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G-028 · REV 2 · CHECKED 2026-10-10 · MODEL v1.0.2 ▾

Drafted with AI assistance. Numbers computed by model v1.0.2 or sourced. Human review: full by BayHeat editorial desk. Licensed review: no page-specific approval recorded.

Technical review: no page-specific licensed approval recorded.

M measured · C computed · S spec · R reference · E estimate

Shop heaters

A 240 V electric shop heater needs a breaker and copper wire. A vented gas unit heater starts at of fuel input. It needs a licensed gas fitter and a flue to the outdoors. A diesel air heater suits only a detached shop with its exhaust and intake outdoors, and only while you are in it. BayHeat does not recommend a torpedo heater in a closed shop.

Jump to the heaters ↓

Shop heater, workshop heater, garage unit heater: the names change. This page compares four types. Each asks something different of your building. The best shop heater is the one your building can feed: a circuit, a gas line or an outdoor exhaust.

Size it before you shop. BayHeat's example 24×24 ft attached 2-car garage in Chicago needs to hold on a design day. Your shop will differ with its insulation, doors and climate. Run the garage heater calculator first, then match that BTU/h to a type below.

The four types, side by side

TypeHeat, class rangeWhat your building must supplyBayHeat verdict
240 V electric unit heaterA dedicated 240 V circuit with a to breaker. No flue, no fuel.GO · PER MANUALGeneral information. Your electrician, gas fitter, local code and the heater's manual govern.For 5.0 kW on a 30 A circuit, with the breaker and wire in the table below. Bigger units need bigger circuits.
Vented natural-gas or propane unit heaterFuel input: Heat output, at 80%: A natural gas line or bulk propane tank, a flue to the outdoors, and a licensed gas fitter.ONLY IFGeneral information. Your electrician, gas fitter, local code and the heater's manual govern.Licensed install, burner height, CO protection, and nothing flammable stored.
Diesel air heaterExhaust and intake routed outdoors, in a detached building, while you are in the shop.ONLY IFGeneral information. Your electrician, gas fitter, local code and the heater's manual govern.Detached, exhaust outdoors, and only while you are in it.Attached: NO-GO. Left running: NO-GO. Details below.
Torpedo (open-flame forced-air)A flue, which it does not have: all of its exhaust stays in the room.NO-GOGeneral information. Your electrician, gas fitter, local code and the heater's manual govern.Any closed shop or garage.

Verdicts assume a detached shop, an attended heater and nothing flammable stored, with a listed electric or gas unit.

Check what the shop stores before you pick a type.

The manuals on this page rule out gasoline, paint and other flammable liquids. Several also rule out dust. The CZ220 manual allows indoor use only, in a dry place. It must be free of gasoline, paint, flammable liquids or combustible dust or materials. The Big Maxx manual rules out dust as well as gasoline, solvents and paint thinner. VEVOR's diesel manual says its heater shall not be used in places with flammable vapor or dust.

If your shop holds finishes or fuel cans, move them out first. Otherwise, heat the room another way. Run your own case through Can I run it?

240 V electric unit heater: it needs a circuit and a shop free of flammables and dust

An electric unit heater has no flame, no flue and no fuel line. An electrician wires it to its own 240 V circuit. The rule, in NEC 2023 §424.4(B): .

HeaterHeat outputRunning currentBreakerWire, NM cableWire, THHN in conduit
240 V, 5.0 kW
240 V, 7.5 kW
240 V, 10.0 kW

All wire is copper. The NM column is cable in a wall, from the NEC 2023 60 °C column. It is BayHeat's conservative figure. The THHN column is single wires in conduit, from the 75 °C column. At 60 A the two differ: NM or THHN. The manual for the unit you buy has the last word on wire.

BayHeat's verdict tool, asked about one case:

GO · PER MANUAL 240 V electric, 5.0 kW on a 30 A circuit

  • Breaker and wire match this heater's nameplate: at least a 30 A breaker on 10 AWG copper (or heavier). (NEC 424.4(B), NEC 2023)
  • Plugged straight into a properly grounded outlet rated for this heater -- no plug adapters, no extension cords. (NEC 250, NEC 2023)

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

A hardwired heater has no plug, so your electrician applies the grounding line to its wiring. The tool covers this one case only. The 7.5 kW and 10 kW units need the larger circuits in the table.

Check the panel too. BayHeat's rule of thumb: before you add a large 240 V circuit to a panel, ask your electrician for a load calculation. NEC 2023 §220.83 is one method. Do it before you buy, not after.

Check the supply voltage. Your shop may be fed 208 V instead of 240 V. Then a 240 V heater, like the Fahrenheat FUH54, draws only about . That is less than the it makes on 240 V.

These figures also assume single-phase power. A three-phase unit heater needs different math, so have an electrician confirm your supply before you order.

Don't buy a plug-in heater as your shop heater

A plug-in heater draws and puts out at most . That warms one workbench, not a room. NEC 2023 §210.23(A)(1) sets the limit for a plug-in appliance. . The portable heater page shows what a garage outlet can run.

Vented natural-gas or propane unit heater: it needs a gas line and a flue

A vented unit heater burns gas inside the unit and sends the exhaust out through a flue to the outdoors. One wall or ceiling mount can heat a whole shop. It asks three things of the building: fuel, a flue, and power for the fan.

  • Fuel. A vented gas unit heater needs a piped natural gas line or a bulk propane tank -- small cylinders alone can't feed it.
  • Flue. The exhaust must leave through the flue the maker's manual specifies. A licensed gas fitter sets the route and pulls the permit.
  • Power. Plan on a 120 V circuit for the fan and controls. BayHeat's class figure is a breaker. The maker's manual sets the exact size.

What BayHeat's verdict tool requires for a garage-type shop:

ONLY IF Vented gas unit heater

  • Installed and permitted by a licensed gas fitter -- this isn't a DIY connection. (BayHeat)
  • Burner at least 18 in above the garage floor, and at least 6 ft up or guarded against vehicle impact. (IFGC 305.3 / 305.5, IFGC 2021)
  • 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)

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

A shop in a separate commercial building may fall under other rules. Your gas fitter and local code office decide.

Dust changes the pick. A separated-combustion unit, such as the Modine Hot Dawg HDS below, draws its combustion air from outside the room. Modine's HDS product page says it is “Designed for environments where dust, dirt, or fumes are present.” That keeps dusty shop air out of the burner.

It does not make a flammable atmosphere safe. No heater on this page is rated for a solvent or gasoline atmosphere. The Modine manual's DANGER line: “Appliances must not be installed where they may be exposed to a potentially explosive or flammable atmosphere.” Store solvents, finishes and fuel somewhere else, and don't run the heater while you use them.

Don't buy the Big Maxx for a dusty woodshop. The Big Maxx manual says never where gasoline, solvents, paint thinner or dust are present. It suits a clean shop or garage.

Gas cylinders alone don't count as a fuel supply here. See the propane page for vented propane and why a Buddy-type portable heater is a different tool.

Diesel air heater: detached shop only, and only while you're in it

A diesel air heater is a small parking-heater-style unit. Its output runs from . In BayHeat's estimate, even the top end only matches a 5.0 kW electric heater. Makers' labels can claim more, so read the rated output in the manual. It carries no UL or CSA listing for building heat.

No UL/CSA listing for building heat. VEVOR’s manual for its 8 kW diesel air heater lists “Living room, garage” under places it can not be used for constant heating. Exhaust and intake outdoors only; CO alarm required.

The same manual says the heater shall not be used in places with flammable vapor or dust.

Every one of these has to hold at once, in a detached shop with the exhaust and intake outdoors:

ONLY IF Detached shop, attended

  • 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)

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

NO-GO Attached to a house

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

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

NO-GO Left running while you are away or asleep

Unattended or overnight use isn't within this heater's scope.

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

The diesel heater page has the cost per hour against electric and the full exhaust rule.

Torpedo heater: don't buy one for a closed shop

A torpedo is a forced-air heater with an open flame. It burns propane, kerosene or diesel with no flue, at up to in BayHeat's class range. It is a construction heater. All of its exhaust stays in the room.

NO-GO

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

Open-flame forced-air heaters are excluded for any enclosed garage, full stop.

  1. 1.Never run a forced-air "torpedo" (open-flame) heater in an enclosed garage -- this is a BayHeat rule, stricter than some manufacturer manuals. C BayHeat
  2. 2.Use a listed hardwired electric heater, a vented gas unit heater, or a mini-split instead. C BayHeat

Safer alternatives for your situation: 240V hardwired electric, Vented gas unit heater, Mini-split heat pump.

In a closed shop the exhaust has nowhere to go. BayHeat points you to a 240 V electric unit heater, a vented gas unit heater or a mini-split heat pump. Check any heater with Can I run it?

What each type costs to run

The table gives the same heat from each fuel: for one hour. That is the full output of a 5.0 kW electric heater.

Electricity, natural gas and propane use Illinois prices. Diesel uses the Midwest (PADD 2) regional average. The price dates are 2026-07 (electricity), 2025 annual (natural gas), 2026-03-30 (propane) and 2026-09-21 (diesel). The calculator re-runs it at your state's prices.

TypeFuel pricePer hour, same heat
240 V electric unit heater
Vented natural-gas unit heater
Vented propane unit heater (bulk tank)
Diesel air heater

At these prices, electric heat costs what natural gas does for the same heat. That gap shrinks where electricity is cheap or gas is dear. A torpedo is not priced, because BayHeat does not recommend one. Install cost is not included: get quotes for the circuit, or for the gas line and flue.

Buy: by the circuit and the fuel you have

Price is a range class, never a live number. Check the real price on the retailer's page before you buy.

Paid links: we earn a commission if you buy through links on this page, at no cost to you. As an Amazon Associate, BayHeat earns from qualifying purchases.

240 V · 5.0 kW · 30 A

Comfort Zone CZ220 5,000W ceiling heater

A 5.0 kW ceiling heater on its own circuit. The FUH54 is the same class in a higher price class. The CZ220 manual's maximum ceiling height is , and BayHeat's example garage has a ceiling. For a taller shop, read the FUH54 manual's mounting height first. The CZ220 manual also asks for a dry place free of combustible dust.

Manual: not where gasoline, paint or flammable liquids are used or stored. Indoors only, in a dry space free of combustible dust.

Manual: not where gasoline, paint or flammable liquids are used or stored.

Check price on Amazonor the FUH54 ↗
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Price class: $$ (CZ220), $$$ (FUH54)

240 V · 7.5 kW · 40 A

Dr. Infrared DR-975 7,500W shop heater

The maker rules out residential and household use, so this heater suits a commercial shop, not a home one. If you are unsure which yours is, ask the maker first.

Manual: “WARNING – RISK OF FIRE, DO NOT USE AS A RESIDENTIAL OR HOUSEHOLD HEATER.” Also not where gasoline, paint or flammable liquids are used or stored. Ask Dr. Infrared whether your garage counts as residential before you buy.

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Price class: $$$

240 V · 10.0 kW · 60 A

Dr. Infrared DR-910F 10,000W 240V hardwired shop heater

The largest electric class here. The maker rules out residential and household use, so it suits a commercial shop, not a home one. Check the panel before you order.

Manual: “WARNING – RISK OF FIRE, DO NOT USE AS A RESIDENTIAL OR HOUSEHOLD HEATER.” Also not where gasoline, paint or flammable liquids are used or stored. Ask Dr. Infrared whether your garage counts as residential before you buy.

Check price on Amazon
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Price class: $$$

Vented gas · clean shop

Mr. Heater Big Maxx 50,000 BTU forced-air unit heater (propane or natural gas)

Natural gas or propane, vented, connected by a licensed gas fitter.

BayHeat advises a licensed gas fitter and the permit your town requires. Manual: in a residential garage the bottom of the heater must be at least 8 ft above the floor. Never where gasoline, solvents, paint thinner or dust are present.

Check price on Amazon
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Price class: $$$

Vented gas · dusty shop

Modine Hot Dawg HDS, separated-combustion vented gas unit heater

Separated combustion keeps dusty shop air out of the burner. It is not rated for a solvent or gasoline atmosphere.

BayHeat advises a licensed gas fitter and the permit your town requires. Manual: “Appliances must not be installed where they may be exposed to a potentially explosive or flammable atmosphere.” Separated combustion takes burner air from outdoors; it does not make a room with solvent or gasoline vapor safe.

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Price class: $$$$

Diesel air · detached shop, attended

Diesel air heaters

The cost per hour, the exhaust rule and what to look for are on their own page.

Read the diesel heater page →

More circuit detail is on the 240V heater page and the electric heater hub. Every fuel side by side is on the garage heaters by fuel page.

Safety

Any fuel-burning heater needs CO protection in the shop itself. Run a CO monitor in the shop whenever the heater runs. Choose one whose data sheet covers the shop's temperature range. An alarm in the house cannot tell you what the air in a separate building holds.

If the shop is attached to a house, add UL 2034 alarms in the house. Put them by the garage door and outside each sleeping area. IRC 2021 R315 covers the house: .

A fixed electric heater adds no CO, but it still needs the breaker and wire in the table above. Your electrician, gas fitter and local code edition govern.

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

Safety add-on · for the house

Kidde C3010 10-year sealed-battery CO alarm (UL 2034)

This alarm is for the house, outside each sleeping area. It is not rated for an unheated shop.

Paid links: we earn a commission if you buy through links on this page, at no cost to you. As an Amazon Associate, BayHeat earns from qualifying purchases.

Check price on Amazon
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Data sheet: meets UL 2034 and is rated 40–100 °F for living areas. It goes in the house outside sleeping areas (IRC 2021 R315), not in an unheated garage. Source ↗

Next step

Pick the type your building can support, then check your own case. The calculator sizes the heat load and the circuit. The verdict tool gives a verdict for each heater type.

Size your shop free →Check my heater →

Related

Sources

  1. [1] NFPA 70, National Electrical Code, 2023, NFPA. Retrieved 2026-09-25.
  2. [2] International Fuel Gas Code, 2021, ICC. Retrieved 2026-09-25.
  3. [3] International Residential Code, 2021, ICC. Retrieved 2026-09-25.
  4. [4] Comfort Zone CZ220 Series ceiling mounted heater owner's manual, Comfort Zone (Lowe's copy). Retrieved 2026-10-09.
  5. [5] Comfort Zone CZ798CA2 milkhouse heater instruction manual (Canadian Tire copy), Comfort Zone / Canadian Tire. Retrieved 2026-10-09.
  6. [6] Fahrenheat FUH54 / FUH54C installation, operation and maintenance instructions (5200-11195-000), Marley Engineered Products. Retrieved 2026-10-09.
  7. [7] Dr. Infrared Heater DR-975 owner's manual, Dr. Infrared Heater. Retrieved 2026-09-30.
  8. [8] Dr. Infrared Heater DR-910F 10,000W 240V wall/ceiling garage heater owner's manual, Dr. Infrared Heater. Retrieved 2026-09-30.
  9. [9] Mr. Heater MHU50 / MHU80 / MHU125 operating instructions and owner's manual, Enerco Group (Mr. Heater). Retrieved 2026-09-30.
  10. [10] Modine HDS/HDC separated combustion gas-fired unit heaters, installation and service manual 6-584.12 (April 2018), Modine Manufacturing. Retrieved 2026-10-09.
  11. [11] VEVOR diesel air heater user manual, 8 kW, VEVOR. Retrieved 2026-09-30.
  12. [12] Kidde C3010 sealed battery carbon monoxide alarm data sheet, Kidde. Retrieved 2026-09-30.
  13. [13] Electric Power Monthly, Table 5.6.B, average retail price by state, US Energy Information Administration. Retrieved 2026-09-25.
  14. [14] Natural gas residential price by state, annual, US Energy Information Administration. Retrieved 2026-09-25.
  15. [15] Weekly heating oil and propane prices, residential, US Energy Information Administration. Retrieved 2026-09-25.
  16. [16] On-highway diesel prices by PADD, US Energy Information Administration. Retrieved 2026-09-25.
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