Start here

Quick, low-risk steps

  1. List all hot water activities that may happen at the same time (showers, laundry, dishwasher).
  2. Record your current water heater's model, fuel type, and age from the rating plate.
  3. Check if your home has natural gas, propane, or only electric service.
  4. Note the space where the heater is installed, including ceiling height and nearby walls.
  5. Look for existing vent pipes, drain pans, and expansion tanks near the current unit.

How Tank Water Heaters Work

A tank water heater keeps a reservoir of water hot and ready. When you turn on a tap, hot water leaves the tank and cold water enters to be heated. The fuel source—gas, electric, or heat pump—determines how the water is warmed.

Tank size is measured in gallons. A unit that is too small may run out of hot water during busy times. One that is too large wastes energy keeping extra water hot. A professional can calculate the right size based on your household's peak usage.

  • Stores 20 to 80+ gallons of hot water
  • Heats water continuously to maintain set temperature
  • Available in gas, electric, and heat pump models
  • Recovery rate affects how quickly the tank refills with hot water

Sizing for Your Household

Sizing is not just about the number of bedrooms or bathrooms. The key is the first-hour rating (FHR), which tells you how much hot water the unit can deliver in an hour starting with a full tank. A professional will estimate your peak hour demand by adding up the gallons used by each activity that might run at the same time.

For example, a shower may use 10 gallons, a washing machine 7 gallons, and a dishwasher 6 gallons. If two showers and the dishwasher could run together, you need an FHR of at least 26 gallons. This is a simplified example; a pro will use detailed worksheets and consider your specific fixtures.

  • First-hour rating (FHR) is more important than tank size alone
  • Count simultaneous hot water uses, not just people
  • A professional can perform a detailed peak demand calculation
  • Oversizing wastes energy; undersizing leads to cold showers

Fuel Type and Installation Considerations

Your choice of fuel affects installation cost and complexity. Gas water heaters need proper venting to remove combustion gases. Electric models require a dedicated circuit. Heat pump water heaters need sufficient air volume and may produce cool exhaust air.

Switching fuel types—for example, from gas to electric—may require new wiring, a panel upgrade, or gas line capping. A licensed plumber and possibly an electrician must evaluate your home's infrastructure. Permits are typically required for replacement or new installations.

  • Gas: requires venting and combustion air
  • Electric: needs adequate electrical capacity
  • Heat pump: needs space and may cool the surrounding area
  • Fuel switching often adds significant cost and work

Installation Scope and Professional Questions

Replacing a tank water heater involves more than swapping the unit. The installer must check the condition of pipes, valves, venting, and the drain pan. They should also verify that the expansion tank is present and working if required by local code.

Ask your plumber about the total scope: removal and disposal of the old unit, any needed upgrades to gas lines or electrical circuits, permit fees, and commissioning the new heater. A written quote should list all these items so you can compare bids fairly.

  • Removal and disposal of old water heater
  • Permit and inspection requirements
  • Gas line or electrical circuit evaluation
  • Venting or condensate drainage check
  • Expansion tank and pan drain compliance

Take this with you

Evidence and scope checklist

  • First-hour rating (FHR) needed for your peak demand
  • Fuel type: gas, electric, or heat pump
  • Existing venting condition and compatibility
  • Electrical circuit capacity for electric or heat pump models
  • Space dimensions and air volume for heat pump units
  • Expansion tank requirement per local code
  • Drain pan and discharge piping
  • Permit costs and inspection scheduling
  • Old unit removal and disposal
  • Warranty terms for tank and labor
Open the interactive private worksheet →

Common questions

What homeowners ask next

What size tank water heater do I need?

Size depends on your household's peak hour demand, not just the number of people. A professional can calculate the first-hour rating you need by adding up simultaneous hot water uses. Tank size alone is not a reliable guide.

Can I switch from a gas to an electric water heater?

Switching fuel types is possible but may require electrical upgrades, gas line capping, and new venting considerations. A licensed plumber and electrician should evaluate your home's infrastructure and local code requirements.

Do I need a permit to replace my water heater?

Most jurisdictions require a permit for water heater replacement. The installer typically pulls the permit and schedules an inspection. Check with your local building department for specific rules in your area.

Evidence

Sources used for this guide

Research checked July 31, 2026

Optional next step

Need an on-site professional?

Use the guide and worksheet first so you can describe the situation and compare the full scope. A referral is optional; you can also contact a licensed local provider directly.

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We have not enabled a provider route for this site. Use the checklist to contact and verify local providers yourself; urgent hazards should go to the appropriate emergency or public service.