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Old 06-20-2011, 07:44 PM   #15
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Right after WWII Buckminster Fuller designed a pre-fabricated house that had an early form of radiant heating. The inner and outer walls were metal and the heater blew hot air into the empty space between them, warming the inner walls, which then radiated heat into the interior. The only problem with it was that the inside of the cupboards got quite warm. I wonder if anyone has ever tried this with an Airsteam?
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Old 06-21-2011, 02:47 PM   #16
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Right after WWII Buckminster Fuller designed a pre-fabricated house that had an early form of radiant heating. The inner and outer walls were metal and the heater blew hot air into the empty space between them, warming the inner walls, which then radiated heat into the interior. The only problem with it was that the inside of the cupboards got quite warm. I wonder if anyone has ever tried this with an Airsteam?
The basic idea seems like a good one. Putting air in the walls might be a bit problematic though in that there also needs to be some space for insulation and we only have about 1-1/2" of space to work with in an Airstream wall. Reflective foil like I used in my walls might be the answer for that problem.

It would indeed be nice to take advantage of the large aluminum surfaces that make up the inner skins of an Airstream to help warm the inside. Putting hot water PEX tubing inside the wall could very well work but it might be a bit tricky to figure out how to attach the tubing. Ideally one would like to attach the tubing to the back side of the inner skin in a way that provides nice thermal transfer from the PEX tubing to the aluminum skin. There would potentially be a lot of chances to accidentally puncture the tubing when installing the inner skins and other accessory items. I have given some thought to mounting some tubing on the inside surface of the ceiling in my Airstream. There is somewhat more surface area available up there than there is on the floor because of all the furniture that gets in the way. I could easily enough visualize someone using an approach something like the heated towel bars or other radiant devices that are surface mounted. I looked into some of them but felt that they were a bit expensive. I am going to start with the pipes in the floor and see if that gives me enough heat for my purposes. If not I may add other heated surfaces or perhaps a fan forced water heated radiator of some sort.

Malcolm
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Old 07-28-2011, 11:03 PM   #17
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pulled from the depths of lurkdom

Malconium,
Your ambitious and ingenious project was inspiration to finally register and become a poster to the airforums. While I have been a lurker/dreamer for a while, last week I purchased a 71 Sovereign and will soon be full timing. The details of my project will be saved for others threads.
I have worked in construction on and off for the last decade and have had opportunity to install a few radiant heating systems. I like your idea of using “planks” for flooring giving access to the plex if ever the need arises. I try to plan for things to go wrong, because I am paranoid and things usually do. (Correlation between the aforementioned events has yet to be documented.) Having access would make me happy.
However, I am curious what medium you were planning to pack around the plex. My installations utilized gypcrete. Gypcrete is a great product for radiant heated floors, but I could not recommend it for an Airstream; its combination of weight and rigidity, would not be positive. I have done a few searches for a lightweight heatsink alternative, but have yet to find anything that trips my trigger.

Do you have plans for a heatsink?
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Old 07-29-2011, 02:14 AM   #18
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Malconium,
Your ambitious and ingenious project was inspiration to finally register and become a poster to the airforums. While I have been a lurker/dreamer for a while, last week I purchased a 71 Sovereign and will soon be full timing. The details of my project will be saved for others threads.
I have worked in construction on and off for the last decade and have had opportunity to install a few radiant heating systems. I like your idea of using “planks” for flooring giving access to the plex if ever the need arises. I try to plan for things to go wrong, because I am paranoid and things usually do. (Correlation between the aforementioned events has yet to be documented.) Having access would make me happy.
However, I am curious what medium you were planning to pack around the plex. My installations utilized gypcrete. Gypcrete is a great product for radiant heated floors, but I could not recommend it for an Airstream; its combination of weight and rigidity, would not be positive. I have done a few searches for a lightweight heatsink alternative, but have yet to find anything that trips my trigger.

Do you have plans for a heatsink?
First of all welcome to posting on the forum. Posting and interaction through posts has been an interesting thing for me.

Relative to your question I am familiar with various types of material that has been used to encapsulate radiant heat tubing. I built a house in the late 70's that had copper tubing buried in the concrete slab on the main level and something similar to gypcrete on the second level. I have also heard of using sand. The problem with using one of these types of products in an Airstream is not only one of weight. The other issue is that they are not really good for a heating system that you need to be quickly responsive like we need in our Airstream. My house took at least 24 hours for the radiant heating system to come up to temperature and stabilize. Once stable we left the thermostat alone. The thermal mass of the concrete or light weight concrete is a nice thing in that it helps even out the temperature but not a nice thing for systems that need to come up to temp quickly. One approach is to have aluminum plates with grooves in them for the PEX tubing. The aluminum plates transfer the heat very quickly and evenly to the bottom side of your flooring. It makes the system more expensive than I wanted mine to be though. It turns out that air actually makes a reasonably good transfer medium and heat sink for a system like what we need. It does not take too long to heat up but it does provide some amount of thermal mass. That is the approach that I decided to take for my installation.

I hope that helps,

Malcolm
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Old 07-29-2011, 02:23 AM   #19
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Only problem is during 'Open House', no one wants to leave your cosy trailer.

Great photos, great idea, great craftsmanship
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Old 07-29-2011, 03:47 PM   #20
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Warmboard

I had forgotten the Warmboard option, likely because at 7 bucks a square foot there is just no way. ($223.00 for a 4x8 sheet)

After searching a bit, I found a website were people were making their own warmboard Router my own ply for " warmboard": | Breaktime

I'll post more later
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Old 07-29-2011, 04:18 PM   #21
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Ambitious project.

The typical output for a radiant floor is 18-25 BTU per square foot. Your floor area is around 200 square feet, which means you'll have 5,000 BTU output, max, a little more than you would get from a 1500 watt heater. I think you'll find that it works really well down to 50 degrees or so.

Your 300' pex loop will hold around 3 gallons of water and so the water heater should shut off after around 5 minutes on a cold start. You shouldn't hit the time limit.
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Old 07-29-2011, 07:17 PM   #22
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Glycol

As luck would have it, this morning I was on a job and ran into the guy who taught me about radiant flooring.

He recommends using a glycol heating system with a heat transfer block between the hot water and the glycol. The water warms the glycol and the glycol is pumped through the floor. The amount of heat lost in the transfer is negligible (2 or 3 degrees). The benefit is, in event of a heater failing, the lines will not all freeze. He explained, frozen plex is a bad deal.
He showed me a couple of pictures of a recently installed hot water heater/glycol system and it is pretty neat. The heat transfer box was tiny for a house and for a trailer it could be smaller than and old style box of matches
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Old 07-29-2011, 08:27 PM   #23
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Mathish

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Ambitious project.

The typical output for a radiant floor is 18-25 BTU per square foot. Your floor area is around 200 square feet, which means you'll have 5,000 BTU output, max, a little more than you would get from a 1500 watt heater. I think you'll find that it works really well down to 50 degrees or so.

Your 300' pex loop will hold around 3 gallons of water and so the water heater should shut off after around 5 minutes on a cold start. You shouldn't hit the time limit.
I am neither a heat (or any other type) of engineer, nor do I play one on TV or online, but I know a “typical” radiant heat installation with 1/2in plex is 25BTU a sq. ft. based on a 16 inch on center configuration. If you double up the plex (8 inch on center) then, using my higher math skills you get 50BTU a square foot.

Checking post #5, Malconium is using 1/2 plex 6 inches on center----making his configuration 62.5BTU a square foot. Using your provided figure of 200 sq. ft, that makes 12,500BTU. (The chosen heater provides more than enough to handle that load)

Standard BTU recommendation for the coldest climate zone in the United States, for a “well” insulated home is between 50 and 55BTU’s. This Airstream could be much less than “well” insulated and still fall within guidelines for the coldest climate zone, (Malconium lists Portland, OR as home and Portland’s heating recommendation is between 40 and 45 BTU’s).

All and all, Malconium should keep toasty to –10F. (give or take)
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Old 07-30-2011, 12:24 AM   #24
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Finally a trial run...

At long last my wife and I are going to be taking out our Airstream for a one week trial run starting tomorrow. We will be staying in Central Oregon where the projected night time lows will be in the mid to high 40's. This should give us a pretty good chance to test the system out. Hopefully things work properly since I have not really been able to test the heat output thus far. I did install the thermostat along with a relay that is able to switch on my hot water pump just fine. I will report in on the results - maybe even mid week depending on whether or not the advertised WIFI connection really works at the campground.

Malcolm
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Old 07-30-2011, 08:21 PM   #25
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I am neither a heat (or any other type) of engineer, nor do I play one on TV or online, but I know a “typical” radiant heat installation with 1/2in plex is 25BTU a sq. ft. based on a 16 inch on center configuration. If you double up the plex (8 inch on center) then, using my higher math skills you get 50BTU a square foot.

Checking post #5, Malconium is using 1/2 plex 6 inches on center----making his configuration 62.5BTU a square foot. Using your provided figure of 200 sq. ft, that makes 12,500BTU. (The chosen heater provides more than enough to handle that load)
The problem with this line of reasoning is that making the spacing more narrow doesn't increase the BTU output by any significant degree, because 16" spacing is enough to heat the floor evenly. There aren't cold spots between the lines that could be heated up by an extra line. I've confirmed this with an infrared thermometer, and it's something that the industry relies on. The only way to increase the BTU output is to make the floor much hotter, because the BTU output is proportional to the temperature difference between the floor and the surrounding air. The 25 BTU/sf figure is based on a floor temperature of about 15 degrees above ambient. To get 62.5 BTU/sf the floor would have to be about 40 degrees above ambient or around 105-110 degrees which is both uncomfortably hot and detrimental to the life of the flooring.

Quote:
Standard BTU recommendation for the coldest climate zone in the United States, for a “well” insulated home is between 50 and 55BTU’s. This Airstream could be much less than “well” insulated and still fall within guidelines for the coldest climate zone, (Malconium lists Portland, OR as home and Portland’s heating recommendation is between 40 and 45 BTU’s).

All and all, Malconium should keep toasty to –10F. (give or take)
Good luck with that.

Check the BTU thread I started. Airstreams have more heat loss than similar sized houses. It takes around 30,000 BTU to maintain a 30' trailer warm at -10 even with no wind.
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Old 07-30-2011, 09:37 PM   #26
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Though I am not even a novice when it comes to this type of heat, I have a question/comment.
If the floor system does not suffice in colder climates, could an automotive type heater core with a fan be added, as a secondary forced air/convection heat source, that runs only when the radiant floor system is not sufficient? One more valve and a different thermostat would take care of the additionally need controls. This could be added up front near the heater or in the cabinet under the sink, or both, without modifying the floor.

Or, could a more simple solution be to add some forced air into the space beneath the floor with a grilled opening or two to let the air flow, allowing radiant and convection at the same time?
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Old 07-31-2011, 12:35 AM   #27
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I have no desire to go camping in any place where the outside temperature is -10 degrees. I also am aware that the system that I have installed will have some limit as to how cold the outside temperature can be while still staying comfortable on the inside. I have a couple of back up strategies if I decide the radiant heating is not enough by itself for the type of places I want to go. I do have my eye on a fan forced radiator style heating unit that I can easily add to the existing system should I decide to do so. There are lots of places where I could tap off of the existing radiant hot water tubing. I have for example paid careful attention to where my tubing is in the floor so that I could even tap in somewhere in the middle of the run. That could be under the end of the bed in the bedroom, under the couch in the living room or under the kitchen cabinets. Here are a couple of sites that have some units to chose from:

Radex Hot Water Forced Air Heater for Boats.* Manufacturer: Dickinson Marine

Rear Air Conditioners Heaters

Welcome to ProAir LLC -- Auxiliary Heaters

If I am camping at an RV park with electricity I could also take along an electric heater of some sort for supplemental heat.

The long and short of it is that I am perfectly willing to take it a step at a time and see how it works out. I have a source of enough hot water to do the job one way or another so I think I can find a way that works for me with some experimenting.

Malcolm
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Old 07-31-2011, 01:04 AM   #28
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Hot water

Jammer, thank for your input. I read your BTU threads and you have done solid work.
While I have worked with different heating systems in home and commercial environments, this is my first Airstream. You presented factors, I did not consider, when working in this arena.

I did a quick search and found radiant heat websites, backing up my 25 BTU’s for 16 on center flooring and 50 BTU’s for 8 on center flooring figures, but I do not believe they assist my original proposition.

Please instruct me if I am mistaken, but I believe your position is based on the insulating properties of an Airstream and the properties of radiant heat flooring. For enough heat to rise from the floor and comfortably heat an Airstream in below zero weather, the floor must be heated to an absurd degree. (Or to restate) Regardless of the amount of hot water running through a floor, only a certain percentage radiates, so to achieve enough radiating heat to heat a very cold Airstream, you must have an insanely hot floor.

The answer then, for someone who wishes to utilize a radiant heating system in an Airstream, is either, refrain from camping in cold weather or super insulate their Airstream (reading the many, many, threads on the trials and troubles associated with that enterprise)
I suppose a third option, for those who like warm floors, would be to use the radiant heat system as supplementary. (The aforementioned options are not exclusive)

Did I get it?
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