Same house, same thermostat setting, and the bill is 30% higher than last winter. It's rarely one big thing — usually two or three small ones stacking up.

Inside: The six usual suspects, ranked · The filter check, first · The thermostat setting that costs the most · Duct leaks, drafts and gaps, blocked vents, aging equipment · The honest cost comparison · When to stop and call a pro · Troubleshooting · Printable bill-check checklist.

Doing it yourself: free to check; a new filter runs $4–20, and most of the rest of this list is a setting, not a purchase.
Calling a pro: a basic furnace inspection runs $80–100, an advanced tune-up with cleaning $125–200. Professional duct sealing, if leaks turn out to be significant, runs $500–4,000, averaging around $2,250; duct cleaning alone runs $275–500.

5 pages of labeled diagrams, parts lists and real numbers — no filler, no 40-minute video. Temperatures and measurements in both Fahrenheit/Celsius and feet/meters, so it works wherever you are. Ends with a printable checklist.

Instant PDF download: print it for the garage or follow it on your phone with the parts in hand. Yours to keep, no subscription.

Need more than this one job? The Heat Kit bundles all 5 furnace and heating-system guides — 25 pages — for $14.

The Fix-It Playbook — Why Your Heating Bill Jumped