Radiant Heat: the Pros and Cons

Radiant heat ... is it really going to save the world? I mean, I've been listening to all the Radiant PR people and they talk about it like it's the greatest thing since sliced bread. Pardon me for being a little bit more realistic.

I grew up on Long Island, NY, right near a town called Levittown. (you may have heard of it, thousands and thousands of identical post WW2 housing). The funny thing is ... every house in Levittown had radiant heat. The only thing I remember about it was ... everyone who lived there bitched about the heat. By now, it has all been replaced with something else. (they used copper pipe, the concrete would corrode it after 30yrs or so). Now they use PEX plastic ... which may or may not last any longer. Time will tell.

To be fair ... I will say, I have radiant scattered throughout my house and I love it. But, I really don't use it as for heating ... just to keep the tile nice and toasty.

The pros and cons ... Pros first...

1)Because of the huge surface area of heating element ( like ... the whole floor) you can use much cooler water (somewhere around 100deg or so). Boilers run the most efficiently at the lowest temperatures and ... those new super 98% efficient condensing gas boilers are ONLY efficient at low temperatures. Compared to a standard boilers 85% ... you can save a lot of fuel. Running your regular boiler at a lower temp will save fuel too, but not as significantly.

2) It's really nice and warm on your feet. And with a higher mean radiant temperature (the heat that radiates from all the surfaces of your house) you'll feel warmer in a slightly cooler house.

3)It's an even heat. The house stays at whatever temp you set it, not much fluctuation.

4)There are some really cool things you can do with radiant. Like, heating the tile walls in the shower... amazingly nice when you first get in. Hang on ...Let me digress a bit into "mean radiant temperature". All the surfaces around you radiate heat. You may barely notice it, but it's why a room with a lot of windows feels cold at night, even if the air is the same temperature. If more surfaces are warm, you feel warmer because of that radiation. And if everything is colder, you feel colder.

Now, back to the cool things... Heated towel bars, heated mirrors that never fog, even heated ceilings. And one of my favorites ... heated moldings. You can put radiant panels alongside big windows, the panels offset the cold glass making the room feel inviting even on cold dark days. And YES ... I would recommend these things to everyone.

Now the cons ...

1)You need a really high tech, electronic boiler to get that high efficiency. These are more expensive, complicated to install, and harder to maintain. And there is a good chance they won't last anywhere near as long as the cast iron relic you had before. You may save enough on fuel to buy, maintain and replace it, but all that still comes out of your eventual savings.

2)It takes a long time to warm the house up. Not a problem during peak heating season, but lousy for spring and fall when you open the windows during the day and just want to break the chill on cold nights. All the heat stored in the floor ends up out the windows and then it's a few hours to get them warmed up again.

3)Forget about Day-night thermostats. The lag time on these systems is way too long for clock thermostats to work well.

4)The whole "radiant" thing isn't all it's cracked up to be. You think of how nice a fireplace feels on your face and you expect the same thing. One problem, remember how cold the parts of you that aren't facing the fire got? Well, the only parts of me that face the floor are my feet, my chin, and the bottom of my gut. The rest of me misses out on the radiant experience. (unless you add some of the "cool stuff" I was talking about)

5)It doesn't work that well with insulating floorings like carpeting. And it reeks havoc on hardwood floors (even if they tell you otherwise). It really works best with tile and laminate floors. If you have mixed floor surfaces you may need some extra controls to keep the heat even from room to room.

6)Some people find warm floors irritating. (My wife hates it). It does get hot if you stand in one place barefoot for a while. And if you keep the floors cooler, you may not be able to keep your house warm enough. My system is set up to modulate the floor temp based on ambient conditions. I had to lock it on the lowest setting to keep my wife from hurting me in my sleep.

7)The radiant coils in the flooring are slightly LESS efficient than conventional heat. Heat moves faster by conduction though a solid than by radiation through air. You are losing more heat through the frame of the house than you would have if only the air was being heated directly. Probably more than they are willing to admit. Good insulation and air sealing will help. (Good air sealing is the key to everything ... always start there)

SO, to sum things up. Radiant itself isn't more efficient, but it does allow you to use a SUPER efficient boiler. And it does have some flaws.

In my not-so-humble opinion ... Unless you are starting from scratch with a completely new gas fired system, radiant isn't going to save you that much money, if any at all. BUT, if your goal is a really nice comfortable house, there are plenty of places where radiant is the perfect choice. Personally however ... I think some rooms are better off with other types of heat.

A system that I've used before in some high end housing, that I really liked is ... Radiant floors along with a hydronic coil in the the AC ducts. You absolutely get the best of both worlds. Fast immediate heat from the HVAC system and nice even soothing heat from the radiant. You can shut the floors down in the spring and fall and just use the coils to break the chill at night. In the dead of winter, the floors will keep the house nice and even, and the coils will allow you to still use your day-night thermostats with some success.

In my house it's a combination of radiant and baseboard. I'm still using a traditional cast iron boiler, so mine doesn't approach the efficiency of the newer systems, but the house is really comfortable ... all the time. Eventually, I'll probably add a coil to the AC ducts and eliminate the baseboard. Then I'll be able to spring for a condensing boiler and really see some payback.

p.s. I'll talk about condensing boilers in another post. and .. before I forget ... air sealing , air sealing, air sealing ... buy a can of foam and do it now.

tom