Tankless Water Heater

Equipment and Systems - Water Heaters pillar

Also known as: on-demand water heater, tankless

A water heater that heats water on demand through a heat exchanger instead of storing hot water in a tank. Continuous flow, zero standby loss.

Tankless water heaters fire a high-BTU burner (typically 150,000 to 199,000 BTU/h gas) only when hot water is drawn, eliminating standby losses entirely. Continuous flow rate of 6 to 11 gallons per minute. Installed cost in Ontario: $2,800 to $5,500. Lifespan 15 to 20+ years versus 10 to 12 for tanks. Two retrofit catches: gas tankless typically needs a 3/4 inch gas line (existing 1/2 inch line will starve the unit), and condensing tankless requires PVC venting (cannot reuse existing B-vent chimney).

See the full Ontario HVAC and home energy glossary or browse the Water Heaters pillar.