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Water Heaters · InstallDirect Vent Water Heater Installation
Direct vent water heater installation puts a sealed-combustion gas tank against an outside wall and vents it through a coaxial pipe: exhaust leaves through the inner pipe and combustion air arrives through the outer one, with no fan and no electrical supply. It is the gas tank to choose when the house has no usable chimney and you want hot water to continue through a power outage. The catch is distance: the vent kit is short, so the tank has to stand near the wall it vents through.
A direct vent tank is sealed from the room. The burner sits behind a gasketed door, draws outdoor air down the outer pipe and sends flue gas out the inner pipe by natural buoyancy, so no air from the mechanical room is used for combustion. That removes two classic problems of a chimney-vented tank: back-drafting when a range hood, dryer or bath fan pulls the house negative, and a furnace room too tight to supply combustion air. On the standard models the pilot flame powers the gas valve, so there is no cord to plug in.
It suits three kinds of house. One is where the furnace was upgraded to a sidewall-vented high-efficiency unit and the old masonry chimney is now oversized for the water heater alone. Another has no chimney at all, such as an electrically heated townhouse or bungalow that later got gas. The third has a small closed mechanical room in a finished basement, where a chimney-vented tank cannot get enough air.
The vent is the constraint. Each model is certified with its own coaxial vent kit, and the allowed length is short compared with a fan-driven power vent: usually a straight run through the wall or rim joist directly behind or beside the tank, with extension kits for a little more. With no fan, the vent cannot be run across a basement. If the tank must sit in the middle of the house, a power vent water heater is the right product, and the trade-offs are laid out in power vent vs direct vent.
Outside, the termination has to meet CSA B149.1 and the manufacturer's instructions, whichever is stricter. For a residential tank the code keeps the terminal at least 30 cm above grade, 30 cm from a window or door that opens, 0.9 m from the gas meter's regulator vent and 1.8 m from a mechanical air intake. We also set it above the usual snow line on that wall, since a buried terminal shuts the burner down. The wall is measured before the tank is ordered, because the clearances can rule out a location.
A direct vent tank is the right choice when
- There is no chimney, or the chimney is unlined and too large for a water heater on its own
- The existing tank spills flue gas at the draft hood when exhaust fans run (signs of a back-drafting water heater)
- The mechanical room is small, closed off or shared with a dryer
- You want hot water during a power outage without a generator
- The tank location is on or beside an exterior wall with a clear spot outside for the terminal
How it works
Inside, we measure from the tank position to the exterior wall and check the gas line size. Outside, we check the terminal position against windows, doors, the gas meter, air intakes and grade. If the wall fails, you hear that before any tank is ordered.
The old tank is drained and removed and the new one set in place. The coaxial vent kit is assembled through the wall and sealed inside and out, the gas connection is made and leak-tested, and the water lines and relief-valve discharge pipe are connected.
The pilot is lit, the burner flame and gas pressure are checked, and the joints are tested again hot. We confirm the house has working carbon monoxide alarms, show you how to relight the pilot and take the old tank away. Start with a free written quote.
Common questions
Will a direct vent water heater work in a power outage?
Yes, on the standard models. The pilot flame generates the small voltage that holds the gas valve open, and exhaust leaves by natural draft, so nothing depends on household power. A power vent tank, a tankless unit and an electric tank all stop in an outage. If that matters to you, confirm the quoted model has a standing pilot and no fan, because some sealed-combustion tanks with a blower need an outlet.
How far from the outside wall can the tank be?
Not far. The maximum vent length is set by the manufacturer's certified kit for that model, with limited allowance for elbows and extensions, so the tank normally stands against or beside the exterior wall. We check the model's installation manual against your layout before quoting. If the run is too long for any direct vent model, a fan-assisted tank is the alternative.
Can a direct vent tank replace my chimney-vented water heater?
Yes, provided the tank can stand at an outside wall with a legal spot for the terminal. It is a common answer when a new high-efficiency furnace has left the water heater alone on an oversized chimney. The other answers are a chimney liner sized to the water heater, or a power vent tank. The old chimney connection is capped when the tank changes.
Who is allowed to install a direct vent water heater in Ontario?
The gas connection and venting must be done by a TSSA-licensed gas technician working for a registered contractor, to CSA B149.1. Whether your municipality also wants a permit when a new wall opening is cut varies, and we check with the building department. Ontario requires working carbon monoxide alarms in any home with a fuel-burning appliance. Other tank types are on our water heater services page.
What are the drawbacks of a direct vent tank?
Three. The tank has to live at an exterior wall. The coaxial vent needs a larger opening than the plastic pipe of a power vent, and its terminal gets hot, so it cannot sit where people brush past. And the choice of sizes is narrower, mostly 40 and 50 gallons. Against that, there is no fan to fail and no fan noise.