Can a furnace and water heater share a PVC vent?

Author: Allan Homenick  |  Last update: Tuesday, June 2, 2026

If both the water heater and furnace are natural gas, then yes, they can be vented together.

Can a furnace and water heater share the same vent?

Can A Furnace And Hot Water Heater Really Share A Vent? In short, yes. However, there are certain factors that allow a furnace and hot water heater to share a vent – this is very important to know. Firstly, the type of furnace and hot water heater play a big role in whether these two systems can share a vent.

How far should a water heater be from a furnace?

You need at least 24" in front of the furnace and water heater as well as 24" to the left of the furnace. The other side of the furnace and water heater leave at least 12". You will need to run that air intake pipe to the outdoors.

How close can PVC be to a water heater?

Hot and cold should be piped in metallic piping, copper in most cases, at least 18” from the unit before transitioning to the existing piping. Also, plastic piping should not be within 6” of the vent.

Can two gas appliances share a vent?

Multiple gas or oil furnaces or boilers, as well as hot water heaters, can be vented into one flue.

Understanding Improvements to PVC Gas Ventilation | Ask This Old House

How many fixtures can share a vent pipe?

A horizontal wet vent could have as few as two fixtures or as many as ten fixtures but not more than two fixtures of any type can be connected to the system.

Can a gas furnace be vented out the side of the house?

If your furnace has an AFUE rating of 90 percent or above, it will have a flue pipe that goes out of the side of your house.

Can I use PVC for a water heater vent?

Similar to the power vent design, a power direct vent water heater can utilize PVC piping to reduce installation costs. It is important to note that they also require an electrical outlet near the water heater for installation.

Why is CPVC not used anymore?

Fragility and Brittleness. ASTM F441 CPVC pipes can become brittle over time, particularly under stress or extreme temperatures. This brittleness makes them more prone to cracking and failure. In colder climates, this issue is exacerbated as pipes can freeze and break easily.

How much heat can PVC withstand?

PVC can handle temperatures up to 140°F (60°C). CPVC handles temperatures up to 210°F (99°C). PVC and CPVC thermoplastics are highly resistant to acids, alkalis, alcohols and many other corrosive materials. Both materials are ideal for process piping installation and most service piping applications.

Can a water heater and furnace be next to each other?

Technically, it's possible, especially with electric water heaters and some types of furnaces. However, this isn't always recommended. Both appliances draw a significant amount of power. If they're on the same circuit and operate simultaneously, it could overload the circuit.

What are the venting requirements for a gas hot water heater?

VENTING REQUIREMENTS

50 cubic feet of combustion air must be provide for each 1,000 Btu input of the water heater. Single wall metal venting must have 6” clearance to combustible materials. Double wall B-vent material must have 1” clearance to combustible materials.

What is the clearance code for a furnace?

Furnaces and air handlers within compartments or alcoves shall have a minimum working space clearance of 3 inches (76 mm) along the sides, back and top with a total width of the enclosing space being at least 12 inches (305 mm) wider than the furnace or air handler.

What is the minimum distance between a furnace and a water heater?

Clause 4.14. 2 says an appliance needs 24" clearance where service could be necessary.

Can the water heater and HVAC be in the same room?

Here are some rooms where these appliances may be housed together: Utility Room: Utility rooms are often designed to accommodate HVAC equipment and water heaters. These rooms are typically well-ventilated and have the necessary clearances to ensure safe operation.

Why is my furnace exhaust pipe so hot?

Over time, dust, dirt, pet hair, and other debris accumulate in and around your furnace vents and ducts. This makes your furnace work harder to push warm air throughout your home and can result in overheating.

Why is CPVC bad for plumbing?

A larger issue with CPVC is that it is not chemically resistant to all chemicals; this leads to drain and drainage system failures.

Is it worth replacing CPVC with PEX?

PEX (cross-linked polyethylene) pipes are often preferred over CPVC (chlorinated polyvinyl chloride) for several reasons: Flexibility: PEX tubing is flexible and can be bent and curved without the need for fittings, making it easier and faster to install in tight spaces.

What happens if you use PVC instead of CPVC?

PVC is only intended for cold water and has a maximum service temperature of 140° F for pressure applications. Not only can CPVC handle higher temperatures than PVC, but its increased temperature resistance enables it to perform better within PVC's working range.

Can a furnace and water heater share a vent?

Yes. Our home was originally equipped with both an oil burning furnace and water heater, each having a separate 4″ flue connected to a common, 8″ stack that vented through the roof. There was never any problem with this arrangement over 40 years of operation.

Can I use PVC to vent my furnace?

High-efficiency furnaces use PVC pipes to vent the exhaust gases out of the home, and manufacturers are very specific about how the installation should be done. As a home inspector, how far should I go to make sure the vent is properly installed?

Why not use PVC for HVAC?

PVC duct cannot withstand the transportation of pressurized liquids and is not suitable for plumbing projects. In addition, the heat limitations of PVC duct, which can withstand temperatures up to 140°, may not be best suited for HVAC systems that are likely to transport extremely hot air on a frequent basis.

What are the rules for venting a furnace?

The combustion air, which brings air into the furnace should point down and the exhaust should snorkel up and then elbow out. Keeping in mind the combustion pipe and exhaust pipe should be 12” vertically apart and they should be above anticipated snow levels.

Can I run a plumbing vent out the side of my house?

The good news is that your plumbing vent can indeed be run horizontally. When figuring out how to lay the pipes within your walls, it's more important to remember the clearance that is required by your spill line (the point where water overflows a tub, sink, or toilet).

Why can't you use b vent horizontally?

No. Per the sizing tables, all orientations must terminate vertically with a UL listed rain cap, otherwise the appliance may not vent properly.

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