Installing hydronic radiant floor heating when building a new house?
February 1, 2012 7:28 PM   Subscribe

Installing hydronic radiant floor heating when building a new house?

Planning on building a house w/ ICF's and SIP's for the roof. Few questions about hydronic floor heating.

Plan on using solar to heat it, in Boulder, lots of sun, will it be able to keep up?

Is it a bad idea to skip the HVAC and just stick w/ floor heating if we don't want air conditioning? Would ventilation be a big concern?

Would it be a bad idea to run a different zone out to the patio for those cool spring and fall evenings? What about during winter if we're not using it?

I know it will take a long time to change the temp of the house, any other disadvantages? Any other advice in general?
posted by no bueno to Home & Garden (8 answers total)
My wife and I recently bought a house with hydronic radiant heating, and we absolutely love it. We use a separate water heater for it though; not sure how well solar would work.

"Would it be a bad idea to run a different zone out to the patio for those cool spring and fall evenings?"

I seriously doubt you'll be able to heat an outdoor patio with radiant heating. The heat will simply dissipate into the environment. And if you're not using it, the water would likely freeze up in the winter.
posted by mikeand1 at 7:34 PM on February 1, 2012

Response by poster: I know it won't warm the actual outside but I figured warming up the concrete would make a noticeable difference when it's cool and we're hanging outside. I've also read that you can put some glycol into the water to prevent it from freezing. I figured while we were running it, it wouldn't be that much extra provided it won't cause too much trouble.
posted by no bueno at 7:43 PM on February 1, 2012

"I figured warming up the concrete would make a noticeable difference when it's cool and we're hanging outside."

I kind of doubt it. But I admit that we've never cranked up our heating to the point where the floor was more than 70 degrees or so. You can barely tell the heat is on if you put your hands on the floor.
posted by mikeand1 at 7:54 PM on February 1, 2012

Adding: Radiant heat is like a really fine suit. You don't notice it's there until you look for it, but it creates a great environment. It's very subtle and natural. The temperature is constant, and there's no air blowing around.

After living for years in a drafty house with forced air heating -- where the temperature was constantly fluctuating, and one area would be too hot while another was too cold -- it's like heaven.
posted by mikeand1 at 8:06 PM on February 1, 2012

I live in Fort Collins. One room in our home is a converted garage space, with tile on a levelled but uninsulated, unheated slab. That floor is always frigid. So I'd forget the hydronic patio idea. You're better off with a chiminea or propane heater, or a sweater.

Otherwise, I think this sounds like a great idea if you insulate the home well. One nice thing about solar hydronic heating is you can tie a water heater into the loop as your fall-back option for cold, cloudy days. You could even build in the ability to add a water heater later, and see if you need it. If you're concerned about ventilation, you might consider a heat-recovery ventilator (HRV).

As a data point, some family friends lived in a passive solar house here in Fort Collins that had nothing but south-facing glass (no hydronic floors) and a woodstove. They said there were only a handful of days each winter where they needed the stove. A good green building pro should be able to evaluate your design and tell you how it will perform, whether you need additional heating capacity, etc. If you can't find a knowledgeable passive solar specialist in Boulder, you're not trying hard enough ;^)
posted by richyoung at 8:48 PM on February 1, 2012

Hydronic heat is terrific. Solar for hot water is also excellent. Unfortunately, I don't think you can effectively do the first with the second.

To be more precise, you'll need the most energy going into the slab when the house is otherwise losing the most heat. That will be at night, and in cloudy periods. So, you'll probably still need some sort of heating system that can keep up. With that in place you can check if solar can offset some of the heating costs in an affordable manner.

This is a terrific evaluation for an energy nut architect. How well the whole house will perform will really depend on orientation, overhangs, window area, glazing types, floor finishes, and the type of systems you install. With all those factors, a custom solution will get you higher performance, maybe even to the point that the high insulation and solar gain IS enough to go with radiant. But, without a professional and detailed support for the idea, plan on a boiler of some sort.

As regards the terrace, you aren't going to get enough heat out of the slab to make it comfortable by itself. I've heard of heated slabs for pool decks, and of course for snow melt, but that is more about the temperature directly in contact with the deck, it doesn't provide significant comfort for those sitting well above it. There are other radiant heater options (often gas) that are available if you find you do need more warmth for extending the deck season.
posted by meinvt at 9:10 PM on February 1, 2012

I have radiant baseboard, and it's awesome. And I hear nothing but good things about the in-floor heating.

I think solar is great, but I would suggest installing a back-up heater for nighttime. The thing about passively heated houses is that they need a lot of thermal mass to have enough inertia to remain heated at night and on cloudy days.

As for the patio thing, I would certainly try it. Making sure that it is on a completely separate circuit so that it can be cut off (and possibly drained) when you aren't using it, and that you insulate the bottom of the outdoor slab so that the heat you are putting into it isn't getting sucked right into the ground.

(Another highly efficient option to consider is a heat pump that uses a ground loop as a heat sink/source. You dig a well, or if you have the option, lots of trenches, and feed a loop of water into it. Since the ground below the frost line is a constant source of 50 deg F, it is perfect for your application- it's warmer than the air in winter, and cooler than the air in summer. It is expensive to install, but super cheap to run.)

With a modern, tightly constructed house, I do think ventilation would be a concern. I would definitely make sure the house has ducts installed, even if you don't plan on using them, because it would really suck to realize you do want V/AC at some later point and have to figure how how to get it installed. They make high velocity ducts now that are little 1.5 or 2 inch tubes that are home-run to central points which makes installation cheaper and also less obtrusive. Spend your money on an air handler, a good filter and a good air-to-air heat exchanger for outside air ventilation.
posted by gjc at 5:19 AM on February 2, 2012

I have radiant heat in the floors of of my house that were installed when the house was built in 1956. I honestly love these floors. We've sort of outgrown our house but I don't want to move because I know our new house probably wouldn't have the radiant heat.

Seconding that the most work is done at night. I can tell how cold it is outside by how hot my bathroom floor is in the morning.

Around here there are a few houses that have extended the radiant heat out to their driveways. It doesn't actually make them warm but it does mean that they don't have to shovel the walk when it snows. No ice to worry about either. I think you would get a similar effect with your patio.

We don't have any kind of HVAC ducts in our house at all. In the warm weather we use a swamp cooler and crack open a few windows at the back of the house. I really don't miss forced air one little bit. None of those nasty allergens collecting in ducts to worry about.
posted by TooFewShoes at 6:41 AM on February 2, 2012

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