Can Tankless Water Heater And Furnace Share Vent?

Tankless water heater consumer have a furnace thinks about can tankless water heater and furnace share vent? Yes, they can share a vent but not in all cases. An efficient furnace and tankless water heater can share a vent if they are appropriately sized. Builders build homes with water heaters and furnaces venting through on the head.

Sometimes they make a single way of venting for both the water heater and furnace. Sharing vent is typical for the standard furnace in a ratio of 80% furnace and 20% water heater venting. In those cases, the old vent pipe is too large.

When installing a new water heater, you should change the vent pipe according to the water heater’s needs. It ensures that the water heater heats the vent pipe and gets exhausted out of the house perfectly.

Can Tankless Water Heater and Furnace Share Vent

There are some things required for the venting system of a tankless water heater. You or your installer should know these required items :

Venting Outside

It’s evident that hot air exits outside through the venting system. So the outline is outside.

Uncommon Venting

It’s not so similar to other appliances’ venting. You can not share a tankless water heater’s venting system with another appliance through pipes. It does not use any chimney for venting outside of the house.

Use of Special Pipes

Pipes used for venting a tankless water heater are made of stainless steel. It passes corrosive gases outside. Tankless water heater does not use any other alternative for venting. So it’s a must to get stainless steel pipes.

Slope or Drain

The venting system needs a slope or drains near the exhaust outlet. From the heat exchanger, the slope is downhill. You can also make a drain. It helps to prohibit condensation from coming back to the heater. If the condensate gets closed to the heat exchanger, then it may lose its life by years.


The venting of a tankless water heater should be as small as possible. Because it helps to exit combustion quickly and thoroughly. As we know, stainless pipes are used for venting, but they are expensive. Pipes are mandatory for the venting process successful.

You may put the ventilation near the place where it will exit combustion. It saves you from buying extra pipes.

Water Heater Venting System And Its Benefits

For tankless water heater installation is a bit complex matter. A plumber inspects your house and fits the water heater properly. Without the venting process, a heater can’t run inside the home. You may get confused with the question,

Can tankless water heaters and furnaces share vents? Some factors are bellowed to keep in mind while installing water heater ventilation that will help you to get a clear concept:


We need a small space for installation. It saves 16 square feet of space. An exhaust vent and a larger area are needed for adequate air. If your water heater is installed outside of the house, then no venting is needed as it frees up indoor space.


Multiple options are available for renting a water heater. Tank. Fewer water heaters vent combustion through walls or roofs. Some water heaters use a motorized fan to exit the flaming air. The tankless water heater uses expensive stainless pipes for the venting process. It is a bit expensive but safe.


Technology adds condensing in the mini tankless water heater. It makes a water heater 96% more efficient than others. Installation expense becomes less than usual for a tankless water heater. Not metal, but PVC can be the exhaust vent. These unique features attract consumers.


Tankless water heater featuring a concentric vent gives you extra safety. It can be 5″ in size. Having both intake and outtake pipes remains cool to touch, and warm air keeps inside that pipe. Accidentally, a leakage happens sometimes. The concentric vent lets hot air come out of the pipe and keeps your home safe during leakage.

Recess Box For Tankless Water Heater

In this modern technology era, a tankless water heater fits inside the wall. For that purpose, it needs a recess box. For non-condensing tank-less water heaters, home builders offer recess boxes. Its benefit is to remain inside of the home’s framing and not hanging off the side.


  • 01. Can I use a vent for both the furnace and water heater?

Ans. Well, there is a limited measurement of sharing events. It applies only to standard-efficiency furnaces. 80% or below 80% efficiency furnace can share vent with gas water heater By installing water heater correctly, and you can share furnace (80%) and water heater (20%).

  • 02. How much distance can I vent a tankless water heater? 

Ans. You may put a distance of three inches pipe for venting—no extra clearance for pipes through the wall. You can get a benefit from concentric vents. When a leakage happens in the inner exhaust, the exhaust air will remain within the intake pipe and not spread at home.

  • 03. Can my water heater with a tank be connected to the furnace?

Ans. The water heater has a heat exchanger. It has a connection with a furnace. A boiler or heat pump can also be alternatives to a furnace in relativity with a heat exchanger. Its heat source is fuel. Fuel can be gas or electricity. Water heaters based on gas are old, and electric water heaters are new in the market.

  • 04. Should I vent the water heater horizontally? 

Ans. You can vent the water heater horizontally if you want to. Sometimes vertical lines or chimneys are not fit for your house. You can then use horizontal ventilation, as it is cheaper than a chimney, saving money. It has another extra benefit of venting through the wall and bringing combustion air.


From the above description, we answer Can tankless water heater and furnace share vent? The furnace and water heater both need a vent to exhaust. A pipe and silicon jacket is needed for water heater venting. It is not atmospheric but a powered vent. Better not to share the vent with other appliances.

But with high efficiency, you can share a furnace vent. It gets condensate out. Condensate may eat up standard materials. Using PVC can solve that problem. Getting a plumber is good for you to decide to share the vent or not after inspecting your house.

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