LIVE image
In his book Your Green Home, Alex Wilson refers to radiant floors as "a great heating option for a poorly designed house." He goes on to explain that the heating requirements of an extremely well-insulated home with a properly airtight envelope, even in most cold climates, will most likely result in an overheated house if the radiant floor is warm enough to actually feel warm underfoot — which is the main selling point of these systems. If passive solar is a design feature, the slow response of high-mass radiant floor systems can also contribute to overheating. The expense of a wall-to-wall radiant floor system would generally be better spent, he says, on improving the envelope's insulation and airtightness, and downsizing the space conditioning system, particularly in new construction. For more information, see the article "Radiant-Floor Heating: When It Does — and Doesn't — Make Sense." But radiant floor heating can be a good choice under the right circumstances. Mostly, those situations exist in expansive commercial buildings with tall ceilings, particularly where inordinate air changes occur: fire stations, garages, hangars, where the large area of warmed mass provides quicker recovery with less energy. In residences and small commercial structures, radiant floor heating makes the most sense for buildings with standard levels of insulation and typical double-glazed windows — particularly when they're located in climates with small cooling needs. Retrofits of older houses in cold climates fall into this description. Underfloor radiant hydronic heating retrofit systems that install between the joists below existing wood floors are available from a number of sources. Metal plates or "fins," usually aluminum, that fit tightly around the tubing and make continuous contact with the floor significantly improve heat transfer; but in general, the more layers there are between the radiant heat source and the occupants, and the less thermally transmissive those layers are (think wall-to-wall carpeting), the more diminished the warm-floor effect will be. And for radiant floors to work well — particularly the "staple-up" variety — there also needs to be insulation underneath, which is too frequently overlooked. Often, simply insulating a floor can provide rich rewards without installing the heat delivery system. The other retrofit option for radiant hydronic floors is installing the heat-delivery system above the existing floor (which raises issues about doors that will have to be adjusted, cabinets that end up too short, and trim that needs to be dealt with). This is often accomplished by embedding hydronic tubing in about 1.5" of self-leveling, cementitious material — a process that can add up to a gallon of moisture loading to the building per installed square foot, and could potentially require temporary or permanent structural augmentation. Some of these flowables also have admixtures that may present VOC concerns. While "wet" installations provide extra mass for thermal storage, that extra mass means that they react more slowly to changes in thermostat settings as compared to a lower-mass system — which may or may not translate to reduced energy use, depending a good deal on how the occupants operate the system. There are a growing number of above-the-floor, dry-install, lower-mass (e.g., faster-response) options for radiant hydronic floor retrofits. One of them is the first, and so far only, radiant-hydronic-floor heat-delivery product to be listed in GreenSpec. It took several months of pondering and deliberation before we made the decision. GSC Modular Radiant Flooring Panels, which are installed on top of an existing floor structure using screws (which avoids VOCs from adhesives, and means that the panels are reusable), incorporate preformed channels on the underside to accommodate radiant tubing. The 1.25-inch-thick panels are made using a recycled-plastic tray into which a lightweight concrete incorporating flyash and recycled-glass aggregate is precast, avoiding moisture-loading the structure. The panels weigh seven to eight pounds per square foot.
Even though hydronic radiant-floor heating systems using high-efficiency components can use less energy than conventional forced-air furnaces, the sentiment that improving the envelope in order to use a significantly downsized heating system of any type that costs less to install — and more significantly, to operate — is unchanged. But low-temperature hydronic floor (or wall) heat, particularly when used in conjunction with solar and renewable energy, is an option that can warrant a review when considering the structure as a system, especially in the increasingly critical challenge of retrofitting our existing housing stock.

If you enjoyed this article, sign up for BuildingGreen email updates

*

Comments


— Share This Posting!

Recent Discussions

posted by ccnyIP
on May 20, 2015

I Have been in construction for many years and am now finishing my degree in mechanical engineering. I am truly amazed at reviews of many things...

posted by pmelton
on Apr 30, 2015

Here's a quick explanation of what a hygrothermal...

posted by pmelton
on Apr 29, 2015

John, I'm sorry to hear about your troubles. Based on my conversation with Peter Yost, our resident building scientist, it sounds like you've...

Recent Comments


The Building Envelope: Our Third Skin

Robert Riversong says, "I helped mix and install wood-chip clay-slip in a double-wall envelope, and it was done thoughtfully with a mixture of aggregate sizes, including..." More...

steven case says, "Hi Tristan I was wondering if you new or now of anyone that is living in a house of clay chip. I would be interested in speaking with them...." More...

Tristan Roberts says, "Hi Steven, the material you are referring to is usually called light clay, or sometimes Leichtlehm, from the German. It can be made with straw or..." More...

steven case says, "I just finished a class about clay and wood chip infill for walls have you ever done any testing or an article about them. All the oldest homes still..." More...


What Is a Hygrothermal Building Assessment?

Robert Riversong says, "As all water transport mechanisms and driving forces other than gravity are bi-directional (water is indifferent to which way it moves), there are..." More...