Air Leaks, Stack Effect, and What You Can Do Right Now
When Chicago turns brutal, it’s easy to blame the furnace. But most of the time, the furnace isn’t failing—your home is losing the fight because heated air is escaping and cold air is being pulled in faster than your system can comfortably replace it.
The good news: there are DIY steps you can take today that make a real difference. And if you’re still struggling after that, the long-term fixes are straightforward: air sealing, insulation, and smart airflow.
Do This Right Now (DIY steps that help today)
1) Mix the air to reduce room-to-room extremes
Uneven temperatures are often an air movement issue, not a “need more heat” issue. – Forced-air heat (furnace): Set the thermostat fan to ON (or Circulate) to keep air moving and reduce hot/cold pockets.
– Radiators/boiler heat: Use ceiling fans on low or a small box/floor fan to gently push warm air off ceilings and into cooler rooms/hallways.
– Radiators in winter + SpacePak in summer: You can run the SpacePak blower in winter as a strategic mixing tool—circulate air toward the rooms that always lag (over garages, outside corners, far bedrooms).
2) Turn down indoor humidity during extreme cold
If you’re seeing condensation or ice on the window, your home is retaining more moisture than the glass can tolerate.
– Turn off or dial down the whole-house humidifier.
– Run bath fans during showers and the range hood during cooking.
– If a room is consistently wet on windows, it’s usually a sign of high humidity + low glass temperature.
3) Protect pipes before they become an emergency
Frozen pipes almost always happen in the same “usual suspect” locations.
– Open sink base cabinets on exterior walls.
– Leave doors open to problem rooms (especially bathrooms).
– Drip vulnerable fixtures that are on exterior walls or over garages/crawlspaces (drip hot and cold if lines are separate).
– Keep problem rooms above the danger zone—don’t let a back bathroom go cold with the door shut.
4) Stop the obvious drafts you can reach safely
Even simple draft control helps when the pressure difference is intense.
– Make sure the attic hatch is sealed and closed tightly.
– Check the garage-to-house door weatherstripping.
– Close and latch fireplace dampers when not in use.
– If you have a ton of recessed lights under an attic, understand: each one can behave like a tiny
Why This Happens in Chicago (the simple building-science truth)
Stack effect: your house becomes a chimney
Warm air rises and escapes at the top of the house. The escaping air creates a vacuum that pulls cold air in from the bottom. The colder it gets outside, the stronger this effect becomes.
Wind pressure: the “bellows” effect
When it’s windy, your home is pressurized on one side and depressurized on the other. If the building envelope is leaky, wind drives cold air into the structure rather than around it.
Together, stack effect + wind pressure can make your house feel like it’s breathing—in cold air low, out warm air high—all day and all night.
The 3 Chicago Cold Thresholds (and what they reveal)
1) Below 0°F: the systems check
Below-zero temperatures expose comfort weak spots: cold bedrooms, drafty halls, and rooms that remain cold even when the furnace is running.
Focus: mix air + manage humidity + stop obvious drafts.
2) Below −10°F: weak spots become emergencies
Below −10°F, “it’s always been fine” becomes frozen pipes, bathrooms that can’t recover, and a furnace that seems unable to keep up.
Focus: protect pipes + keep temps steady + increase circulation.
3) Wind chills below −30°F: margin for error disappears
Wind chills primarily concern human safety, but wind itself still drives pressure through a leaky home. This is when drafts get aggressive and comfort turns into safety planning.
Focus: reduce drafts + keep vents/combustion exhaust clear + protect plumbing proactively.
When DIY Isn’t Enough (the permanent fixes that make it stay solved)
If you’re doing the DIY steps and still struggling, it usually means the home has one or more of these issues: – Attic bypasses (can lights, plumbing chases, open wall tops).
– Leaky rim joists and band boards.
– Garage-to-attic connections that let fumes, cold, and pressure move freely.
– Under-insulated exterior walls in older homes.
– Cantilevers/floors over garages that were never properly air-sealed.
These are exactly the problems that air sealing and insulation are designed to solve—permanently.
The takeaway
Extreme cold doesn’t create problems out of thin air—it reveals what was already true. If one room always loses first, or you’re fighting window ice and pipe fear every cold snap, that’s not “just winter.” That’s your home asking for a better air seal, better insulation, and better airflow.
If you want help finding the exact weak points in your home, Chicago Green Insulation can diagnose the pathways and recommend the right fix—without guessing.
With ten years of experience selling spray foam insulation in Chicago, Tom Decker is THE person to call and the Chicago Green Insulation is the organization to hire when you are looking for top notch quality and performance as well as someone who can deal with the needs of code officials, home owners and general contractors. Call the others in Chicago, if you are interested in the cheapest price, call Chicago Green Insulation if you are interested in using your dollars to make Chicago a better city for all of us!
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