The short answer
Each type wins in a different house. Use these as a first cut, then check the house:
- Choose a new tank when the current setup works, you want the lowest installed cost, and running out during a long morning is not a problem.
- Choose tankless when you have gas, an outside wall the unit can vent through, and a household that runs out of hot water or wants the floor space back.
- Choose a heat pump when you have an electric tank today and a roomy basement or utility room that stays above 40°F all year.
How each one works
A tank water heater keeps a fixed volume of water hot around the clock. When a long shower or the dishwasher drains it, you wait while it recovers. Gas tanks recover faster than electric ones.
A tankless (on-demand) water heater has no storage. When a tap opens, a burner fires and heats the water as it passes through a heat exchanger, so the supply does not run out as long as demand stays within the unit's flow rating. It also avoids the standby loss of keeping a tank hot all day.
A heat pump water heater is an electric tank that moves heat from the surrounding air into the water. The U.S. Department of Energy puts it at two to three times the efficiency of a conventional electric tank (DOE). See heat pump water heater installation for what the space needs.
Efficiency and lifespan
The Department of Energy finds tankless units 24 to 34% more energy efficient than a storage tank in homes that use 41 gallons of hot water a day or less (DOE). The saving shrinks as daily use rises, because a busy household keeps a tank's stored water turning over.
On lifespan, the same DOE guide gives most tankless units more than 20 years and storage tanks 10 to 15 years (DOE). Hard water shortens both unless the tank is drained or the tankless heat exchanger is flushed on a schedule.
What makes a conversion cost more than a swap
A like-for-like tank replacement reuses the gas line, the vent and the water connections. A conversion to tankless usually changes all three, and each change is a line on the estimate:
- Gas line and meter. A 40 or 50 gallon gas tank typically draws 30,000 to 50,000 BTU/hr. A whole-house tankless unit can draw several times that at full fire, so the pipe from the meter is sized against the unit before it is quoted.
- Venting. An indoor tankless unit needs its own vent, usually through an outside wall. It cannot share the old chimney the way a tank did.
- Condensate drain. Condensing units make acidic water and need a drain, usually through a neutralizer.
- Power and valves. The unit needs an outlet for its controls and fan, and isolation valves so it can be flushed.
- Removal and haul-away of the old tank.
Can a tankless water heater run two showers?
Yes, if it is sized for it. A tankless unit is rated in gallons per minute at a given temperature rise. New shower heads sold in the U.S. are limited to 2.5 gallons per minute, so two showers and a kitchen tap can call for 6 to 7 gallons per minute at once.
Winter is the test. Incoming water is colder in January, the unit has to raise it further, and its flow at that rise drops. A unit that keeps up in July can fall short on a cold morning if it was sized for summer. Size to your peak use in January.
What Northern Virginia houses need for tankless
Gas is common here: 45% of Arlington homes and 54% of Fairfax County homes heat with utility gas, according to the Census Bureau's 2020 to 2024 American Community Survey (table B25040). A house already on gas has the supply; the question is whether its pipe is large enough.
Venting is the second constraint. Townhouses and attached homes often have one exterior wall to work with, condominium associations usually control what goes through an outside wall, and in local historic districts such as Old Town Alexandria or downtown Leesburg a vent visible from the street can need review by the architectural review board. The vent route is settled on the site visit, before the price.
Water hardness is the third. Scale builds up faster in a tankless heat exchanger than in a tank, so harder water means more frequent flushing. Each area page lists the local water supplier's published hardness.
Why some plumbers advise against tankless
The objections are real and they are about fit, not the technology. A conversion costs more up front. An undersized unit disappoints in winter. A unit installed without isolation valves is hard to flush, and one that is never flushed scales up. A tankless unit also takes a few seconds to fire, so the wait for hot water at a distant tap can be slightly longer unless the unit recirculates.
None of these is a reason to avoid tankless in a house that suits it. They are the checks that decide whether yours does.
Getting an estimate for either
We install tank, tankless and heat pump water heaters across Northern Virginia, and we are an authorized installer for Rinnai tankless and Bradford White tank water heaters. Tell us what you have now (fuel, tank size and age) and we will say on the call which way your house points, then put every line of the job on one free, itemized estimate.
Start with tankless installation, tank replacement or the water heater overview.