Water heater replacement cost

The capacity on the label is how much water the tank holds. It is not how much hot water you get, and the difference runs in both directions.

Downwards, because you never empty a tank cleanly: cold water enters at the bottom as hot leaves the top, and the last portion of a draw is lukewarm. Upwards, because the burner or element is working the whole time you are drawing, so the tank is refilling with hot water as you use it.

The figure that captures both is the first hour rating: how much hot water the unit can deliver in one hour starting from full. That is what should size a tank, and it is why two tanks of the same capacity are not equivalent.

If you read one section on this page, make it this one. It explains almost every disappointing tankless installation in the country.

A tankless water heater does not have a flow rate. It has a flow rate at a temperature rise. The burner can put a fixed number of BTUs per hour into the water; how many gallons a minute that heats depends entirely on how far it has to raise them.

Incoming water in Miami arrives at about 75°F. In the far north it can be 38°F in February. Reaching 120°F is a 45°F rise in the first case and 82°F in the second — nearly double the work for the same gallon.

The box advertises the flow at a small rise, because that is the flattering number. A unit sold as “8 GPM” might deliver that at a 35°F rise and barely half of it at 75°F. Nothing is wrong with the unit; the specification was read in the wrong climate.

This is also why the complaint is seasonal. A tankless installed in September works beautifully, and in January the shower goes cold when someone runs the kitchen tap. Nothing has broken. The groundwater dropped fifteen degrees.

This is the decision behind most of the searching people do about water heaters, and it is not one-sided in either direction.

The honest summary: tankless wins on lifespan and on never running out, and it wins clearly where gas is cheap and the install is straightforward. It loses where the extras are expensive, where the climate makes the rise severe, or where the household simply never exhausts a tank.

The failure mode is worth a thought too. A tank that fails usually fails by leaking forty gallons onto the floor; a tankless unit stops making hot water. If the heater lives above finished space, that difference is worth real money.

A heat pump water heater is a storage tank with a small heat pump on top. Instead of making heat, it moves it: it takes warmth out of the air in the room and puts it into the water. That is why its efficiency figure is above 3 when everything that burns fuel is below 1.

In running cost it is not a marginal improvement, it is a different category — roughly a third of what a resistance electric tank costs to run, and often less than gas depending on local prices. Over the fifteen-year comparison in the table above, that gap frequently exceeds the entire purchase price of the unit.

Federal and utility incentives for these units change often enough that quoting an amount here would be wrong within months. Check what is current before buying — the sums in the table above are before any of it.

The gap between a water heater’s price and its installed cost is bigger than almost any other appliance in a house, and with tankless it is bigger still. These are the lines that do it.

The gas line is the one that catches most people converting to tankless. A storage heater burns perhaps 40,000 BTU/h; a tankless unit can want 199,000. The half-inch line that fed the old one will not carry that, and the new run has to go back to wherever the pipe is big enough — which might be the meter.

For electric tankless, the equivalent is the panel. A whole-house unit can want more current than an older house’s entire service, and the upgrade is frequently the single largest line on the quote.

Most water heaters are bought in a hurry, standing in a wet basement, from whoever can come today. That is the most expensive way to buy one, and it is avoidable.

A planned replacement is a scheduled job at a normal rate, with time to compare options, check whether a heat pump unit fits, and get more than one quote. An emergency replacement is an out-of-hours call-out, a like-for-like swap because it is what is on the van, and frequently some water damage on top.

Sizing follows the federal energy guidance: peak-hour demand against first hour rating for tanks, and flow at temperature rise for tankless. Incoming water temperatures are a survey by climate zone, using the seasonal low — because a tankless unit that works in August and fails in January was sized against the wrong month. Running cost is computed from daily use, the rise and the unit’s efficiency, at national average energy prices of $1.35 a therm and $0.17 a kilowatt hour. Everything is on the sources page, dated.

One assumption worth stating, because it moves the tank size directly. The peak hour is built from how long each fixture actually runs — ten minutes for a shower, five for a kitchen sink — rather than assuming everything runs flat out for an hour, which is how rule-of-thumb sizing talks people into a tank a size too big. Showers also carry a minimum tied to household size: in a house of four, at least two people shower in the same hour whether or not you ticked two.

Your own energy prices are the biggest variable in the comparison table, and they vary by more than a factor of two across the country. If yours are far from the national average, the ranking can change — which is worth knowing before treating the table as settled.

Nothing you type is sent anywhere — the whole calculation runs in your browser.

First hour rating and temperature rise are the two that decide whether you get the hot water you were expecting. The rest is vocabulary.