Michael Schonlau is building a house in Omaha, Nebraska, where he can expect 6,000+ heating degree days a year. He’s planning on putting a radiant-floor system in the basement slab of the ranch-style home with a footprint of about 1,600 sq. ft.
In a recent posting on GBA’s page, Schonlau asked whether he’ll have to install radiant loops under the subfloor of the first floor as well as the basement — or will the heat generated in the basement migrate upstairs and keep the house comfortable?
“Please assume the house will be well-insulated and air sealed, with ‘good’ windows,” he wrote. But will that be enough to keep his wife’s toes warm through a long Nebraska winter?
It’s been done
GBA senior editor Martin Holladay tells Schonlau it can be done, but “but only if you aim for near-Passivhaus levels of airtightness, insulation, and window quality.”
Dan Kolbert is more optimistic.
“We’ve built a couple of houses on slabs with no heat distribution on the 2nd floor,” Kolbert says. “They were good, but certainly not Passive House.”
One of the houses had double-glazed windows, “not huge R-value,” very good solar orientation and a sprawling layout. Radiant-floor tubing was extended to the second floor, but after two winters the client had no interest in second-floor heat distribution.
The other house was much tighter. Here again, heat in only the first-floor slab was enough to keep the house toasty.
“I essentially agree with Martin, though, only disagreeing in what the threshold might be,” says Kolbert. “An energy model (and someone who knows what to do with it) would help make the decision.”
Robert Riversong, however, isn’t so sure it’s going to work.
“Unless your house is very energy efficient (32,000-45,000 btu/hour maximum design load), then a…