A water heater bid can be one line (“replace 50-gallon gas, $X”) or two pages. The one-line bid is hard to compare and easy to pad later. This guide covers what to decide before you call, what Washington’s code requires, and what a good quote lists.
Consumers’ Checkbook, which surveys Puget Sound plumbers, found that “prices varied dramatically for the same work”. Getting three bids for an installation such as a water heater saved about $300 on average compared with taking one (updated November 2024). Get at least three, in writing.
Tank, tankless or heat pump
- Tank (storage), gas or electric. This is the like-for-like swap most people get. It is usually the simplest job, because the venting, gas line or circuit is already there.
- Tankless (on-demand), usually gas. It heats water as it flows, so it is sized by flow rate, not gallons. The Pacific Northwest National Laboratory’s (PNNL) Building America guide warns that in an existing home, “the available size and pressure of the natural gas lines” may decide whether a unit can be installed. It says most gas tankless units need at least a ¾-inch line, where ½-inch is typically enough for a tank. It strongly recommends sealed-combustion units. In hard-water areas, it says many makers recommend yearly professional cleaning of the heat exchanger, and that flush valves should go in at installation.
- Heat pump (hybrid) water heater. It moves heat from the surrounding air into the tank. It needs space and air, a condensate drain, and the right circuit. ENERGY STAR’s installer guide says most 240-volt models need at least 700 cubic feet of air space, some as little as 450, and some 120-volt models built to replace gas units need more than 700. See heat pump water heater rebates in Washington for the full checklist and current utility rebates.
Sizing
- Tanks are sized by first-hour rating: the gallons of hot water the heater can supply in an hour starting full. DOE says to pick a model whose first-hour rating at least matches your household’s peak-hour demand. The rating is on the yellow EnergyGuide label.
- Tankless units are sized by the largest flow you use at one time (for example, a shower plus the dishwasher) at the temperature rise you need. PNNL’s guide gives Seattle’s average groundwater temperature as about 52°F, so a tankless unit here has to raise incoming water a long way in winter. It also notes that some low-flow uses like hand washing need under 0.5 gallons per minute, which not every tankless unit can deliver.
- Heat pump units switching from gas need upsizing. ENERGY STAR says to size up for a gas-to-heat-pump conversion because of slower recovery, and that a 120-volt unit typically needs to go up two sizes, for example from a 40-gallon gas tank to a 65-gallon heat pump unit.
Ask each bidder what size they are quoting and why. If two bids quote different sizes, you are not comparing the same job.
What Washington’s code requires
Plumbing permits and inspections are run by your city or county, not the state. Rules vary, so check locally. The items below come from the state code and from city and county guidance.
- Permit. Des Moines quotes UPC 502.1: it is unlawful to install, remove or replace a water heater “without first obtaining a permit”. Kirkland requires a mechanical permit for a gas unit and a plumbing permit for an electric one. Switching from gas to electric adds an electrical permit, plus a mechanical permit if the old gas line is capped or removed. Kirkland wants the inspection scheduled within 48 hours of installation, by the contractor if one did the work.
- Seismic strapping. Washington amends UPC 507.2: water heaters “shall be anchored or strapped to resist horizontal displacement due to earthquake motion”, with straps in the upper third and lower third and at least 4 inches between the lower strap and the controls. King County specifies two 20-gauge sheet metal straps. Des Moines says perforated iron strap (plumber’s tape) is not acceptable.
- Expansion tank. King County says that on a closed system, where water can come in but not flow back out, “an expansion tank or other approved thermal expansion device must be installed”. Des Moines cites UPC 608.3 for the same rule.
- Relief valve discharge. Under the state code’s section 608.5, the temperature and pressure (T&P) relief pipe must be full size with no valves, must not be trapped or exposed to freezing, must end 6 inches to 2 feet above the floor or ground pointing down, must not be threaded at the end, and must not discharge into a water heater pan. There is an exception for a replacement heater where no drain existed before.
- Garages and gas. King County requires a fixed barrier, such as a metal post, between a garage water heater and where a car parks, and a separate gas piping permit if any gas piping is installed or changed. Kirkland reminds installers to keep or reconnect the bonding wires.
Who can do the work. L&I lists water heaters as plumbing-trade work, which needs a state plumber certificate. Check the company’s contractor registration and the installer’s certificate with L&I’s Verify tool. L&I says that when you hire a contractor, the contractor normally takes out the permit, and being asked to get it yourself is a warning sign.
What it costs (indicative only)
Our research found no citable Washington price survey for tank or tankless replacement, so we don’t publish a number for those. For heat pump water heaters, ENERGY STAR (February 2, 2024, national) gives $1,500 to $3,000 for the unit and $1,000 to $3,000 more for labor and materials, before incentives. Treat these as rough national figures, not a quote.
What a quote should itemize
A good bid names each of these, or says it isn’t needed:
- Brand, model number and type (tank, tankless or heat pump).
- Capacity in gallons and first-hour rating, or flow rate for tankless.
- Removal and haul-away of the old heater.
- Seismic straps, expansion tank, relief valve discharge piping and drain pan.
- Water connections, shutoff valve and any repiping.
- Gas: venting, gas line resizing and the gas piping permit, if needed.
- Electrical: new circuit, breaker or panel work, and who does it.
- Heat pump: condensate drain or pump, ducting if used, and the circuit (120 V or 240 V).
- Permit fees and who schedules the inspection.
- Any utility rebate or instant discount, and whether it is already deducted.
- Washington sales tax. WAC 458-20-170 says contractors collect retail sales tax on the full contract price for consumers.
- The manufacturer’s warranty and the installer’s labor warranty, in writing.
For residential jobs of $1,000 or more, RCW 18.27.114 requires the contractor to give you a disclosure statement about lien rights before work starts.
Warranties: parts vs labor
The manufacturer’s warranty and the installer’s warranty are separate. Rheem’s ProTerra heat pump product page, for example, lists a “10-Year limited warranty for tank and parts, 1-year full in-home labor warranty”. After the labor period, you pay someone to diagnose the fault and swap the part, even if the part is free. Ask:
- How long is the tank warranty, and how long are parts and labor covered by the manufacturer?
- Does the installer warranty its own work, and for how long?
- Who registers the unit and who files a claim?
Red flags
- “You don’t need a permit for a swap”, or a request that you pull the permit.
- No model number on the quote.
- A tankless quote that doesn’t address gas line size or venting.
- Plumber’s tape used as a seismic strap.
- A relief valve pipe piped into the drain pan, capped, or fitted with a valve.
- A rebate promised that isn’t on the utility’s own website, or a heat pump model the bidder can’t confirm is on the qualified list.
- A bid with no contractor registration number. L&I tells homeowners to look for the number on the written bid and check it with Verify.
Questions to ask each bidder
- What size and model are you quoting, and how did you size it?
- Is my system closed, and does it need an expansion tank?
- Who pulls the permit, and who schedules the inspection?
- For tankless: is my gas line big enough, and where will it vent?
- For a heat pump: is there enough air space, where will the condensate go, and does it need a new circuit?
- What is in the warranty from the maker, and what labor do you cover?
- Is any rebate already taken off this price?
Find licensed installers in our water heater directory, or see how plumbers price their work before you compare quotes.