Radiant heating

[malconium]

Bryan,

I think your calcs generally fall in line with what I am expecting. They actually go into more detail than I have so far - and thanks for that. I ran the whole idea by someone locally who does radiant heating and they felt what I was proposing was feasible. I also spoke with someone at the website I posted earlier about the approach. On the PEX tubing they are sized by ID by the way.

What I was thinking of doing was putting the heating tubes at 6" on center and putting them under the entire floor not just the living areas themselves. It occurred to me that this would help keep everything in the AS warm including the things in my storage spaces. I generally thought that these extra areas would not draw as much heat as the open areas so this would not really hurt anything and might actually help. I calculate that my total floor area is about 200 square feet. Tubing everywhere at 6" o.c. should give me right around 400 square feet if I calculated correctly.

I do like the looks of the Excel heater especially for its price point. If it were in a comparment that was isolated from the interior air I suppose that it could still be insulated so that it would not actually be entirely outside.

Over59,

One of the interesting problems with using a continuous flow water heater has to do with the regulation issue. The RV500 for example turns on when it senses enough difference in temperature between the input and output sides of its plumbing. If there is not enough difference it might not turn on. It could be that the Excel would actually have an advantage here.

I am counting on a few assumptions for this to work. For one thing I am installing reflective foil insulation with the expectation that I will have better insulation - especially relative to radiant heat loss. I am also counting on the 6" on center tubing placement to be a bit of an overkill compared to what I have been reading about for typical installations.

I am basically just going to follow my assumptions and see what happens - just like with the roof paint.

[bryanl]

> This would seem to need alot of careful designing.

that would be one way. trial and error would also not be out of order as both the risk and costs can be rather low.

> Design assumptions?

generally you would be talking about a thermostat regulated mechanism (circulating pump powered via thermostat) that could provide acceptable heating at some given worst conditions. A starting point would be the existing nominal heating systems which deliver about 20k to 25k BTU/hour from a forced air furnace for the larger Airstreams. One potential limitation would be an existing RV water heater capable of maybe 10k BTU output.

> there is the question of how fast the water should circulate at what temperature.

The guide here is standard practice for floor radiant heating. This is a low flow rate with a 10 - 15 degree loss in the loop. This usually translates to about 300' of half inch tubing with the usual pumps.

> Less water is good. For 3 gallons it only takes 6 minutes. So the pump
> needs to move at least 1/2 gallon a minute.

http://www.heatinghelp.com/newsletter.cfm?Id=161
indicates that a half inch pipe is good for a gallon and a half per minute in a secondary circulation system. a 400' loop would need a pump good for a 24' head.
- this is close to your calc, which is comforting.

interesting stuff, there is a lot of design information, from the high end HVAC engineer stuff to the backyard mechanic stuff, out there. The pump is really the only critical component and availability is likely to be more important that close specification.

[malconium]

Bryan,

I have been thinking that I would find a pump at a marine supply place. I took a look at the various pumps at the following website and it seems like there are quite a few water pumps that can handle from 2 plus gpm.

http://www.defender.com/category.jsp...1|51&id=299222

One of the pumps that looks promising is on the following page:

http://www.defender.com/product.jsp?...6443&id=151097

This pump puts out 3.3 gpm, is rated for continuos duty and is supposedly quiet. Do you think that 3.3 gpm would be too much flow for the application?

I wish there was more information posted about noise levels.

Malcolm

[Over59]

Cool, learned stuff again. Why do they call it head? Is this the resistance equivalent of pushing water out of a boat from X feet below the surface. I see pumps with amp draws dependent of the head (lift?).

These pumps tend to draw alot of juice. More than some hot air fans.

[bryanl]

Oh boy, another history of words lookup! ;-)

If I get it right, head refers to the pressure the pump can create. If so, then 33' of head means about 15 psi of pressure is available from the pump (1 atmosphere). A typical RV water supply pump can get up to 45 psi or so which would be nearly 100' head. I think the pump current draw is going to be pretty much proportional to water volume times pressure. A circulating pump only needs to generate enough pressure to get flow through the pipes and only enough volume to get a flow that provides for effective heat transfer.

The heat flow is a matter of temperature difference and that is fairly low in hydronic systems. Loop input at, say 130F with 70F floor temp means maybe a 60F dif while output temp of 115F means a 45F dif. This is why a lot of surface area is needed to get much heat to the room. The transfer efficiency is probably not a problem because it shows mainly in the circulating pump - all other losses generally trend towards heat into the room.

The other side of head would be the draw or lift of a self priming pump. This isn't a concern with a circulating pump but it is for the RV water supply pump. It takes some pump to be able to lift water more than 5-10 feet to its input. This side of things depends upon atmospheric pressure pushing the water up to the pump.

as for the 3.3. gpm pump, I wonder what kind of pressure that is against? at 7amp my guess would be a rather high pressure as it sounds about like what a typical RV supply pump provides and consumes. Another potential problem appears to be heat and a good hydronic heat circulating pump needs to be designed to operate with hot water.

For efficiency I think you need a pump that is designed for low head (less than 15 psi or 33 feet) and high temperature water. Half inch pipe in a typical 300' run seems to require a 24' head and under 2 gpm for optimum heating. It should probably not draw more than a couple of amps at most, if that.

[malconium]

If anyone is interested in using hotwater heat but wants to have a radiator/fan installation somewhat like what was mentioned earlier in a referenced post take a look at the following web page (near the bottom). This marine supply company has two different sizes of hot water forced air heaters that look like they could very well work just fine for an AS. They are capable of outputs from 12,000 to 24,000 btu, have a built in fan that runs on 12v with a small power draw and are pretty compact. It seems like they would be able to run from hot water from a water heater.

http://www.dickinsonmarine.com/shop5...s/SPECSRAD.doc

Malcolm

[malconium]

Thanks to Bryan here is a pointer to a source of a couple of pumps that sound like they would work just great for hot water radiant heating. They are a little spendy but their specs sound like they would be perfect for the application. They are designed to handle hot water, run very quietly and have brushless DC moters for very long life. Check them out.

http://shop.altenergystore.com/items...~0~Tp~~Bc~.htm

Malcolm

[Over59]

Now if you used a pulsating dimmer switch and a brushless pump could you adjust the flow and amps? If you adjust the voltage on those pumps you are adjusting the flow rate? It is also a way to fine turn the system.

Still, there is no way I am letting water have that kind of access to my new floor. I'll stick with the hot air for off grid and the AC heat pump online. You have an interesting design project.

[JeepinAudiophile]

I am planning on installing radiant heating in my 68' tradewind. I agree with over 59 that the thought of giving water access to my newly replaced floor kinda scares me. I have found an electric elements that can be laid under the flooring tiles. Of course this means you have to be plugged in to use the radiant heat. I can't remember the company that makes it, but i will rummage through my files and find the company. It would be nice to be able to use the radiant heat when not plugged in- but for me, the possibility of water damage outweighs the niceities of having radiant heating when boon-docking. --Chad--

[malconium]

The concern relative to water damage and the floor is, of course, a valid one. That is a primary reason I installed a Polyboard subfloor. I have been intending to install hot water radiant heat right along so the decision to use Polyboard (which is completly waterproof and rot proof) was part of that larger plan.

Electric radiant heaing solutions are available from a number of sources. I do not know for sure if there would be any issues relative to the total current required when plugged in, though. What are you anticipating your total wattage to be for your electric floor heating system?
Malcolm

[markdoane]

Originally Posted by JeepinAudiophile

. . . I have found an electric elements that can be laid under the flooring tiles. Of course this means you have to be plugged in to use the radiant heat. . . . but for me, the possibility of water damage outweighs the niceities of having radiant heating when boon-docking. --Chad--

I don't think you could get enough heat flux to do more than take the chill off. In wood (non-masonry) floors, the electric heat cable is limited to 10w/sq ft. So for a 88 sf ft area, you could only get about 880 watts (3000 btu/hr), less than a hair dryer.

Would be really nice for those cool (but not freezing) mornings, though.

[pamelake]

There are several companies (Warmquest is one) that make very thin electric coils or mesh to install under wood or tile flooring. This is what I would like to do in my '74 Tradewind. Nice, quiet, even heat when you are plugged in seems nice (and not too expensive). I wonder what the problems would be? I would love to hear from someone who has done this. Thanks, Pam

[markdoane]

Pam,

I did this in my 'indoor' bathroom. It was tile on backerboard with the wire set in thinset. It's a lot of work if done in thinset. I don't even know if thinset would work in an airstream.

If you install under a wood floor, you need to 'superinsulate' the floor, or else you lose too much heat to the belly. If you install it above the subfloor, it would need to be in grooves or between firring strips.

I used wire from http://www.warmlyyours.com/
There prices were half of what it costs at Home Depot.

[malconium]

Here are several sites that supply electric radiant heating materials.

This one has a product that can be installed under laminate flooring without any thin set:

http://www.warmlyyours.com/

This site offers, among other things, a low voltage system:

http://www.warmzone.com/RadiantHeat/RadiantHeat.asp

These guys were the choice of "Ask This Old House" and etc.:

http://www.nuheat.com/homeowners/experts.cfm

This company offers a lot of different sizes of standard mats:

http://www.suntouch.net/

I think in general that radiant floor heating systems require less energy than forced air systems because of the radiant heat delivery mechanism. One of the sites mentions 41 watts per square foot as being enough to keep the floor at 80+ degrees. I suggest checking the vendor claims closely before concluding that these systems are only capable of keep the chill off.

Malcolm

[markdoane]

Originally Posted by malconium

. . . One of the sites mentions 41 watts per square foot as being enough to keep the floor at 80+ degrees. I suggest checking the vendor claims closely before concluding that these systems are only capable of keep the chill off.

Malcolm

Yeah, I'm all for that! Where did you get that number? I would believe 41 Btu/sqft, but not 41 w/sqft. I think that would curl your flooring and fry your toes.

[malconium]

Don,

You are right - it would appear that I got watts and BTUs mixed up. The following is a quote from the site listed below:

"Nuheat produces 12 watts per square foot or 41 BTU at full power producing a floor temperature of 88 - 92 degrees Fahrenheit"

The site with the above quote is:

http://www.nuheat.com/homeowners/features.cfm

Malcolm

[jerri]

I am new to this, or would that be rivetless.
Radiant Flooring is going great. 1/2 In pex roughed in. 300 feet in all which gives you about 3 gallons of liquid. One RV 500 modified at the factory to specs (exspensive).Rayon cutting boards milled and machined to mount the pipes into between the chassis members ( exspensive) I will do my best to get photos for you. Bubble wrap insulation with foil sides (expensive again). Work in progress.Threading 300 feet of pipe in the chassis PRICELESS!!!!!!!!!!!!!!!

[malconium]

Jerri,

Sounds interesting and I will be looking forward to your photos.

Malcolm

[FranyPul]

I may be coming in a little late on this, but I'm happy to see that others have considered radiant heat and that I'm not entirely out of my mind. Have you all hear of Warmboards? They are supposed to go in like a regular base floor, have grooves cut out for piping, and all lined with, I think, aluminum. Any floor type can go on top of it. Because I have to replace my floor anyway, I was hoping to go with the Warmboards and put bamboo on top.

(no I can't afford this)

Kim

[malconium]

Originally I was thinking of using aluminum fins that would snap around the radiant heating tubes to help distribute the heat. Lately I have been thinking of taking another approach. I have not been able to work on my AS for a while because of other things but that doesn't stop me from thinking about various aspects of the pending remodel. At anyrate I asked a local company that supplies radiant heating things for DIY installations what they would think about just having the tubing fastened to the floor and no aluminum fins. They told me that actually the air around the tubing would work OK to get the heat distributed - it just might take a little longer.

I had originally been thinking of stapeling radiant foil insulation on top of my Polyboard floor, then putting 1x2 strips on top at about 6" on center. I was going to center the plastic tubing in between the 1x2 in aluminum fins that would span from 1x2 to 1x2. The 1x2 was going to support the final flooring. I was thinking about using some form of floating floor that could span 5" gaps. Maybe laminate, bamboo or cork. As an alternative I could envision using something like 1/4" underlayment plywood on top of the 1x2's with the finish floor on top of that (if the floor was flexible).

I was thinking about the support issue recently and it occurred to me to wonder if I really needed the 1x2 to support a floating floor if I was not going to use the aluminum fins. I went and looked at some of the PEX tubing at Home Depot and I find that it is actually very stiff. So I am wondering what would happen if I fastened down my PEX tubing at about 6" on center and just set my floating floor directly on top of it. What I do not know is how flexible the tubing would get when it warms up. It does seem like having it full of water would also help improve its crush resistance.

So my current thinking is this:

1.) Add a layer of reflective foil insulation on top of the Polyboard subfloor.

2.) Lay out my PEX tubing at about 6" on center and staple it down to the Polyboard.

3.) Install a floating floor directly on top of the PEX tubing. I might pick a variety of floating floor that has a foam or cork backer layer that could deform where the staples are that hold down the PEX tubing.

I would appreciate any feedback that anyone would have on this bare bones approach. Especially if anyone knows what the crush strength of the PEX tubing would be at temperature.

Thanks,

Malcolm