So the vast majority US houses are heated in winter by forced air systems. Some kind of fuel heats heats up air, and that air is distributed throughout the house. Notably exception would be wood stoves and radiant floor heating. The heat rises so usually a fan is used to make sure the air is mixed throughout the house.
Since our house was too insulated to put in a wood stove (and we didn't want to mess with the wood issue), and we had lived in places in Europe that had the radiant heating systems - we opted for that. Essentially tubing is placed in the floor, which is then encased in concrete - once the thermostat recognizes the need for heat, hot water is pumped through the floor - thus heating the house.
That's the 50,000 foot view, here's the painful details ...
Since it is not a common idea in Indiana, and hence there is a tendency to only put it in higher end homes - the initial estimates on doing this kind of HVAC system were RIDICULOUS (as in $45K). In the end we ended up doing a lot of the manual low skilled work ourselves and only calling in the experts to do the hard stuff - end cost was around $6K, I think.
Step 1: Find a radiant floor supplier.
Through several phones calls, I found a plumber/HVAC guy (thanks Eugene !) that gave me the confidence that I could actually tackle this - even though I was DIY incompetent. He got me in contact with an actual radiant floor supplier ... Viega. What they were able to do was take my house plans, and setup a tubing map for the basement and first floor (we didn't bother (and didn't need in the end) heating the second floor).
The detailed tubing maps show you how you need to run the PEX tubes in the basement and first floor. They have a little software program that takes into account exterior walls, etc; and so you end up with an effiicient distribution system. For example, you want the floor next to an exterior wall to be heated with the hottest water, and you want the tube lengths to be relatively equal (although they can adjust later).
Also make sure they know how you want to heat the hot water ... they should be able to size the heater or tell you how many BTU's/hour you need. Since there are so many different ways to heat water, you want to make sure they know your plans.
Step 2: Lay the tubing at the right time.
In the case of the basement, the four loops for the 800 square foot space needed to be installed BEFORE they poured the concrete in the basement (or crawlspace) - pretty early in the building process. Since you need something for the tubes to hold on to, and gravel wouldn't cut it - we had to put down 4' X 8' metal wire (something you put for the concrete floor anyway) and attach the tub with zip ties. Totally low skilled manual work that you can total do on your own. Seriously ... you CAN do this on your own, but even if you hired someone, we're talking an $8-$9/hour, not a $30/hour kind of job in this part of the country.
In the case of the first floor, the 6 loops for the 1400 square foot space needed to be installed basically after the drywall was installed. Why? Better fit and finish. Although you have to make sure the concrete guys don't throw concrete on the walls willy nilly, it makes a total sound proof basement and removes the need for baseboard trim on the first floor (which can cost a lot), since the 3" of concrete make a nice clean finished line.
You do install PEX tubing differently when you're dealing with plywood, since instead of zip ties and metal wired sheets, you are stapling the tubing (carefully) to the plywood. A power nailer with a $20 attachment will protect the tubing from being stapled - but even if that happens, it's not a huge deal. You basically just do what any plumber learns on his first day of class - cut out the bad pex, and join the two ends together with a metal joint that probably has a technical name I should know - see, I'm not a DIYer.
Other keys to keep in mind ...
- Keep some excess PEX tubing on each termination, but don't feel like you have to go crazy ... the plan from Viega will tell you where the end goal of all the tubes need to end up, but it's not like you can't extend the tubing easily on the final steps.
- Make sure your lumber supplier knows that you intend on putting 3"+ of concrete down on the first floor - since the floor will need more support from the extra weight. We did I-Joists, which we probably would have done anyway for their no squeak abilities. Also put down Sturdi-floor plywood. You are guaranteed that your concrete will crack (that is part of it's charm), but the Sturdi-floor will keep it to a minimum if the floors are poured correctly.
- Don't get amateur concrete pourers ... not all are created equal. You want guys who are clean (so you don't get concrete on the walls), and you want them to understand that this isn't some sidewalk outside, but will end up being the finish floor of your house. Again, the floor will crack, but no sense making it easy for them, or not putting in expansion joints. Also spring for the pump truck - you'll need it to get the control you want.
- Worst possible disaster is if you have a hole in the PEX tubing and the concrete is poured ... you can't fix that. So ... test the system JUST before the pour by pressurizing it (plumbers do it all the time and know how (I used a low tech bicycle pump). And once you know it's fine, guard it like a hawk. For example, ANYONE walking on the floor should be watch so they don't puncture it (hard to do, but again, you don't want the 1% chance to become a reality, because you'll have a mess).
Step 3:
Setup the heater and water distribution manifolds. You (or rather your radiant installer) do this once you have the proper utility and electricity installed in the house - so this is one of the last things you do in building your house.
Again, your Viega reseller or supplier should be able to tell you what heating unit you can use. They are usually resellers of a certain product and know how to install them. This bit takes a good two days, and it's not a job for a newbie plumber (even though it's 90% plumbing work) - make sure they have experience installing this type of heating unit and radiant heating system. Viega reseller should know the right people (otherwise how else would they be able to sell their equipment).
Essentially the system works like this ...
House drops below thermostat set point and sends a call to the heating system to send up more heat. A small water pump moves water through the boiler (which has also automatically turned on) and run the hot water through the manifold (think 1 big in, 1 big out, with the in and out loops connected in the middle.). These manifolds can be manually turned on and off, so if you have an area of your house that you don't want heated (e.g. guest bedroom), then you have true zone heating. Once the house reaches temperature then the pump and boiler turn off ... pretty basic.
Unfortunately it requires a whole bunch of things like an expansion tank, small pumps, controllers, and a lot of (expensive) copper tubing. Keep in mind the water is essentially closed - so you hardly ever add water once it it initially primed. That means water that might start at 135, might go through the floors and drop down to 105 before going back into the boiler. But heating from 105 to 135 is a lot better than starting at 70 or 50.
I would have to look at my notes again, but taking the the heating element out of the equation (since that all depends on your energy source, house size, and insulation), I want to say half of the cost was materials, and the other half was labor. Of the labor, the majority (90%) was for doing the final manifold install (I didn't pay myself but in coffee). But even if you don't want to lay the tubing yourself - say two people at a high $10/hour should only take one full day for each floor (in my case 1400 square feet) - so $200 smacks per floor - cheap.
WHAT DID WE LEARN?
- The hard part is the technical design and manifold install - which would be the case with any HVAC system. But you can find the experts to help you. You should know early on in the design process of your house if this is going to work for you.
- It's cleaner, since you're not blowing hot air around ... in fact, we don't have any air supply or returns except for what we needed for the HRV or Humidifier, so the look in an open house is cleaner.
- The system is incredibly efficient. Funny story ... initially when the system was installed (Sept), and when it started to get really cold (end of Dec), we noticed that the system had a hard time keeping the first floor at temperature ... we had it set at 70, but we saw it dropping to 68 or 69 when it was really cold. So we called the installers in to take a look. Turns out they had 5 of the 6 loops on the first floor (and 2 of the 4 loops in the basement) shut off by mistake. So essentially we had 1 loop heating the entire first floor, when it was only meant to heat 1/6th of that floor. Once they turned the right knobs, we never had an issue.
- Concrete rocks. Don't make the mistake of putting in a radiant floor heating system and then castrate it with a carpet or wood flooring. A rug here or there is fine, but you don't want the heat to be smothered by an insulating material - especially carpet. I'll do an entire post on concrete later, but in short - you can stain it easily to be any color or texture you want (so why add another expensive floor covering on top of it), it's not a cold and harsh (quite the opposite when you have hot water heating it regularly). And best of all ... concrete can be cleaned ... really cleaned ... and cleaned easily. Once you see the dirt that you pull up from a concrete floor, you will ask yourself what is really sitting in your carpets. I'm not a clean freak, but I'll never go back to carpet ... ever.
- There is nothing like radiant floor heating - and once you live in a house with it, you'll NEVER EVER go back to forced air. Forced air needs to heat the whole house, and since heat rises, that's a lot of volume to produce and move. With radiant floor heating, you are heating solid objects, and most of the (subtle) heat hits your feet first and stays in the bottom 7' of the room. I don't know about you, but if my feet are warm, then I'm comfortable. I think we made a mistake in those huge Victorian homes when we removed the steam radiators (essentially another form of radiant heating) and replaced it with forced air.
