Natural gas tankless heater requirements

When looking at your natural gas tankless heater requirements, start with the venting requirements:

If you live in a non-freezing area you can install some models outside without needing venting, otherwise the units are designed for indoor installation with exhaust venting.

Generally the water heaters should be installed where the vent length is as short and straight as possible.

Gas line sizing for natural gas tankless water heaters:

Tankless water heaters draw many more BTUs than a tank water heater, so ensure your gas line is sized properly with the gas line running as short a distance as possible.

Combustion air requirements for a natural gas tankless water heater:

The combustion air requirements only apply to indoor installations where air is drawn from the room in which the water heater is installed. Some of the Bosch tankless water heaters (250SX, 2400E) have a separate air intake allowing for air to be drawn from the outside.

For the other indoor installations, the amount of combustion air should be a minimum volume of 50 cubic feet per 1,000 BTU per hour rated input.

If installing a gas water heater in an area smaller than the combustion area suggested, the installer must make two openings, each one within 12 inches of the top and 12 inches of the bottom of the space. The total free area should be 1 square inch per 1,000 BTU/hr of rated input if the air is taken from inside the house, reducing the requirement to 1 square inch per 4,000 BTU/hr if the air is taken from the outside.

Since gas tankless heater requirements can be quite technical, find the information you need regarding venting and make up air for the specific water heater which interests you, from the specifications, installation guide or the dealer, who will also be aware of any local code requirements.

Remember too that gas tankless water heaters can't be installed inside a mobile home, bedroom, bathroom or any confined living space normally kept closed.