How To Vent Garage Heater Through Wall

Garage heating is a must in the colder weather. You may be able to withstand occasional drafts in spring and other not-so-cold seasons. However, getting through the winter without heating is asking for trouble.

For one, you need the heat to prevent various items inside the garage from freezing, including plumbing pipes. Moreover, working in a frozen garage exposes you to a myriad of health issues.

However, garage heating also means you need to plan for a venting system. Read on to learn the importance of such venting, garage heater venting requirements, and how to vent your garage heater step-by-step.

Do Garage Heaters Need to Be Vented? 

Let’s begin with why you should vent garage heaters. What are the dangers of working in a heated garage without proper venting? It all comes down to how garage heaters work. Most garage heaters are natural gas heaters followed by propane heaters, i.e., fossil fuel furnaces. Electric heaters come a distant third because of the cost disadvantages of electric heating.

Fossil fuel heaters burn fossil fuels in a burner unit and use a heat exchanger to harness the heat, which then exits the furnace via a supply air plenum into the room. The majority use a fan to blow the warm air throughout the room.

Unfortunately, these heaters also produce significant amounts of toxic exhaust fumes. For instance, burning natural gas produces lots of carbon dioxide and moisture and minor traces of carbon monoxide, sulfur dioxide, and nitrogen dioxide.

All the above gases are dangerous. The latter three are extremely dangerous, capable of causing suffocation and death in a matter of minutes, even in small quantities. For example, it takes just a few seconds to lose consciousness when exposed to carbon monoxide. Carbon dioxide and moisture aren’t as toxic.

However, the two can cause drowsiness in large quantities. Moreover, moisture can easily cause rusting of the heater and accelerate property damage. Above all, carbon dioxide and moisture form carbonic acid when the two interact.

Carbonic acid is a corrosive chemical that quickly eats plastic surfaces. Venting is the only way to ensure that the furnace safely removes these toxic gases from the heater and outside the house.

Other Reasons Why You Should Vent Your Garage Heater

Two other reasons why you should vent your heater are;

  • Provide oxygen-rich air for combustion

Healthy combustion requires plenty of oxygen. Unfortunately, the air inside the furnace may not have the required oxygen levels. This can lead to poor burning, characterized by yellow burner flames and low heat output. Proper venting ensures proper airflow, so your heater has as much oxygen as it needs.

  • Prevents indoor oxygen depletion 

If you don’t provide a means for the heater to get fresh oxygen from outside the house, it will use the oxygen inside your home for combustion. This is extremely dangerous because you’re staring at potential oxygen depletion resulting in carbon monoxide poisoning.

Can I Vent My Garage Heater Through the Wall?

Yes, you can vent a garage heater through the wall. It’s recommended as the option of last resort if roof installation is impossible due to obstructions and other reasons. However, it works just fine as long as you follow industry regulations and best practices.

However, beware that through-the-wall furnace venting is only applicable (allowed) for high-efficiency furnaces. Never attempt to vent a low- or mid-efficiency furnace through the wall. The reason is that low-efficiency furnaces bank on buoyancy to get combustion fumes out of the room. The fumes rise naturally because they are hot and lightweight, ultimately exiting through the highest point in the venting system.

So, venting low-efficiency furnaces horizontally (through-the-wall) creates all sorts of problems, such as slowing down the rising fumes. This can result in faster creosote buildup and increased in-pipe condensation.

Garage Heater Venting Requirements 

The installation requirements for garage heater venting systems are covered in the National Fire Protection Agency (NFPA) furnace installation guidelines and International Mechanical Code (IMC). However, you need to pay special attention to the following;

  • Safety: The installation must not pose safety or health risks to the home’s occupants or the general public.
  • Appliance location: Location requirements include the need to make sure the vent system is protected from damage, flooding, icing, and other external factors.
  • Ventilation: Proper ventilation inside the garage is a must. Indeed, the venting system is directly influenced by the quality of ventilation inside the space.
  • Clearance: Sufficient clearance around the exhaust vent is critical. You’ll find relevant guidelines in your local building codes.
  • Access and service space: Finally, all ventilation systems must be installed with access and space in mind.

How Far Should a Garage Heater Be from the Wall?

The garage heater should be at least 36 inches from the wall. Also, make sure the bottom of the heater is raised at least 72 inches from any combustible material.

How Much Clearance Is Needed for a Garage Heater Vent?

The typical requirement is at least three feet above any forced air inlet located within ten feet. Additionally, the vent terminal must be 12 inches clear of any obstructions horizontally, vertically, and 12 inches above windows, doors, or any other gravity air inlet into the building.

How to Vent a Garage Heater Through the Wall 

Now, let’s discuss how to vent your garage heater through the wall. It’s a straightforward process if you have basic DIY skills. However, don’t hesitate to call the experts if you need guidance.

What You Need

  • Tape measure
  • Pipe crimper
  • 5-inch reciprocating saw
  • Galvanized hanger straps
  • High-temperature silicone caulk
  • Calk gun
  • Cordless drill
  • Snips
  • Sheet-metal galvanized duct (4-inch)
  • Sheet metal galvanized elbows (4-inch)
  • 4-inch B-vent pipe (2-inch)
  • B-vent termination cap (4-inch)
  • Sheet metal screws
  • Pencil
  • Ladder

How to Vent a Garage Heater Through the Wall Step-by-Step

You’re ready to begin installation once you have the above requirements. Remember that you also need a second pair of hands to help you throughout the installation process. Proceed as follows once that’s covered;

  1. Ensure you have the correct duct diameter and enough pipe length 

Many people begin by cutting the hole right away. However, it’s much better to kick things off by ensuring that you have the right pipe/duct as it sets the stage for proper and efficient venting. So, start by ensuring that the duct diameter matches the diameter of your heater’s flange. You can check the original packaging for the dimensions.

Alternatively, use a tape measure to measure the pipe diameter then compare it with the heater’s flange. The standard value is two inches. Next, ensure enough duct piping to vent the heater through the wall.

Measure the distance between the heater and the stop in the wall where you’ll install the vent. Then compare the length with the length of pipe at your disposal. If everything is good, proceed to step #2.

2. Locate the best vent location

We’ve discussed clearance requirements and how far the heater should be from the wall above. However, there are a few more things to consider when choosing a wall vent location for a garage furnace.

For instance, you must only install the vent on an exterior wall. Secondly, air vents work best close to the ceiling. The best idea is to follow the manufacturer’s installation guidelines and your local codes.

You can get your local codes from the local fire department. Of course, the location will also depend on your furnace’s position. The location must be perpendicularly above the center of your vent flange.

An easy way to mark the location is to temporarily connect the 90° duct elbow to the flange and another elbow to the full-size duct pipe. Then temporarily fix the straight pipe on the first elbow and, using a pencil, trace an outline of the elbow on the wall. Once done, draw a second, larger circle around the first one. Cutting a bigger circle gives you more room for maneuver.

3. Cut the vent hole

You need a power drill and reciprocating saw for this process. Starting with the hand drill, cut a small ¼ or ½ inch hole around the perimeter of the larger hole, so it’s easier to remove the portion of the wall.

With that done, pick up the reciprocating saw and place begin cutting out the marked portion of the wall. Make sure to cut all the way to the outside of the house. It can take several minutes to complete the process.

4. Insert the duct

At this stage, you can now install the vent/duct system. Different people approach the process differently. However, we believe it’s best to begin by sending the duct pipe through the wall then attaching the middle piece of the duct portion to the heater flange first.

Once done, head outside and attach the pipe to the vent flange on the exterior wall using deck screws. You’re free to use a screwdriver or power drill for this process as long as you tightly fasten the vent to the wall.

From there, patch the system with roof flashing and plumber’s tape around the vent base outside the house. Also, patch up any seams along with the ducting. Use metal snips to adjust the installation if needed.

5. Final touches 

You’re almost done. For the final lap, ensure the duct run is straight and fit a vent cap at the vented tip outside the house. Make sure the cap is secure enough.

Next up, secure the duct joists to the flange using screws where necessary. That’s all. Your garage furnace vent installation is done. You can now test run the system to see if it works to your desires.

Other Ways to Vent a Garage Heater

The only other way to vent a garage heater besides through-the-wall venting is through the roof or ceiling. The two mean the same thing, and the process is known as vertical venting.

The process is almost the same as venting a heater through the wall, except that you’ll cut a hole in the roof instead of the wall. Of course, you also need to a hole through the ceiling.

Find the perfect location for the vent pipe, mark it and cut out that portion of the ceiling. Then use a straight object to mark the roof location and cut out the portion. With that done, you can now lower the duct into the garage through the roof, install the flashing and vent cap, then secure the vent.

Then, get back into the house and connect the remaining duct pipes before finishing off by connecting the duct to the furnace flange. Roof venting is perfect because it allows the furnace to take advantage of the buoyancy of hot air and the stack effect to naturally remove hot exhaust gases outside the room.


That’s all. Now you know how to vent a garage heater through the wall. More importantly, you also know why venting the garage heater is important. Although DIY installation is OK, never hesitate to call the pros if you run into technical issues.