Tankless vs tank water heater: which fits your house

Both heat the same water. What decides the choice isn't the marketing, it's what your house can feed and what you ask of it. Here's the honest breakdown.

What a tank does well

• Simple swap: a same-size tank replacement is the cheapest, fastest water heater job there is
• No utility upgrades: it uses the gas line, vent, and electrical service you already have
• Works through outages: a gas tank with a standing pilot keeps making hot water when the power's out
• Decades of installers: every plumber in the county has swapped thousands of them

The tradeoffs: it holds forty or fifty gallons whether you're using them or not, it takes floor space, and when the tank rusts through it lets go all at once.

What tankless does well

• Space: it hangs on a wall and gives the floor back
• Continuous hot water: it heats on demand, so back-to-back showers don't drain a tank
• Longer service life: tankless units typically outlast tanks when they're maintained
• No tank to rupture: leaks happen at fittings, not as fifty gallons on the floor

The tradeoffs are the catch most quotes skip:

• Gas supply: a tankless burner draws far more gas at full fire than a tank. Older homes often need a larger gas line run to the unit, which is real work, not an accessory
• Venting: most units want a sealed stainless or PVC vent to an outside wall, not the old flue
• Electrical: even gas units need power for ignition and controls, so a dead unit means no hot water at all
• Hard water: King County water runs soft to moderate, but the heat exchanger still wants periodic descaling or performance drops

How to decide

• Same spot, same fuel, tight budget, household's happy with the tank → tank
• Finishing a basement or ADU, short on floor space, or the tank died and you're remodeling anyway → get the tankless quote too
• All-electric house → the picture changes. Electric tankless draws enormous amperage; a heat pump water heater is usually the better electric upgrade, and that's a separate conversation

Ask the plumber who calls what a same-size tank swap runs versus a tankless conversion for your house, and have them price both. The delta between the two numbers is the real decision.