So, Grasshopper, what shall we discuss today?
(Sigh) Been watching reruns of “Kung Fu,” have we?
Sorry, sometimes I can’t help myself. What wonders of radiant heat shall we kick around today?
Well, a customer asked me about radiant ceiling the other day. I’ve installed plenty of radiant floor, but radiant ceiling? That doesn’t make any sense to me
Ah, radiant ceiling. And its second cousin, radiant wall. Both nice ways to heat.
But why wouldn’t you put it in the floor? I mean, heat rises, right?
Whaddya mean, “Nope?” They taught us this in fifth-grade science. Heat does too rise.
Heat doesn’t rise. If it did, explain the sun to me.
Yeah, the sun. The big, hot, yellow thing up in the sky? I know you’ve seen it.
What does the sun have to do with anything?
Well, it’s proof every day that heat doesn’t rise.
Good Lord, you’re cryptic. What are you talking about?
Well, where is the sun?
You just said it yourself. Up in the sky!
Where in the sky?
So, heat doesn’t rise. If it did, the sun wouldn’t work. Heat doesn’t rise, it radiates. More precisely, heat transfers from a warm surface to a cooler one. The sun’s surface is a tad warmer than the Earth’s surface, so heat radiates from there to here.
OK, I get that. But everyone says heat rises.
Heat doesn’t rise. Hot air rises. At least it does in an enclosed room. Heated air gathers at the ceiling, where it doesn’t do us much good.
Now you get it. Anyway, radiant ceiling is a lot like the sun. It radiates heat from a warm surface, the ceiling, to cooler surfaces, the floor and the walls.
Is it as comfy as a radiant floor?
It actually creates a higher degree of comfort than either forced air or baseboard can, it’s just not as nice as radiant floor.
Well, if it’s not as good, why would you bother?
Well, sometimes it’s the only option you have left. Or sometimes you need a little extra heat when the floor alone can’t get the job done.
OK, that makes sense. Gimme some examples.
Let’s say you’re doing a retrofit job, and you can’t, for whatever reason, do anything with the floor. You may be able to put some tubing in the ceiling, or even the wall, to heat the room. Some people even use it in bedrooms.
Radiant ceiling in bedrooms? Why?
Well, let’s say the customer wants radiant in the whole house, but the “B” word rears its ugly head.
“Budget.” Anyway, the bedrooms are all carpeted with the carpet and pad from hell. In order to keep the radiant solution intact, you can install radiant ceiling. It’s powerful - anywhere from 25 to 45 Btus per square foot, depending on how it’s installed - and it responds quickly. You could also use radiant ceiling - and radiant wall - to make up the difference when the radiant floor falls just a little short.
You mean “supplemental” heat?
Yeah, but I hate that phrase. It indicates that radiant “can’t” heat a room. Sometimes that’s true, but sometimes we just don’t want to get all of the heat out of the floor. Remember, with radiant floor we have standards for maximum surface temperatures - 80 degrees F for hardwood floors, and 87.5 degrees F for all others.
I know about those.
And since we’re dealing with radiant heat, a radiant floor gives off heat based exclusively on its surface temperature. The warmer the surface, the more Btus the floor gives off. Let’s say a room with a hardwood floor has a heat load of 40 Btus per sq. ft. That’s kinda high, but let’s pretend. To heat that room, the floor surface temperature will need to be around 85 degrees F. That’s outside the guidelines. It’s not that the floor can’t deliver enough heat; it’s that we don’t want it to deliver all that heat, so we can protect the hardwood.
So can’t we just put more tubing in the floor?
Nope. It’s not a matter of getting more out of the floor. We don’t want any more heat out of the floor. We need to make the radiator bigger. And to do that, we’ll put tubing in the ceiling, or the wall.
How much do I put in?
There you go again.
Well, it does. You can install tubing with aluminum heat emission plates in the ceiling or wall, and, done right, you can get about 45 Btus per sq. ft. with 120-degree F water. With a plywood and aluminum panel, the output goes down to only about 25 Btus per sq. ft. Our room needs 40 Btus per sq. ft. from the floor, but at an 80-degree F maximum surface temperature, we can only get 30 Btus per sq. ft. So we’re 10 Btus per sq. ft. short under design conditions. If the room is 450 sq. ft., we’re 4,500 Btus short. Some quick math tells me we’ll need about 100 sq. ft. of radiant ceiling or radiant wall to heat the room when it’s really cold outside.
Cool. Anything I need to watch out for?
Well, a couple of things. Obviously with radiant ceiling you’d like to put the tubing near the outside wall, where it’ll do the most good. If it’s a cathedral ceiling, you’ll start at the base of the ceiling and go up only to about the 12- to 14-ft. level. The higher the radiant ceiling panel is, the less effective it would be.
What does Mickey’s dog have to do with this?
Not the dog, the planet.
You’re in to the solar system this month, aren’t you? Is your Venus in retrograde?
No, but your bad moon will be rising in a minute. Look, Pluto is the farthest from the sun. And it’s the coldest planet. The farther away a radiant ceiling is from the surface it’s trying to heat, the less effective it’ll be.
Ah-ha! Anything else, Mr. Spaceman?
If you’re doing radiant wall, start at the floor and only run the tubing up to about 4 ft. or so. Know why?
I have a guess. Does it have to do with the release of the radiant vector from the flat panel surface vis-à-vis the panel’s orientation to the cooler surfaces in the remainder of the enclosed space?
WHAT!? Where’d you get that?
I heard an engineer say it once. He was quite pleased with himself.
Well, that may be true, but the real reason you don’t go up much higher than 4 ft. with radiant wall is that people like to hang pictures.
And they use nails, right?
Yep, nails. Also know as tube-finders.
Tube-finders, I get it. What else can I do with radiant wall and/or ceiling?
Well, think about bathrooms. You can have more fun with radiant in bathrooms than you’d think humanly possible. Think tiled-in showers. Wouldn’t some tubing in the walls of the shower be awesome? When you’re wet and naked, it’s way better to be warm, wet and naked than it is to be cold, wet and naked.
Can’t argue with you there.
Lots of people warm the walls and deck around big whirlpool tubs. You can put tubing in the walls behind the towel bar - a poor man’s towel warmer - and behind the mirror to help keep it from fogging up. And let’s not forget the kitchen. You can even put tubing under granite countertops.
Why would anyone want to put tubing under a countertop?
Well, mostly because you can.
Put tubing under the countertop. Look, granite countertops, if they aren’t warm, are cold, right?
Right. But if we run some tubing under those countertops, they won’t be.
Won’t be what?
Cold. They won’t be cold. They’ll be warm. Which is nice.
But c’mon, isn’t that a bit excessive? I mean, do people really need heated granite countertops?
Of course they don’t. When you think about it, they don’t need granite countertops, period. Warm or cold. But why do you think people buy them?
Because they have more money than brains?
Possibly. But think about it … people buy granite countertops quite simply because they can. People sell them because other people buy them. And people buy them for any one of a number reasons - because they like the look, because they like the feel, because they like the durability. Hell, they may even think granite improves virility. I’m not sure the “why” matters. And if they buy granite countertops, the least we can do is heat ’em.
OK, I see your point. But doesn’t it cost too much?
Whose money is it? Yours?
Well, no. But …
No, it’s not yours. Let the customer decide if it costs too much. It’s his money, not yours. And you know what? It may not cost any more at all to heat the countertops.
You heard me.
I heard you, but I’m not sure I get you.
Why should you be any different? Look, you usually have tubing left over on a job, right? Just use that stuff. You can just run the leaders from the kitchen heating loops through the countertops, and voila, heated countertops at no extra cost.
And the customer will have heated granite countertops.
Which is nice. And why do people buy radiant heat in the first place?
Because it’s so comfortable.
Which is very nice.