Timing, availability, and the Metra schedule problem.

Two facts drive most of what follows. Contractors have a fixed number of crews. And most people replace a furnace the week it dies, which is the same week everyone else’s dies.

Why the week you shop matters

A contractor with a full calendar prices differently than one with a gap next week, and a price you cannot use for three weeks is not much use if your house is 58 degrees. Whichever situation you are in is worth naming out loud when you call, because it changes which companies are worth your time.

The heating and cooling calendar

December through February. Furnace season. Emergency replacements crowd the calendar, prices firm up, and equipment for popular models can run short. Not the time to shop if you have any choice.

April through May. The first shoulder. Heating is winding down, cooling has not started, and crews have room. Good pricing, good availability, and time for a site visit without anyone rushing.

July through August. AC season. Same dynamics as winter, in reverse. The first real heat wave produces a wave of failures and a wave of estimates.

September through October. The second shoulder. The best window for a combined furnace and AC replacement, because you can test both before either season arrives.

Ask for the installation window

Get it in writing next to the price. “Within five days” and “within three weeks” are different products at the same number, and a contractor who cannot commit to a window should say so rather than guess.

Then weigh the two together yourself. If one estimate is $400 cheaper and two weeks later, sometimes $400 is worth two weeks. In July, in a house near the Des Plaines with no shade, it may not be.

If you can wait until after the Memorial Day parade

If your system is working and you are replacing it on your own schedule, you are in the strongest position a homeowner can be in. Say so when you call. Contractors know that planned work fills gaps in their calendar, and they price it accordingly.

This is also the case where a site visit before final pricing costs you nothing but an hour, and it is worth having.

If the house is colder than the Roosevelt bleachers

If the system is down, see the page on emergencies. The short version: you have more time than it feels like, and a repair to get through the week is often the better first move than a five-figure decision made in a cold kitchen.