Tankless or Tank Water Heater: Which Is Right for Your Middle Tennessee Home?
Short answer: a gas tankless water heater fits best in a home that already has natural gas. It suits a household that runs out of hot water, and owners who plan to stay put. A tank water heater still wins on upfront price and on a quick swap. In an all-electric home, a tank is often the better buy.
In the federal government’s 2020 home energy survey, 74 percent of Tennessee homes heated water with electricity. We install both types across Nashville and Middle Tennessee, and our tankless water heater installation page covers the switch.
How do tank and tankless water heaters compare?
A tank keeps a set amount of water hot all day. ENERGY STAR notes that standby can make up 96 percent of a tank’s operating time each day. A tankless unit heats water only as it flows through, and it is rated in gallons per minute.
| Tank water heater | Tankless water heater | |
|---|---|---|
| How it heats | Keeps a full tank hot all day | Heats water as it flows through |
| Hot water supply | Runs short once the tank empties | Steady, up to its flow limit |
| Installed cost, national guides | $600 to $3,100 | $1,400 to $5,600 |
| Expected life | 10 to 15 years | Up to 20 years |
| Gas input under federal rules | 75,000 BTU an hour or less | Under 200,000 BTU an hour |
| Space | A tank on the floor | A box on the wall |
| Hard water upkeep | Flush sediment from the tank | Descale the heat exchanger |
The costs span two national cost guides, and the life spans come from Department of Energy guidance. The costs are market numbers, not our price list.
What does Middle Tennessee’s hard water do to each one?
Limestone puts calcium in the Cumberland River, which supplies Nashville’s tap water. Metro Water Services’ latest water quality report puts total hardness near 100 milligrams per liter. That is about 6 grains per gallon, and the report calls it moderately hard. Treatment at the plant does not remove it.
Hardness differs by utility. Rutherford County’s utility district has reported harder water than Nashville’s. Smyrna softens its water at the plant with lime, to a target of 55 to 75 milligrams per liter.
Smyrna’s report links hardness to white flakes and deposits in water heaters. Your utility’s annual water quality report lists your number.
Both types collect scale. Department of Energy guidance says tank scale settles at the bottom, where it hurts flow and performance far less. In a tankless unit, scale can narrow the path through the heat exchanger and shorten the unit’s life.
Makers set tankless flushing schedules from twice a year to once every three years, the same guidance notes. One maker’s guide calls for descaling once a year in moderately hard water. A tank maker’s guide calls for a drain and flush at least once a year, too.
Does your home have the gas line and venting for a tankless unit?
Federal efficiency rules define a home gas tank heater as one with 75,000 BTU an hour of input or less. A home gas tankless heater can be rated just under 200,000. Department of Energy guidance says the gas line serving the unit usually needs to be 3/4 inch. If yours falls short, a tankless switch calls for new gas line installation sized for the load.
Venting changes too. One maker’s guide says a condensing tankless unit can vent through plastic pipe, since its exhaust runs cool. It cannot share a vent with other appliances or vent through a chimney. It also makes acidic condensate that needs a drain, and local codes may call for a neutralizer.
Permit rules differ by town. Metro Codes says a water heater swap that changes the fuel type needs a permit. In Lebanon, the city code calls for a gas permit to install a water heater or gas piping. The codes office for your address has the final word.
What if your home is all electric?
Census figures on home heating fuel show how gas use varies across the area. Utility gas heats about 73 percent of occupied homes in Brentwood, but 14 percent in La Vergne. One national cost guide puts an electric-to-gas conversion at $400 to $2,000 or more.
An electric tankless unit is the other route. Department of Energy guidance says it saves about 12 percent at best over an electric tank. Most whole-house electric units draw 50 to 200 amps. Some need more circuits or a larger electric service.
Which one fits your household size?
A tank is sized by gallons and by its first-hour rating, the hot water it supplies in an hour. One cost guide matches a 40-gallon tank to 1 or 2 people and a 50-gallon tank to 3 or 4. When the tank runs dry, you wait while it reheats.
A tankless unit is sized by flow. ENERGY STAR lists a shower at 2.5 gallons per minute and a clothes washer at 3.3. Two showers at once need about 5 gallons per minute.
Colder incoming water cuts a unit’s output, so winter water sets the size. A large household may need a bigger unit or two units. Each unit also needs a minimum flow of 0.4 to 0.9 gallons per minute before it fires.
Which costs less to run in Tennessee?
Energy Department guidance puts tankless running costs 5 to 40 percent below a tank’s on the same fuel. In the department’s field tests, savings depended on how people drew water. Short draws saved less, and savings peaked near 50 gallons a day.
ENERGY STAR compares its gas tankless models with a standard gas tank. It puts the savings at about $95 a year for a family of four. Fuel costs less here than the national average. Federal energy data for last year put Tennessee’s home natural gas price at $11.84 per thousand cubic feet, against $15.34 nationwide.
Power is the same story. In July 2026, Tennessee homes paid an average 13.71 cents per kilowatt-hour, against 18.31 cents nationally. Lower fuel prices shrink the dollars any efficiency upgrade can save.
The upfront gap is the larger number. National cost guides put the labor alone for a tank-to-tankless switch between $600 and $2,500. A larger gas line adds $350 to $2,000 in one guide. For the tank side, read what a tank water heater replacement costs in Tennessee.
So which one should you choose?
A gas tankless unit makes sense when your home has gas and you plan to stay a long time. It also fits a household that keeps running out of hot water, or a tight utility closet. In moderately hard water, plan on a yearly descaling.
A tank makes sense when your home is all electric or when upfront cost matters most. It also fits when the old tank has failed and you need hot water back with the least work. Our tank water heater installation page covers that swap.
Want help choosing between tank and tankless?
We install tank and tankless water heaters in homes across Nashville and Middle Tennessee. La Vergne sits at the center of our service area. Read more about switching to a tankless water heater, then call or text (615) 723-2488. We look at the job and put the quote in writing.