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Hot Water · Gas InstallGas Water Heater Installation
Gas water heater installation is decided by the vent the house can take. A tank on a lined chimney is atmospheric, a tank with a fan and plastic pipe out the side wall is power vent, and a sealed tank on an outside wall is direct vent. A like-for-like install runs $1,200–$2,500, takes 2–4 hours, and is done by a TSSA-licensed gas technician to CSA B149.1.
The three vent classes are not interchangeable, and the house picks for you more often than the brochure does. An atmospheric tank needs a chimney with a liner sized to it and uses no electricity, so it keeps making hot water in a power failure. A power-vent tank pushes its exhaust through certified plastic pipe to a side wall, which frees it from the chimney but ties it to a 120-volt outlet. A direct-vent tank is sealed: it pulls combustion air in and sends exhaust out through the wall behind it, needs no power, and has to sit on or near an outside wall.
Housing era usually settles it. 1950s–60s bungalows and 1970s–90s subdivisions were built with the tank and furnace sharing one chimney; once the furnace was replaced with a condensing unit vented in plastic, the water heater was left alone on a flue too large for it. That tank needs a chimney liner or a change of vent class, and we check the flue before pricing anything. Most 2000s+ houses were built with a fan-assisted tank venting out the rim joist, and power vent water heaters have a page of their own.
What a licensed install includes is set by the gas code, CSA B149.1, and none of it is optional. The gas line gets its own shut-off valve within reach of the tank and a sediment trap, a short capped drop leg that catches pipe scale before it reaches the gas control. The vent is sized from the code tables for the tank's input, around 40,000 BTU an hour on a 40 or 50 gallon tank, and the mechanical room is checked for enough combustion air. The relief valve gets a full-size discharge pipe run down toward the floor with no valve or cap on it.
If the tank being removed is a rental, it belongs to the rental company and has to go back to them. The account holder calls first for the removal terms and a return authorization number, we drain and disconnect the tank, and it is returned the way the contract says, with a receipt. The buyout arithmetic is its own subject on our rental buyout page. Owning usually wins: $25–$45 a month in rent comes to $4,500–$8,000 over 15 years.
What decides which gas tank goes in
- A masonry chimney or B-vent with a sound liner: an atmospheric tank is the simplest fit and needs no outlet
- No usable chimney, or a furnace that already vents in plastic: power vent, provided there is an outlet and a side wall the pipe can reach
- A tank on an outside wall in a tight or finished basement: direct vent, which takes its air from outdoors
- Household size as a starting point: 40 US gallons for two or three people, 50 for four, 60 for five or a soaker tub
- Clearances: the new tank's height and diameter against the vent connection, the stairs and the mechanical room door
How it works
We read the old tank's rating plate, inspect the chimney or vent run, measure the gas line and check for an outlet and a floor drain. The written quote names the vent class and the tank size.
Gas off, water off, tank drained and carried out. The new tank is set level, piped with a shut-off and sediment trap, vented to the code tables and filled before the burner is lit.
Every gas joint is leak-tested, the burner is fired, and the draft is checked at the hood with the exhaust fans and dryer running. The relief valve and temperature setting are confirmed, and a rental tank goes back with its paperwork. To start, book a free quote.
Brands: We install gas tanks from Rheem, Bradford White, A.O. Smith and John Wood, and service them afterward.
Common questions
Can I switch from atmospheric to power vent, or the other way?
Yes, but it is a venting job as well as a tank swap. Going to power vent means a new plastic vent run to a side wall, a termination with the required clearances from windows, the gas meter and grade, and an outlet beside the tank. Going back to atmospheric only works with a chimney and a liner sized for the tank.
Do I need a permit to replace a gas water heater?
The gas connection must be made by a TSSA-licensed technician working for a registered contractor anywhere in Ontario. Whether your municipality also wants a building or plumbing permit depends on what changes: a like-for-like swap is treated differently from new venting or relocated piping. Permits for water heater replacement in Ontario sets out the cases.
What is a sediment trap and why does the code want one?
It is a tee with a short capped nipple pointing down, installed in the gas line just ahead of the tank's gas control. Pipe scale, thread cuttings and moisture drop into the nipple instead of travelling into the control, where they would hold a valve seat open or block the pilot orifice. A flexible connector by itself is not a sediment trap.
Will a gas water heater still work in a power outage?
An atmospheric tank with a standing pilot and most direct-vent tanks use no household electricity, so they keep heating when the hydro is out. A power-vent tank will not fire without its blower. For houses on rural lines that lose power in ice storms, that difference is worth weighing against the convenience of sidewall venting.
Can you install a gas tank where there is an electric one now?
If a gas main serves the street and a line can be run to the mechanical room, yes, though it is a larger job than a swap: gas piping, a vent route and combustion air all have to be created from nothing. On rural lots beyond the gas mains, a propane model or a better electric tank is the realistic choice.