Radiant Floor Heating

Sure, you've heard about it. Perhaps you've even seen Rich Trethewey of This Old House talking the stuff over on a snowy Sunday afternoon. But here are the facts- radiant floor heating is the most comfortable heat available, bar none. Another huge benefit is the fact that it is much more efficient than conventional heating systems, because it uses lower boiler temperatures. The technology has been around for a many decades, but few people really understand the advantages, and sadly a lot of heating contractors don't either.

Why Is Radiant Heat More Comfortable?

Radiant heat is like the sun's heat. It travels through the air until it finds an object (did you ever notice how hot the pavement gets in mid summer?). Typical heating systems rely on “convection”.  Convention simply means that the heated air will rise, and the cooler air will fall (unless it's forced warm air, which is driven by a blower). Have you ever put on clothes that seemed to be cold? How about crawled into a bed that seemed rather chilly under the covers? That's what happens with convective heating- the air is warm, not the surrounding objects in your home. With “warm air”, your skin is tricked into thinking that the living environment is comfortable, until your skin has to give up its heat to another object! This subject becomes physiological as well: Have you ever stood next to a glass window or door and felt the cool air against your skin? Next time this happens, find a thermometer and go back to that window. Unless you have a literal draft of air coming in through the jams, you won't see the thermometer go down! That's because your body is giving its heat over to the glass, and therefore cooling off our skin! Remember, our skin is a breathing organism. That's why it's possible to feel comfortable with radiant heat at 68 F, yet feel cold and clammy with a convective heat source at the same room temperature.

Efficiency With Radiant Heat

hampshire county radiant heatAs mentioned above, lower boiler temperatures equates to lower fuel bills. I'll have to get a bit technical to explain. For example, the average heating system is designed to circulate water between 180 F to 200 F. A properly designed radiant heating system will operate at around 130 F (actually, this can vary quite a bit depending on the flooring material used and where the heating tubing is placed). A commonly accepted rule of thumb is to figure 1% fuel savings for every 3 F you can lower the system temperature. [Example- a conventional system's 190 F vs. a radiant system's 130 F would be 20% more efficient (190-130=60. 60/3=20%)].

Hold on, it gets ever better! Most radiant heating contractors will figure into their quotes a control device called an outdoor reset. Don't skimp- this thing is for real. During the course of the heating season it will monitor the outside air temperature and adjust the boiler water temperature accordingly. Virtually all conventional systems have a basic boiler “aquastat”. The aquastat has a “high limit” that tells the burner to shut off when it reaches that pre-set limit point. Conversely, the outdoor reset control only squeezes out of the boiler what it needs to heat the house. The only time it won't be all that beneficial are the days that are “design conditions” (explained later). Here in New England, the Pioneer Valley of Western Mass. to be specific, we heat about 7 to 9 months out of the year. How many of those days do you think we're at 0 F outdoors? Perhaps a better question would be, "How many hours?”. Most heating pros realize that we are at design conditions about 1% of the heating season. That means 99% of the heating season the conventional heating system is oversized!

Even the boiler itself will waste heat with a conventional aquastat. Think about it. If you're boiler has to crank up to 180 to 200 F every time there is a call for heat, we assume that it will cool down on its own, right? It doesn't take a mechanical engineer or physics major to understand that the conventional boiler will want to shed off that heat in a big hurry. Think of it this way: what will shed off 10 F quicker, a cup of hot cocoa at 150 F or a cup that you made for your little kiddo (not as hot as yours), say around 110F? The hotter cup will cool down faster. In heating terms, this means that you are wasting a lot of fuel without the reset control. They can also be retro-fitted onto an existing system.

Design condition is when the boiler is running at its maximum potential (or, it could mean the heating distribution system is at its maximum potential). In any case, most of us installers in Western Mass design a system for 70 @ 0 F outdoors (we at Wilson Services, Inc actually design a system at 68 for radiant heating, for the reasons mentioned).

Some folks ask for a -20 design temp, but it will hog a little more fuel than the 0 design system (still with me? Hang in there, I'm almost done! ). And the -20 system will cost a bit more to install. If you take a very cold winter month for example, one might think is was at about 15 all month here in the Greater Northampton area, but the National Weather Service reported a civilized average 31.8 high, 15.1 low and a 23.5 average on a very cold January several years ago. Not ONE day had an average of less than O F! So why design a heating system to heat at under 0 F?? If you insist on spending it, your heating contractor will gladly accept your money. If you’re having a heating system installed and the heating contractor hasn't specified a design temp., a red flag should go up.

Negative Reports About Radiant Heating?

Some of you reading may only be aware of bad stories; perhaps you had radiant heat growing up and the pipes corroded (no one knew the cement ate copper back in the 1950s). Or maybe it was in the ceiling and the pipes froze (the control systems back then are now on display at the Smithsonian...). In more recent times (1990's), there was a radiant heating manufacturer that faced many lawsuits because their product failed over and over again. Believe me when I say- those days are over, IF you chose a contractor installs PEX tubing according to the manufacturer's specs, and by gosh most of us do. But trust me on this: you really should either ask or make sure it's specified in the contract.