Tankless Water Heaters
Updated February 20, 2026
Energy-efficient units that heat water on demand without storing it in a tank. Perfect for homes with limited space.
Overview
Tankless water heaters heat water on demand as it flows through the unit -- no storage tank. Turn on a hot water faucet and the heater fires instantly. Endless hot water as long as you are within the unit flow capacity. Gas-fired models (most powerful) handle whole-house demand. Electric models work for point-of-use (single fixture) applications. Energy savings of 20-35%% vs tank heaters because there is no standby heat loss. The tradeoff: higher upfront cost, potential for cold-water sandwich (brief cold burst between draws), and flow rate limitations during simultaneous multi-fixture use.
Key Features
- Heats water on demand -- no tank, no standby heat loss
- Endless hot water supply (within flow rate capacity)
- Compact wall-mount design saves floor space
- Gas models: 8-11 GPM flow rate, handles whole-house demand
- Electric models: 2-5 GPM, best for single fixtures or small apartments
Sizing & Selection
Size by flow rate (GPM) and temperature rise. Calculate: add up the GPM of all fixtures that may run simultaneously. Then calculate the temperature rise needed (desired output temp minus incoming groundwater temp). In cold climates (40 degree F inlet water), you need more heating capacity than warm climates (70 degree F inlet). Gas: 8-11 GPM handles most homes. Electric whole-house: 4-8 GPM, may struggle with simultaneous fixtures in cold climates.
Installation
Gas tankless: requires a dedicated gas line (often larger than a tank heater), Category III stainless steel venting (not standard B-vent), and condensate drain. Electric tankless: requires a very heavy electrical circuit (100-150 amps for whole-house models). Both mount on a wall. Professional installation required. Gas tankless venting and gas line sizing are the most common installation challenges.
Maintenance
- Descale (flush with vinegar) annually in hard water areas. Scale buildup inside the heat exchanger reduces efficiency and can cause error codes.
- Clean the inlet water filter every 6-12 months.
- Check the venting annually for blockages or deterioration (gas models).
- Most units display error codes when service is needed -- consult the manual for your specific model.
- Tankless heaters last 15-20 years with proper maintenance -- significantly longer than tank heaters.
Buying Tips
- Rinnai, Navien, and Noritz are the three top residential gas tankless brands. All are excellent.
- Gas tankless is the only practical whole-house option. Electric tankless works for point-of-use only in most climates.
- A recirculation pump (-300) eliminates the wait for hot water and solves the cold-water sandwich issue.
- Budget ,500-3,500 installed for gas whole-house. The energy savings (-200/year) plus the longer lifespan (15-20 years) offset the higher upfront cost.
- If you have hard water, a whole-house water softener or descaling system is strongly recommended to protect the tankless heat exchanger.