He plans to build a house, says the caller, and the estimates he got for heating systems are expensive and confusing. Could I help him pick a heating system? How could I without knowing anything about the heat load of his house? The house doesn’t exist yet, the caller explains, there is only a sketch. So, how can we talk about heating systems? We should, instead, talk about designing an energy efficient house. A house is a system. The more energy efficient, the smaller the heating system and the less fuel to heat it. The heat load of a house must be known before one can responsibly address how to heat it and what that will cost. – The caller assures me that the house will be tight, well insulated. – How tight, I ask, how well insulated? How will the extra moisture a tighter house inevitably traps be handled? – He doesn’t know.
I doubt people would buy their next car from an auto parts store and hire a trusted contractor to put it together. Yet most people think of a house as a collection of its parts – from framing lumber, to windows to heating systems. As a result, most of our houses, regardless of how old, are cold, drafty and expensive to heat. The average Maine house loses a third to two-thirds of its heat through air leaks, for example. And we, homeowners, are vulnerable to hordes of sales people trying to sell us whatever house components they have to sell – from insulation to replacement windows to improved heating systems – as the cure for our troubles. Be it a new house-in-planning or an existing old cape to be improved, without a coherent, well-reasoned systemic plan it is easy to fall victim to this parts-oriented sales force, spend a lot of money, yet end up with a poorly functioning house. Worse: we are apt to make decisions based on how much a thing costs – the only information we are in position to evaluate – rather than how well it might perform, year after year. If we succumb to sales-pitches instead of buying precisely what we need and why, we are likely to pay more than we need to yet be disappointed in the end. My caller, for example, may end up buying a heating system based on price, which may be oversized for his eventual house, cost too much to operate, or won’t satisfy his comfort needs.
So, building a new house or fixing up an old one, it is best to begin with a plan based on sound science. Investing the time and money in this planning will pay for itself in performance and savings. Planning is the most cost-effective first step. It starts with a firm performance goal, based on which all the components can be evaluated and specified. No more buying stuff based on some sales pitch, tradition, or mere price. A good plan, not the latest widget on the market, will make your house work as a system, providing comfort as cost-effectively as possible.
The world’s best performing buildings are designed and built to meet the following Passive House standards: (1) no more than 15 kWh of heating energy per square meter of floor space per year (1.4 kWh/sq.ft./yr); (2) no more than 120 kWh of total energy (11.1 kWh/sq.ft./yr), including the above; (3) no more than 0.6 air change per hour at 50 Pascals indoor-outdoor pressure difference, as tested by a blower door; and (4) deviation from predetermined comfort conditions no more than 10% of the time.
The measures to be taken to achieve these results can be summarized in 5 points: (1) Super-insulation, appropriate to the local climate (R-55 or more on all six sides of the heated building envelope here in Maine); (2) No thermal bridges, like wood framing or metal components that interrupt the continuous super-insulation layer; (3) Airtight construction, achieved by a single, properly positioned, uninterrupted, vapor-impermeable air-barrier; (4) Sufficient controlled ventilation with heat recovery, to remove excess moisture and provide the appropriate supply of fresh air; and (5) Super-energy-efficient, thermal bridge-free windows and doors. There are no prescriptive requirements. Passive house designers are free to meet the standard’s performance requirements any way they choose but, once built the house must pass a test, rather than just an inspection. This encourages innovation. There are no patents or trade secrets involved in designing a passive house, but there is a growing body of international knowledge and experience all qualified practitioners are free to draw on.
Summer is on its way. The opportunity to avoid another expensive winter in a cold and drafty house is upon us. As a matter of record, buildings that meet the passive house standard consume 90% less energy than the average of recent vintage conventionally constructed buildings. New house or old, this is where to begin. Plan. Invest in help as you need it. Join the local energy cooperative. Learn. Don’t buy anything until you are sure of exactly what you need. It makes no economic sense to newly build anything less efficient than a passive house. With an existing house, the idea is to come as close as possible to passive house performance.
Stay tuned. Detailed information to follow.