Tankless vs tank water heater

A tank water heater stores hot water in a cylinder; a tankless unit heats water as it flows. The tankless unit is more efficient on paper, but the installed cost is higher and the saving depends on how much hot water you use and what you pay for fuel. The payback is the number that decides the comparison.

How the two work

A tank heater keeps a cylinder of water hot around the clock, which means it loses heat through the tank walls even when no one is using water. That standby loss is why its efficiency is lower, and it is also why it can deliver hot water immediately at several fixtures at once.

A tankless heater fires only when a tap is opened, so it avoids standby loss. Its output is limited by its capacity, measured in flow rate and temperature rise, and it may not serve several showers at once in a cold climate. A gas tankless unit needs a larger gas line and a stainless steel vent, which are significant installation costs.

An electric tankless unit avoids the venting but requires a large electrical circuit, often more than a typical home has available. That electrical work can add substantially to the installed price and is frequently the reason the payback never arrives.

Source: Freddie Mac Primary Mortgage Market Survey, as published at freddiemac.com/pmms. National averages for conforming loans; your rate depends on credit, points, loan size and property.

Installed cost and the rate context

A tank replacement is one of the cheaper plumbing jobs because it reuses the existing connections. A tankless installation is more involved: it needs a new unit, often a new gas line or electrical circuit, a vent, and sometimes a water softener to protect the heat exchanger from scale.

If the work is financed, a secured home equity product is usually cheaper per dollar than an unsecured loan. Freddie Mac publishes the national average mortgage rates that secured products are priced against, and the table below is that survey.

Ask for the installed price, not the unit price. A tankless unit advertised at a low price frequently requires several hundred dollars of additional work, and the installed total is what matters.

Running cost and payback

The running-cost advantage of a tankless unit comes from eliminating standby loss, which is a larger share of use in a small household and a smaller share in a large one. A household that uses a lot of hot water will save more in absolute terms, but the standby loss is also a smaller fraction of its consumption.

The payback is the installed premium divided by the annual saving. If the premium is large because of venting or electrical work, the payback can exceed the life of the unit, which is the honest reason many installers still recommend a tank. Ask for the calculation in writing with your fuel prices.

A tank unit is also cheaper to repair and easier to replace, and its lifespan is shorter. Those costs belong in the comparison. A tankless unit with a longer life may still be the better long-run choice even when the payback is long, but the decision should be made with the numbers rather than the marketing.

Capacity and comfort

Capacity is the tankless trade-off. A tank unit can serve several fixtures at once because it has a reservoir; a tankless unit's output is limited by its burner or element. Ask the installer to size the unit against your peak demand, including the number of showers and the incoming water temperature.

A cold climate lowers the incoming water temperature, which requires a larger temperature rise and therefore a larger unit. That is why a model that performs well in a warm region may be undersized in a cold one. The sizing calculation should use your winter groundwater temperature.

Ask whether the installer will add a recirculation system for instant hot water at distant fixtures. It improves convenience and increases energy use, so it is a trade rather than a free upgrade.

Financing the installation

The example below uses the Federal Reserve H.15 bank prime loan rate and a standard amortising schedule. It is arithmetic from a published rate, not a quote, and it shows what financing adds to the installed premium.

Worked example, with the assumption stated: $4,500 borrowed at the Federal Reserve H.15 bank prime loan rate of 6.75% (published 2026-09-16) repaid over 36 months on a standard amortising schedule. That gives a monthly payment of $138.43, total interest of $483.59 and a total repayment of $4,983.59. This is arithmetic from a published rate, not a quote: a real APR includes fees and is set by the lender from your credit, so your figures will differ. If the annual fuel saving is small, the interest on the premium can exceed the saving for years. Run the payback with your own fuel prices before financing.

If the installer offers a plan, ask for the total of payments and compare it with a personal loan over the same term. The cheapest route is usually cash, then an interest-free plan, then a loan.

Maintenance and lifespan

A tank heater needs the anode rod checked and the tank flushed to remove sediment, and it eventually rusts through. A tankless unit needs descaling where the water is hard, which is the single most important maintenance item and the one most often skipped. Scale is the leading cause of tankless failure in hard-water areas.

Ask the installer what maintenance the specific unit requires and how often, and whether a water softener is recommended. In a hard-water area the softener is sometimes the difference between a long-lived heat exchanger and an early failure.

Ask for the warranty on the heat exchanger separately from the rest of the unit, because the two often carry different terms. The heat exchanger is the expensive component, and its warranty is the one that matters.

Where these figures come from

Related pages

• Water heater costs by state and province
• How to pay for a water heater
• Plumbing costs
• Loan payment calculator

Frequently asked questions