How To Estimate Garage Heater Size ?

One rule of thumb for estimating the size of an electric garage heater is to use the “law of 10.” This means using 10 watts of heating power per square foot of floor space in your garage.

For an electric heater, the best way is to abide by the law of 10. That is 10 watts per square foot of floor space.

For example, if your garage is 500 square feet, you need a heater with a minimum output of 5,000 watts (500 x 10 = 5,000).

Assuming a 20 ft. x 25 ft. garage with a ceiling height of 8 ft., the total volume of the space is 4000 cubic feet (20 x 25 x 8). To estimate the required wattage for heating the garage, we can use the formula:

Wattage = Volume (cubic feet) x Temperature Difference (Fahrenheit) / 3

When estimating the required BTU for a gas garage heater, the process is similar to that for an electric heater. The main difference is that instead of using watts, we use BTU per hour (BTU/hr) as the unit of measurement.

To convert watts to BTU/hr, we can use the following formula:

1 watt = 3.412 BTU/hr

So, if you know the wattage of the electric heater, you can convert it to BTU/hr by multiplying it by 3.412. For example, if the electric heater has a wattage of 5,000 watts, the equivalent BTU/hr would be:

5,000 watts x 3.412 = 17,060 BTU/hr

How to Estimate the Size of Heater Needed for Your Garage

For the above table, the recommended wattage for infrared heaters was set to 7.5 watts per square foot to provide a conservative estimate. The calculation criteria for infrared heaters is multiplying the square footage by 7.5 to determine the needed wattage.

Infrared heaters are measured in watts, like electric heaters, and the calculation criteria is similar: multiply the square footage by a certain number of watts per square foot. The recommended wattage for infrared heaters is typically higher than for electric heaters, ranging from 10-20 watts per square foot.

Heat loss calculation: Determine the amount of heat loss from your garage through various sources and choose a heater with the appropriate BTU output to heat your garage effectively.

The calculation criteria for electric heaters remain the same: multiply the square footage by 10 to determine the wattage needed. For gas heaters, the calculation criteria are to multiply the square footage by 50 to determine the BTUs needed.

For the option with a ceiling height of 10 feet, the calculation criteria for electric heaters is to multiply the square footage by 10 and the ceiling height divided by 8 to determine the wattage needed. For gas heaters, the calculation criteria are to multiply the square footage by 50 and the ceiling height divided by 8 to determine the BTUs needed.

Factors To Conisder While Chosing Heater For Garage

Again, please note that this table only provides a general estimate, and other factors such as insulation, climate, and desired temperature may also affect the size of the heater needed.

1. Start By Measuring Your Garage Size

When it comes to selecting a heater for your garage, the size of your garage is an important factor to consider. A heater that is too small will struggle to heat the entire space, while a heater that is too large will consume more energy than necessary and result in higher energy bills. Choosing a heater that is appropriately sized for your garage is important.

A 5000 watt electric heater would be sufficient for a garage of size 20*20 feet.

The size of your garage is measured in square footage, and the larger your garage, the more heating power you will need to heat the entire space effectively.

A small garage, such as one that measures 10 feet by 10 feet, will require a heater with a lower BTU output and wattage output compared to a larger garage, such as one that measures 30 feet by 30 feet or more.

In general, a small garage will require a heater with a BTU output of 5,000 to 10,000 and wattage output of 1,500 to 3,000.

A medium-sized garage will require a heater with a BTU output of 30,000 to 40,000 and wattage output of 8,800 to 11,700. A large garage will require a heater with a BTU output of 50,000 or higher and a wattage output of 14,600 or higher.

2. Ceiling Height

The height of the ceiling affects the size of the space that needs to be heated and the heat distribution within that space.

For electric heaters, the wattage and coverage area of the heater should be chosen based on the height of the ceiling. If the ceiling is high, a heater with a higher wattage and larger coverage area will be required to provide sufficient warmth to the space.

This is because heat rises and can accumulate at the ceiling, leaving the lower areas of the garage colder.

A higher-wattage heater can produce more heat to overcome this problem and provide warmth to the entire garage.

Gas heaters also need to be chosen based on the ceiling height of the garage.

The BTU (British Thermal Unit) output of the heater is an important consideration. For a high ceiling, a gas heater with a higher BTU output will be required to provide sufficient heat to the entire space. The type of gas used in the heater is also a consideration, with natural gas and propane being the most common options.

3. Insulation Level

The insulation level in your garage can vary depending on the age of your garage, the type of construction, and the type of insulation used.

A well-insulated garage will have insulation in the walls, ceiling, and possibly even the floor. In addition, the insulation should be thick enough to provide a sufficient thermal barrier. If you have a garage with good insulation, you will require less heating power to maintain a comfortable temperature compared to a poorly insulated garage.

For example, a small garage with good insulation may only require a heater with a BTU output of 5,000 to 10,000, while a small garage with poor insulation may require a heater with a BTU output of 15,000 or more to effectively heat the space.

4. Heating Speed

The heating speed of a heater refers to how quickly the heater can warm up your garage to a comfortable temperature.

In general, larger garages will require heaters with a higher heating speed compared to smaller garages. This is because larger garages will take longer to warm up and require more heating power to maintain a comfortable temperature.

Additionally, garages with poor insulation will also require heaters with a higher heating speed, as they will lose heat more quickly and take longer to warm up.

5. Climatic Conditions

Areas with high humidity or extreme temperatures may require heaters with additional features to effectively maintain a comfortable temperature.

6. Fuel Type

The type of fuel used for heating a garage can play a significant role in determining the size of the heater required. Different types of fuel have different heating capacities, efficiencies, and costs.

• Natural gas heaters are among the most efficient and cost-effective options, with an average efficiency rating of 80-90%. The cost of natural gas varies by region, but it is generally cheaper than other fuel sources.
• Propane heaters have an efficiency rating of around 70-80%. The cost of propane varies depending on location, but it is typically more expensive than natural gas.
• Electric heaters are the least efficient and most expensive option, with an average efficiency rating of 95%. However, electric heaters are often favored for their ease of installation and maintenance.

7. Purpose Of Garage

Let’s take a closer look at each type of garage and how it can impact your heater selection:

8. Windows and doors

The number and quality of windows and doors in the garage affect the insulation and air circulation of the space.

Poorly insulated windows and doors can result in heat loss and higher energy consumption, while proper insulation can help retain heat and minimize energy use.

9. Garage door openers

The presence of a garage door opener can also affect the heating needs of a garage. Garage door openers can allow cold air to enter the garage, resulting in higher heating requirements. It is important to consider the insulation of the garage door and the frequency of use when choosing a garage heater.

10. Heat tolerance

The heat tolerance of equipment and vehicles stored in the garage is also a consideration. Some equipment and vehicles may require a specific temperature range to function properly. It is important to select a garage heater that can provide the required temperature range without overheating the space.

11. Humidity levels

Humidity levels in the garage can affect the efficiency and performance of a heater. High humidity can reduce the effectiveness of a heater and increase the risk of corrosion and mold growth. It is important to ensure proper ventilation and consider a dehumidifier when selecting a garage heater.

12. Number of cars/vehicles

Calculating BTUs for Garage Heaters

Whereas electric garage heaters are rated according to wattage, gas garage heaters are rated according to BTUs (British Thermal Units).

While it all sounds exceptionally high-tech, it’s actually quite straightforward. Each BTU is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

Even though gas heaters are heating air and not water, this is the standard method of referring to heating capacity.

To work out the size of a gas garage heater, you multiply the wattage by 3.41. Using 4500 as an example, the measurement would be as follows: 4500 x 3.41 = 15,345 BTUs.

Another more exact way to estimate the heater size for your garage is to calculate the number of watts or BTUs required to correlate with your desired temperature rise.

For example, a garage measuring 20 feet by 20 feet with an 8-foot ceiling and moderate insulation requires approximately 30,000 BTUs to raise the temperature by 30 degrees Fahrenheit.

Use a rating of 5 if your garage space has no insulation, 1.5 if it has minor insulation, one if it has average insulation, and 0.5 if it has reliable insulation.

Once your measurements are in order, you can determine the required number of BTUs by following the below equation:

By implementing the previous example of a 20 x 22 garage (average insulation,4,400 cubic ft. and a 25F desired temperature rise) the formula would be:

(1 x 4,400 x 25) / 1.6 = 68,750 BTU.

To convert into watts, you would then divide by 3.41.

68,750 / 3.41 = 20.161 watts.

In this example, it would be unlikely that you could find an electric garage heater rated for 20.161 watts. You would either need to purchase and install a gas heater or multiple electric heaters.

The only other option would be to increase the volume of insulation in your garage walls. This would then reduce the overall amount of energy needed to heat it.

Garage BTU Requirements

Typically, the estimated BTU requirements for a garage can range from 30 BTUs to 60 BTUs, depending on the climate zone of the location.

Gas Heater Size Based on Garage Size and Climate Zone