Tired of running out of hot water? That’s not a problem with one of these compact, ultra-efficient units that heat water as you need it.

Here are two things to consider before buying one:

Cost and Installation.

Prices range from about $170 for small gas-fired units to more than $2,000 for high-output heaters that can supply two showers at the same time; $1,000 is about average.

This is definitely a job for a pro, as it involves making leak-free water, vent, and gas connections, in the case of gas or propane units, or upgrading the wiring and circuit-breaker panel, in the case of electric units.

So if you find the right price point and you’re not worried about installation, keep in mind the maintenance.

Gas-burning tankless water heaters should operate for 20 years or more, two or three times longer than tank-type heaters. Tankless electric units have shorter life spans, on the order of 7 to 10 years.

Ultimately, make the decision that’s best for you and your home when considering a tankless water heater.