Winter Weather – Chimney Effect

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This winter is breaking records for deep snow and extended cold. We’ve had deeper cold, but there haven’t been the usual thaws between our cold stretches. As for the snowfall, it’s hard to imagine it could get much deeper. It’s a long dig down to find your rapidly dwindling firewood pile!

It’s true that deep snow can help to insulate the lower part of your walls, but it’s not the best insulation. Maybe the best we can say is that it’s a good reminder to think about tightening up the house before next winter gets here. Now is the time to start scheduling and planning spring and summer projects, including weatherization.

Usually, when people think about buttoning up their homes, they think about adding insulation or replacing old windows with more efficient models. And it’s true that you should consider these steps, particularly if you’re already planning to renovate part of the house. If you’re going to be opening up an outside wall or moving a door or window anyway, that’s the time to upgrade your energy efficiency in that part of the house.

That said, adding more insulation or upgrading windows is not necessarily the most cost-effective way to save energy. The biggest bang for your buck, if your only goal is weatherization, is to seal up the cellar and the attic first.

Why is that? Because a house acts like a chimney. It’s called the “stack effect,” as in “smokestack.” Cold air moves upward as it warms. This creates an updraft in every house. If the house is tightly sealed, the updraft is slight, but if the seams in the cellar and the attic aren’t properly sealed, the updraft will be a significant engine for heat loss. Cold air will be pulled in through every gap low down and pushed out through every gap high up. The insulating value of the walls and windows doesn’t help stop the drafts.


Winter Stack Effect


Luckily, sealing up the bottom and top isn’t as expensive a project as you might think. What it requires is an attention to detail. You have to search out all the leaks and then seal them with weather stripping, caulk, spray foam, small chunks of foam board, plastic sheeting, and tape – none of which is particularly expensive compared to, say, a new high efficiency window.

Where are those air leaks? At all the seams in your house’s shell:

• Around pipes and conduits that go through the foundation, outer walls, and roof, and also from the top floor into the attic (the plumbing vent pipe, for example).
• Where the sill of the house rests on the foundation.
• Where the top floor meets the eave of the roof.
• At cellar bulkheads and around outside doors.
• Around the door from the cellar to the ground floor.
• Around the doorway or hatch that leads from the top floor to the attic.
• Around ceiling lights, particularly recessed light fixtures, which allow the updraft to move from the upper floor into the attic.
• Around fan vents in the bathroom or over the stove.

All of these seams can be sealed or, in the case of junction boxes and recessed fixtures, boxed over with pieces of foam board sealed with glue, spray foam, or tape.

It can require a bit of crawling around and squeezing into tight places, and you really do need the right equipment to apply caulk, spray foam, and cut foam board, along with gloves and masks for protection, but you can see that this is not the same level of tear-out-and-rebuild that wall insulation and new windows require.

A good way to start is to get a home energy audit from a certified energy auditor. (Get references first!) The auditor will test for leaks and measure the insulating value of your walls and windows. Then they will give you a report with list of steps you can take to button up and save energy, prioritized by cost and return on investment.

In almost every case, you’ll find that dealing with the stack effect will be the first or second item on their list, due to its relatively low cost for high reduction in heat loss.

Even better, your house will feel warmer and more comfortable without the drafts.

But don’t forget that you need to schedule and start planning now, while this year’s snow is still on the ground. By next fall, every contractor in the region will already be busy buttoning up houses.

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