underbelly with the space heater running on high. (sorry, no pictures during the mod process).

If you are interested the materials I used included:
- 1x Patton utility space heater from Wal-Mart, about 19. Lowes had a similar model but with more finely tunable controls for a few dollars more, but they were closed when I got the one from Wal-Mart.
- 1x 6" duct takeoff from Lowes (needed to keep the space heater from triggering the overheat protection)
- 1x 6" to 4" duct reducer
- 1x 5' 4" drier duct or flexible duct
- 1x roll of aluminum ducting tape
- 1x Wireless thermometer (optional)

Procedure:
- Cut a 4-5" hole under the sink island (if you have one, another cabinet would do so long as it has open access to the underbelly).
- If you have insulation between the floor and the underbelly, push the mat insulation to the side and cut a 4" hole in the fabric between the floor and the underbelly. Try to keep this one closer to 4" or slightly smaller to help create a natural seal around the flexible duct in the next step.
- OPTIONAL: install wireless thermometer to monitor underbelly temps
- Push the flexible duct into the hole and try to get it to lay flat in the underbelly so the hot air is not being pushed against the underbelly but into the cavity of the underbelly. Ensure the end of the duct is not facing towards the optional wireless thermometer to minimize the affect it has on the measured temps.
- Attach the 6" duct takeoff to the space heater, centering it against the exhaust grating as best able, secure with aluminum ducting tape
- Attach the 6" to 4" reducer to the 6" takeoff, secure with aluminum ducting tape
- Attach the flexible duct to the 4" end of the reducer, secure with either aluminum ducting tape or a screw type clamp.

Turn on and enjoy a warmer underbelly. Adjust space heater when desired temp is reached in the underbelly.

Side note: to make this mode the most effective, ensure all gaps in the existing expanding foam insulation on the outside are plugged. I also used some old wool socks (redneck maybe?) to wrap around the slide out supports where they exit the frame to help prevent heat loss in these areas.
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Old 01-11-2016, 07:53 PM   #2
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Should work fine....I did a mod also....went to Arizona.
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Old 01-11-2016, 08:23 PM   #3
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Unfortunately, I do not have the mobility mod...yet. For now, I follow work.
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Old 01-12-2016, 07:58 AM   #4
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Simple, and works; thanks for posting, MG.

To improve upon how well it works, I would think adding something like R-Tech 2" foam board (its R-7.7), sandwiched between the belly coroplast and the frame (entirely) and seal every opening with the gentle expanding foam in a can. Also, and not forgeting the area beyond the frame... to the outside wall.

I don't see spray foam as an option, due to the mess, but it wouldn't it be awesome?

Not sure where you are, but with the arctic wave coming down from Canada yesterday / today maybe you will get a good test on your mod (unfortunately!).
WW
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Old 01-12-2016, 09:12 AM   #5
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Great Idea

Good Job!
It does remind me of Apollo 13 and what they did to survive.....
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Old 01-12-2016, 07:54 PM   #6
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Quote:
Originally Posted by WolfWhistle View Post
Simple, and works; thanks for posting, MG.

To improve upon how well it works, I would think adding something like R-Tech 2" foam board (its R-7.7), sandwiched between the belly coroplast and the frame (entirely) and seal every opening with the gentle expanding foam in a can. Also, and not forgeting the area beyond the frame... to the outside wall.

I don't see spray foam as an option, due to the mess, but it wouldn't it be awesome?

Not sure where you are, but with the arctic wave coming down from Canada yesterday / today maybe you will get a good test on your mod (unfortunately!).
WW

I do not know if I will go that far, but I do intend to open up the belly and insulate the water lines themselves for added cold weather protection. I did think about doing some kind of insulation along the frame i-beams if none exists, but until I open it up my plans are all visionary.
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Old 01-12-2016, 08:44 PM   #7
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I also did the mod and works wonderful. I have a 29hfs, so my hole in the floor is in a different location. I had a freeze up last winter and lucky nothing broke. I cut my hole under the breaker box, a 4" hole. Anywhere else there isn't enough room as WW stated about the area between the wall and frame rail. I wanted originally to go under water heater, but there is a cross member right down the center. I cut a hole under breaker box and then screwed down a 4" high cfm 12 volt fan. If you ever put your hand around your furnace as it runs you will notice it puts a lot of heat off. So now the fan runs constantly either forcing warm cabin air or hotter when the furnace runs. I also filled in any cracks as well in the underbelly with spray foam, the black poly foam of course.
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Old 01-13-2016, 08:50 AM   #8
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Quote:
Originally Posted by mark.g View Post
I do not know if I will go that far, but I do intend to open up the belly and insulate the water lines themselves for added cold weather protection. I did think about doing some kind of insulation along the frame i-beams if none exists, but until I open it up my plans are all visionary.
Taking the coro down isn't that big a job. Based on what you want to do, it will afford you the opportunity to: insulate the pipes, insulate the tanks, add tank heaters, tidy up wiring, add wiring and cabling for future Inverter... Solar... more 12v outlets... more 120v outlets... speaker wires... you name it. When I put it back up, I sealed all holes or gaps with Great Stuff.

Not sure of the big XLRs, but 4' x 8' sheets of a rigid foam board should span across the rails and the end cutoffs can be fashioned to insulate the spaces outside the rails; towards the side walls. Some foam types aren't exactly water resistant, but the styrofoam stuff is, so I read. I would go no less than 2".

Since we can do nothing about the heat loss or heat transfer at the side walls; and improving the attic space would be difficult, getting the floor up to snuff is something we can do.
WW
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Old 01-20-2016, 08:50 AM   #9
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Well after the last single digit drop we woke up to no cold water, the hot water was still running just fine. The cold water began running again after the temps warmed back into double digits.

I decided to cut into the underbelly to see if I could figure out why we only had hot water and while my heater mod did make a huge difference. It was insufficient to propagate the entire underbelly due to the trailer crossmembers which only have a hole on the roadside of the rig for the water lines/electrical. There just was not enough air flow to push the warmer air from the mid section under the kitchen to make its way to where the water lines drop down into the underbelly by the low point drains to keep the cold water lines above freezing.

To address this, I moved the space heater outside underneath the rig and routed the duct up through the coroplast so that it would keep the lines warm where they drop down into the underbelly as well as propel warmer wire down the entire length of the rig where the water lines run. Since this was an unobstructed path I felt confident that the warmer air would make its way down the entire frame.

Last night we dropped down to 13* as measured by my mini weather station, it snowed 2-3 inches, and we woke up to running water on all accounts. I was a little concerned that the space heater would not be very effective trying to heat the outside air before pumping it into the underbelly, but it has been able to keep the temps, as measured near the entry point, in the high 60s to low 80s range depending on the ambient air temperature outside.

This is all without skirting BTW. I intend to make a more permanent solution before next winter, but the long-term forecast has us above 20* for the lows, so I am confident that I will not have any more problems with frozen water. Along with a more permanent heating solution I intend to insulate the water lines since they run along the channel in the I-beam frame which is just transferring the cold temps to the water lines since the I-beams themselves are not insulated.

Hope this helps anyone else who may be using their rigs in cold climates.
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Old 01-20-2016, 09:13 AM   #10
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Mark, why not duct both sides of the little heater and cut another hole? It sounds like you had a small section of cold water line freeze. Be nice to know where.
WW
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