Heating a workshop or garage presents unique challenges that home heating systems are not designed to handle. Unlike living spaces with consistent insulation and minimal air exchange, workshops contend with uninsulated concrete floors that act as massive heat sinks, large overhead doors that leak air along their entire perimeter, and walls that may have little or no insulation. Add to this the frequent opening of doors to move materials in and out, and you have a space that can lose heat faster than many heating systems can produce it.
Most garage and workshop owners underestimate their heating needs because they apply residential heating rules of thumb. The common guideline of 20 BTU per square foot works for well-insulated homes with 8-foot ceilings and minimal air infiltration. Workshops often need 30 to 50 BTU per square foot depending on insulation quality, ceiling height, and how often large doors are opened. A 500 square foot shop that would theoretically need 10,000 BTU by residential standards might actually require 25,000 to 40,000 BTU to maintain comfortable working temperatures in cold climates.
The type of work you do also affects heating requirements. Woodworking with stationary tools allows you to stay in one area, making spot heating with radiant or infrared units practical. Automotive work that requires moving around a vehicle demands whole-space heating. Metal fabrication and welding generate their own heat but also require ventilation that exhausts warm air. Understanding these factors helps you choose not just the right BTU capacity, but the right type of heating system for your specific workshop needs.
Enter your workshop dimensions and conditions below. Our calculator factors in ceiling height, insulation quality, climate zone, and door usage to provide an accurate BTU recommendation for your space.
Based on your space and climate conditions, you need approximately 45,000 BTU of heating capacity.
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BTU stands for British Thermal Unit, a measure of heat energy. One BTU is the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. For heating purposes, BTU ratings indicate how much heat a unit can produce per hour. Understanding the math behind BTU calculations helps you verify whether a heater recommendation matches your actual needs.
The basic formula for calculating required BTUs is: Cubic Feet multiplied by Temperature Rise multiplied by an Insulation Factor, divided by a time constant. For a quick estimate, multiply your square footage by ceiling height to get cubic feet. Then multiply by the temperature difference between outside and your desired inside temperature. Finally, apply a multiplier based on insulation quality: use 1.0 for excellent insulation, 1.5 for basic insulation, and 2.0 or higher for poor or no insulation.
For example, a 600 square foot shop with 10-foot ceilings has 6,000 cubic feet. If you need to raise the temperature 40 degrees Fahrenheit and have basic insulation, the calculation is 6,000 times 40 times 1.5, divided by 60 (minutes per hour), giving approximately 6,000 BTU per minute or 36,000 BTU per hour for steady-state heating. However, this only accounts for maintaining temperature once reached. Initial heat-up and heat loss through doors, windows, and gaps requires additional capacity, which is why our calculator adds safety factors based on your specific conditions.
The calculator also accounts for variables that simple formulas miss. Concrete floors absorb significant heat until they warm up. Large overhead doors lose heat even when closed due to gaps and thin panel construction. Opening a 16-foot garage door for even 30 seconds exchanges most of the warm air in the shop with cold outside air. These real-world factors explain why practical BTU requirements often exceed theoretical calculations by 25 to 50 percent.
Choosing the right heater type is as important as selecting the correct BTU capacity. Each heating technology has distinct advantages and drawbacks that make it better suited for specific workshop conditions and use patterns.
Forced air heaters use a fan to blow air across a heat exchanger, distributing warm air throughout the space. They heat rooms quickly and provide even temperature distribution when properly sized. Propane and natural gas forced air units are the most common choice for garage workshops because they combine high BTU output with reasonable purchase prices. The main drawback is that they stir up dust and debris, which can be problematic in woodworking shops. They also lose effectiveness in spaces with very high ceilings since warm air rises and stratifies near the roof. Forced air heaters work best in well-insulated shops with ceiling heights of 12 feet or less where whole-space heating is the goal.
Radiant heaters warm objects directly through infrared radiation rather than heating the air. This makes them highly efficient in drafty or poorly insulated spaces because the heat goes directly to people and objects rather than escaping through gaps and walls. Tube-style infrared heaters mounted overhead are popular in commercial garages and larger workshops. They excel in high-ceiling spaces where forced air would waste energy heating unused volume near the roof. Infrared heaters provide immediate warmth when turned on, unlike forced air which takes time to heat the entire air volume. The downside is uneven heating: areas directly under the heater are warm while corners and shadows remain cold. They work best for spot heating specific work areas or in shops where you spend most of your time at a single workstation.
Unit heaters, often called hanging heaters or suspended heaters, mount from the ceiling or wall and combine a burner with an integrated fan. Brands like Modine Hot Dawg and Reznor are popular choices for permanent garage installations. These heaters connect to natural gas or propane lines and vent exhaust outside through the wall or roof. They operate similarly to forced air but are designed for permanent mounting rather than portable use. Unit heaters are the professional choice for dedicated workshops and heated garages because they free up floor space, provide consistent heating, and last for decades with minimal maintenance. Installation requires gas line work and venting, making them a larger upfront investment but the most trouble-free long-term solution.
Electric heaters convert electrical energy directly to heat with nearly 100 percent efficiency at the point of use. They produce no combustion byproducts, require no venting, and have simple installation requirements. Portable electric heaters plug into standard outlets for instant heat. Hardwired 240-volt units like the Dr. Infrared DR-966 or NewAir G73 provide more substantial output for larger spaces. The main limitation is BTU capacity relative to cost. Electricity rates make operating costs two to three times higher than natural gas in most areas. Electric heaters also require significant amperage: a 5,000-watt heater draws about 21 amps on a 240-volt circuit. They work well as supplemental heat or for mild climates, but gas options are more practical for primary heating in cold regions.
Convection heaters warm air that naturally rises and circulates through the space without fans. This includes torpedo-style propane heaters and some ventless gas units. They operate quietly since there is no blower motor but heat distribution is less even than forced air. Convection heaters work well for temporary heating during occasional cold-weather work sessions. Many woodworkers use them for occasional garage projects when dedicated shop heating is not justified.
Based on performance, reliability, and value, these heaters consistently rank among the best choices for garage and workshop heating. All products listed below are available through Amazon with verified customer reviews and reliable shipping.
The Mr. Heater F274830 Big Buddy (ASIN: B01DD6C10I) delivers 18,000 BTU and runs on disposable propane cylinders or connects to a standard 20-pound tank with an optional hose. It features a built-in fan for better heat distribution and multiple safety shutoffs including tip-over protection and low oxygen sensing. The Big Buddy heats spaces up to 450 square feet and works well for occasional shop heating or as supplemental warmth while a larger system catches up.
The Dr. Infrared DR-988 (ASIN: B00EU2T8GG) produces 17,065 BTU from a 240-volt electrical connection. This rugged workshop heater features an adjustable thermostat, heavy-duty construction, and a built-in carrying handle. At 5,600 watts, it provides meaningful heat output for spaces up to 600 square feet in moderate climates. The DR-988 is ideal for shops where running a gas line is impractical or where clean, fume-free heat is preferred.
The Modine Hot Dawg HD45AS0111 (ASIN: B002FCCXX4) is a 45,000 BTU unit heater designed for ceiling or wall mounting. It connects to natural gas and vents exhaust through a side-wall or roof vent. The aluminized steel heat exchanger carries a 10-year warranty. Modine Hot Dawg heaters are widely considered the industry standard for residential garage heating and are installed by HVAC professionals across North America. For larger shops, the HD60 (60,000 BTU), HD75 (75,000 BTU), and HD100AS0111 (ASIN: B002FCCXU8, 100,000 BTU) models provide additional capacity.
The Mr. Heater MH60QFAV (ASIN: B01DD6CLCC) produces 60,000 BTU from propane and features Quiet Burner Technology for reduced operating noise. This portable unit heats spaces up to 1,500 square feet and includes high/low heat settings with thermostat compatibility. The continuous ignition system ensures reliable operation even in windy garage conditions. For even larger spaces, the MH125QFAV (ASIN: B01DD6C10I) delivers 125,000 BTU and heats up to 3,125 square feet.
The Heatstar HS45LP (ASIN: B0040JI3YK) is a 45,000 BTU low-intensity radiant heater designed for overhead mounting. It warms objects and people directly without heating the entire air volume, making it efficient for high-ceiling shops and drafty spaces. The unit runs on propane and works with standard thermostats for automatic operation. Radiant heaters like this excel in spaces where forced air would waste energy heating unused vertical space.
Proper installation affects both safety and heating performance. While portable heaters can simply be placed and plugged in, permanent installations require careful planning and often professional assistance.
Position heaters away from combustible materials including wood, paper, chemicals, and finishing products. Gas heaters require specific clearances to combustibles as listed in their manuals, typically 18 to 36 inches. Overhead mounting keeps heaters away from work activities but requires adequate ceiling height. Wall-mounted units should point away from windows and exterior walls where heat can escape. Consider airflow patterns: heaters near garage doors help recover temperature faster after the door opens but may also lose more heat directly outside.
Vented heaters require exhaust piping to the exterior. Power-vented units use a blower to force exhaust outside and can run horizontal through walls. Natural draft units rely on heat rising and need vertical runs through the roof. Category 3 venting with stainless steel or AL29-4C pipe is required for most modern high-efficiency units. Never improvise venting with materials not specified by the manufacturer. Carbon monoxide from improper venting is invisible and deadly.
Natural gas heaters require properly sized supply lines. A 45,000 BTU heater needs approximately 45 cubic feet of gas per hour, which typically requires 3/4-inch pipe for runs up to 100 feet from the meter. Larger heaters or longer runs need larger pipe. Propane installations involve different sizing rules because propane has higher energy content per cubic foot. Always have a licensed plumber or gas technician install or verify gas connections.
Even gas heaters need electricity for fans and ignition systems, typically a standard 120-volt outlet. Electric heaters have substantial power demands. A 240-volt, 5,600-watt heater needs a 30-amp circuit with 10-gauge wiring. Larger 10,000-watt units may need 50-amp circuits with 6-gauge wire. Run dedicated circuits for heaters rather than sharing with other equipment to avoid tripped breakers during cold-weather startup.
For automatic operation, mount thermostats at working height (4 to 5 feet) on an interior wall away from heat sources, windows, and exterior doors. Poor thermostat placement causes short cycling if placed too close to the heater or continuous running if placed near cold spots. Many unit heaters accept standard 24-volt thermostats; check compatibility before purchasing.
Natural gas is the most economical option if you have an existing gas line to your garage. Operating costs are typically 50 to 70 percent lower than propane and two to three times lower than electricity. Propane heaters offer high BTU output without requiring gas line installation, making them ideal for detached garages or temporary heating needs. Electric heaters are the cleanest option with no combustion byproducts, but their operating costs are highest and BTU capacity per dollar is lowest. For permanent shop heating in cold climates, natural gas is usually the best investment if feasible.
Forced air heaters warm the entire space quickly and provide even heat distribution in well-insulated shops with normal ceiling heights. They cost less upfront than radiant systems but stir up dust. Radiant and infrared heaters warm objects directly rather than heating air, making them more efficient in drafty spaces, high ceilings, or for spot heating specific work areas. If you work at a single bench or machine most of the time, radiant heat focused on that area can be more comfortable and economical than heating the whole shop. For general-purpose workshops with 8 to 10-foot ceilings and decent insulation, forced air is typically the practical choice.
Vented heaters exhaust combustion gases outside and are required for permanent installations and higher BTU outputs. They are safer for extended daily use because they do not add moisture or combustion byproducts to the air. Ventless or vent-free heaters burn extremely clean and use oxygen depletion sensors for safety, but they add water vapor to the air and are typically limited to 30,000 BTU or less. Many jurisdictions restrict ventless heaters in living spaces; check local codes. For a dedicated shop you use daily, vented heating is the better long-term choice. Ventless heaters work well for occasional heating of detached garages where venting is impractical.
Ceiling height directly impacts the cubic footage you need to heat. A 400 square foot shop with 8-foot ceilings has 3,200 cubic feet of air. The same footprint with 12-foot ceilings has 4,800 cubic feet, requiring approximately 50 percent more BTUs. With 16-foot ceilings, you have 6,400 cubic feet and doubled heating requirements. High ceilings also cause stratification where warm air rises and stays near the ceiling while the work area remains cold. For shops with ceilings above 12 feet, consider radiant heaters that warm objects directly, destratification fans that push warm air back down, or forced air heaters oversized by 25 to 50 percent to compensate.
Insulation has a dramatic impact on both heater sizing and ongoing fuel costs. An uninsulated garage might need twice the BTU capacity of a well-insulated one to maintain the same temperature. More importantly, the poorly insulated space will burn through fuel twice as fast continuously. Adding R-13 wall insulation and R-30 ceiling insulation to an uninsulated garage can reduce heating costs by 40 to 60 percent. Insulating the garage door with a kit costing $50 to $100 often provides the best return on investment since doors are the largest heat loss surface. If you plan to heat your shop regularly, investing in insulation before buying a larger heater almost always makes more financial sense.
Operating costs depend on local fuel prices, but typical relative costs per 100,000 BTU are: natural gas at $0.80 to $1.20, propane at $1.50 to $2.50, and electricity at $2.50 to $4.00. To calculate monthly costs, estimate your daily BTU usage. A 45,000 BTU heater running 4 hours daily at half capacity produces about 90,000 BTU per day. At $1.00 per therm for natural gas (100,000 BTU), that costs roughly $0.90 per day or $27 per month. The same heat from electricity at $0.12 per kWh costs approximately $3.00 per day or $90 per month. These differences compound over a heating season, making fuel choice an important long-term financial decision.
Essential safety features include oxygen depletion sensors (ODS) that shut off the heater if oxygen levels drop too low, tip-over switches for portable units, and overheat protection that cuts power if the unit gets too hot. Flame rollout sensors detect if combustion occurs outside the intended chamber. High limit switches prevent the heat exchanger from overheating. For permanent installations, look for heaters that are CSA or UL certified and match the certification to your fuel type (natural gas or propane). In workshops with flammable materials, solvents, or finishing products, choose sealed combustion heaters that draw combustion air from outside rather than from the shop.
Most natural gas unit heaters accept standard 24-volt heating thermostats. Basic non-programmable thermostats cost $20 to $40 and work fine for manual operation. Programmable thermostats let you preheat the shop before you arrive, typically for $40 to $100. Smart thermostats like Nest or Ecobee work with many heaters and allow control from your phone, useful for starting heat remotely. Some electric heaters have built-in thermostats; others require line-voltage thermostats rated for the heater amperage. Portable propane heaters often include built-in thermostats or work with optional thermostat accessories from the manufacturer. Match thermostat voltage and wiring to your specific heater model.
Garage doors are typically the largest source of heat loss in a shop. A single-layer steel door might have an R-value of only 2 to 4, while insulated doors range from R-8 to R-18. A 16-foot wide door represents 140 square feet of surface area; at R-4 with a 40-degree temperature difference, that loses roughly 1,400 BTU per hour just through the panel. Gaps around the perimeter add significant air infiltration. Opening the door briefly exchanges most of the warm air in the shop. Weatherstripping the door perimeter, adding bottom seals, and installing an insulation kit on the door panels can reduce standing heat loss by 50 percent or more. For shops in cold climates, an insulated door is one of the best investments for long-term comfort and fuel savings.
Standard residential furnaces are not designed for garage installation due to combustion safety concerns. Garages may contain gasoline, solvents, and other flammable vapors that could ignite from furnace flames. Building codes typically prohibit installing residential furnaces in garages unless they are completely isolated in a sealed closet with combustion air from outside. Purpose-built garage heaters have sealed combustion chambers or are designed for the environment. Some manufacturers make separated combustion unit heaters specifically rated for garage installation. If you want furnace-style heating with ductwork, consult an HVAC contractor about proper equipment and installation that meets code requirements for your area.