What a Water Heater Costs to Run

Water heating is typically the second-largest energy load in a home, behind heating and cooling and ahead of everything else combined. Yet the water heater sits in a basement or a cupboard and gets no attention until it fails, at which point it is replaced under time pressure with whatever is available.

That is an expensive way to make a decision about something that will run continuously for a decade or more.

What the running cost is made of

Three components, and they respond to different fixes.

The energy to heat water you actually use. Proportional to how much hot water you draw and how far it has to be raised in temperature. Incoming water is colder in winter, so this component is seasonal.

Standby loss. A tank keeps water hot continuously, losing heat to the surrounding space even when nobody draws any. This runs 8,760 hours a year and is the component people overlook.

Distribution loss. Heat lost from pipes between the tank and the tap, plus the water run off while waiting for hot to arrive — which is both energy and water wasted.

The water heater operating cost calculator separates these, which matters because the right intervention depends on which dominates.

Fuel type dominates the comparison

The largest single determinant is what it burns, and the differences are substantial.

Electric resistance is the most expensive per unit of heat in most places. It converts electricity to heat efficiently, but electricity is expensive per unit relative to gas.

Natural gas is usually considerably cheaper to run where available, though a conventional gas tank loses some heat up the flue continuously.

Propane and oil sit higher, tracking their fuel prices.

A heat pump water heater is the outlier worth knowing about. Like a heat pump for space heating, it moves heat rather than creating it, and delivers several times more heat energy than the electricity it consumes. Against electric resistance it typically cuts running cost by around two thirds, which is the largest single saving available in this category.

The caveats are real: it needs adequate air volume around it, it cools and dehumidifies the space it sits in — welcome in a humid basement, unwelcome in a heated utility room — it is slower to recover, and it costs more up front. Where it fits, the payback against resistance is short.

The energy cost calculator is where you convert your own rates into a comparison rather than relying on general claims.

The cheap changes that actually work

In rough order of return.

Lower the thermostat. Many are set well above what is needed. Around 49°C is a common recommendation, balancing energy against the bacterial growth risk of setting it too low — do not go below about 49°C on a stored-water system for that reason. Every degree lower reduces both standby and heating energy.

Insulate the tank, if it is an older model that is warm to the touch. Modern tanks are generally well insulated; older ones are not, and a jacket is cheap. Follow the manufacturer's guidance on gas units, where covering the flue or air inlets is dangerous.

Insulate the first few metres of pipe, particularly the hot outlet. Cheap, quick, and reduces both standby and distribution loss.

Fit low-flow fixtures and aerators. Water heating cost is driven by volume, so reducing flow reduces energy directly. Showers are the dominant draw in most households — the water usage calculator and the household water breakdown cover where it goes.

Fix hot water leaks. A dripping hot tap wastes heated water continuously.

Drain sediment periodically. Sediment insulates the burner from the water in a gas unit and reduces efficiency, as well as shortening tank life.

Use cold for laundry. Modern detergents perform well cold, and heating is most of a wash cycle's energy.

Tankless is not automatically cheaper

Tankless units eliminate standby loss entirely, which sounds decisive and is only part of the picture.

What they save is the standby component. In a household using a lot of hot water, that is a small share of the total, so the proportional saving is modest.

What they cost is considerably more to buy and install — frequently requiring a larger gas line, a different flue, or a substantial electrical service upgrade for electric models.

Where they excel is in low-use households, second homes, and situations where standby loss is a large share of consumption, or where continuous supply and the space saving matter more than the arithmetic.

The honest summary: tankless is a fine product whose energy case is weaker than its marketing, and whose non-energy advantages — endless hot water, compact size, long service life — are often the better reasons to choose it.

Sizing a water heater matters more than efficiency

An undersized unit produces cold showers; an oversized one costs more to buy and loses more standing heat.

The figure to size against is not tank volume but first hour rating — how much hot water the unit can deliver in the busiest hour, which combines stored volume with recovery rate. The first hour rating guide covers estimating your peak hour, and the water heater sizing calculator does the arithmetic.

This is worth working out before the current unit fails, because a replacement bought in an emergency is chosen from what is on the van.

Where the water heater fits overall: it is the second-largest load, so it deserves attention after the building envelope. Air sealing and insulation addresses the largest load, and the energy audit guide covers establishing which of the two dominates in your particular house.