Also known as demand-type or instantaneous water heaters, tankless water heaters are an option to avoid unnecessary heating costs related to standby heat loss. That's because instead of holding a tank of water that continually heats throughout the day, tankless water heaters provide hot water only as needed. Just turn on a faucet and you get hot water instantly.
Tankless water heaters come in both gas and electric options, so you don't have to decide between a gas (vs. an electric) water heater if you already have a preferred type. Tankless water heaters work by drawing in cold water when you turn the tap on, instantly heating the water as it passes through a gas burner or electric element.
There is a tradeoff when choosing to go with a tankless water heater. To start, you'll only get hot water if you're drawing less than a few litres a minute. That's enough for a shower or a bath. Multiple showers or a shower plus your washing machine or dishwasher running may be too much for just one tankless water heater.
Be prepared for a substantial initial cost when purchasing and installing each tankless heater. However, since a tankless heater can last twice as long as a traditional water heater, and they have easily replaceable parts, this potentially offsets their initial price.