The short answer
Before choosing a tankless water heater, settle how much hot water you run at the same time, whether gas or electric fits your home's gas line, panel and venting, how it will be maintained, what happens in a power outage, and whether the savings fit your household. Those answers decide whether a conversion is straightforward or expensive.
A tankless water heater can last longer and use less energy than a tank, but only when it’s matched to how your household uses hot water and to what your home can supply. Before you choose one, settle a handful of questions: how much hot water you run at the same time, gas or electric, where it will vent, how it will be maintained, and whether the savings fit your household. The answers decide whether your home is a straightforward conversion or an expensive one.
How much hot water do we use at the same time?
Tankless heaters are sized by flow rate, in gallons per minute, not by how many gallons they store. ENERGY STAR puts it simply: the more likely you are to have the shower, dishwasher and clothes washer going at once, the larger the flow rate you’ll need. It lists a shower or bathtub at an average of 2.5 gallons per minute and a clothes washer at 3.3. See ENERGY STAR’s gas tankless guidance.
Think about your busiest moment, like two showers running in the morning. The U.S. Department of Energy notes that if you use hot water in several places at once, you may need two or more tankless heaters to keep up.
Florida helps here. The My Florida Home Energy tankless fact sheet says incoming water in Florida averages about 72 to 77 degrees. Warmer incoming water means the heater has less work to do. Read the Florida tankless fact sheet.
Gas or electric, and can the house support it?
This is often where the real cost sits.
- Gas. ENERGY STAR says the installer should check whether your existing natural gas line is big enough, how the combustion gases will be vented, and whether electricity is available near the heater for models with forced venting.
- Electric. There’s no venting, but the Florida fact sheet notes that electric models often require upgrading the home’s electrical service.
Ask your plumber to look at your gas line, panel and venting route before you settle on a model, not after.
Where will it go?
A tankless unit takes up less space than a tank, but it still needs the right spot. Ask where it will be installed, where the vent will exit, and how far it sits from the bathrooms and kitchen. ENERGY STAR also notes that your installer may need time to order the right model, and that installing one may take longer than a standard water heater.
What maintenance will it need?
Mineral scale is the main upkeep issue. The Florida fact sheet recommends flushing a tankless heater with distilled vinegar about every 6 to 12 months, following the owner’s manual, and suggests an isolation valve kit to make that easier. Your manufacturer’s instructions for your model come first.
Ask whether service valves are part of the installation. In one Bonita Springs home, our technician installed valves on an existing tankless heater and then flushed it to descale the system. With valves in place, future flushes are simpler.
What happens when the power goes out?
The Florida fact sheet is clear that tankless heaters provide no hot water during a power outage, and gas models often need electricity too. In hurricane country, that’s worth knowing before you choose.
Will it actually save us money?
It depends on how much hot water you use. The Department of Energy’s Energy Saver guide says that for homes using 41 gallons or less of hot water a day, on-demand (tankless) water heaters can be 24% to 34% more energy efficient than conventional storage tank water heaters. For homes that use a lot of hot water, around 86 gallons a day, the gain is 8% to 14%. The same guide says most storage heaters last 10 to 15 years, while tankless heaters can last more than 20.
Tankless units cost more up front, and some homes need gas line or electrical changes to install one. We’ll tell you honestly which kind of job yours is.
Is the hot water instant?
Not exactly. The Florida fact sheet notes that a tankless heater still takes time to reach its set temperature, and the water still has to travel through your pipes to the tap. Most units also need a minimum flow, usually 0.5 gallons per minute or more, to switch on.
Which brands, and what warranty?
We install tankless units from Rinnai, Navien, Eemax, EcoSmart and Stiebel Eltron. Equipment warranties follow each manufacturer’s terms and vary by model, so ask to see them for the unit you’re considering. Our own workmanship carries a one-year labor warranty.
Talk it through before you buy
Bring your answers to these questions to a plumber who will look at your fixtures, fuel, panel and venting before recommending a size. We install, flush and descale tankless water heaters, and we’ll give you a straight read on whether one fits your home.
Learn more about water heater repair and installation, or call (239) 542-0787.
Author: Tropical Plumbing Co.. Qualified review: Nathan Lowmaster, owner, Florida Certified Plumbing Contractor CFC1431517.