Home HVAC Unit in Garage: Critical Code Requirements You Can’t Ignore!

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Can you put the Home HVAC Unit in Garage?

HVAC systems are an integral part, of most US homes, but finding relevant codes and regulations can be challenging. One common question is whether you can place an HVAC unit in the garage.

The building code allows placing a Home HVAC unit in the garage provided:

• The unit is in an air-sealed cabinet.
• The furnace doesn’t use solid fuel.
• Systems serving living spaces don’t supply or return air to/from the garage.

In short, house and garage HVAC systems must be separate.

Check local codes for stricter rules. Ideally, place the HVAC unit in the basement or attic, using the garage only as a last resort.

Read this post till the end, if you must put the HVAC Unit in the Garage.

The Home HVAC System

HVAC is short for Heating, Ventilation & Air Conditioning. HVAC is an essential part of most homes in the US. 

Without HVAC in your home, you would be shivering through the winters and sweating it out during the summers.

The Concept

The functions of heating and cooling a building have been around for some time. Ancient civilizations such as the Egyptians, Romans, and Chinese knew a thing or two about keeping a building cool. 

The concept of cooling using wet reeds, aqueducts, and fans, invented by them, are adopted by the present-day HVAC systems.

Initially, HVAC systems were installed only in major public buildings. As the technology advanced and costs came down, homes could afford central heating and air conditioning.

Today the HVAC system of a house is compact and mostly kept out of sight. 

We just know that we can get as comfortable as we want at the press of a button! Pretty awesome!

The HVAC Unit

The HVAC unit is a bit like the heart and circulatory system in our body. The heart of the HVAC is the equipment and the circulatory system is the ducting.

The heart of the home HVAC Unit will have the following components:

Heating:

Furnace – where the heat is generated.

Heat Exchanger – where the cold air pulled in from the house gets heated by the furnace and is pushed back into the house.

Cooling:

Condensation Unit – where the refrigerant gives off heat to the outside air and is cooled.

Evaporator Coil – where the cold refrigerant absorbs the heat from the warm home air passing over it.

Controls:

Thermostat – controls the switching on or off of the HVAC based on set temperature.

Ducting:

Supply – the air from the HVAC is taken to different parts of the house and released through vents.

Return – The air from the different parts of the house is collected and brought to the HVAC.

Building Code for HVAC Unit in Garage

The 2021 edition of the International Residential Code (IRC) states the following concerning ducts that penetrate garage walls and ceilings:

R302.5.2 Duct Penetration: Ducts in the garage and ducts penetrating the walls or ceilings separating the dwelling from the garage shall be constructed of a minimum No. 26-gauge (0.48 mm) steel sheet or other approved material, and shall have no openings in the garage.

There are two important reasons there can not be any air leakage between the garage and the dwelling (living zone of the house).

a) Carbon Monoxide

Carbon monoxide (CO) is the most toxic component of car exhaust.  It is produced from the incomplete combustion of gas. 

You can’t even detect it because it is colorless, odorless, and tasteless. But it’s a killer because it

“displaces oxygen in the blood and deprives the heart, brain and other vital organs of oxygen. Large amounts of CO can overcome you in minutes without warning — causing you to lose consciousness and suffocate.”

OSHA

Cars idling in the garage, even for short while, can create enough carbon monoxide to be lethal if it finds its way into the house.

This is the reason the 2021 edition of the International Residential Code (IRC) specifies:

M1601.6 Independent Garage HVAC Systems: Furnaces and Air Handling Systems that supply air to living spaces shall not supply air to or return air from a garage.

b) Fire Hazard

The garage has a high potential for starting fires because of the abundance of flammable materials such as gas, oil, lubricants, and paint. This is the reason the 2021 International Residential Code (IRC) has the following codes for attached garages.

R302.5.1 Opening Penetration (applies to Garage Entry Doors)

You may be interested to read, my earlier blog post, 15 Important Garage Entry Door Questions Answered [Updated for 2024]!

R302.6 Dwelling Garage Fire Separation (applies to adjoining Garage Walls & Ceilings)

My post on 10 Reasons Why It Is Better To Drywall A Detached Garage also talks about the building code for adjoining walls of attached garages.

Information Source: 2021 edition of the International Residential Code (IRC)

I highly recommend getting one of these; Kidde AC Plug-In Carbon Monoxide and Explosive Gas Detector Alarm. It protects you and your family from 2 deadly threats; carbon monoxide and explosive gas.

Can an HVAC System Be in a Garage?

The garage should be the last resort for locating the home HVAC Unit. Do it only if you do not have a basement, an attic, or any other suitable location within the house. 

Building America Solution Center of The Office of Energy Efficiency & Renewable Energy is clear in its guidelines.

In essence, the guideline is, to try not to locate the HVAC Unit in the Garage, but if you must, keep it separate from the garage space.

Climate Controlled Garage

There are many reasons to incorporate climate control in your garage. I have explained the benefits of a climate-controlled garage in detail in my earlier blog post How To Make Sure Of Best Climate Control For Your Garage.

The main benefits are:

• Making the garage a comfortable place to work, relax, or have some fun with family & friends.
• Enhancing the life of several parts of your car. Batteries, tires, and the paint job last longer.
• Allowing you to store gear that is sensitive to temperature fluctuations, high humidity, or exposure to dust.
• Prolonging the life of the garage itself such as the floor & door.
• Saving money on energy bills. Not all climate controls are active and use energy. Some like insulation are passive and reduce energy consumption.

Tempting as it may be, connecting your home HVAC Unit ducts to heat or cool your garage is not acceptable. You will straight away be violating the IRC Building Code, Section M1601.6

M1601.6 Independent Garage HVAC Systems: Furnaces and Air Handling Systems that supply air to living spaces shall not supply air to or return air from a garage.

What Type of AC is Best for a Garage?

Based on the code you can not cool your garage using the home HVAC system. So what do you do?

The best solution is for the garage to have its own, preferably ductless, HVAC system. Fortunately. this can be done by simply installing a Mini Split Ductless Air Conditioner. Here is the one, I recommend.

Make sure to get a model with sufficient cooling power for your needs. Typically an 18000 BTU should be fine for a 3-car garage.

• 18000 BTU Mini Split Ductless Air Conditioner from Air-Con Int.
• It is a high-efficiency air conditioner, heater, and dehumidifier all in one.
• Built with pro-grade materials for a long life.
• WIFI ready with optional additional remote.

Bottom Line

The bottom line is that if you have a basement or attic then the HVAC Unit must be installed there. Settle for installing the HVAC Unit in the Garage only as a last resort.

Ensure that the HVAC Unit in the Garage is installed within an air-sealed closet.

Further, adhere to M160.2.1 of the IRC code and ensure that Furnaces and Air Handling Systems that supply air to living spaces shall not supply air to or return air from a garage.

A mini-split ductless three-in-one air conditioner (air conditioner, heater, and dehumidifier all in one) can be used for climate control of the garage, completely independent of the house HVAC System.

Thank you very much for reading the post. I do hope you found it informative and useful.