Best Propane Tankless Water Heater – Buying guide
Calculating water usage needs
To work out how much hot water your home might need at any one time, survey how many water outlets are running simultaneously during your peak usage periods. This might be in the mornings when multiple people are showering, or in the evenings when the laundry machine and dishwasher are running while the kids take a bath.
Once you’ve noted down your peak usage period, check the flow rate of each outlet that’s being used. Some appliances will list their GPM requirement on their label, while you may need to perform a quick google search to find out others. For example, here are some common flow rates for household appliances.
To get a steady stream of hot water that won’t be affected when multiple outlets are turned on, you’ll need a tankless heater that can match your maximum GPM needs. Of course, the incoming flow rate for many homes won’t meet this number in the first place, so your heater may only be able to go so high.
How many GPM (flow rate) for a propane tankless hot water heater do I need?
- If you live in a mild climate, in an apartment or small townhouse, a heater with a flow rate of 3-5 GPM will be adequate (for average usage habits).
- If you live in a mild climate, in a small to mid-size home, a heater with a flow rate of 4-6.5 GPM will meet your needs (for average usage habits).
- If you live in a mild climate, in a large home, or with a large family, look for a heater with a flow rate of 6-10 GPM (for average usage habits).
- If you live in a colder climate, add 1-2.5 GPM to the above.
When choosing a propane tankless water heater, check the minimum and maximum water pressure requirements of each unit, as heaters need a certain incoming pressure to properly process your water.
If your incoming water pressure is too low for your heater (a common problem with well water), you may need to purchase and install an electric pump. A pressure regulator will help deal with an incoming pressure that’s too high.
How much propane does a tankless water heater use?
Most homes with tankless water heaters will use between 0.5 and 2 gallons of propane per day, leading to average annual propane needs of between expect to use somewhere between 200-700 gallons of propane per year for hot water.
This variance is mostly due to the number of people within the home, as well as the seasonal climate. A family of two may only use 10-15 gallons per month, whereas those with teenage or adult children may go through 40-55 gallons.
The difference between incoming and desired water temperature is often known as “temperature rise” and is a key factor in propane consumption. The bigger the temperature rise, the more energy a heater will need to deploy.
You can easily find out the temperature rise in your area by identifying your ideal water temperature and deducting the local groundwater temperature from that figure.
Most homes receive water that’s between 40 and 70 degrees. Here’s a heat map from Rinnai to help you estimate your local climate.
How long do 100 gallons of propane last?
When thinking about how much propane heaters need, it’s also important to consider heater efficiency. Most tankless heaters have efficiency levels between 80-95%, so your choice of product will affect how quickly you’ll go through 100 gallons.
Propane consumption also depends upon the types of appliances a heater is running. Taking a shower might cost you between 12,000 and 17,000 BTUs, and there are about 85-95,000 BTUs for every gallon of propane (again, depending upon efficiency). As a result, 100 gallons of propane could last for 500+ showers, if that was the only appliance you used.
Is propane cheaper than electric power?
In most areas, it’s currently cheaper to heat your water using propane than electricity—however, as we move towards a greener economy, this may not always be the case.
It’s also worth considering that electric tankless heaters are often slightly cheaper to buy and install than gas models, meaning that any propane bill savings are initially offset by the initial retail and installation price.
How to maintain a tankless propane water heater
All popular tankless water heaters are longer-lasting and more reliable than traditional tank water heaters. In fact, the US Department of Energy estimates the lifespan of tankless heaters and +20 years.
Hard water & flushing
To reach that full lifespan, heaters should be regularly maintained, with the most common job being to remove a buildup of scale from the heating elements. All copper heating coils are susceptible to scale, as they attract hard minerals like calcium and magnesium in water as they heat them.
Leaving scale around heating elements can drastically reduce heater performance. To remove it, you’ll need to use a circulating pump to run a descaling solution through the heater.
Descaling solutions are available at hardware stores, or you can make your own using vinegar or bleach.
Alongside scale buildups, heater components can begin to corrode, especially if incorrectly fitted. We recommend having a professional service your heater on a semi-regular basis, as they’ll be able to swap out any corroded parts before they seriously affect hot water function.