So many people have asked us about radiant floors that we figured it was time to give them a page of their own. Thus far we have managed to find three different groups of radiant floor products. Two of these are distributed by our local dealer so we will most probably end up going with one of these.
The big names in radiant floor heating are the Thermafloor and the Wirsbo lines. Therma-floor is actually not a complete radiant package but just the gypsum based concrete that is used as a part of the radiant floor system. If the Wirsbo name sounds familar you are probably someone who watches Hometime on PBS. They have used this system several times.
Lennox is now advertising a radiant floor system and they have teamed up with the Wirsbo folks to provide a very nice package using the Wirsbo tubing, manifolds and controls and a Lennox power plant. We met our local Lennox dealer, Ackerman Heating and Air Conditioning in Colfax, WA at the Moscow Home show recently and it looks like they will be doing this work for us. Once we have windows and floors figured out they will work up our system for us. The Lennox power plant provides both domestic/potable hot water and the heat for the radiant system out of a 90% efficient gas furnace. It is quite the system!
Now you are asking "why a radiant floor?" Well, how many times have you dragged yourself out of bed on a cold winter morning and been jarred awake as your warm feet hit the cold vinyl floor in the kitchen or bathroom? Ever lay or sit down on a cold floor and then had a hard time getting going again? These are just two of the reasons to go with a radiant floor. The other is energy efficiency. We all know that heat rises, actually though, heat doesn't rise; heated air rises but heat is a localized phenomenon. With a typical forced air system the warm air comes through a register creating a warm zone in the immediate vicinity of that register. This warm air rises to the ceiling leaving cold spots in your room. So, to get the area you live in (near the floor) to a certain temperature you have to heat all the air above that space to a higher temperature than you are looking for near the floor. With radiant heat, you warm the space near the floor first so it is more comfortable at living level using far less energy.
Okay, so you want to know how a radiant floor heat system goes together and you don't want to follow the links above to get the info and you haven't watched a This Old House or Hometime project in the past several years. In brief there are two types of radiant systems. One uses PEX tubing running under the floor through which is piped a warm fluid (typically water but some systems use mineral oil). The other type uses electrical heating elements in place of the fluid filled tubes. Electrical systems are really better suited as supplemental heating in small areas, like a bathroom, and not for whole house heating.
In either case, these tubes or wires are generally encased in a gypsum concrete to act as a thermal mass, protect the heat tubes/elements, and give you a level floor. Gypsum concrete is used because it weighs considerably less than regular concrete, about 9 pounds per square foot when poured to a 1.25 inch thickness. This is great if you are pouring a concrete slab anyway (it doesn't have to be light weight concrete...standard old concrete works just fine too. You can also mount the radiant tubes under the wood subfloor and use aluminum reflectors and insulation to direct the heat upward. This means you don't have to engineer the floors for the extra weight and is generally more cost efficient. You don't get the thermal mass of the concrete but it really doesn't make a big difference. This is especially true in a log home where the walls are already a significant thermal mass.
Oh, and the myth about not being able to use radiant heat under carpet? Well, it turns out that if you just run it like a normal part of the system the carpeted room won't get up to temperature very well. But, if you zone it and feed it differently off the temperature mixing manifold (computer controlled valves mix hot and cool water to give you the proper temperature) so it gets hotter water than the rest of the house you are just fine.
You do have to be careful, especially with wood floors, to keep the temperature of the fluid circulating under your floor at 85F or lower. Any higher and you will dry out the wood floor and ruin it.
Okay, so what about cost. Well, radiant floor heat does indeed cost substantially more (20 to 50% more) than a more traditional heating system. However, the improved efficiency and comfort level provided by a radiant floor heat system will pay for itself in a few years. Radiant floor systems are easily "zoned" so that you are only heating the spaces you need to heat. The biggest disadvantage of a radiant floor system is that if you decide you want to take a space from 60 degrees to 70 degrees it takes substantially longer to do this than with a forced air or electrical system. If you use a thermal mass such as concrete this can take even longer. However, with a log home you are working on thermal mass/inertia so it is really more energy efficient to maintain a constant temperature than jump temperatures around all the time.
Depending on local codes and state regulations some sort of air exchange system must be used. In today's "tight" houses you would have a very unhealthy house if some sort of fresh air supply system were not installed. In the state of Washington a certain percentage of the air must be exchanged over a given time period. This can be done in a variety of ways. The cheapest method is to created intentional air leaks around windows and doors. Then a whole house ventillation fan on a timer cycles every so often and draws warm (and polluted) air from the house and exhausts it outside while fresh air from outside is drawn in through the vents/leaks around the doors and windows. This might be a great system when the outside air temperature is pretty warm but what about those times when the outside air is -30F?
A better way to go (and yes, it costs more) is to go with a fresh air heat exchanger. As fresh air is drawn from the outside is warmed by the house air (through a heat exchanger, the two air supplies don't actually mix) being exhausted using a principle known as Counter-Current Exchange. I won't get into the principles of this but suffice it to say that it works very well. This same principle keeps duck feet from freezing to the ice they are walking on...yes, really.
We will add more to this page as we learn more about this system.
Last Modified: 02 April 2000
The purpose of this web site is solely to keep our family and friends informed with the latest info on our log home project. Any mention of a particular company or product is not an endorsement in any manner or form unless otherwise specified. All images, plans and other information contained within these web pages (not including links to other companies of course, for which we take no credit or blame) is copyrighted by Kevin M. Imel, 1998-2000 except as noted. Any use without the expressed, written consent of the author is expressly forbidden and you will be hunted down like the scurulous rat that you are and beaten senseless with a smelly dish rag...or worse!