Concentration of CO2 in the Atmosphere

Deep Energy Retrofit in Montpelier, VT Achieves Net-Positive Results

By George Harvey

A recent retrofit in Montpelier, Vermont is notable, partly because the house was a prime candidate for improving efficiency, and partly because of what the retrofit achieved.

Deep energy renovations by Montpelier Construction have taken this Montpelier, to a net-positive status. They make more energy than they consume! Note the solar system on the right. Photo courtesy of the owner.

Deep energy renovations by Montpelier Construction have taken this Montpelier, to a net-positive status. They make more energy than they consume! Note the solar system on the right. Photo courtesy of the owner.

The house is what is called an atomic ranch. In the middle of the last century, this style was thought very modern. It typically has a low roof with wide overhangs and an emphasis on picture windows. While this combination may be featured in many solar homes, it will only work for that purpose if it is engineered properly, and the chance of doing that by accident is pretty small. In this case, the orientation of the house was with a north-south roof axis and the overall design did not have solar heat in mind. This meant that the four picture windows represented a large area for heat to be lost.

Adding insult to injury, the insulation was inadequate, and the house air sealing was poor, by modern standards. In time, a garage was added on the south side of the building, further reducing the possibility of any solar gain. With the garage, the area of heated space was increased to 4000 square feet.

Super efficient windows from Ireland. Photo courtesy of Malcolm Gray, Montpelier Construction.

When the house was built, in 1962, it had a very modern heating system. It was entirely electric. When that turned out to be expensive, an oil furnace was installed with base-board hot water heat. Though the boiler was very efficient, for the time, it did not bring the building to anything like the modern standards. Recently, the house has often been empty during the winter, but even so, with all its inefficiencies it was burning 2300 gallons of oil per year.

Aside from the fact that it looked ultra-modern to people in the era that produced “The Jetsons,” this house was in many ways like the vast majority of the older houses in the Northeast. It is representative of the problems many homebuyers face with older buildings.

Now, the atomic ranch has undergone a deep energy retrofit, largely with the guidance of Malcolm Gray of Montpelier Construction, located in Barre, Vermont. The structure itself was altered for efficiency. Each of the four picture windows, which were six by five feet, was replaced with a pair of casement windows. A bow window also was replaced the same way. All windows and doors were upgraded with Passive House certified products The new windows were from Klearwall, in Ireland, and have tempered glass with an insulation value of R-11. New doors were from the same source, with similar levels of efficiency.

Air Infiltration was reduced by two-thirds, with numbers for blower door tests being reduced from 4800 cubic feet per minute to 1630. The number of air changes per hour was reduced from 0.8 to 0.25. A tight house needs to have controlled ventilation to bring in air that is pre-heated by extracting heat from the outgoing air. It also needs moisture control. These needs were addressed with an energy recovery ventilation system by Memphremagog Heat Exchangers in East Montpelier.

New insulation was installed, of course. The roof got twenty-four inches of blown cellulose bringing it up to an R-90. A two-to-three-season sun room, was given five inches of polystyrene, only an R-20, but a large improvement over solid brick, and all insulation of the house was improved.

The heating system was replaced by a ground-source heat pump with three wells, each 150 feet deep. Though this is probably the most efficient active heating a house can get, it is an expensive installation. The decision to install a ground-source heat pump was at least partly based on tax incentives that were not available for air-source systems.

The heat delivery system for the basement and ground floor were replaced with one made by Myson Comfort. The old hot water baseboard heaters in the split level and second floor were retained in use.

Electricity for the house is provided from a ground-mounted 10-kW photovoltaic array installed by Sustainable Solutions of Marshfield, Vermont. The panels can be seasonally adjusted for tilt. A backup propane powered generator was also installed.

Asked whether the house has net-zero energy use, Malcolm Gray said, “The system is too new, and the numbers are not all in.” But in the meantime, he is hoping to find it is net-positive.

Learn more about Montpelier Construction and their expertise with deep energy practices at, or call them at 802-229-6575.


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