Learn me: solar water heat, on the cheap.

So I was walking through Menards today with my mother, and it was brought up that she wants to replace the plywood on boards on the slab that is the backroom/entryway floor (maybe 100 sq ft) with tile, and electric radiant floor heat (backroom and adjacent laundry/utility room is an old enclosed slab porch, insulated but unheated besides the dryer and water heater and whatever leaks out of the house).

After shooting down electric heat (house has 100 amp service and a overstuffed breaker box), I suggested using the propane fired water heater and pex(rip out the plywood floor, lay tube, pour more concrete, lay tile), that was not considered permissible because propane is already a big enough bill and the water heater is a cheapo unit without the best efficiency rating to begin with. Solar was brought up.

How feasible is it to hack this sort of thing together cheap? Say, $200+the pex. Roof above the room is pretty flat (membrane) and west facing, south facing garage roof (steel) not far away(about a 4ft jump). Is this something that could be accomplished by a old truck radiator in a box? Circulation pumps? How is nighttime handled, enough thermal mass in the slab to get by (not stone cold at 6AM), is some sort of accumulator needed? Using said installation as a water heater preheater (all year) too was discussed, you do that with some sort of solar heated tank with an exchanger coil in it feeding the water heater, right?

Also, how stupid are these questions?

I dunno how effective solar heat would be there -- you need heat the most when it's cold out, which also tends to be the time when there isn't very much sun. My pool has a solar water heater (installed by previous owner) and supposedly it helps keep the temperature up enough to add a month or so to each end of the warm-enough-to-swim seasons. It doesn't seem to do much in January.

Assuming the house doesn't have a natural gas supply, propane sounds like the right answer to me.

what about using the exhaust heat from a furnace to heat the water thought a rad type device.

it would work like a reverse car cooling system.

In reply to codrus:

That did occur to me a minute ago, this is Michigan we're talking about.

In reply to The Canadian:

Primary heat is a woodstove in the basement, you might have something there, wrap the exhaust pipe in copper or something to that effect.

BrokenYugo wrote: In reply to The Canadian: Primary heat is a woodstove in the basement, you might have something there, wrap the exhaust pipe in copper or something to that effect.

check this out. i made a similar one for my shop

Woodstove Heat Exchanger

The Canadian wrote:

BrokenYugo wrote: In reply to The Canadian: Primary heat is a woodstove in the basement, you might have something there, wrap the exhaust pipe in copper or something to that effect.

check this out. i made a similar one for my shop Woodstove Heat Exchanger

I could see a copper pipe and automotive coolant based design working quite well for radiant in floor heat. Would be potentially tricky getting the flow rate right, but probably be pretty inexpensive if you're a decent fabricator.

I had a house once with radiant slab which was heated only with a standard water heater. It worked, kinda.

The house was in south GA. The slab was plumbed at construction, and had insulation underneath and thermal breaks to the exterior. It barely worked.

I am going to say no. It ain't gonna work in MI. You would have to embed the pipes in the slab to get any transfer, and you need the insulation under and the thermal breaks to the exterior. You are going to need more BTU's of heat generated than I had. Your rooftop system is going to be prone to freezing. And it will most certainly be freezing cold at 6AM. You MIGHT feel a little bit in the late afternoon, if everything works well.

I built a crazy plumbed rooftop system in Costa Rica once, but again, it doesn't get nearly as cold as MI.

A plumbed system has thickness that cannot be hidden under the tile like an electric tape system. Sorry.

If you take too much heat out of the combustion gases there will be parts that condense out and will reek havok on the wood stove. Big no no. Unless of course you actually have a condensing wood stove, highly unlikely. The stuff is highly corrosive, thats why high efficency furnances have pvc vents.

100 square feet? Seems like electric floor heat might actually be the most viable. Even with that overloaded panel box.

Two of these, plugged into an outlet, and you're done. http://www.amazon.com/gp/product/B00067ASOA/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=1944687622&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B000BR0M32&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0KZ6JGSYAHYGQ5BDAT7B

You could use a vacuum-evacuated solar heater panel. These even work in the winter because they capture solar heat while being insulated from outside temperatures. They're even used on arctic bases.

My cousin lives in Alberta, Great White North. It gets cold up there. As an uncle who had a bakery told me, "This is the deep freeze. It's 30 below zero in there. When it's 40 below outside, we go in there to warm up."

So my cousin is a farmer, and in the winter, he worked on his stuff in a Quonset hut type shop with a concrete slab. The slab was poured with the pipes in it for radiant heat, and he used two large home type water heaters and a small pump to run the whole thing. There was also an air separator gizmo on the line to burp out any air and that was it. It was a pretty good size shop. It kept the whole thing warm enough for him to work up there in the middle of the winter. And as my uncle said, he lived there his whole life and had never been "snowed in." My cousin then added that sometimes you have to take the snowmobile to the tractor to plow your way out, but, yeah, that's not "snowed in."

GameboyRMH wrote: You could use a vacuum-evacuated solar heater panel.

Not for $200. And even if you could, that's just the collector, not the circulation system. And it certainly won't be warm at 6AM.

Existing concrete. No pipes.

The correct answer for this one is electric floor heat. That, or fuzzy slippers.

How about solar HEATED fuzzy slippers??

SVreX wrote: How about solar HEATED fuzzy slippers??

Hey that could work. A couple of RC plane battery packs with extras for rotation, some motorcycle grip heaters, a solar charger stuck to a window, and your feet will always be warm with very little energy cost

In reply to GameboyRMH:

Damn. I thought I had it, but you definitely won that round!

Solar hot water panels will, at some point, leak. Always.

Wire some of these into the slippers https://www.sparkfun.com/products/11288

DaveEstey wrote: Solar hot water panels will, at some point, leak. Always.

I get about 1 leak every 4 years on average from the system at my house, but much of that was from a creaky old system that was recently overhauled.

I did something similar, but not water. LINK
It actually works better on bitter cold days. Think about it, when it's really cold on Jan and Feb (here in MI) it's always sunny. The clouds trap the heat in close to the ground.
Where in MI are you?
The one I built is small and designed to be inefficient for the WAF (wife approval factor) but it puts out hot air within minutes of full sun.