How to Choose the Right Size On-Demand Propane Water Heater for Northern Climates

When it comes to selecting an on-demand propane water heater for a northern climate, several key factors must be considered to ensure you get the right size unit that can meet your household’s hot water demands efficiently. This comprehensive guide will walk you through the essential steps to determine the optimal size of your on-demand propane water heater for your northern home.

Calculating the Desired Flow Rate

The flow rate is the amount of hot water your household requires at any given time. To calculate the desired flow rate, make a list of all the hot water-using appliances and fixtures in your home, and note their individual flow rates in gallons per minute (GPM). Then, add up the flow rates of the devices you expect to use simultaneously to determine the total flow rate needed.

For example, if you have a shower head with a 2.5 GPM flow rate, a bathroom sink faucet with a 0.75 GPM flow rate, and a dishwasher that requires 1.5 GPM, your total desired flow rate would be 4.75 GPM. It’s important to account for the maximum simultaneous usage to ensure your on-demand heater can keep up with the demand.

Determining the Necessary Temperature Rise

how big on demand hot water heater propane northern

The temperature rise is the difference between the incoming water temperature and the desired hot water temperature. In northern climates, the incoming water temperature can be quite low, especially during the winter months, so a higher temperature rise may be necessary.

As a general guideline, you should aim for a temperature rise of 70-80°F. To calculate the required temperature rise, subtract the expected incoming water temperature from your desired hot water temperature. For instance, if the incoming water temperature is 45°F and you want the hot water to be 120°F, the necessary temperature rise would be 75°F (120°F – 45°F).

Accounting for Climate Considerations

In northern climates, the water heater may need to work harder to maintain the desired temperature due to the colder ambient temperatures. This can affect the size and power requirements of the on-demand propane water heater you choose.

As a rule of thumb, for every 10°F decrease in the average outdoor temperature, the water heater’s input capacity should increase by approximately 4%. For example, if the average outdoor temperature in your northern location is 30°F, you may need to select a unit with 8-12% more input capacity compared to a similar household in a milder climate.

Prioritizing Energy Efficiency

When selecting an on-demand propane water heater for a northern climate, it’s crucial to prioritize energy efficiency. Look for units that are Energy Star rated and have a high energy factor (EF) rating, which indicates how efficiently the heater can recover and maintain the desired water temperature.

A higher EF rating typically means the unit has more efficient recovery time, lower standby losses, and fewer cycling losses, which can translate to significant energy savings and lower operating costs over the life of the water heater. Aim for an EF rating of 0.90 or higher for optimal efficiency.

Considering Additional Factors

In addition to the primary factors mentioned above, there are a few other considerations that can influence the size of the on-demand propane water heater you choose for your northern home:

  1. Number of Bathrooms: The more bathrooms in your home, the higher the potential for simultaneous hot water usage, which may require a larger capacity unit.

  2. Hot Water Appliances: The presence of hot water-intensive appliances, such as washing machines, dishwashers, and jacuzzis, can significantly increase the overall hot water demand, necessitating a more powerful on-demand heater.

  3. Shower Schedules: If your household has similar shower schedules, where multiple people may be using hot water at the same time, you may need a larger on-demand heater to meet the peak demand.

By carefully considering these factors, you can ensure that the on-demand propane water heater you select for your northern home is properly sized to provide reliable and efficient hot water for your household’s needs.


  1. Tankless Water Heater Sizing Guide – eComfort
  2. What Size Propane Gas Water Heater Do You Need? – Kauffman Gas
  3. Sizing a New Water Heater – U.S. Department of Energy