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Maine home can stay at 70 degrees without a furnace, even when it's freezing out

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In the middle of a Maine winter, a super insulated house keeps its family warm. There's no furnace — just a small heat pump. The same heat pump is used to cool the home in the summer months.

A MART?NEZ, HOST:

What if you could design a house that on a cold day would stay at 70 degrees inside without running the furnace? It's already being done. Building upon the work of North American passive solar pioneers of the 1970s and '80s, today's passive houses are even better at keeping warm or cool without much energy. Keith Shortall of Maine Public Radio visited one of these houses in the tiny town of Hope.

KEITH SHORTALL, BYLINE: As I arrive at the home on a rural road in the rolling hills of Hope, I check my phone for the temperature.

AUTOMATED VOICE: It's 31 degrees outside.

(SOUNDBITE OF CAR DOOR SLAMMING)

SHORTALL: I'm greeted at the front porch by Patrick McCunney, a mechanical engineer who moved from Philadelphia to this newly built 1,500-square-foot passive house with his wife and their two young daughters a little over a year ago.

UNIDENTIFIED CHILD: Hi.

SHORTALL: Hello.

PATRICK MCCUNNEY: So, welcome...

SHORTALL: Thank you. So it's 31 outside right now. But it's very cozy in here.

MCCUNNEY: Yeah, exactly. It's about 70 degrees in here. And it's - you know, once you set that temperature, the house - because of its air tightness and, you know, amount of insulation, it maintains that temperature pretty efficiently.

SHORTALL: So you don't have a furnace going?

MCCUNNEY: No furnace, just this small little heat pump.

SHORTALL: The same heat pump is used to cool the home in the warm summer months. Most of the heat is provided by the sun, which streams in through a wall of windows on the south side of the home and on to a rooftop solar array that, McCunney says, on bright days like this will generate four times as much energy as the house needs. That means that the only heat or electricity bill they pay in the winter is the connection fee to their local electric utility, about $13 a month. The builder of this passive house, Alan Gibson of the Maine-based firm GO Logic, says they do cost about 10% more to construct than conventional homes simply because they have more stuff in them.

ALAN GIBSON: There's more insulation. There's more care taken to making it airtight. There is a ventilation system. There's better windows and doors. And people have a hard time getting beyond that, even though we can show them pretty easily that the economic payback is there.

SHORTALL: Gibson says a conventional home that might cost $400,000 could run about 40,000 more to be made into a passive house. But it would use just 10% of the energy. And, says one advocate of passive design, it can also be used in warmer, more humid parts of the country.

NAOMI BEAL: This is a system that works no matter where you are globally.

SHORTALL: Naomi Beal is executive director of the nonprofit passivhausMAINE. She says with some modifications, the same principles of super insulation, airtight construction and a mechanical heat-retaining ventilation system can keep buildings cool with very little energy.

BEAL: The heat recovery system will free heat or pre-condition the air as it comes in. And in the southern climates, then, it's a similar system, although the air is being precooled as it comes in rather than preheated. That's the efficiency. That's where the savings are.

SHORTALL: The national organization Passive House Institute U.S. says it has certified more than 7 million square feet or more than 7,000 units in 42 states and provinces.

For NPR News, I'm Keith Shortall.