The best time to schedule a home project is rarely when you first need it.
HVAC
Peak: June–August. Sweet spot: March–May and September–October.
Roofing
Peak: September–November. Sweet spot: April–June.
Windows
Peak: April–May and October. Sweet spot: January–March and November.
Furnaces
Peak: October–December. Off-season discount window: July–August.
The universal rule
If your system is failing now, replace it now. If your system is still working but aging, plan the replacement 2–3 months before peak season for that trade.