finished basement. The heat pump is rated to provide warm air with outdoor temperatures as low
as 17°F (minus 8°C). When temperatures drop
below that and the house requires more heat, a
heating element in the ductwork automatically
turns on, providing a backup system. although
the flow of air from the vents is at very low force,
the house stays warm throughout.
A Stiebel-Eltron Accelera 300 provides hot
water. The 80-gallon heat pump water heater has
an energy factor of 2. 51, the best on the market
according to the manufacturer. Its maximum
power draw is 2. 2 kilowatts. In more than a year
and a half, our household of three has never run
out of hot water. The mechanical room becomes
quite chilly, but so long as we keep the door
closed, the cool air the system emits doesn’t
affect the rest of the finished basement.
To insulate the original exterior walls, which were now stripped down to the 5/8-inch plywood sheathing,
the team spray foamed the entire exterior. Carpenter Tom Cuccaro came up with a way to frame over the
sheathing and around the window/door openings so that spray foam could be applied.
To insulate cinder block basement walls, the team
installed a wall of 2x3 studs held 2 inches off the
block walls. They sprayed behind and between
these studs with 4 inches of closed-cell foam. This
resulted in an R- 27 wall, with a loss of only 4-½
inches of space.
Copyright © 2012 by the American Solar Energy Society Inc. All rights reserved.
system production and our energy consumption.
We can turn off a light and watch the numbers
change, right on our computer screen.
our insistence on using no fossil fuels for energy creation led us to choose an air-source heat
pump HVAC system and a heat pump water heater, both powered by the PV system. Our HVAC
contractor recommended the most efficient air-source heat pump he could find: a Mitsubishi Mr.
Slim ducted system (we decided against the Mr.
Slim ductless mini-split for aesthetic reasons).
The system is coupled with two Mitsubishi air
handlers, one for the main floor and one for the
Creating a Super-Insulated envelope
To supply a constant exchange of fresh air
to our airtight house, we installed a lifebreath
heat-recovery ventilation (HrV) system. For
windows, we wanted to incorporate some passive solar benefits while minimizing heat loss.
The south side has a large triple window on the
main floor, and a double patio door plus a large
window on the walk-in basement level, to let in
midday sun. The west side includes an all-glass
sliding door and other large window openings.
a local window retailer directed us to highly
efficient Starmark Triple Heat Shield windows,
made by Pennsylvania-based OKNA. We chose
white cellular composite triple-pane, krypton-filled casements, each with a U-value of 0.16
(for the whole window assembly). They have
the highest insulating qualities I could find and
are attractive and well built.
For insulation, we tried to follow Building
Science Corp.’s “5-10-20-40-60 rule” for insulation levels in homes in cold climates: R- 5 windows, R- 10 under slab, R- 20 foundation walls,
R- 40 house walls and R-60 roofs. In the existing
part of the house, the rafters were 2x6s and the
walls were 2x4s. To get a lot of insulation in this
existing framework, we chose dense-packed cellulose insulation in between the rafters and in
wall cavities, 4 inches of polyiso rigid foam on
the roof and closed-cell spray foam covering the
exterior walls. My Building Performance Insti-tute-certified specialists paid special attention to
creating an airtight “shell” with no (or minimal)
In order to pack 11 inches of cellulose between
the rafters, we had to attach another 2x6 to the bot-
A 5.16-kilowatt PV system is mounted on the roof
of the addition, designed to face south at the optimal pitch.
this way of building and chose durisol’s cement-bonded, wood fiber ICFs.
Lighthouse Solar designed a 5.16-kilowatt
photovoltaic (PV) system, comprising 24 Sanyo
HIT 215-watt modules mounted on the roof. A
Sunny Boy 6000-US inverter is mounted on the
same side of house as the meters. lighthouse
Solar included lightgauge, its real-time data-monitoring software, which allows us to track