Nuheat is a cable system that requires a mortar or thinset. Is that the planned substrate?

around me, electric is about 3 times the price than other fuels like propane oil, or gas. A real lot more expensive than wood.
Is electric cheaper in Maine? I pay about 0.12$/kwh in NJ.
Is the house completely electric?

I believe that it would be very hard to use the heat for a few hours per day. The wood above the elements is an insulator, so it will take a while to warm up. Energy will also flow down to heat the subfloor and srtucture below.
Another problem is the hardwood which does not like changes in temperature at all. The coefficient for expansion for wood is far greater than the heated mortar its setting on so the floor will be really creaky and could buckle or split. Radiant heat under wood is accepted and works within limits. One of those limits is a low rate of temperature change. This is why the Radiant Panel Assoc. recomends a constant flow reset loop.

Bill, constant flow is nice, but I don't see anywhere that the RPA "recommends" that for wood floors. Also, electric elements should heat up fairly quickly.

John, why are you looking at mortar under wood? why not just use a mat that doesn't require that?

Somehow the notion of generating electricity at a net solar efficiency of 10-15% vs. solar-thermal for a net of 50% (at lower system cost) doesn't feel like the math is gonna work favorably, even when the higher cost of a hydronic radiant and solar thermal storage installation is included. Maybe it does, but I've not seen it work that way... yet.

But if the installed cost of PV crashes (as it should, given the low production cost of CIGS-technology PV) I may revisit those equations.

To be sure, a 12kbtu/h design-day heat load means the seasonal thermal requirements will also be modest (you may spend as many btus/year on heating hot water as on space heating, which would be very unusual in Maine.)

Dana1:

I'm counting on the cost of PVs coming down over the next two years.    The small 6-panel solar awning on the house will go up in 2010, but the barn and its larger array not until 2011.    I'm guessing within two year's time, PV costs will be much more reasonable.    The tax incentives now available will help that much more.

I'd considered going with a wind turbine for the electricity, but the design of the barn and its Solar South facing roof just make it ideal for PVs.    Plus, it'll be silent and no one will see it but the birds.


John

be careful if you consider wind. I believe a recent study has basically proven small turbines are a net energy loser, their effectiveness overall is directly related to their size.

Zmesh low voltage elements are a slow growth heat. It doesn't require a mortar and it actuall will bring the wood up in temperature (never warmer than 85*) at the same rate as the element itself. Since the element is a bronze screen (9 or 12" wide), it comes with a 25 year warranty and you can nail your hardwood directly over (through) it without effecting the system (screen...holes..) .

I can send you some pictures of projects we've installed under exotics, short or wide plank, hard or soft woods.

Always maintain the woods' mositure content. Radiant or not, if you don't pay attention to it, you'll have problems.

In a correctly designed floor and system, you will see temperature changes in about 45 minutes.

Your EnvironII looks interesting. Is it a foil? You show a pic with it in between layers of padding and carpet. What if (scenerio) a child pokes a metal object through the carpet?

I mistakenly discussed the EVII system for this application, that's why I removed it from the discussion. It is not designed to be used in any glue-down application, FYI.

Environ II panels are made of a pattern of a fixed-resistance heating element, “sandwiched” between two layers of aluminium foil laminate. The EVII system is controlled by a GFCI controlled thermostat in case something like this were to ever happen. To be honest, we haven't had this scenario.

Thanks for your note!

Is it a filament or a wire? What is the thickness? Is it repairable if damaged?

I believe this is getting a little OT, because the EVII system is not designed to be used in the application that lambabbey is discussing.

The EVII system uses an insulated wire, not a filament, for safety. It is 1/16" high. For reliability's sake, we do not recommend repairing it.

This concludes my OT banter. Sorry, lambabbey!

I think this get can be repaired once it is damaged. Nuheat mats and the cable system can be wired to any number of thermostats. So it is convenient too.

By now you have likely made a choice, but for anyone who hasn't I can tell you that adding nuheat under our tile in the bathroom is great. I can keep the thermostat lower than I used to for that area but it still feels nice. What I liked over other options such as solar water and tubes is it is only ~1/16th inch thick. If I were building new then I'd do a boiler / solar and circulate hot water in the slab. But for existing installations this was not an option and I've been happy so far (~5 years). The tile installer had no problems with it and the added installation costs were minimal. I'm looking at adding it to a 20x30 space and also powering it with PV at least part of the day. This also removes my need for storage as I would be storing the soar as infloor heat. Again if I were starting from scratch I'd do in slab hot water but I'm not willing to cut my slab up or add a 2-3inch lift to my existing slab to add the tubes. If I were doing a space that had a raised floor then I'd consider adding the hot water heat in between the floor joists, but keep track of the weight of the water!