Natural gas and propane are two very similar fuels which are gaseous at normal ambient temperatures. They are both readily available and clean-burning fuels for tankless hot water heaters and other appliances. For gas tankless water heaters, typically, natural gas would only be an option for your home or other building where it is already available (piped in by your local utility company).
Propane is also called LP gas or sometimes simply LPG. The L stands for liquefied, indicating that propane can be fairly easily liquefied and stored by putting it under moderate pressure. Liquefying the gas causes it to require much smaller storage containers. Conversely, natural gas requires much higher pressures to liquefy it, so it is normally stored and transported as compressed gas (which requires considerably more storage volume per unit heat). The availability and convenient storage is why LPG is a popular fuel for home BBQs.
So what would cause you to choose one or the other for your tankless water heater?
Pros and Cons of Natural Gas Tankless water heater
- Piped into many homes, it is typically considerably cheaper per BTU than propane.
- Readily available for many home or business tankless water heaters.
- Cannot easily be stored for mobile use because natural gas changes from a liquid to a gas at quite a low temperature. This means a much larger storage container is needed to store the same amount of energy as found in propane. Practically, this means natural gas tankless water heaters are limited to non-mobile applications where the natural gas is already piped in.
- While natural gas filling stations are available, there are not nearly so many places as well so you propane.
- Not all homes have natural gas piped to them, and using stored compressed natural gas for tankless water heaters is largely impractical.
Pros and Cons of Propane Gas Tankless water heater
- Widely available; easy to find (both for home delivery and for filling mobile tanks such as an RV).
- Most RVs already use propane if you are considering tankless propane water heater.
- Propane has more energy per gallon than does natural gas, partially making up for the price difference.
- Because it is stored and transported as a liquid, it does not require large storage containers for applications such as tankless water heaters for RVs.
- Some homes may not have natural gas piped to them.
- More expensive than natural gas.
- To fill your tanks, you must either take your tanks to a filling station or schedule a propane delivery (which may be prohibitively expensive for small quantities but is both cost-effective and common for homes that utilize propane).
Popular makers of propane tankless hot water heaters include Rheem, Bosch, Rinnai, Eccotemp and others and generally are very similar to the same manufacturer’s natural gas units. Reviews for tankless propane water heaters are largely very similar to the corresponding natural gas tankless heaters.
For more information, check out our guide and full review of: