Section 3
Ground water temperature by state for tankless sizing
This page lists the ground water temperature range for 50 states, the District of Columbia and Puerto Rico from Rinnai's ground water map. It also lists the temperature rise to 105 F and to 120 F. Colder inlet water means a larger rise and a lower flow from any heater.
3.1 Four ground water maps
Manufacturers size with a map of average ground water temperature. Four maps are compared here. The state table uses the Rinnai map, which has the most detail.
| Source | Bands | Notes |
|---|---|---|
| Rinnai map, 06/2022[1] | 35, 37, 42, 47, 52, 57, 62, 67, 72, 77 F | Hawaii and Puerto Rico: 75 F. Canada and Alaska: 35 to 42 F. |
| EcoSmart sizing sheet[2] | 9 zones, 37 to 77 F in 5 F steps | Flow table calculated to a 105 F set point. |
| Stiebel Eltron Tempra guide[3] | 42, 52, 62, 72 F | Maximum flows calculated for 105 F water. |
| US EPA map after Collins, 1925[4] | 5 to 25 C isotherms (41 to 77 F) | Average shallow ground water. |
All four maps put the coldest water along the Canadian border and in the high Rockies. All four put the warmest water in south Florida and south Texas. The maps differ in detail, so the state table gives a range.
3.2 Ground water range by state
| State | Range on Rinnai map | Sizer preset | Rise to 105 F | Rise to 120 F |
|---|---|---|---|---|
| Alabama | 62 to 67 F | 62 F | 43 F | 58 F |
| Alaska | 35 to 42 F | 35 F | 70 F | 85 F |
| Arizona | 52 to 72 F | 52 F | 53 F | 68 F |
| Arkansas | 57 to 62 F | 57 F | 48 F | 63 F |
| California | 47 to 72 F | 47 F | 58 F | 73 F |
| Colorado | 37 to 52 F | 37 F | 68 F | 83 F |
| Connecticut | 47 F | 47 F | 58 F | 73 F |
| Delaware | 52 to 57 F | 52 F | 53 F | 68 F |
| District of Columbia | 52 to 57 F | 52 F | 53 F | 68 F |
| Florida | 67 to 77 F | 67 F | 38 F | 53 F |
| Georgia | 57 to 67 F | 57 F | 48 F | 63 F |
| Hawaii | 75 F | 75 F | 30 F | 45 F |
| Idaho | 42 to 52 F | 42 F | 63 F | 78 F |
| Illinois | 47 to 57 F | 47 F | 58 F | 73 F |
| Indiana | 47 to 52 F | 47 F | 58 F | 73 F |
| Iowa | 42 to 47 F | 42 F | 63 F | 78 F |
| Kansas | 52 to 57 F | 52 F | 53 F | 68 F |
| Kentucky | 52 to 57 F | 52 F | 53 F | 68 F |
| Louisiana | 62 to 67 F | 62 F | 43 F | 58 F |
| Maine | 37 to 42 F | 37 F | 68 F | 83 F |
| Maryland | 52 to 57 F | 52 F | 53 F | 68 F |
| Massachusetts | 47 F | 47 F | 58 F | 73 F |
| Michigan | 37 to 47 F | 37 F | 68 F | 83 F |
| Minnesota | 35 to 42 F | 35 F | 70 F | 85 F |
| Mississippi | 62 to 67 F | 62 F | 43 F | 58 F |
| Missouri | 52 to 57 F | 52 F | 53 F | 68 F |
| Montana | 42 to 47 F | 42 F | 63 F | 78 F |
| Nebraska | 47 to 52 F | 47 F | 58 F | 73 F |
| Nevada | 42 to 62 F | 42 F | 63 F | 78 F |
| New Hampshire | 42 F | 42 F | 63 F | 78 F |
| New Jersey | 47 to 52 F | 47 F | 58 F | 73 F |
| New Mexico | 52 to 62 F | 52 F | 53 F | 68 F |
| New York | 42 to 47 F | 42 F | 63 F | 78 F |
| North Carolina | 52 to 62 F | 52 F | 53 F | 68 F |
| North Dakota | 37 to 42 F | 37 F | 68 F | 83 F |
| Ohio | 47 to 52 F | 47 F | 58 F | 73 F |
| Oklahoma | 57 to 62 F | 57 F | 48 F | 63 F |
| Oregon | 47 to 57 F | 47 F | 58 F | 73 F |
| Pennsylvania | 47 to 52 F | 47 F | 58 F | 73 F |
| Puerto Rico | 75 F | 75 F | 30 F | 45 F |
| Rhode Island | 47 F | 47 F | 58 F | 73 F |
| South Carolina | 62 to 67 F | 62 F | 43 F | 58 F |
| South Dakota | 42 to 47 F | 42 F | 63 F | 78 F |
| Tennessee | 57 to 62 F | 57 F | 48 F | 63 F |
| Texas | 57 to 72 F | 57 F | 48 F | 63 F |
| Utah | 42 to 57 F | 42 F | 63 F | 78 F |
| Vermont | 42 F | 42 F | 63 F | 78 F |
| Virginia | 47 to 57 F | 47 F | 58 F | 73 F |
| Washington | 47 to 52 F | 47 F | 58 F | 73 F |
| West Virginia | 47 to 52 F | 47 F | 58 F | 73 F |
| Wisconsin | 37 to 42 F | 37 F | 68 F | 83 F |
| Wyoming | 37 to 47 F | 37 F | 68 F | 83 F |
State ranges were taken from the map image. A state that crosses two color bands has a range that covers both.
3.3 Limits of a ground water map
Each temperature is an average for ground water. Rinnai's map says its zones are general, and that the actual inlet temperature can shift with local variation and the season[1]. EcoSmart notes that ground water temperature varies seasonally[2]. A city supply drawn from a lake or river can be colder in winter than nearby wells. A thermometer in a cup of cold tap water, taken once the temperature stops falling, gives the inlet temperature for a specific building.
Eccotemp's help article suggests assuming 50 F when the temperature is not known, because a low assumption avoids an undersized unit[5]. The Rinnai map shows water colder than 50 F for roughly the northern third of the country.
Notes and sources
- Rinnai, non-condensing tankless brochure with United States Ground Water Temperature Map and V53De table, 06/2022 (PDF hosted by Woodstove Pro)
- EcoSmart, electric tankless sizing sheet with zone table, 105 F set point (PDF)
- Stiebel Eltron, Tempra and Tempra Plus sizing guide with ground water map (PDF)
- US EPA, average shallow ground water temperature map (after Collins, 1925)
- Eccotemp Help Desk, How to Select the Right Size Tankless Water Heater