What tankless actually does
A tankless water heater has no storage tank. A flow sensor fires the burner or elements the moment a hot tap opens, and the water is heated as it passes through. Close the tap and it shuts off. A Department of Energy Building America study found tankless gas heaters saved roughly a third on water heating compared with tank heaters, though savings vary a lot with how much hot water a household uses. Nothing sits in a tank losing heat all day. They also don't rust through and flood a garage, because there's no tank.
The trade-offs, honestly
- Never runs out — within limits. A tankless unit heats at a fixed rate. The colder the incoming water, the less flow it can bring to full temperature. East Tennessee's winter inlet water makes that rating matter: a unit sized for summer showers can feel underpowered in January if two showers and a dishwasher run at once.
- Installation costs more. The unit itself costs more than a comparable tank, and gas units typically need a bigger gas line and dedicated venting; electric units can need new circuits and panel capacity. It costs more to install and less to run, and it tends to last longer — the Department of Energy estimates about 20 years for tankless against about 15 for tank heaters.
- Maintenance is real. Minerals build up in the heat exchanger. In this area's water, an annual vinegar flush (descale) is standard upkeep, which a plumber can set up as yearly maintenance. A tank heater asks nothing of you for years; a tankless unit rewards a maintenance habit.
Sizing: flow and temperature rise
Tankless units are sized by two numbers: the flow rate you need at once (each shower is roughly 2 gallons per minute, so two simultaneous showers means about 4 gpm) and the temperature rise — how many degrees the unit must lift the incoming water. Colder groundwater in winter means a bigger rise for the same shower, which is why the plumber will size for the coldest month, not the average. Undersized units don't fail; they just deliver lukewarm water at high flow, which is the most common tankless complaint.
What the install involves
- The plumber checks the house: gas meter and line size (gas units), panel capacity (electric), and where the unit and its venting can go.
- The old tank is drained and removed, or sometimes kept as a backup in utility setups.
- The unit is mounted, connected to gas, water and power, and vented to code.
- It's commissioned: flow tested at a fixture, temperature set (about 120°F is the standard recommendation), and the installer shows you the flush valves for future descaling.
- Permits are pulled where required, as with any water heater work.
Conversion installs (tank to tankless) are a bigger job than a swap — plan on most of a day.
What affects the price
Factors, not figures: gas versus electric, whether the gas line or panel needs upgrading, venting route and type, how far the unit sits from the fixtures it serves, and whether a water filter or softener is added ahead of it. Ask the plumber to compare the total installed cost against a standard tank so you can judge the payback for how long you'll stay in the house. If your existing tank just needs a part, see water heater repair first — a fix can buy years. And if you'd rather keep the simple route, water heater replacement with a modern tank is a perfectly good choice.
Is it right for a Johnson City house?
Often, yes — especially in smaller households that spread hot water use across the day, homes short on space, and rental or vacation properties where a leaking tank sitting empty is a risk. Larger households with true simultaneous demand need a bigger unit or a staggered routine. If your tank is fine and you're curious, ask during any service call; the plumber can measure your gas line or panel and tell you what a conversion would take in your specific house.