How to Install a Gas Water Heater
The guide details the comprehensive process of selecting, locating, safely ventilating, and installing a gas water heater—emphasizing proper sizing based on household needs, ensuring adequate combustion air and drainage, addressing common installation challenges like sediment buildup and ventilation in confined spaces, and outlining steps for safely removing and replacing existing units to ensure efficient and safe operation.
Installing a gas water heater is a significant task, even for professionals. Due to their relatively high failure rates (every 8 to 12 years), plumbers often perform this job. Below are the major steps involved in installing a gas water heater, along with maintenance tips to extend the tank's life.
Water Heater Selection
Gas-fired water heaters have high output ratings compared to other types. The size of the heater depends on the number of people and bathrooms in a home. Most manufacturers provide sizing tools on their websites. Gas heaters often require smaller tanks, and some models heat water so quickly that they don't use a storage tank at all. This guide focuses on the common tank-type heaters.
Water Heater Location
After selecting an appropriate heater, consider the burner's size, which determines the amount of gas and air needed for proper combustion. Most gas water heaters use room air for combustion. If installed in a mechanical closet, the room must be ventilated. In basements, the space must be large enough to provide combustion air for all appliances.
Guidelines for ventilation and safe location are detailed in the International Plumbing Code and the manufacturer's instructions.
Location Red Flags
When replacing an existing heater, sometimes the installation space has been altered, such as a finished basement with appliances in a small, airtight room. This is unsafe and may require additional ventilation. Water heaters should be located in rooms with a floor drain or another way to drain the heater, which is helpful in case of leaks.
Draining old heaters can be challenging due to sediment buildup, which can clog the drain valve. Experienced plumbers use transfer pumps to quickly drain tanks.
Removing an Existing Water Heater
Before draining, disconnect the unit from its power source.
How to Turn Off the Electricity
Standard vent water heaters use mechanical controls and have no electricity. Power-vented heaters plug into a standard outlet; unplug to de-energize.
How to Turn Off the Gas
There should be a gas shut-off valve within a few feet of the appliance. Quarter-turn valves are common: parallel to the pipe means open, perpendicular means closed. For brass valves, use a small adjustable wrench and turn slowly to avoid breaking the valve.
How to Turn Off the Water
Turn off the valve on the cold water line serving the heater. There should not be a valve on the hot side; if there is, remove it.
How to Drain the Water Heater
With water, gas, and electricity off, drain the heater:
- Run a transfer pump and open the hot side of the kitchen faucet to drain hot water piping.
- Open the furthest, highest fixture to drain remaining water.
- Remove venting system fittings as needed.
Once drained, disconnect the piping. If installed correctly, there will be fittings on the gas and water lines for easy disconnection. Move the heater out of the way, using a cart and a helper if needed.
Installing the New Gas Water Heater
Keep the new unit in the box while moving it. The new heater will be lighter due to the absence of sediment. Follow these steps:
- 1.Set the new heater in place, level it, and use rubber isolation pads if it has no legs. In a garage, reuse the existing stand.
- 2.Align the vent and repipe the water lines. Adjust vent fittings as needed for proper flue gas passage.
- 3.Inspect the vent system for integrity and proper termination.
- 4.Check for soot, rust, or blockages.
- 5.Use flexible connectors for water piping to accommodate height differences and ensure code compliance. Save the gas connection for last.
Pro Tip: If the old unit had a flexible gas connector, consider repiping with black steel fittings to meet code requirements for a shut-off, drip leg, and union.
- 1.Test all gas fittings, then fill the heater with water. Turn off any open faucets. When water runs steadily, the heater is full and ready to fire.
- 2.For power-vented types, plug in, turn on, and light the heater. Bleed air from the gas line if needed.
- 3.Once fired, the heater will take about 45 minutes to reach temperature. Use this time to review the installation checklist.
Pro Tip: Check gas pressure while the unit is running and off. Verify draft through the flue, exercise the relief valve, and perform combustion analysis to ensure a clean burn and no carbon monoxide.
Water Heater Maintenance
Annual maintenance is recommended and typically includes:
- Flushing sediment
- Exercising the relief valve
- Cleaning the vent blower (if present)
- Inspecting the flue
- Checking the thermostat control
Inspect the anode rod using a large ratchet and 1 1/16” socket. Do this while the heater is full to prevent twisting and damage. Replace the anode if it is significantly corroded.
Pro Tip: Do not remove the anode rod, even if you have smelly water. Removing it can cause bigger problems later.
While professionals make the job look easy, improper installation can be dangerous. Consider expanding your knowledge with online plumbing courses to ensure safety and quality.
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