The best garage heater depends on your garage size and climate: a 1-car garage needs 15,000–25,000 BTU (a 5,000W electric or small propane unit), a 2-car garage needs 30,000–45,000 BTU (natural gas forced-air), and a 3-car garage needs 45,000–75,000 BTU (ceiling-mounted gas unit). No standard 120V portable space heater can adequately heat an uninsulated garage in cold weather.
Garages are the toughest residential spaces to heat — uninsulated walls, massive air leaks around the door, and a concrete slab that acts as a heat sink. This guide covers every garage heater type with real BTU calculations, operating costs, and installation data.
Garage Heating Requirements by Size
Standard residential heating rules don't apply to garages. An uninsulated garage needs 30–50 BTU per square foot, roughly 3× more than a living room.
Insulate first, heat second. A garage door insulation kit ($80–$200) plus wall foam board ($200–$500 DIY) cuts BTU requirements by 40–60%. An insulated 2-car garage might need only 20,000 BTU instead of 45,000 — saving hundreds yearly.
The 5 Types of Garage Heaters
1. Natural Gas Forced-Air (Ceiling-Mount)
The gold standard for regular garage use. Ceiling-mounted units connect to your gas line and deliver 30,000–75,000 BTU with a built-in fan. Professional installation is required.
Best for: 2+ car garages, daily use, cold climates (IECC Zone 5–7). Cost: $300–$800 unit + $500–$1,500 install. Operating: $0.30–$0.75/hr at $1.20/therm.
2. Propane Forced-Air (Torpedo/Salamander)
Portable propane torpedoes produce 30,000–80,000 BTU with zero installation. They heat fastest of any option. However, they produce CO, consume oxygen, create noise, and require ventilation.
Best for: Occasional use, no gas line available. Cost: $100–$300 unit + propane at $3.50–$5.00/gal. Operating: $0.50–$1.50/hr.
3. Propane Radiant/Infrared (Mounted)
Wall- or ceiling-mounted propane infrared heaters warm objects directly with radiant heat, effective even in drafty spaces. Quieter than forced-air, excellent for spot heating at a workbench.
Best for: Workshops, high-ceiling garages. Cost: $200–$600 + install. Operating: $0.25–$0.60/hr.
4. Electric Forced-Air (240V Hardwired)
These plug into a 240V outlet or are hardwired, producing 10,000–17,000 BTU (3,000–5,000W). No combustion, no CO, no venting. Adequate for insulated 1–2 car garages.
Best for: Insulated garages, moderate climates, chemical-sensitive workshops. Cost: $150–$500 unit + $200–$500 for circuit. Operating: $0.50–$0.85/hr.
5. Electric Infrared (120V/240V)
Portable or wall-mounted infrared for garages. 120V models max at 1,500W (5,120 BTU) — only useful for zone heating. 240V models reach 3,000–6,000W.
Best for: Workbench zone heating, supplement to main heater. Cost: $80–$300. Operating: $0.25–$1.00/hr.
Complete Garage Heater Comparison
Monthly Operating Costs Compared
Natural gas wins on operating cost — roughly half the price of electric and one-third the cost of propane per BTU.
Garage Heater Sizing: How to Calculate
Formula: BTU needed = Garage sq ft × BTU/sq ft factor × (Temperature rise ÷ 10)
| Insulation Level | BTU/sq ft per 10°F rise | 500 sq ft, 30°F rise |
|---|---|---|
| Uninsulated | 10–12 | 15,000–18,000 BTU |
| Partially insulated | 7–9 | 10,500–13,500 BTU |
| Well insulated | 5–7 | 7,500–10,500 BTU |
Example: Uninsulated 2-car garage (500 sq ft) in Cleveland, OH. Outdoor: 20°F, target: 55°F (35°F rise). BTU = 500 × 11 × 3.5 = 19,250 BTU minimum. A 30,000 BTU gas heater provides headroom for bitter cold days.
Real-World Garage Heating Examples
Example 1: Weekend Woodworker — 2-Car Garage, Minnesota
Setup: 500 sq ft, partially insulated. Outdoor: 0–20°F. Target: 55°F. Weekend use only, 6–8 hours.
Solution: Mr. Heater Big Maxx 50,000 BTU natural gas ceiling-mount ($380 + $800 install).
Cost: ~$0.60/hr. 8 hrs × 8 weekend days/month = $38.40/month peak winter. Garage reaches 55°F in 35 minutes. A ceiling fan in reverse helps push warm air down.
Example 2: Daily Workshop — Detached Garage, Colorado
Setup: 400 sq ft detached, no gas line. DIY-insulated. Outdoor: 15–35°F. Target: 60°F. 4–6 hours daily.
Solution: Fahrenheat FUH54 5,000W electric 240V ($180 + $350 for circuit). Cost: $0.65/hr at $0.13/kWh. 5 hrs/day = $97.50/month.
With insulation, the electric unit maintains 60°F adequately. A supplemental propane radiant at the workbench helps on sub-15°F days.
Example 3: Occasional Use — 1-Car Garage, Tennessee
Setup: 240 sq ft, uninsulated. Outdoor: 25–40°F. Target: 55°F. 2–3 hours, a few times per week.
Solution: Dr. Infrared DR-966 6,000W electric ($200 + $300 for 240V). Cost: $0.66/hr at $0.11/kWh. ~10 hrs/week = $26.40/month. Heats to 55°F in about 20 minutes.
Example 4: Professional Auto Shop — 3-Car, Wisconsin
Setup: 800 sq ft, insulated ceiling, partial wall insulation. Outdoor: -10 to 20°F. Target: 60°F. 10 hours daily, 5 days/week.
Solution: Modine Hot Dawg 75,000 BTU natural gas ($650 + $1,200 install). Cost: ~$0.90/hr. 10 hrs × 22 days = $198/month peak winter. The unit maintains 58–62°F consistently even on -10°F days.
Insulate Before You Buy: The Math
| Investment | Cost | BTU Reduction | Annual Fuel Savings |
|---|---|---|---|
| Garage door insulation kit | $80–$200 | 15–25% | $50–$150 |
| Wall insulation (batts, DIY) | $200–$500 | 20–30% | $80–$200 |
| Ceiling insulation | $150–$400 | 10–20% | $40–$120 |
| Weatherstripping (door seals) | $30–$80 | 5–15% | $20–$80 |
| Total package | $460–$1,180 | 50–70% | $190–$550 |
The insulation pays for itself in 1–3 heating seasons and lets you buy a smaller, cheaper heater.
Garage Heater Safety Rules
Critical garage safety rules:
- Never use propane torpedo heaters near gasoline, paint, or solvents — open flame ignites fumes.
- Install a CO detector for any combustion heater (gas or propane).
- Ensure ventilation for unvented propane heaters — crack a window or the garage door.
- Mount heaters high to keep the heat source away from floor-level combustibles.
- Check manufacturer clearance ratings — most gas units need 3+ feet from combustibles.
- Never leave torpedo heaters unattended. Turn off when leaving.
Decision Framework: Which Garage Heater to Buy
Use this quick decision tree:
Do you have a natural gas line to the garage?
- Yes → Gas ceiling-mount forced-air (best long-term value)
- No → Continue below
Do you use the garage daily or only occasionally?
- Daily → Install a 240V electric heater (insulated garage) or run a propane gas line (uninsulated)
- Occasionally → Portable propane forced-air or radiant
Is your garage insulated?
- Yes → Electric 240V (3,000–5,000W) is likely sufficient
- No → You need gas/propane output levels, or insulate first
Key Takeaways:
- No 120V portable heater can heat an uninsulated garage. You need 240V electric, gas, or propane.
- Natural gas ceiling-mount heaters offer the best operating cost: $0.30–$0.75/hour.
- Insulate first — it cuts BTU needs by 50–70% and pays back in 1–3 seasons.
- Size your heater at 30–50 BTU/sq ft for uninsulated garages, 15–25 BTU/sq ft for insulated.
- Always install a CO detector with any combustion heater.
- For occasional weekend use, a $150 propane torpedo works. For daily use, invest in permanent gas or 240V electric.
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