Can You Vent Water Heater Together With Gas Furnace? 

There is a growing emphasis on efficiency and space-saving in modern homes. Both in the sense of saving energy and allowing yourself enough space to love where you live. Connecting water heaters and furnace vents are an increasingly popular option to save space, but it also comes with many hazards if done incorrectly.

For major safety reasons, you should not vent a water heater with a gas furnace. Back-drafting and overheating are major concerns if the vent connection is not done properly, which can lead to potential fires. However, the best option to connect these vents is with a system that includes a vent fan.

This article is going to outline the general mechanisms of water heaters and furnaces to give you a good sense of how they work. Then we will outline the possible safety hazards and how exactly to connect the vents. Continue reading to get the basic information for these appliances and if connecting the vents makes sense for your home!

How Does Venting Work With Water Heaters?

First of all, there are several different types of water heater vents that could be in your home. The first are direct-vent heaters. These systems use air for combustion that is drawn from a vent pipe that runs through an exterior wall or the roof. These systems use outdoor air and are not subject to the effects of back drafting.

Then there is atmospheric venting, where an upward-sloping vent duct typically connects to a common vent. This system works solely through the principle that hot air rises. So it does not next an extra pump or fan to move the hot air. 

Finally, there is power venting, where electric water heaters have a quiet blowing fan to push the hot air out. This fan is usually on top of the water heater and has vertical or horizontal ducts.

Different systems use different materials. Your ducts duct may be metal or plastic, depending on the type of vent system. If you are looking to connect a water heater and gas furnace, these ducts must be made out of the same material. 

How Does Venting Work With Gas Furnaces?

Additionally, there are three types of gas furnace vents. Understanding how these work in comparison to your water heater vent can help you determine if you can connect them! They align similarly with water heater vents, and matching systems can be more easily connected.

First is the direct vent which uses one pipe to pull air from outside to bring it to the combustion chamber, and another to let the gas escape once it is used.

How Does Venting Work With Gas Furnaces

These vents go vertically or horizontally. Then there is the natural vent, which pulls air in through a pipe and lets it naturally leave through a B-vent pipe. The natural vent is more susceptible to back-drafts. Finally, there is the sidewall power vent. This vent uses a fan to push the uses gas outside.

Can You Vent a Water Heater Together With a Gas Furnace? 

The simple answer to this question is yes! You can connect a water heater vent to a gas furnace. The real question is, should you? There are some major potential drawbacks of this connection that can put your home in danger. 

The first of which is backdraft, when the exhaust of the water heater is not pushed out of the home properly and can pollute your air with carbon dioxide. This effect creates an area with too much carbon dioxide that can’t find its way outside. With enough back-draft or time, this creates flammable conditions. This means a fire could occur if there are sparks nearby.

The best way to avoid this situation is to have different vents for the water heater and gas furnace. Installing a fan to help expel this exhaust from the vents could be another solution, but if it works improperly you could create a dangerous environment. Different vents can cost additional ductwork, but it is certainly the safer option.

How Do You Vent a Water Heater With a Gas Furnace? 

Even though venting your water heater with a gas furnace is not recommended, it is possible if you need it. You will need to collect and locate these items in order to vent a water heater with a gas furnace. You will need a furnace, a water heater, some pipe fittings (including a tee connector), duct tape, a screwdriver, a drill, and a saw. Be sure that both of your appliances are made of the same material, usually either all-metal or all-vinyl.

If both the furnace and water heater are located in the same room, it is best to install the furnace and water heater vents next to each other. This will save you space and money as you do not need extra material to connect them. However, if they are not together you will need to install the furnace vent as close as possible to the water heater. In general, the vents for both these appliances should be placed as high as you can put them on an exterior wall.

The first step is to disconnect the vent pipe from the water heater. Then you will need to connect the vent pipe from the furnace to the water heater. Then you will identify the vent pipe on your water heater and the furnace. For safety, you will need to turn off the breaker to your furnace and water heater.

Then you will build the piping to connect the two appliances. This is when you install the tee connector to ensure air can flow in between the two. The piping has to be the same size for both the furnace and the water heater, if one is 3 inches and the other is 4 inches the connection will not be secure. Then the project is complete!

There is one more thing to keep in mind as you attempt this project. You should ensure that exhaust from the water heater is piped high enough to avoid snow or ice accumulation near the furnace from the outside. This will prevent water from leaking into the vents and causing issues.

Are There Safety Issues With Venting a Water Heater and a Furnace Together? 

There are a handful of safety issues related to connecting the vents of a water heater and furnace. The most common issue is back-drafting which we have mentioned a lot so far! This is because it is a very important and hazardous effect of this type of project.

Back-drafting is when exhaust gases from the water heater fail to exit the home via the vent and instead end up in the house. It usually comes from poor vent design or installation, which is a big danger with DIY projects. This gas is dangerous to breathe in and can pollute your home.

Another issue is overheating. This happens when this exhaust air from the water falls back into the water heater or furnace causing it to get too hot. If these systems are connected and temperatures get too high, then there is a possibility of a fire catching around one of the two appliances.

Both of these issues are huge safety hazards and are hard to avoid until the damage is already done. Water heater systems with fans are the best for avoiding this problem, so if your furnace or water heater has an exhaust fan, then this is the safest instance to connect these appliances. 

Is It Recommended That Water Heaters Are Vented With Gas Furnaces? 

Overall, it is not recommended to vent a furnace and water heater together. If the heat from the furnace back drafts it can cause the water heater to overheat. This could potentially lead to a fire, which is both hazardous and expensive to deal with afterward.

The main pull for connecting these two appliances is to safe space. It makes sense to connect two similar air vents to reduce the price of venting them individually. But user error could lead to the vents not being properly installed and breaking. Which then would lead to even more repair costs down the road.

If you decide that connecting these appliances makes sense for you, it is best to have a professional help you out with it. An HVAC repair friend or someone else who has done this project in the past can help you be sure to complete this project safely and efficiently.

However, if you are nervous or unsure of your ability to install the pipes you should avoid the project altogether. The project does not include that many bonuses for your home overall and is much safer to simply avoid.


It is certainly possible to connect the vents of your water heater with your gas furnace. It helps save space in your home and reduces the need for extra piping. And with matching water heating and furnace venting systems, it can be pretty easy to do.

However, it is not recommended. Connecting the furnace vent to the water heater opens up the possibility of back-drafting and overheating which could lead to fires. In many cases, it truly does not save too much space and can lead to harmful effects in the future if done poorly.

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