Tankless gas water heater

Tankless gas water heaters and important considerations

A tankless gas water heater provides instant hot water and potential energy savings. And a natural gas or propane powered unit generally has a higher flow rate capacity than an electric tankless water heater. 

So these units make potentially ideal whole house tankless water heaters for larger homes with several adult occupants. With that said, there are several important considerations to make before you purchase any tankless gas hot water heater.

Natural gas or propane

Tankless gas hot water heaters can operate off natural gas or propane. The water heater itself will have to be designed specifically for one fuel type. The installation process and the fuel venting is the same for both.

If you intend to change from one fuel type to another (for the sake of cost effectiveness) before you purchase a unit, fortunately most manufactures offer conversion kits. When in doubt consult a licensed home heating professional.

Retrofitting and piping

Since a tankless gas water heater operates on demand, they also require larger fuel draws when heating than storage tank units. This is needed in order to provide the instant hot water.

Consequently more times than not larger gas pipe fittings are needed. Most tankless gas water heaters require a 3/4 inch pipe fitting in order to efficiently operate, while many storage tank units use 1/2 inch pipe fittings. 

So whether you're replacing a gas storage tank for a gas tankless unit, or your adding a tankless unit in conjunction with another water heating source, there is a chance that some minor retrofitting or re piping will be required.

Venting and application

With a tankless gas water heater, air is needed for both combustion (operation) and ventilation. Something that's much overlooked is how essential the right amount of air intake and air exhaust is for an energy efficient performance.

When selecting a particular unit, keep in mind that there are several venting options to choose from. All exhaust travels outdoors but some units vent horizontally, while others vent vertically.

Vertical or horizontal venting determines the point at which venting starts and may determine where the tankless unit is installed or mounted.

Which option you chose can either pre determine or limit the location of installation. So it's best to consider ventilation before purchasing.

Non direct ventilation or fan assisted

• A small and internal electric fan operates to vent the gas emissions outdoors when the unit is operated.
• The same electric fan provides the intake air needed for the unit to operate efficiently. This air comes from the indoor location from where it's installed. 
• This allows for an indoor application, both vertically or horizontally ventilation applies.
  

Direct ventilation or sealed combustion

• The incoming air needed to operate is designed to come directly from the outdoors.
• The unit is seal and doesn't use indoor air for operation. Instead two pipes or a split pipe is installed, one for air intake and the other for exhaust.
• This also allows for an indoor application, both vertically or horizontally ventilation applies.

Outdoor ventilation

• These gas tankless water heaters get combustion air for operation and omit exhaust directly outdoors.
• An outdoor vented tankless gas water heater is designed only for outdoor installation.
• These units are recommended only for warm climate regions to prevent internal freezing of the unit.

Pilot lights vs. IID's

It's important to note that some tankless gas water heaters contain pilot lights. These internal starters are designed to burn continuously. Be advised that this will offset some of the potential home energy savings.

This can be avoided by selecting a tankless gas hot water heater equipped with an intermittent ignition device, also called an IID, instead of a pilot light. These IID's are similar to the spark ignition devices used in newer gas kitchen ovens. They use a small draw of electricity to start the unit and only when hot water is desired. 

Flow rates and regional climate

The flow rates of your hot water consuming fixtures and appliances the unit will service should be considered before hand. Calculating these flow rates and taking into account your regional climate are essential to ensuring that you choose the best tankless water heater for your home.

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