Floor Radiant Heating
 

Inform me...

Looking for info on the hot water kind that goes up under the subfloor of existing construction -- in between the joists.

Thanks!

Been over 30 years.
Used to sell it where I worked.

Upscale homes. Costly. Boiler/circulating pumps/electricity bills.
Install is critical.
We used copper.
You don't want leaks!

But, if done correctly, about the most comfortable heat you can install.
Uniform comfort ... no cold/hot spots.

They use PEX now and super efficient boilers. The pex is great because that means there are no joints under the floor.

Look at IIT's Crown Hall by Miese van der Rohe. These sorts of piped under-floor heating systems have been done for a long time and I can say first-hand that the quality of heating/comfort provided is simply wonderful. These can be fairly efficient systems too (due to proper use of convection).

- what is it about the installation that is critical?

Yes, I will be using PEX.

And, I hope to have Gov. K, and Pres. Obama help me with the cost...

I'm not a salesman for these systems and I've only installed the "in slab" types, both interior and exterior.

But I can't help but think that a system installed in between the joists, after the fact would be as efficient as having the loops under the flooring, above the subfloors? You're heating a whole bunch of space below the subfloor for no reason?

As for what is critical.... working against leaks, now and in the future. Continuous piping is a must.

In floor pex off hot water boilers is very efficient as it puts the heat at your feet, where you need it. The heat is more even in a proper install and unlike forced air does not create drafty conditions (generally speaking) near windows and doors. PEX buried in concrete will heat the concrete and take advantage of its thermal mass, creating a more stable room temperature. It is also easy to zone rooms via independent thermostats and mix control valves. The systems are also basically silent. The types that chase pex between floor joists usually have a fabricated sheet metal plate that nails between the joists, and reflects heat upwards towards the underside of the floor and not into the crawl space. They also have above floor systems that chase through special engineered floors (similar to Pergo). The disadvantage there is you add height to the floor.

Also very useful in the garage slab for melting snow off the Supercharged Hummer.

The under sub-floor installations usually require the joists be insulated after the system is installed... so heat isn't being directed to areas where heat isn't needed..

Whether the installations are installed per spec is another story

http://www.infloor.com/radianttrak.html

Just have to 'reflect' the heat upwards. Easy

When I used to to turn a wrench I worked in this shop where the guy had pipes in the concrete. It was AWESOME! It melted snow away from the doors. It was just awesome!

My dad has done this in two of his houses.

Pros: More efficient than most conventional heating options. Warm floors are great to put your feet down on when it's been a cold night. Very consistent temperatures due to the huge moderating water mass.

Cons: More expensive up front. Long temperature stabilization times due to the huge moderating water mass (e.g. if you leave for 2 weeks and shut the heat off, the thermostat is liable to cycle back and forth, badly underdamped for a couple of full days, before the temperatures settles in the desired region). The risk of leaks is present, and presents the potential for huge problems.

Dad's best luck has been with rubber tubing and an on-demand hot water heater. Set the tubing in the floor with staples, then pour light-weight concrete on top. On top of that, lay a subfloor and flooring material -- but be VERY CAREFUL not to hit the tubes with whatever fasteners you're using. If you're doing, say, hardwood, and you miscalculate the length of the nails, and inadvertently punch one through into a tube, you won't discover it for 6 months, at which point you've got 100 sqft of hardwood to replace.

So it's definitely best in a new construction-type project. I can't imagine seriously trying to make it work as a back-fit.

Dan

RW_ Can you direct me to a link regarding state and federal assistance on this sort of energy-efficient retrofit?

mo

If you're doing it yourself, these guys are pretty helpful:

http://www.radiantec.com/index.php

I've installed the under slab kind, and we used a number of zones that overlapped in case one of the zones leaked. You would just shut it off at the manifold, and didn't have any big dead spots.

Now, my firend had a new ceramic tile floor installed, and he put in some of the electric stuff. It works great, I just saw it today, and it was 4 degrees outside. You could really tell.

Bill

Will these systems, or at least the part embedded in the floor, last for 100 years?

Not yet. Might try Or. Tax Dept.

I got the info from my electric utility (public) and from a co. here that does the installs.


I might last 30 or 40 more years, so that is good enuff for me.

We had the electric one and it was incredible but the power bill was a huge turn off.. We used it occassionally. Socks or mats are by far the best ;-)

Yes.

The only caveat is that the penetration point (where the piping enters the slab) needs to be protected against moisture infiltration/capillary action or wicking, otherwise it becomes a potential failure point for the concrete to break up over time.

Use steel piping - not PVC in concrete, especially when you're dealing with temperature variations. The coefficients of expansion between steel and concrete are very, very close (one of the reasons steel reinforcing bars work so well).

As long as concrete is properly detailed and the appropriate moisture barriers are provided it should last indefinitely - with or without piping/steel inside.

I've read someplace about coupling these with passive solar heating systems - very efficient, low-cost - all you pay for is the circulation pumps and possibly some small level of heat in the storage tank to keep the temps up if necessary. I'm not 100% sure (you should check a specialist) what the circulating medium is - probably not just water since you could use a closed-loop system, probably more likely some sort of glycol mix, which would be better long-term against corrosion anyway - not to mention freezing if the system ever sat idle.

I'll see if I can dig up some links - kinda' busy right now though, but these absolutely are very, very cool systems to implement.

thx - would love to get more info

this will be hot water - not an electrical resistance type heater

[BTW - have elec. in both baths - put them under the tile when had that put in - spendy to run, but feels great]