Radiant Floors: Overkill in a Passive Home? (Part 2)

In part one of this post, we asked if radiant under-floor heat makes sense for a high-performance, passive home. (Read Part One here.)

The Overheating Debate

Executive editor of Environmental Building News, Alex Wilson’s opinion is clear: radiant floors don’t make sense for passive homes.

Overheating is one of many concerns:

In a home with a tight envelope and a very small heating load, even a small amount of heat can cause overheating, and the thermal mass in a radiant floor system increases the risk. This is particularly true in buildings with some level of passive solar gain – the radiant floor may still be delivering heat even after solar gain raises the air temperature.

Alex goes on to question the whole main benefit of radiant flooring: how good it feels to walk barefoot on a warm surface.

When the heating load is very small, the radiant slab has to be maintained at no more than a few degrees above room temperature to prevent overheating… this means that the slab isn’t likely to be warm to the touch. A slab maintained at 74°F will be cooler than an occupant’s skin, so bare feet will conduct heat into the slab.

If the floor feels noticeably warm, your home overheats; if your home is comfortable, the floor feels cool.

Our Conclusion

In conventional homes, radiant floors are a wonderful feature. Alex Wilson agrees: “It’s a great option when we can’t go as far as we’d like with envelope energy performance.”

Even in our own high-performing homes, where envelope performance far exceeds conventional standards, radiant floors can work.

The question is, are they needed? are they worth it?

In our experience at Clarum, radiant floors are not “needed.” Our highly efficient, cost-effective systems do not require under-floor heating to achieve surpassing comfort. If radiant is wanted, Clarum recommends radiant flooring in bathrooms only, as it is a nice feature to have in those particular areas of the house.

“Are they worth it?” is a different question. One has to weigh the costs (financial and otherwise) against the benefits.

According to author and Green Building Advisor Martin Holladay, radiant flooring is “overkill and a waste of money” in a super-insulated, airtight home.

Then again, some passive-homeowners love their radiant floors and enjoy them immensely, even if, from a performance standpoint, the system isn’t strictly necessary.

What do you think?

Do you have a radiant floor? Do you plan to install one? Are radiant floors worth it in your view, or do you think they’re overkill? Please share your thoughts in a comment.

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