Chicago’s nickname has a bigger reputation than its wind statistics. The Illinois State Water Survey puts the long-term average wind speed at O’Hare near 10 mph for the year, and a bit above 11 mph in January. The city is breezy. It is not an outlier among Great Lakes cities, and the Survey says as much: the wind here is not much stronger than it is at other places around the lakes. “Windy City” came from politics and newspapers long before anyone was ranking airport anemometers.
The nickname still points at something real for a house. A steady winter wind, even at 10 or 15 mph, changes the heating load.
Wind finds the leaks the thermometer ignores
On a calm 20°F night, a house loses heat through insulation and through the ordinary gaps in its shell. On a windy 20°F night, those gaps become intakes. Rim joists, recessed lights in a cold ceiling, outlets on exterior walls, and a dried-out sweep at the front door all start feeding the furnace extra work. Older Chicago housing stock, including a lot of Lake County homes, has those gaps. The thermostat still reads 68°F in the hallway. The room over the garage, or the one on the northwest corner, does not.
This is infiltration, and it is why two houses with the same furnace and the same outdoor temperature can have very different bills in December. The wind is doing more of the work than the famous nickname suggests, and less of it than a broken system will. A furnace that is short on airflow makes the problem feel like a capacity crisis. Often the capacity is fine and the filter, the blower, or the return duct is not.
What helps, in order
Weatherstripping and air sealing beat another two degrees on the thermostat. A furnace or boiler that has been cleaned and checked can at least deliver the heat it was sized for, for hours at a time, which is what a windy week requires. High-efficiency equipment needs its outdoor terminations aimed and supported so a west or northeast wind is not stuffing snow back down the pipe. None of this requires believing that Chicago is the windiest city in the country. It requires treating a 15 mph wind at 5°F as a design condition, because in this climate it is a normal Tuesday.
If the house cannot hold temperature once the wind comes up, start with a maintenance visit so you know whether the equipment is the limit. Zima HVAC is based in Mundelein. Call (847) 323-8314.