Average Groundwater Temperatures for the Cities in Montana

Average groundwater temperatures play an important role in determining which tankless water heater to purchase. The reason for this is because in colder climates the groundwaters starting temperature is colder than in warmer climates. This causes the tankless water heater to work harder to increase the water temperature in colder climates, which in turn causes the flow rate to decrease in parallel. For example, if the starting water temperature is 52°F and you need to raise the water temperature to 110°F. Then your tankless water heater needs to be capable of raising the water temperature by 58°F and still have enough flow to support the fixtures you want to simultaneously run.

How Flow Rates are Affected by Temperature

In the example below, you can see the impact that temperature has on flow rates. This example is based on a tankless water heater that has a flow rate rated for 8 GPM.

Temperature ZoneEfficiency
+71 °F100% (8 GPM)
61 – 70 °F73% (5.8 GPM)
51 – 60 °F58% (4.6 GPM)
41 – 50 °F48% (3.8 GPM)
< 40 °F41% (3.2 GPM)


Flow Rates of Appliances

Based on the corresponding flow rates for each appliance that are listed. A tankless water heater that is rated with a flow rate of 8 GPM (gallons per minute) is capable of running these items at the same time in regions with an average groundwater

temperature of 72°F.

Shower = 3 GPM

Kitchen Sink = 1.5 GPM

Washing Machine = 2.5 GPM

Total = 7 GPM

If you take this same exact tankless water heater and install it in a region that has an average groundwater temperature of 52°F (green zone). This will lower that tankless water heater's max GPM output to 4.64 GPM.

Shower = 3 GPM

Kitchen Sink = 1.5 GPM

Total = 4.5 GPM

As you can see before purchasing a tankless water heater it's important to know the impact temperature has on its ability to heat water and its effect on the total GPM needs of your household.

Montana Groundwater Temperature Yearly Average

CityGroundwater Temperatures


59101 |59102 | 59105 | 59106



59801 |59802 | 59803 | 59804 | 59808


Great Falls

59401 |59404 | 59405



59601 | 59602






59701 |59703 | 59750



59715 | 59718


Cut Bank






What Tankless Water Heater Should you buy if you Live in Montana?

Since Montana's average temperature range is between 47°F and 54°F. It is recommended that you select a green zone or light blue zone Tankless Water Heater. To see the recommended Tankless Water Heaters that apply to the light blue and green zone temperatures please follow the link that corresponds to the region of your average groundwater temperature.

Temperature zoneRecommended Tankless Water Heater
< 40 °FTankless Water Heater Recommendations
41 – 50 °FTankless Water Heater Recommendations
51 – 60 °FTankless Water Heater Recommendations
61 – 70 °FTankless Water Heater Recommendations
+71 °FTankless Water Heater Recommendations