The fundamentals aren’t hard to master, but they’re called fundamentals for a reason. Learn them and thrive.

“Gentlemen, this is a football.”

According to legend, Vince Lombardi started every training camp with this little gem, just to remind his players that no matter how great they were last season, it doesn’t mean squat this season. You guys wanna win again this year? Then we go back to the fundamentals -- blocking and tackling, running and throwing, practicing to perfection. The fundamentals aren’t sexy. They aren’t razzle-dazzle, but without them all you have is garnish. No meat, no potatoes. Just parsley and a couple of fruit slivers. And that ain’t much of a meal.

As with anything, you have your fundamentals -- the basic do’s and don’ts -- with radiant floor heating. The fundamentals aren’t hard to master, but they’re called fundamentals for a reason. Learn them and you thrive. Shoot from the hip and … well, you get the picture.

What follows are some of the most frequently asked fundamental floor heating questions I hear during my training programs, and some surprising answers. Enjoy.

What water temperature do I run? How far apart should I put the pipes?

To borrow a phrase from Meatloaf’s girlfriend in “Paradise By The Dashboard Light,” -- Stop right there!!!! Remember, this is a heating system we’re talking about, and “Step One” in designing any heating system is to do a heat loss. Sorry, no shortcuts. Water temperature and tube spacing are the badda-booms of radiant floor heating. But you don’t get the badda-booms without the badda-bings.

Badda-bing No. 1 is do the heat loss. Room by room.

Okay, I did the heat loss. Now what water temperature do I run?

Slow down there, Sunshine. We’re not done with the foreplay yet. When designing a floor heating system, you need to take the heat loss for a room, divide it by the number of square feet in that room and figure out how many Btus per square foot your new floor “radiator” needs to deliver. Yep, it’s another badda-bing. One of the really slick things about radiant floor is that you can design to give just the right amount of heat where it’s needed.

Done. Now the water temperature?

Nope. Next we need to figure out how we’re going to stick it in.

Say what?

The tubing. How are we going to stick the tubing into the building.

Oh. Isn’t putting it in concrete the best way?

Nope, it’s one way. You have at least five ways to install radiant floor heating, and they all work great, provided you do all your badda-bings. You can install the tubing in a concrete structural slab either on or below grade. This way’s the easiest, unless of course you’re trying to heat the first or second floor of a wood-framed home. Then it becomes a tad impractical.

For wood-framed structures, you can staple the tubing to the subfloor and then pour 1-1/2-inch of gypsum concrete or special redi-mix type concrete over that.

I’ve seen that on TV. Isn’t that the right way do to it?

Again, it’s one way. There are others that work just as well. You can install the tubing in between the floor joists below the subfloor, either with or without aluminum heat emission plates. Or you can install the tubing in a special plywood and aluminum underlayment system on top of the subfloor.

Well, which one should I use?

It depends.

Whaddya mean, “it depends”?

During your career, you’ll probably use them all. Each job has different requirements. If the house is already framed, you probably won’t have room for an 1-1/2-inch underlayment pour, so that’s out. You may be looking at joist heating with or without plates.

I’ve heard about those plates. They’re pretty spendy. Do I need them?

It depends.

Again with “it depends.” On what?

Your heat-loss and design calculations will help you decide whether you need plates for a job. If you can satisfy the Btu per square foot heat load without using plates, then great. If not, you’ll probably need them. Plates will do a couple of things for you. First, if you add plates to a joist-heating job and keep the supply water temperature the same, you’ll increase the radiant floor’s potential output 3 to 4 Btus per square foot. That means you can get more heat if you need it. Three to 4 Btus per square foot may not sound like a lot, but over a 400 sq. ft. room it can add up.

Second, if you already have the Btu output you need from the floor, adding plates can lower the required supply water temperature anywhere from 13 to 20 degrees F.

They say the concrete way is better, that it’s more comfortable. True?

It depends.

You’re starting to irritate me. It depends on what?

If it’s been designed and installed properly. From a comfort standpoint, I’ll bet you a thousand dollars right here and now you couldn’t tell the difference between a concrete slab job, a poured underlayment job, a plywood and aluminum job, a joist heating job and a joist heating with plates job -- as long as they were all designed and installed correctly.

Meaning the badda-bing and the badda-boom?

Now you’re catching on.

Well, which installation method is more efficient?

It depends.

Sigh …

Look, lots of folks fall into that trap of thinking that radiant is a low water temperature system, and that lower water temperatures mean a more efficient system. That’s sometimes true, but what radiant really is is a low surface temperature system.

Lower water temperatures in the heating plant, meaning a boiler, water heater for a geothermal system, will enhance the efficiency of a radiant system. But if you’re using a cast-iron gas- or oil-fired boiler, firing that sucker to 180 degrees F for a high limit, and then using a tempering valve to achieve the radiant supply water you’re looking for, then the lower supply water temperature doesn’t matter efficiencywise. The boiler’s making the Btus required with 180-degree F water.

But isn’t radiant supposed to be more efficient?

Well, there’s efficiency and economy. Boilers and furnaces have different efficiency ratings, and that has to do with combustion. Systems, however, are economic. Radiant systems typically use anywhere from 25 to 45 percent less fuel per heating season than a forced air or baseboard system. It’s an economic form of heat delivery.

I get it now. Radiant in general is more economic. You can design in ways to make it even better. Right?

Badda-bing, my man!

So, are we ready for water temperature now?


I figured as much, I was just being optimistic. What do we need to do now?

Floor coverings. What are we gonna use for floor coverings?

This is important?

Hell, yes. All floors have R-values, or insulating factors. You have to know what’s between the radiant mass and the space it’s trying to heat so you can compensate for it. It directly impacts water temperature.

So if there’s a carpet, I’ll need a higher water temperature than if there was tile, right?


So you can’t do carpet with radiant, right?

Didn’t say that. You can. Radiant doesn’t really care. You just need to know what the R-value of the carpet and pad is when you do your design calculations, or your badda-bings. All the manufacturers should have charts and things available to help you figure this out.

Okay, so I have the R-value of the floor. Please tell me we can do water temperatures now!


Nope? Nope? What the hell’s left?!!?!??!?

Nothing, I was just teasing you.

I really don’t like your attitude, mister…

Sorry, I couldn’t help it. No more foreplay, let’s get down to the badda-boom. The right water temperature is based on the Btus per square foot required, the way the tubing is installed and the R-value of the finished floor. Let’s say we have a heating load of 15 Btus per square foot, and are doing joist heating with plates. If the finished floor is, say, a light carpet and pad with a total R-value of 2.0, we’ll need to run water at about 150 degrees F. Since the tube is between the joists, the default tube spacing will be 8 inches.


Right, badda-boom. Feel better?

Man, there’s a lot to know here. Can’t I just skip a few steps to make it easier?

The old shoot-from-the-hip gunslinger mentality, ‘ey? Well, Sunshine, there’s two types of gunslingers out there: the quick and the dead. The streets are littered with guys who “winged” it and paid the price. “Here lies Skip-The-Heatloss Ron. Saved some time, now he’s gone,” or “In memory of Fred ‘The Corner-Cutter’ Rice. Didn’t have time to do it right once. Never got the chance to do it twice.”

Look, radiant heating gives you a chance to make some real money in this business, and to give your customers the best, most comfortable and most economic heating system they’ll ever have. Don’t skip the badda-bing, man. It’ s those badda-bings that make the badda-boom world go ‘round.