Tankless vs Tank Water Heaters for Metro Denver Homes

What actually differs between them?

A storage water heater keeps a tank of water, commonly 30 to 80 gallons, hot at all times. That means heat slowly escapes through the tank walls, a loss the Department of Energy calls standby loss. A tankless, or on-demand, heater has no reservoir. When a hot tap opens, water flows through a heat exchanger and a gas burner or electric element heats it on the spot.

The practical result is a trade. A tank gives you a big buffer of hot water that several fixtures can draw on at once until it runs out. A tankless unit never runs out, but it can only heat so many gallons per minute.

Side-by-side comparison

How much energy does tankless save?

The Department of Energy estimates that for a household using 41 gallons of hot water a day or less, a tankless heater can be 24% to 34% more energy efficient than a conventional tank. For a heavy-use home at around 86 gallons a day, the gain drops to 8% to 14%. DOE also says an ENERGY STAR tankless model could save $100 or more a year.

One detail matters when shopping. DOE notes that gas tankless units with a standing pilot light waste energy and can cancel out part of the standby savings, so look for a model with intermittent ignition instead.

Put those numbers next to the price gap and the payback depends heavily on how long you stay in the house. A tankless unit that lasts 20 years has much longer to earn back its higher installed cost than one you leave behind in five.

Can one tankless unit keep up with your family?

Sizing is where tankless installs go wrong. DOE says that in large households even the biggest gas-fired model may not supply enough hot water for several simultaneous uses, such as a shower running while the dishwasher fills. Gas models deliver higher flow rates than electric ones.

Two things shrink a unit's real output here. First, incoming water is colder in winter, so the heater has to raise the temperature further and can deliver fewer gallons per minute at the setting you want. Second, altitude, covered below. Ask a plumber to size the unit for your coldest-month peak, not an average day. Some large homes end up with two units, which adds cost.

Does Denver's altitude change anything?

Yes, and it is the most Colorado-specific part of this decision. Denver sits at 5,280 feet. Thinner air means less oxygen for combustion, so gas appliances have to be set up for the elevation. Rinnai's technical bulletin for one of its tankless lines, for example, certifies the units up to 10,200 feet and requires different dip switch settings for each elevation band: 2,001 to 5,200 feet, 5,201 to 7,700 feet and 7,701 to 10,200 feet. Denver lands right at the edge of two of those bands, and homes in the foothills sit higher still.

The takeaway is simple: whoever installs a gas tankless unit needs to confirm it is approved for your elevation and configure it to the manufacturer's instructions. A unit set for sea level can run poorly, and the same care applies when a tankless heater is serviced in Denver later. Gas tank heaters have altitude considerations of their own, which is one more reason to use a pro for either.

What does switching from tank to tankless involve?

Replacing a tank with a tank is mostly a swap. Going to tankless is a small renovation. Common pieces of the job:

• Gas supply. Tankless burners draw much more gas at full fire than a tank burner, and the existing line is often too small. Upgrading it is real gas line work, permitted and pressure-tested.
• Venting. Most units need their own vent, often run through a side wall rather than the old chimney flue. Condensing models also need a condensate drain.
• Electrical. Gas units need a standard outlet. Whole-house electric tankless units can need heavy dedicated circuits and sometimes a panel upgrade.
• Isolation valves. A service valve kit makes future descaling much easier and is worth adding during the install.

HomeAdvisor's 2026 figures put tankless installation labor at $600 to $1,900, and the tank-to-tankless conversion work alone at $150 to $2,500 depending on how much changes. In Denver, the water heater itself is a quick permit for single-family homes and duplexes through Community Planning and Development. For a standard swap, compare quotes for a replacement tank heater against the full tankless conversion, line by line.

Do you have natural gas, and from whom?

Most of the metro is served by Xcel Energy. Not everyone is. Castle Rock lists Black Hills Energy as its gas provider, and Bennett lists Colorado Natural Gas. In the Jefferson County mountains, the county says homes are generally on private wells, and some mountain homes may rely on propane rather than a gas main. If your home runs on propane or all-electric, a gas tankless unit may not be practical, and an electric tankless unit is limited in flow. A heat pump water heater is another option, though DOE says it needs a space that stays between 40 and 90 degrees year-round and about 1,000 cubic feet of air around it, which often means a heated basement rather than a garage. Homeowners up in Evergreen or Castle Rock should confirm fuel and utility before choosing.

Does your water favor one type?

Scale is the main enemy of a tankless heat exchanger, and metro water ranges widely. Denver Water describes its supply as soft to moderately hard, harder in the south and in winter. Thornton reports hard water averaging about 230 mg/L. Longmont reports soft water at 1 to 2 grains per gallon. On a hard supply, a tankless unit needs descaling more often, and a softener or scale treatment may be worth discussing, and homeowners researching tankless units in Thornton in particular should plan on regular descaling. Tanks suffer from hard water too, through sediment buildup, but they are more forgiving of skipped maintenance.

Which should you choose?

Lean tankless if: you have natural gas, a household of one to three people, plans to stay many years, limited floor space, and a plumber has confirmed the gas line and venting can be done at a reasonable cost.

Lean toward a tank if: several showers and appliances often run at once, the budget is tight, the old tank just failed and you need hot water quickly, or your home is on propane with no easy upgrade path.

Either way, the installation matters as much as the equipment. If your current tank is still working, the guide to repairing versus replacing can help you decide whether to switch now or plan for later.

A note on gas safety

Any gas appliance change should end with a leak check. If you ever smell gas, leave the house first, then call 911 and your gas utility from a safe place. For most of metro Denver that is Xcel Energy at 1-800-895-2999. Other utilities serve some towns, so the right number is on your gas bill.