Retrofit Radiant Heating
Radiant heating is an efficient and comfortable method for heating. Instead of heating air and blowing it into spaces to mix with the cooler air and increase the temperature, radiant heating directly heats everything around it. When you stand in direct sunlight and feel the heat on you, that is radiant heating. Household radiant heating uses hot water, either from a water heater or from a boiler, to convey heat throughout the house. Some older homes used hot water or steam and radiators, which provided both a direct radiant heating source in the room, as well as indirect heating of the air passing the radiator and circulating into the room by convection. Newer radiant systems turn the entire floor into a radiant heating surface, providing even radiant heat throughout the house.
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For the past several months, I have been slowly installing the tubing for a radiant heating system in my own home. The process isn’t normally really that drawn out. However, since I’m doing the work myself, on available weekends, it’s a slower process than having a crew of professionals come in and do the installation in a couple of days. But, regardless of the time it takes, the installation method is fundamentally the same.
I am lucky in that I have a single story home, so accessing the underside of all floors was relatively easy. Retrofitting radiant heat into a multi-story home would require either removing the ceiling on the level below or fastening the tubing to the existing flooring and then raising the floor level by a couple inches with an overlay of concrete or tile grout. While this can be done, it is a much more involved and expensive process.
Radiant heating is a green choice for heating for a number of reasons. For people with allergies, getting heat without blowing air around through dusty ducts is highly preferable. Water is also much denser than air, so it is more effective a medium for heat transfer. The typical human thermal comfort profile also tends toward having more heat at the extremities (namely the feet) while having slightly cooler temperatures for the head. This very much matches the heating provided by an in-floor system. Warm floors are also very comfortable for smaller children who like to play on the floor. And often, a radiant heating system can be set a little bit cooler than a forced air system because the direct heating from the radiant system is comfortable, even if the actual room air temperature is a little bit cooler (again, think of being in the direct sun on a bright, cool autumn day).
The next step in the process is going to be having the plumbing connected, with a heat-exchanger to transfer heat from our water heater (which was oversized in order to be able to run this system while still providing us hot water in the house) along with the other pipes and valves and bits of equipment necessary to make the system work.
In our installation, we are going to keep our forced air furnace in place for now, in case we get some really cold days that the system isn’t able to keep up with. But the sizing of the system seems to be large enough that we shouldn’t have any troubles with it. We’re all looking forward to having the radiant system up and running in the next couple of weeks.
You can see the PEX tubing (white) fastened to the side of the joist with clips (black) spaced every couple of feet in the photo. The cross pieces shown are left from removing the old ceiling that was in one part of the basement. They turned out to be very handy to help support the tubing in place until I could get the clips hammered into place, but they are not a required part of the system.
An article from ‘This Old House‘ offers more information and discusses the advantages and the process of installing a radiant heating system, as well.
Hi Phil,
was there any concerns with warping/discoloring/cracking of the hardwood floor with radiant floor heat? did you install a humidifier to mitigate any issues?
I already have radiant in-floor heat in my home, using a concrete slab for the ground floor. I also have supplementary hot water radiators upstairs.
It seems to be somewhat less expensive than forced air compared to my neighbours (I would guess roughly 20% saving). I use natural gas with a 120,000 btu boiler (it could be smaller for my 2100 square foot home).
So, it must be 20% “greener” than a forced air installation. (Although how anyone in their right mind can consider burning fuel at a lesser rate “green” is beyond me. Like buying a hybrid…it still uses fuel, still has to be manufactured, etc. Green? Maybe less black.) Now, if it were entirely solar….
Anyway, while the savings are modest, and the “greening” dubious, it is nice to have warm feet. Also, the slab is a heat condensor in summer, absorbing heat in the day (and slightly cooling the home) and releasing it at night (and thus taking some chill off, if any, at night). The cool floor is comfortable in summer, too. So, it is a free air conditioning system in a way. With solar glass and upstairs fans, it actually works pretty well as a passive solution.
And I will say that actually is a pretty “green” air conditioner.
Sorrey to challenge you theory on allergens, but the cleaner air theory is bunk. Circulating air with effective furnace air filtration is much healthier, as you trap allergens and move the air around. If your house is dirty, try cleaning it and going to hardwood or lino floors. How do I know this? You get dust on the furniture in a radiant house too, and my brother in law is a heating consultant with children who have allergies…his choice (and he could have anything as the company provides it) is forced air, high efficiency, multiple furnace, with hepa filtration installed.
The disadantages of radiant are: very slow to react to sudden temperature fluctuations outside (i.e. a sudden Artic front and you are cold for a day until the slab heats up sufficently), and a rise in temperature leaves the house too warm until the slab cools down; another disadvantage is the lack of air circulation that can result in uneven air tempeatures despite evenly heated floors; another disadvantage is that windy and very cold weather can cool a house enough that radiant heat can have trouble keeping up…this of course depends on exterior glass area and overall insulation; finally, wood floors are punished by radiant heat, as it dries the wood out and may cause cracking noises in certain installations.
The former may be partly solved by computers that sense rising or falling temperatures and then pre-empt the situation by increasing/decreasing water temperature.
The second issue may be mitigated with ceiling fans.
The latter issues could be remedied by improving insulation and keeping water temperatures modest. If the climate is very cold, installation must be considered carefully.
If your outside temperatures do not vary to extreems, then you may not experience some of these problems. (I do in my area….cold!).
I like radiant heat, but nothing is perfect, and green is relative.
We gutted our old house in metro Detroit area. My husband wants to put in radiant floor heating with pex tubing (not in concrete) I am trying to find information and examples of homes that have used this in renovation in southeast MIchigan. We are planning to use it as the only heat source. I would like to know if you have finished installing yours and how you like it. Any cautions, suggestions or sources for research in this area? Thanks a lot I appreciate your articles,interesting and well written.
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