What every contractor should know about the Lennox LF24 heater, garage heating options, and basic maintenance
I've been managing maintenance procurement for a mid-sized HVAC service company for 6 years now. Bought a lot of Lennox parts, worked through a lot of warranty claims, and learned a few things the hard way. Below are the questions I hear most often from my own team and from homeowners we deal with.
Is the Lennox LF24 still a good heater, or should I look at heat pumps?
From the outside, it looks like everyone's switching to heat pumps. The reality is mixed. The LF24 is a single-stage gas furnace. If your customer has existing ductwork and natural gas at reasonable rates, replacing like-for-like often wins on total install cost and simplicity. Around 60% of our callbacks on heat pumps in 2024 were for defrost issues or poor insulation in older homes. The LF24 doesn't have that problem.
Heat pumps make sense in milder climates or when paired with solar. For a Midwest retrofit, the LF24 is still a solid workhorse. Not flashy. Not the future. But reliable.
Key specs to check: 80% AFUE (not high-efficiency), upflow/horizontal installation. Controls are straightforward—no proprietary board nightmares like some variable-speed units.
Where do I find Lennox heater parts for the LF24—especially the blower motor and gas valve?
Here's something vendors won't tell you: OEM parts stock isn't consistent between suppliers. In Q2 2024, I had a job delayed 3 weeks waiting on a Lennox OEM gas valve from a regional distributor. Meanwhile, a competitor had it in stock 2 states away. My procurement policy now requires quotes from 3 vendors minimum, but with OEM parts, availability trumps price every time.
For the LF24 blower motor: your standard 1/3 to 1/2 HP PSC motor with 5 microfarad capacitor. Part number is 105189-01 (genuine Lennox). Aftermarket equivalents exist (GE/Century), but I've seen amp draws run 10-15% higher—which means more heat in the control board over 5+ years. Not a dealbreaker if you're fixing a rental property, but for a primary residence I'd stick OEM on the motor.
Gas valve is a Honeywell V440 or V460 series, depending on exact model variation. That part is cross-brand—easy to find. Total cost for both parts (motor + valve): roughly $350-500 at distributor pricing (January 2025). Add your markup.
Can I use a garage heater instead of a Lennox unit for a shop or basement?
Different applications entirely. A garage heater (typically 45,000-75,000 BTU, either infrared or forced air) is meant for uninsulated or semi-conditioned spaces. The LF24 is a central furnace designed for conditioned spaces with ductwork. People assume they're interchangeable because both blow heat. What they don't see is the duct static pressure and airflow design.
If a customer asks about heating a garage or workshop, I usually recommend a separate garage heater over extending the main ductwork. You lose too much efficiency running duct to an uninsulated space. A 50,000 BTU Mr. Heater (vented) runs about $500-800 plus install. Total cost to add a separate zone with the Lennox would be double that, plus ongoing losses.
That said, I've seen people put a Lennox LF24 in a basement shop with minimal ductwork. It works, but it's overkill. The furnace is designed for a 1,500-2,000 sq ft home, not a 600 sq ft workspace.
How often should I change the air filter on a Lennox system? (And how to change it in a car)
Two different things, both overlooked. For the LF24 or any residential forced-air system: standard 1-inch filter every 30-90 days, depending on pets and dust. Use MERV 8 minimum. MERV 11 is fine but can restrict airflow if your ductwork is undersized. I've seen a MERV 13 drop static pressure by 0.3 inches on a 2.5-ton system. Not ideal.
For car cabin air filters (a common side question when homeowners ask about 'hand fan' or 'car filter'): locate it behind the glove box or under the hood. Pop the cover, slide the old one out. It's a 10-minute job. No tools needed for most Toyota/Honda models. I use a Wix 24008 or 24274 for most common applications. Cost: $15-25 at auto parts stores. Changing it twice a year does more for HVAC performance than most people realize.
What are the most common Lennox LF24 heater parts I should stock?
In 2023, after tracking 47 service calls on Lennox gas furnaces across our fleet, I found the top failure points were:
- Pressure switch (S466 or similar) — fails when the condensate line clogs or there's excess wind. About 6% of our calls.
- Flame sensor (Lennox part 105164-01 or equivalent) — 4% of calls. Cheap fix. Clean it with steel wool. Don't replace unless it's cracked.
- Inducer motor assembly (part 100183-01) — about 3% of calls. Expensive ($200-300). Usually fails after 10+ years when the bearings wear out.
- Ignitor (silicon nitride type) — intermittent failures. Stock one on the truck.
I don't have hard data on industry-wide failure rates, but based on our service history, my sense is the LF24 is actually one of the more reliable single-stage furnaces. The trick is knowing which parts fail predictably. The pressure switch is the only one that catches new techs off guard.
Should I replace the Lennox LF24 or upgrade to a heat pump in 2025?
Honestly, I'm not sure there's a universal answer. My best guess is it depends on your local utility rates and climate. If gas is cheap and winters are below freezing for 4+ months, keep the LF24. If you have solar or cheap electricity (under $0.10/kWh) and mild winters, a heat pump might give you better seasonal efficiency.
But here's the thing I see in our cost tracking system: the 'cheap' heat pump installs (under $5,000) tend to generate callbacks for poor insulation, undersized return ducts, or refrigerant leaks within 2 years. The $200 'savings' from a budget heat pump turned into a $1,200 service call for one of our customers last year. The Lennox LF24, for its faults, rarely leaves you with a $1,200 surprise bill.
Ultimately, if the existing ductwork and gas line are in good shape, the replacement cost for an LF24 is roughly $1,500-3,000 (January 2025 quotes from 4 distributors). A comparable heat pump install with a backup heat strip runs $5,000-9,000. The breakeven point depends heavily on your assumption of gas vs. electricity prices over the next 10 years.
Granted, this requires more upfront analysis. But it saves money later.
Prices as of January 2025; verify current rates with local distributors.
