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 Zone	Efficiency
+71 °F	100% (8 GPM)
61 – 70 °F	73% (5.8 GPM)
51 – 60 °F	58% (4.6 GPM)
41 – 50 °F	48% (3.8 GPM)
< 40 °F	41% (3.2 GPM)

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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

City	Groundwater Temperatures
Billings 59101 |59102 | 59105 | 59106	47°F.
Missoula 59801 |59802 | 59803 | 59804 | 59808	48°F.
Great Falls 59401 |59404 | 59405	49°F.
Helena 59601 | 59602	52°F.
Glendive 59330	53°F.
Butte 59701 |59703 | 59750	53°F.
Bozeman 59715 | 59718	54°F.
Cut Bank 59427	53°F.
Kalispell 59901	52°F.