Tankless Water Heater Installation

Last updated September 24, 2026

Tankless installation, whether new or converting from a tank, is one of the places where Colorado's specific conditions matter most, cold winter inlet water and elevation both directly affect sizing and setup.

bathroom interior with plumbing fixtures

Why tankless sizing is different here

Tankless units are rated by flow rate at a given temperature rise, and that rating is usually calculated at a warmer inlet temperature than Colorado sees for much of the year. A unit sized using a generic national number can fall short specifically in winter, when inlet water is at its coldest.

Altitude and combustion

Gas-fired tankless units are combustion appliances just like gas tanks, and the same altitude-configuration questions apply. Confirm with your installer that the specific model and configuration are correct for your elevation.

Converting from a tank

Switching from a tank to tankless usually means new venting, and sometimes an upgraded gas line, since tankless units often demand more gas flow at peak than the tank they're replacing.

What the installation day involves

Mounting the unit, running or upgrading venting and gas supply, connecting water lines, and testing under load. A straightforward like-for-like tankless swap can be a single visit; a tank-to-tankless conversion with new venting or gas line work typically takes longer.

Gas supply sizing for tankless specifically

Tankless units often demand a higher peak gas flow than the tank they're replacing, which can mean an upsized gas line is needed, this gets checked as part of scoping the installation, not assumed from the old unit's line size.

Where a tankless unit can and can't go

Tankless units have their own clearance, venting and combustion air requirements that differ from a tank, a space that worked for your old tank doesn't automatically work for a tankless unit without a proper check.

Ongoing Care After Installation

A new tankless installation should come with a maintenance plan from day one, see our tankless descaling page for what that looks like in Colorado's hard water specifically.

Ask specifically what inlet temperature your tankless sizing is based on, a number calculated for a warm-climate winter will not hold up here.

Tank, Tankless or Heat Pump

Comparing the three main options in Colorado
	Gas tank	Gas tankless	Heat pump tank
Altitude effect	Input derated, slower recovery	Input derated, lower winter flow	None (no combustion)
Venting	Chimney or power vent	Stainless or PVC sidewall vent	None
Typical extra work	Usually none for like-for-like	Larger gas line, condensate drain	240-volt circuit, condensate drain, space
Hard-water care	Flush yearly, check anode	Descale yearly	Flush yearly, clean air filter
Works in a power outage	Standing-pilot models, yes	No	No

Is Tankless a Good Fit?

In Colorado, winter inlet water in the 40s and the altitude derate on gas units both reduce that limit. A household that runs two showers and a dishwasher at once on a January morning needs a unit sized for that demand at those conditions, or a second unit.

Gas Supply

Whole-house gas tankless units commonly draw 150,000 to 199,000 BTU, several times more than a tank. Many homes' gas lines and meters were sized for a tank and furnace only. A gas load calculation, and sometimes a larger line from the meter, is often required.

Venting and Condensate

Non-condensing tankless units need stainless steel venting; condensing units vent through PVC or polypropylene and produce acidic condensate that must drain through a neutralizer. Vent terminations must meet clearance rules from windows, doors and grade.

Electrical

Gas tankless units need a standard 120-volt outlet. Electric tankless units need very large electrical service, often multiple 40- to 60-amp circuits, which many homes can't support without a panel upgrade.

Isolation Valves and Filters

Every installation should include isolation valves for descaling and an inlet filter. In hard-water areas, a scale-prevention system is worth considering.

Altitude Settings

Many tankless units have altitude settings or dip switches, and some require high-altitude kits. They must be set correctly for the installation elevation.

A Typical Front Range Tankless Conversion

In a 1990s Arvada or Highlands Ranch home, a typical tankless conversion replaces a 50-gallon atmospheric tank in the basement. The installer first checks the gas meter's capacity and the pipe size from the meter; many of these homes have a three-quarter-inch line sized for a tank and furnace, and a 199,000 BTU tankless unit may require a one-inch line or a dedicated run. The old tank is removed and the chimney connection capped if no other appliance uses it. The tankless unit is wall-mounted with isolation valves, a sediment filter and, in hard water, a scale-prevention cartridge. A condensing unit is vented through PVC to a sidewall, with a condensate line and neutralizer routed to a floor drain. The unit is set for the home's elevation and tested at multiple fixtures.

Recirculation and Hot-Water Wait Times

Tankless units don't store hot water, so the wait at distant fixtures can be longer than with a tank. Some units include a built-in recirculation pump and small buffer tank; others can pair with an external pump and timer. In large homes, a recirculation loop or a point-of-use heater at a far bathroom solves the wait.

Cold-Water Sandwich

Tankless units can produce a brief burst of cold water between uses, called a cold-water sandwich, when a tap is turned off and on again. Buffer tanks and modern control logic reduce it.

Questions Homeowners Ask

Can one unit serve a whole house? Often, if sized for peak winter demand at altitude; larger homes may need two.

Do tankless units need maintenance? Yes; annual descaling in Colorado's hard water.

Does tankless work during power outages? No; gas tankless units need electricity.

Point-of-Use and Hybrid Options

Not every tankless installation is whole-house. Small electric point-of-use units under a sink can serve a distant bathroom or a kitchen far from the main heater. Hybrid setups pair a tankless unit with a small storage tank to eliminate cold-water sandwiches and improve performance at low flow.

Choosing Between Condensing and Non-Condensing

Condensing tankless units recover heat from exhaust, reaching efficiencies above 90%, and vent through simple PVC. They produce acidic condensate that needs neutralizing. Non-condensing units are simpler but need stainless venting.

What a Tankless Installation Involves

Gas line upgrades, venting, condensate drainage, electrical, permits and labor make up the rest.

Permits and Inspections for Tankless

Tankless conversions usually require gas, plumbing and sometimes electrical permits. Inspectors check gas line sizing, venting materials and clearances, condensate disposal and relief valve discharge.

Mounting Location

Tankless units can be mounted on interior walls with venting or on exterior walls with outdoor models. In Colorado, outdoor models face freezing risk and are less common except in milder areas like the Arkansas Valley.

Tankless in Colorado Mountain Homes

In mountain homes, tankless units must be high-altitude models or set for elevation, and their winter flow will be lower because inlet water is near freezing. Many mountain installations pair a tankless unit with a small buffer tank or choose a larger model to compensate. Freeze protection depends on power, so drain-down plans matter for homes that lose electricity in storms.

Venting and Gas Line Checks

Tankless conversions often need a larger gas line than the old tank used, since a whole-house unit can draw 150,000 to 199,000 BTU/hr. Venting also changes, typically to PVC for condensing models or stainless for non-condensing ones.

FAQs

It can be, when sized correctly for winter inlet temperatures. See our tank-versus-tankless coverage on the sizing guide page for the full tradeoff.

Yes, hard water means tankless units need real descaling maintenance more often than in a soft-water climate. See our tankless descaling page.

Not in the way a tank can, but it can be limited by flow rate if demand exceeds the unit's rated capacity at the current inlet temperature.

Longer than a like-for-like swap, mainly due to new venting and possibly gas line upgrades, the technician will scope it after seeing your setup.

Both are subject to the same combustion-and-elevation principle if gas-fired; electric tankless units aren't affected by altitude the same way.

It depends on household peak demand and winter inlet temperature, see our sizing guide page.

Not necessarily, this needs to be checked specifically, since tankless units often have higher peak gas demand than tank units.

Some models are rated for outdoor installation; whether that's the right choice for your home depends on the specific unit and your climate exposure.