Electric or gas–fired? It′s not just a simple matter of removing a conventional unit and quickly replacing it with a tankless unit. There are specific requirements for each that probably are not already be in place. Gas–fired tankless water heaters require a different sized gas line than that used to heat a conventional unit. Electric tankless units require that you have an adequate number of circuits to support the new unit.


Interior or exterior installation? For interior installation of a gas–fired unit, there are specific venting requirements that must be met in order to pass building code specifications and to ensure your safety. A more cost effective alternative would be to have the unit installed on an exterior wall where no special venting would be needed.


What size unit will you need in order to meet your water demands? It is important to determine the number of fixtures and appliances that will require hot water. Tankless water heaters generate a temperature rise based on the flow rate demanded and each fixture requires its own
gallons–per–minute demand.

For example, a bathroom faucet has a flow rate of approximately .5 gallons per minute (GPM) while the flow rate of a shower can be anywhere from 1.5 to 3.0 GPM, depending on whether or not a low–flow fixture is in place. Used simultaneously, the two faucets demand from 2.0 to 3.5 GPM. If the tankless water heater is of sufficient size, it will be able to meet the demand for water heated to the desired temperature.

If more demand is placed on the unit, (example: using the bathroom faucet and taking a shower while running the dishwasher), the temperature of the water will not be as hot. As the demand increases, the water temperature decreases. Installing a unit that is too small can result in water that is not hot enough if too much hot water is demanded at one time. The proper sized unit, however, will be able to meet the hot water demands while maintaining desired water temperature.