Tankless vs Tank Water Heaters: Which Fits Your Home?

How is a tankless unit different from a tank?

A conventional heater keeps a full tank of water hot at all times, day and night, in an insulated tank. Heat slowly escapes through the tank walls, so the burner or elements cycle on even when nobody is using water. That lost heat is called standby loss.

A tankless heater has no reservoir. When you open a hot tap, water flows through a heat exchanger and a gas burner or electric element heats it on the spot. According to the U.S. Department of Energy, tankless units typically deliver 2 to 5 gallons of hot water per minute, and gas-fired models produce higher flow rates than electric ones.

How do they compare side by side?

The wide tankless range reflects how different conversions can be. Replacing an old tankless unit with a new one is close to a straight swap. Converting a basement tank to a gas tankless unit can mean new venting, a larger gas line and a new electrical outlet, which is where the higher figures come from.

How much energy does tankless really save?

The Department of Energy estimates that for homes using 41 gallons of hot water or less per day, tankless heaters are 24 to 34 percent more energy efficient than conventional storage tanks. For heavy users, around 86 gallons a day, the edge shrinks to 8 to 14 percent. In other words, a couple in a condo near Dupont Circle gets more of a proportional benefit than a family of six in a large Loudoun County home, though both save something.

DOE also flags a catch on gas models: a standing pilot light burns gas constantly and can erase some of the savings. Look for a unit with an intermittent ignition device instead. Since tankless units cost more to buy, the payback comes from lower energy bills over a longer service life, not from the purchase price.

Will one tankless unit keep up with your household?

This is the question that matters most. A tankless heater does not run out of hot water, but it can only heat so many gallons per minute. DOE notes that running a shower and a dishwasher at the same time can push a single unit to its limit in a larger household. Its suggested fixes are installing two or more units, or giving a heavy-use appliance its own heater.

Winter makes sizing harder in this region. When the Potomac and the incoming water mains are cold, the heater has to raise the water temperature further, so the same unit delivers fewer gallons per minute in January than in July. A plumber sizing a unit should base it on your coldest-month incoming water temperature and the number of showers and appliances you actually run at once.

Do you have natural gas, and from whom?

Gas tankless units are the most common choice where gas service exists. Washington Gas serves most of the District and its Maryland and Virginia suburbs, but not every address. Fairfax County notes that Columbia Gas of Virginia serves portions of Chantilly and Herndon, the Maryland Office of People's Counsel lists BGE in parts of Montgomery County, and some outlying homes use propane or are all-electric. Your gas bill shows who your provider is.

Gas conversions often need a larger gas supply line, because a tankless burner draws far more gas while running than a tank burner. A plumber offering gas line work in Washington, DC can check whether your meter and piping can carry the load. Electric tankless units avoid venting but can need large dedicated circuits, which may mean panel work.

If you ever smell gas near any heater, leave the house first, then call 911 and your gas utility from outside. For Washington Gas customers the emergency line is 844-WASHGAS (844-927-4427), option 1. The guide to a gas smell at home explains the steps.

What does the conversion and permit process look like?

Expect the plumber to address venting, gas piping, water connections, a condensate drain on high-efficiency models, and an electrical outlet for the controls. Permits follow the local office:

• Washington, DC. The DC Department of Buildings issues plumbing and gas permits, and its plumbing application covers water heaters.
• Montgomery and Prince George's counties. WSSC Water issues plumbing and gasfitting permits, and gas water heater work must be done under a WSSC permit. That includes homes in Bethesda and across both counties.
• Prince William County. The county publishes a permit packet specifically for gas-fired tankless heaters. A gas permit covers the gas piping and venting, a plumbing permit is needed when water piping is extended more than 10 feet or the pipe material changes, and an electrical permit applies if a new circuit is needed. Homeowners booking a tankless install in Woodbridge should expect all three where they apply.
• Fairfax County and the other Northern Virginia jurisdictions. Check with the county or city permit office for your address.

Does local water hardness favor one type?

Both types collect mineral scale, but tankless units are more sensitive to it because scale coats the small passages of the heat exchanger. DC Water reports District water as moderately hard, averaging about 7 grains per gallon, and nearby suburban systems are in a similar range. Manufacturers typically call for periodic descaling, and some homeowners add a softener or scale filter ahead of the heater. A softener installation for District homes protects every fixture, not just the heater.

Tanks are more forgiving of scale in the short term, but sediment still builds up in the bottom and shortens their life if the tank is never flushed.

Which should you choose?

A tank heater is usually the better fit when:

• The current tank has failed and you need hot water back quickly at the lowest installed cost.
• Several showers and appliances often run together and you do not want a multi-unit setup.
• Gas line or venting upgrades for tankless would be expensive in your house.

A tankless heater usually makes more sense when:

• You plan to stay long enough for energy savings and the longer life to pay back the higher price.
• Your household uses a moderate amount of hot water, where DOE's efficiency gain is largest.
• Space is tight, such as a rowhouse basement or a condo utility closet.
• You are tired of running out of hot water during back-to-back showers.

Whichever way you lean, ask for quotes on both types at the same visit. Seeing the installed price of a same-type tank swap next to a full tankless conversion, with permits, venting, gas piping and electrical work spelled out, makes the trade-off concrete. If the gap is small and you plan to stay, tankless often wins. If the gap is large because the house needs a new gas line and venting route, a new tank may be the sensible choice for now, with tankless revisited at the next replacement.

If your current heater is failing, start with our guide to repairing versus replacing a water heater. For pricing context, see what plumbers charge in the DC area. When you are ready, you can be connected with someone for tankless water heater installation in Washington, DC or a standard tank replacement in the District.