Furnace Replacement in St. Louis, MO

A furnace that stops working has not always reached the end. Furnace replacement is the right call when the heat exchanger is cracked, when the unit is near the end of its life, or when repair bills keep arriving. Otherwise, a part swap often buys several more winters.

When does an aging furnace stop paying its way?

Four signs push the decision toward replacement.

• A cracked heat exchanger. It can leak carbon monoxide into the airflow. CPSC recommends a yearly professional inspection of furnaces and a CO detector that meets UL 2034.
• Age near the limit. Contractor sources put furnace life at 15 to 20 years with maintenance.
• Repeat repairs. A second or third major repair in a few seasons signals general wear.
• Rust and soot. Corroded cabinets, scorched burner areas or water stains below the unit are warnings.

Older housing makes this a live question here. The City of St. Louis has a median year built of 1938, and 58.4% of its homes were built in 1939 or earlier, per Point2Homes. Original equipment in those houses is long gone, but second- and third-generation furnaces are now aging too.

What should you ask before agreeing to a new furnace?

Ask for the failed part to be named and shown. A Google reviewer, Wendy R., had another company recommend a new furnace when the heat would not come on. They said the earlier visit had checked no parts, and Kenan found a capacitor was the cause and fixed it.

Four requests keep the decision honest:

1. Which part failed, and can I see it?
2. What does a repair cost in writing, with the new-furnace quote beside it?
3. Is the heat exchanger intact?
4. What is the age of the furnace, and what would you expect it to need next?

That is the same test we apply to ourselves.

What did Angi report for furnace replacement costs?

Angi's 2026 data for St. Louis put a full HVAC replacement between $4,755 and $11,888, averaging $7,133, with labor at $75 to $150 per hour. Labor makes up $1,500 to $5,000 of a full replacement. That range includes cooling equipment, so a furnace on its own typically costs less.

Fixr lists furnace replacement at $2,800 to $7,500 nationally with a $4,800 average, and natural gas units at $3,800 to $10,000 (page updated January 28, 2026). Neither figure is a Kenan price. Ask the quote to show equipment, labor, permit and old-furnace removal as separate lines, because Fixr's 2026 breakdown shows each can swing widely: labor at $300 to $1,800, permits at $50 to $1,500, removal at $50 to $330. Efficiency tier, venting changes and duct work move the total most. Our furnace replacement cost guide explains what moves the total.

Which replacement furnace fits your house?

Your choices differ in efficiency, staging and venting.

How does a furnace replacement go?

Fixr lists furnace installs at 4 to 10 labor hours. A straight swap sits at the short end, while new vent or gas work adds time.

1. Walk the house, run the heating load calculation and give you a clear, upfront quote.
2. Shut off gas and power and remove the old furnace.
3. Set the new furnace, then connect plenum, return, vent and drain.
4. Reconnect and leak-test the gas line.
5. Fire the furnace and measure temperature rise, combustion and safety switches.
6. Walk you through the thermostat and filter.

Our furnace installation page covers the sizing and venting decisions in detail.

What does a furnace replacement include?

A replacement is more than a swap, because every connection to the old furnace gets a second look. Whether the vent, gas line, plenum, return and thermostat wiring carry over depends on the furnace you pick. A condensing model cannot use the old metal flue, and a two-stage furnace needs a compatible control. The quote should therefore say what is reused and what is new. Work the house needs beyond the furnace, such as sealing a leaky duct or adding a return, gets its own line so you can approve or decline it separately. The scope covers:

• A heating load calculation, so the new furnace is sized to the house and not to the old nameplate
• Removal of the old furnace
• A check of the existing vent, gas line, ducts and thermostat for reuse
• Setting and connecting the new unit, with a gas leak test
• Start-up with temperature-rise and combustion readings, then a walkthrough of the thermostat and filter

What do the permit and license rules cover?

Furnace replacement is permit work in St. Louis County, and the installing contractor pulls the permit. The City of St. Louis requires a City-licensed mechanical contractor under Ordinance 70800 and charges a $25 application fee. Creve Coeur has a licensed St. Louis County mechanical contractor pull the permit, and the city inspects afterward. St. Louis County says filter changes and refrigerant recharges are not permit work, but replacing a furnace is, and its Mechanical Licensing Clerk answers questions at (314) 615-7096. When the job is done, ask for the final inspection record, since that is what closes the permit.

Missouri has no statewide HVAC license, so ask any contractor, including us, for the license number your city or county requires, and the permit in the quote. The federal 25C credit no longer applies to work finished in 2026, per the IRS.

What should you do once the new furnace is running?

Register the model and serial numbers using the maker's steps, and keep the written quote with them. Replace the filter on the schedule you were given, test your carbon monoxide alarms, and note the first-week behavior: odd smells, rattles or rooms that stay cold. A first furnace maintenance visit before the following winter keeps small drifts from turning into no-heat calls. If you went with a condensing model, check that the drain stays clear when the season starts.

Why Kenan Corporation for a furnace decision

The question is whether the person advising you gains from a bigger job. The company's founding answers that.

• Repair when it makes sense. The founder, Kenan Bruce Martz, started the company in 2010 after 20-plus years at St. Louis area HVAC companies, wanting to bring honesty and fairness back to the trade.
• Pricing described fairly. Amy A., a Google reviewer, called the furnace work done in freezing weather reasonably priced.
• Options on paper. We give you a repair price and a replacement price, and explain the gap.
• Open 24 hours. Google shows 4.6★ across 29 reviews, checked in October 2026.

Where are furnaces most often due for replacement?

Replacement calls track the age of the housing. Each line below uses census survey or Point2Homes figures for that place, with minutes from our base near Spanish Lake in normal traffic.

• Jennings, about 20 minutes: the median home dates to 1955, so a newer furnace on 1950s ducts is the usual case and the duct check matters as much as the unit.
• Florissant, about 20 minutes: 38.5 percent of homes were built in the 1960s, and sizing should come from a load calculation, not the old nameplate.
• University City, about 30 minutes: 38 percent of housing was built in 1939 or earlier, so planning starts with whether a duct path exists at all.
• Richmond Heights, about 35 minutes: a median build year of 1947 means an old chimney may need checking before you choose a condensing furnace.
• Lemay, about 45 minutes: 24 percent of housing dates to 1939 or earlier and 1,902 homes to the 1950s, so second- and third-generation furnaces are common.
• Shrewsbury, about 45 minutes: the 1980s are the largest build decade at 21 percent, so check your furnace's age against the 15 to 20 year range.
• Affton, about 50 minutes: 31 percent of housing is from the 1950s and 81 percent of homes heat with gas, so postwar brick ranches on gas furnaces are the typical job.
• Mehlville, about 55 minutes: 37 percent of occupied homes heat electrically, which puts a heat pump on the table next to a new gas furnace.
• Ballwin, about 55 minutes: a median build year of 1976 makes the age of the current furnace, not the house, the question to settle first.