Gas Water Heater Installation

Is it hard to install a gas hot water heater?

The plumbing half isn't. The gas and vent half is where skill matters. A.O. Smith strongly recommends a professional installer for its gas tanks, citing venting, the fuel line and removing the old unit. Most areas require a permit, and A.O. Smith's manual says to follow local and state codes, or NFPA 54 (the National Fuel Gas Code) where none exist, and to have a code official inspect the work. Check with your local building department before you start.

Location and combustion air

A.O. Smith's gas tank manual sets out the basics:

• Indoors, upright, in a spot that won't freeze, with at least 24 inches of clearance in front.
• Not in a bathroom, bedroom or a normally closed occupied room.
• No gasoline or other flammable liquids or vapors stored nearby.
• In a garage, a vehicle stop so a car can't hit it.

Combustion air is the part people skip. The manual calls for 50 cubic feet of room volume per 1,000 BTU per hour of total input from every gas appliance in the space. A small closet with a furnace and a water heater often fails that test, and then the manual calls for two permanent outside air openings.

Venting: atmospheric, power vent and direct vent

An atmospheric vent relies on hot exhaust rising up a vent pipe. A.O. Smith's manual recommends at least 12 inches of vertical pipe off the draft hood before any elbow, and requires an upward slope of at least 1/4 inch per foot on horizontal runs. Single-wall pipe needs 6 inches of clearance from combustibles. After installation, the manual has you pass a newly extinguished match near the draft hood opening after 5 minutes of burner operation and confirm the smoke is steadily drawn in. If it drifts or blows away, the vent isn't drafting, and that's a carbon monoxide problem.

A power vent water heater uses a fan to push exhaust out, usually sideways through a wall, which frees you from needing a chimney. The fan needs electricity, and Fixr says adding a power vent and its electrical connection can add $300 to $1,000 to the job. HomeGuide puts power vent models at $350 to $500 more than direct vent models. Propane and natural gas power vent models work the same way; the gas valve and orifices are set for one fuel or the other.

Don't connect a power-vented appliance into a shared atmospheric vent. A.O. Smith's manual prohibits common venting with a power-vented appliance.

Tools and parts

• Pipe wrenches, adjustable wrenches, tubing cutter
• Gas-rated pipe dope or yellow gas tape
• A manual gas shutoff valve, a sediment trap and a ground joint union
• Vent connector pipe and fittings matching the heater's flue
• Copper or CPVC for the T&P discharge
• Drain pan, expansion tank if needed, water connectors
• Soapy water in a spray bottle for leak checks

How a gas water heater install goes

Mistakes to avoid

• Skipping the sediment trap. Debris and moisture in the gas line end up in the gas control valve.
• A flat or downhill vent connector. Exhaust stalls, spills at the draft hood and comes back into the room.
• Lighting a half-empty tank. The manual says to fill it completely first.
• Running the relief line into the drain pan.
• Testing for leaks with a flame. Use soapy water or a gas leak detector.

Cost and when you need extra work

Fixr's installed range for a natural gas tank is $700 to $2,700. Adders show up fast: HomeGuide lists a gas line upgrade at $350 to $2,000, first-time venting at $500 to $1,500, and replacing existing venting at $100 to $600. A permit typically runs $50 to $200. Going from electric to gas costs $400 to $2,000 or more. For the full breakdown, see water heater installation cost.