# Solar Radiant floor heat.



## thom (Nov 3, 2006)

joasis said:


> What do you guess for actual slab temperature average? Did you run the loop directly on the EPS or up in the slab?


I would guess the floor temperature to be in the 90's. In bare feet it feels warm, not hot.

I set 6X6 remesh on top of the EPS with chairs (3" I think but it was 25 years ago) so the pipe is approximately centered in the 6" slab. 

The reason for 6" slab was more heat storage. My thought was to store the heat in the space where it would be needed. It has worked well.


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## protechplumbing (Oct 10, 2008)

Interesting. :thumbup: Thom, could you list your equipment? Do you mean a drain down system or a drain back system? What I'm asking is, does the system actually drain down and must be automatically refilled with potable water on each startup cycle or does it drain back into an atmospheric tank for re-use? What type of collectors are you using? Plates or vactubes?


_"I asked about open or closed system because my current system is an outdoor wood boiler that is open. The boiler itself is rusting out, I'm noticing corrosion on the copper pipes and have had to replace a couple of iron heaters due to leaks. My most recent understanding of the problem is that being an open system allows a continuous supply of oxygen into the system, thus feeding the rust. _

_The collectors I have in mind sound the same as what Thom described in his system, definately open. I'm thinking all plastic lines (for the transfer from the collector to the storage tank) and isolating the collectors from the rest of the system with a heat exchanger in the storage tank. Then the rest could be pressurized with an expansion tank and remain closed._

_Any thoughts from the resident experts?_

_Good Luck_
_Dave"_​ 
Not a good idea. Most collectors have stagnation temps beyond what plastic can handle. I've never done it, but I know people that have and it didn't end well......


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## Joasis (Mar 28, 2006)

My wife is wanting to change the new home design completely now that we are a few weeks from concrete pour, and look at earth sheltered, my original choice.....all about energy efficiency...and if we do that, radiant floors won't be needed, but if we (she) changes her mind again, it is a definite change in the original plam sice we get about that same sunny days as Thom does, might as well cash i for free.

Next trip out Thom, I would like to stop and see your home, if you are willing.


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## nhmaster3015 (Sep 6, 2008)

Unfortunatly at this time, the cost of the equipment and installation necessary to reliably heat with solar is far in excess of any cost and or comfort savings. The same radiant floor slab, piping, controls pumps and valves mated to a mod con boiler such as a Veissman, 
Buderus or Lochnivar will out perform the solar panels in every catagory. Nobody is challanging whether or not solar can be done, it has been. But in every case the cost has been so high as to never pay itself back. In northern climates the results are even worse. When you get into the heating aspect of solar, in order for the system to be effective you either need massive and expensive storage and or a massive and expensive slab. Either way a few cloudy days and your back up is on line. Happens more than you think. There are charts available that list average sunny and cloudy days for your region. Most solar experts agree that on a cost benefit basis, what makes most sense at this time is 3 panels and an 80 gallon storage tank for domestic hot water. Even this set up has limitatations and about a 20 year pay back.


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## Joasis (Mar 28, 2006)

The difference in geography and skills being a factor, some of us can do this dirt cheap. 

I know a hvac guy that built a condenser unit, or rather, rebuilt it without a cooling fan and immersed it in a small swimming pool.....would this system be practical if you actually had to buy it? Nope, but it works for him. Keeps the pool warm......and this is how I look at solar...it isn't really practical for most, but with a few skills and the geographic location, very doable.


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## protechplumbing (Oct 10, 2008)

.........:sad: 
I think you should add "for my part of the world". In Florida solar pays for it's self very quickly. You are also not factoring in political and environmental costs that are "externalized" from most economic analysis, but that is a whole other topic that could be argued to death. The majority of the systems I install in my part of the world pay for themselves in less than 6 years. That's before you factor in government incentives as well. Incentives are in place to offset the costs of fossil fuels with externalized costs. Some setups work out to be less than 3.5 years and work better than the conventional system they replaced. We actually install systems that pay for themselves INSTANTLY. We finance the installation. The finance payments are less than the amount of energy costs that the system displaces. The customer pays nothing out of pocket and will see savings on their first bill.

Please don't speak for everyone everywhere. When you make comments like that, please make sure to state that it applies only to your outfit. It’s very misleading information.



nhmaster3015 said:


> Unfortunatly at this time, the cost of the equipment and installation necessary to reliably heat with solar is far in excess of any cost and or comfort savings. The same radiant floor slab, piping, controls pumps and valves mated to a mod con boiler such as a Veissman,
> Buderus or Lochnivar will out perform the solar panels in every catagory. Nobody is challanging whether or not solar can be done, it has been. But in every case the cost has been so high as to never pay itself back. In northern climates the results are even worse. When you get into the heating aspect of solar, in order for the system to be effective you either need massive and expensive storage and or a massive and expensive slab. Either way a few cloudy days and your back up is on line. Happens more than you think. There are charts available that list average sunny and cloudy days for your region. Most solar experts agree that on a cost benefit basis, what makes most sense at this time is 3 panels and an 80 gallon storage tank for domestic hot water. Even this set up has limitatations and about a 20 year pay back.


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## nhmaster3015 (Sep 6, 2008)

Fair enough, except that I did mention geographic location as a factor. Even so, show me real proof that any solar heating system (not domestic hot water) installed at normal prices by professional installers will pay for itself in 6 years. I'm not talking about something put together by an engineer who had half the stuff donated and did the work for free. I'm talking a system with an average install price of well over 20 grand which is average for anyone installing a solar "heating system"


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## protechplumbing (Oct 10, 2008)

My bad, I was referring mainly to domestic HW and pools. I don't know of any radiant systems that pay off in 6 years.


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## nhmaster3015 (Sep 6, 2008)

I lived in Punta Gorda for about 10 years and am reasonably familiar with solar systems down south. The ability of the panels and systems is by far improved in the southern lattitudes because you get the sun at a better azimuth and for a longer duration.


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## J87513 (Jan 15, 2007)

you can do it during the day for sure. just don't use water as transfer fluid. you will have to use a glycol like radiator fluid if it freezes where you live. you would need an "Active" solar DHW system. have the solar and the boilder on a close loop system with a heat exchanger for the radiant fluid.

all that the solar does is pre-heat the boiler.


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## protechplumbing (Oct 10, 2008)

J87513 said:


> you can do it during the day for sure. just don't use water as transfer fluid. you will have to use a glycol like radiator fluid if it freezes where you live. you would need an "Active" solar DHW system. have the solar and the boilder on a close loop system with a heat exchanger for the radiant fluid.
> 
> all that the solar does is pre-heat the boiler.[/quote]
> 
> ...


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## solartech (Jul 23, 2009)

I have a isolated gain sunspace that provides about 40% of the heat needed for my 4000 sq. ft. Montana home. This is designed to keep cool during summer months and gradually provide more heat into the winter months. By cool, I mean that we start most summer days at 65 degrees and top out at about 75. Our summer nights drop into the 50's and daytime temps are in the 80's and 90's. Winter days, with an outside temperature of ZERO, will start in the lower 60's and can top out into the mid 80's. Shading, insulated thermal mass, proper glazing and natural air flow allow this space to share its thermal characteristics with the rest of the house. 
If you are just looking to heat your home, passive design is proven and has no plumbing or collectors that will freeze up or mechanical components that can fail. If you are using this in combination with domestic water heating, an active system can do a good job heating water all year round. 
Passive design and radiant heat work very well together and have proven track records. Good design is always based on your location and microclimate. My sunspace is 16 x 34 with 140 sq. ft of south facing, double pane glass. The slab is 10 inches thick (exposed aggregate) with 2 inch xps outside, 4 ft. deep and 1 inch xps below slab. The walls are an R-38 and the ceiling is R-45. I built this addition in 1985 (on a double wide starter home) and then added 3800 ft of home to it in 1993. Our propane bill reached a yearly high of $1300 for last year. If we were using natural gas, that would have been about $750 for the entire year. (Heat and DHW).


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## solartech (Jul 23, 2009)

Flashheatingand-

Boise has excellent potential for solar and your heating degree days is about 5300 hdd versus my Belgrade, MT at 8300 hdd. We get great solar energy at both of these locations and with proper design, we can easily control inside temperatures. I use vertical, south facing glass and overhangs that will fully shade that glass during summer months. May 21 has the same solar angles as July 21 and I choose to block more sun during mid summer and give up some of the solar potential in late April and May. This has been a good trade off here, as we can reach the upper 90's for weeks, during August and the cold snaps are shorter in the spring. 
I have worked with active and passive systems and experience shows that good passive design will out perform an active system. After 30 years of doing this, I know that tax credits disappear, antifreeze gets old, pumps and controls fail, but windows, concrete and overhangs can last the life of your home.


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## solartech (Jul 23, 2009)

MY FAT FINGERS Boise is about 5800 heating degree days. Weather design data is available at the *DOE's energyplus* web site under _weather data_ . You can get quite site specific and If you go to weather underground you can often find a site near your own back yard.


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## flashheatingand (May 3, 2008)

I went to a seminar earlier this year. The setup was not practical. Contractor cost was about $7,500 after all was said and done. Many people are willing to spend extra, but when a regular water heater cost about $400.00, one has to be realistic.

By the way, here's a concept. Take a hose and coil it on the roof, and then let it feed the Domestic water heater. During the winter months, you could detach the hose. It would be relatively cheap and simple. And, it would likely knock down the gas bill during the warmer months.


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