A Habitat for Humanity Passive House in Vermont. Image: Chris Miksic, CPHC, Montpelier Construction.
Greg Whitchurch
You know how after your furnace has gotten the house all warm and cozy, a little while later it comes on again – and then again? What happens to our heat? Does it wear out, or just fade away?
No. It escapes! Your precious heated air leaks out through holes and cracks, through wall sockets, around windows and doors. It’s sucked in and then blown outside by your dryer and anything that burns fossil fuels. Those appliances use your breathable air for combustion and then force the poisonous exhaust outside – sucking cold air back inside. (If you cook with gas, then those toxic fumes just circulate around your house until they’re able to escape with other heated air.)
In addition, in a conventionally built home, heat that is touching your walls is conducted outside through thermal bridging. A typical home has its sheetrock or paneling nailed to the studs, which are good conductors of heat; they transfer it directly to the sheathing nailed to their other side, where the heat disappears. Many doors and windows and their frames are conductors of heat as well.
Finally, heat radiates through windows. South-facing windows might allow more warmth in than they let out while the sun shines on them, but other windows and the nighttime rob us.
Watching this 90 second video will enhance the rest of this article: http://bit.do/PH90.
Zooming through the -40F degree wind chill in a helmet and snowmobile suit can be comfy cozy. But if we instead dressed ourselves in the manner of “the modern home,” it would be more like going snowmobiling with holey jeans, a jacket, sneakers, work gloves, and a pair of goggles. But, the building code and many builders don’t seem to see the parallels. Remember, the building code simply describes the worst home you can legally build.
Passive House plan with ground source heat pump. Image: Wikipedia
Most heat loss in modern homes is through air leakage – inadequate insulation usually comes in second; thermal bridging, third. The air leakage is like a very small window left open year ‘round, but when leaks are spread both low and high, the “chimney effect” amplifies air movement – popular windows and doors are often not much better than older versions. To address these issues properly requires a highly insulated envelope (walls, roof, and foundation); triple-paned windows created for south vs. north exposures; and taped membranes to air seal and protect against moisture problems.
Proper attention to home design makes our homes more resilient, longer lasting, more healthful for the occupants, cheaper to own and operate, safer, and more valuable as an investment, to say nothing of being far less polluting. And the home itself doesn’t have to cost more.
WARNING: Side effects will include: no drafts, ladybugs, mice, cluster flies, or cold windows and cold rooms; fewer allergic reactions, very much lower heating and cooling costs, no poisonous explosive fuels or exhausts; smaller net-zero and backup power system options.
How might one move from past practice to the future? Well, actually the future has been here for a while. Advances in science and engineering have allowed designers to analyze local climate, land formations and trees, seasonal positioning of the sun. This gives the designer heretofore unimaginable opportunities for optimizing design choices. With the latest insulations, membranes, and HVAC systems, those choices lead to an affordable comfortable home. Thousands of institutional, residential, and commercial buildings throughout the world have also been built to these standards.
There are continuing education courses for builders and architects to bring them up-to-date on the latest materials and practices in their fields. If you hire someone without proper certifications, you risk a poor outcome for your renovation or new build. Utilizing new materials in the wrong way can be worse than just doing things the wasteful, expensive, old-fashioned way.
Few of us would choose to go back to tube TVs and ice boxes. Just so, anyone who’s lived in a Passive House home is never likely to settle for less. There are financial incentives and free expert advice to help build responsibly. (Efficiency VT: http://bit.do/evt-res, Capstone: http://bit.do/capstoneweather, and Passive House Institute: http://bit.do/phius can help. For folks outside Vermont, see pages 16-17 in this issue.)
If your builder says, “A building has to breathe;” or s/he just wants to staple up a membrane as an air or moisture barrier; or they advise you to avoid specifying a blower door number; or they say you’ll need a furnace or boiler; then you need to look further. Many professionals have proven they can build to an above-code certification like Passive House, LEED, or Efficiency Vermont’s High Performance Home program. All of these require independent testing, so you get guaranteed results rather than broken promises.
Someone who claims they’ve been building “high efficiency” or “high performance” homes is like a car salesperson telling you their car is “economical” and “safe” without giving you the EPA figures or the NHTSA ratings. A nice website with beautiful pictures and glowing references doesn’t guarantee up-to-date practitioners or efficiency. Check out their certifications. See if they’re listed with Efficiency VT. Ask about certified projects. Some builders scare clients away from current design and building standards by saying they cost too much — this is false, and they’re indirectly admitting they aren’t up to snuff.
My parents live in a Passive House. Their TV, cooking appliances, bodies, and refrigerator give off enough heat to keep them cozy so far this fall. Their thermostat is set to 70, but the heat hasn’t come on yet. When the sun is out on even the very coldest winter days, they need no help from their 500W air source heat pump. Their total energy bill for a whole year is less than $500. (It’s an all-electric home – see link in bio.)
So, the answer to “How much heat do you need for your house?” is: Only as much as you let get away. IF you’re willing to do your homework, you can find experts who will guarantee far more than just another beautiful home.
For decades the Whitchurches have heated their house, water, and food with cordwood and now have solar PV and hot water. Greg is a board member of Vermont Passive House and owns a net-zero Passive House addition in Middlesex, Vermont. http://bit.do/vgbnphc (802)223-2416.
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