Fort Collins is a heating town — 5,797 heating degree days against 624 cooling degree days (NOAA 1991–2020) — and winter here is a long season, not a cold snap. January highs average 45°F and lows 18.3°F, with about 150 freezing nights a year and around four nights at or below 0°F. Your furnace runs from October to April, and the difference between a quiet winter and a January emergency is usually decided in September or October, when a tune-up is a routine visit rather than a rescue. This is the checklist we would run through on our own homes.
Winter furnace maintenance checklist: September–October, book the tune-up
The single most important item on the list is the timing. Book a furnace tune-up in September or October, before the heating season. Fort Collins contractor-published tune-up prices run $80–$150 (Cool Ducts and Allen Service, 2026), and a real visit covers flame sensor cleaning, a gas pressure check, a heat exchanger inspection, blower and filter checks, and a full heating-cycle test. A weak igniter or a dirty flame sensor found in October is a routine fix; the same fault found in January, when the furnace locks out at 2 a.m., is an emergency. And if your furnace is past 15 years old, the autumn visit is also the decision point: a replacement planned in October — which triggers a mechanical permit through the City’s Accela portal — is a calm, quoted job, and any new furnace installed since 1 January 2026 must meet Colorado’s HB23-1161 ultra-low-NOx standard of 14 ng/J or less.
Autumn furnace costs, at a glance.
| Item | Published figure | Source |
|---|---|---|
| Furnace tune-up, September–October | $80–$150 | Cool Ducts and Allen Service, 2026 |
| Ultra-low-NOx furnace replacement, installed | $7,000–$10,000 | Lion, Fort Collins, 2026 |
Monthly through winter: the filter
Check the filter every month from October to April, and replace it when it is grey and matted. A clogged filter is the most common cause of the problems we are called about in winter: restricted airflow trips the high-limit switch, the burners shut off, the blower keeps running, and the house gets cold air from every register. Match the filter to what your system was designed for — a MERV 13 filter in an older furnace not built for it chokes airflow and causes the exact problem you are trying to prevent. During wildfire smoke season, MERV 13 or HEPA filtration plus activated carbon is the right defence; UV lights do not remove smoke.
Before the first hard freeze: the condensate drain
Modern condensing furnaces produce condensate that drains away through a small line, and in a cold snap that line can freeze if it runs through an unheated space — tripping a safety switch that shuts the furnace down. Before winter, confirm the drain flows, the line is insulated where it runs through cold spaces, and the outdoor termination is clear. If your furnace died on a cold night last winter for no apparent reason, a frozen condensate drain is a likely suspect. Freeze protection in Fort Collins is about pipe freeze and condensate-drain freeze — not ice dams, which are not a local problem.
Safety: the items that are not optional
Carbon monoxide detector. Test it monthly, replace the batteries, and replace the unit itself on the manufacturer’s schedule. A cracked heat exchanger is a carbon monoxide risk, and the detector is the only thing that will tell you. Flame colour. A steady blue flame is normal; a yellow or orange flame, or soot around the burner compartment, means call a technician and do not run the furnace. Vents and returns. Keep every supply register and return vent open and unblocked — closing returns to “balance” the system starves the furnace for air and trips the high-limit switch. Clearance. Keep the area around the furnace clear of stored boxes, paint and chemicals. Vacant-home setbacks. If you leave the house empty in winter, do not set the thermostat below 55°F — frozen pipes cost far more than the gas you save.
Comfort: the dry-air problem
Fort Collins winters are dry. Indoor humidity commonly falls to 15–25% in winter, against a target of 30–50% relative humidity, and the city’s water is soft (about 2 grains per gallon), so the dry-air story here is about humidification, not scale. A whole-home humidifier, fitted to the furnace, is the genuine local comfort upgrade — it makes 68°F feel like 70°F, cuts static and dry skin, and protects wood floors and furniture. Ask about it during the autumn tune-up, when the system is already open. And if anyone in the house has allergies, the same visit is the time to talk about filtration for winter, when the house is sealed up and the air is recirculated for months.
The full checklist at a glance
- September–October: book the tune-up; ask for an honest read on the igniter, flame sensor and heat exchanger.
- Monthly: check and replace the filter; test the carbon monoxide detector.
- Before the first freeze: confirm the condensate drain flows and is insulated; check the outdoor vent termination is clear.
- All winter: keep registers and returns open; keep the area around the furnace clear; do not set an empty house below 55°F.
- Call a technician if: the furnace locks out more than once in a week, you smell gas, see soot, hear clicking without ignition, or the flame is yellow or orange.
One last note on age. Nearly half of Fort Collins housing was built before 1990, and a huge cohort is on its second or third furnace. If yours is past 15 years and has needed repeated repairs, the autumn tune-up is the moment to price a replacement — Fort Collins contractor-quoted ultra-low-NOx furnaces run $7,000–$10,000 installed (Lion, Fort Collins, 2026) — rather than paying for another winter of repairs. There is no Xcel furnace rebate for 2026 installs and no federal credit for property placed in service after 31 December 2025, but a dual-fuel replacement pairing a heat pump with a new furnace does qualify for the live heat-pump rebates as of November 2026.
Get help with HVAC in Fort Collins
Work through the list in September or October, and your furnace will be ready for the first hard freeze. DNA Refrigeration Heating & Cooling handles furnace maintenance, furnace repair and humidifier installation across Fort Collins — call us at (970) 932-2324. We are open 24 hours, 7 days a week.