Diesel heaters for a garage

At the Midwest regional 2026-09-21 diesel price and Illinois' 2026-07 electricity price, a 17,000 BTU/hSFrom a manual or spec sheetHEATER_CLASSES.diesel_air.outputBtuh — lib/planner/catalog.tsReport a problem diesel air heater costs about $1.06/hr to run flat out, against $0.96/hr for an electric resistance heater putting out the same heat. Diesel only overtakes electric once electricity costs more than about 21.3 ¢/kWhCComputed by our enginecrossoverElecPerKwh x 100 — solved from costPerMMBtuDelivered() for elecPerKwhReport a problem — closer to California or Hawaii rates than the Midwest's.

A diesel air heater burns like a parking heater's cabin unit: a small combustion chamber, a fuel pump sipping from a jerry can, and a fan pushing warm air out. It has none of a vented gas unit heater's UL or CSA listing for building heat, so this page treats it strictly as a detached-garage, exhaust-outdoors tool — see the safety section below before you buy one for anything else.

Cost per hour, computed at today's prices, not a spec-sheet estimate

Delivered heat costs $62/MMBtu on diesel at $6.68/gal and a 78 %EAn estimate, labeled as an assumptionETA.dieselAir — lib/planner/fuels.tsReport a problem combustion efficiency, against $56/MMBtu for electric resistance. Both prices are dated 2026-09-21 (diesel) and 2026-07 (electricity) — check the calculator for your own state's numbers instead of Illinois'.

At those prices, electric resistance is the cheaper fuel here — the crossover sits at about 21.3 ¢/kWhCComputed by our enginecrossoverElecPerKwh x 100 — solved from costPerMMBtuDelivered() for elecPerKwhReport a problem for electricity, and Illinois runs 19.2 ¢/kWhRA code or reference citationPRICES.IL.elecPerKwh x 100 — EIA Electric Power MonthlyReport a problem today. Diesel's case gets stronger in high electricity-price states and weaker wherever diesel itself runs expensive at the pump — it's never a fixed answer, only today's two prices run through the same formula.

No UL/CSA listing for building heat — read this before you buy one

Detached garage, exhaust and intake outdoors: ONLY IF

Every one of these conditions has to hold, together, not just the ones that are convenient:

• A permanent install of a heater with no listing needs your code official's approval, and tell your insurer. (IRC M1302.1, IRC 2021)
• Exhaust passes through the maker's metal wall thimble, at the maker's clearance to combustibles. (Manufacturer manual)
• The exhaust ends at least 4 ft from, and at least 1 ft above, any door, operable window or air inlet, and stays above the snow line. (IFGC 503.8, IFGC 2021 (borrowed -- written for a different appliance class))
• Put a UL 2034 CO alarm in the house outside each sleeping area (code, for new homes and permitted work). BayHeat also advises one by the garage door, and a low-level CO monitor in the garage rated for its temperature range while this heater runs. (IRC R315 (house alarm); BayHeat (garage door and monitor), IRC 2021)
• Never run it while sleeping, and fill the tank outdoors. (Manufacturer manual)

Attached garage: NO-GO

Unlisted diesel heaters aren't a safe permanent install for an attached garage.

• This class carries no UL/CSA listing for building heat -- BayHeat doesn't recommend a permanent install of an unlisted diesel heater in an attached garage. (BayHeat)
• Use it in a detached garage only, or switch to a listed electric or vented-gas heater for an attached one. (BayHeat)

Exhaust not yet routed outdoors: NO-GO

Exhaust isn't routed outdoors.

• Diesel exhaust must be routed outdoors through the maker's own thimble kit -- never run it with the exhaust indoors. (Manufacturer manual)

Your electrician and your local code edition govern. General information. Your electrician, gas fitter, local code and the heater's manual govern.

Don't buy this class expecting a permanent, unattended fix

Don't buy a diesel air heater to heat an attached garage full time. Buy a listed electric or vented natural-gas unit heater for that job instead (see the fuel hub). A diesel heater's manual scope is a detached space, attended or thermostatically monitored, with its exhaust kit installed — not a set-and-forget house-adjacent heater. Heating a workshop? The shop heater guide sets diesel beside 240V electric and vented gas, and says why a torpedo is out.

Buy: 5 kW and 8 kW classes, plus the exhaust kit the safety rule requires

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Next step

Check my heater and garage → for a verdict specific to your own situation, or compare every fuel at your own state's prices.