Colorado Water Heater Rules: What Applies to Your Home

Water heater rules in Colorado changed more in the last few years than in the decade before. A state emissions law now governs which gas water heaters can be sold and installed. A federal efficiency standard is set to reshape electric tank water heaters. Denver adopted electrification rules that apply to some buildings and not others.

The result is confusion, and some of it gets used to rush homeowners into decisions. This guide from The Electricians and Plumbers sorts out which rules apply to your home, based on the fuel your water heater uses and where you live. It also covers what each rule does not do, which matters just as much.

None of these rules force you to replace a water heater that works. Every one of them applies when you buy and install a new unit.

The Short Version: Rules by Water Heater Type

Find your current water heater in the table, then read the sections that apply to you.

Colorado's Gas Water Heater Emissions Law

The water heater limits in Colorado House Bill 23-1161 took effect on January 1, 2026. The law sets limits on nitrogen oxide emissions from new gas fired water heaters and furnaces. Nitrogen oxides contribute to ground level ozone along the Front Range, and this law targets the gas appliances in homes and buildings.

The law limits how much NOx a new water heater can emit for each unit of energy it uses. There are two categories:

• Water heaters with a rated input up to 75,000 BTU per hour have the stricter limit of 10 nanograms per joule.
• Larger water heaters, up to two million BTU per hour, are held to 14 nanograms per joule.

Most residential tank water heaters fall in the lower input category. Most whole house gas tankless units fall in the higher one.

A model that meets these limits is usually labeled ultra low NOx. The emission limits apply to new units manufactured, distributed, sold, or leased in the state, and the law includes an alternative compliance path for certain ENERGY STAR certified models. Units that were already in Colorado inventory before the law took effect could still be sold after that date. That supply does not last forever, which is why compliant models make up a growing share of what is available.

What the Law Does Not Do

The law does not ban gas water heaters. Compliant gas tank and tankless models are made by major manufacturers and remain available.

It does not require you to replace a working water heater, and it does not stop a licensed plumber from repairing the one you have. Replacing a thermocouple, a gas valve, or an anode rod on an existing unit is a repair, not a new installation.

It also does not apply to electric or heat pump water heaters.

The Propane Exemption

The original law relied on emissions testing developed for natural gas equipment. Many propane models could not show compliance, and some disappeared from the Colorado market as a result. The legislature responded with a bill that exempts propane fueled furnaces and water heaters from the emission limits until January 1, 2031.

If your home runs on propane, standard propane water heaters can be sold and installed under that exemption. Plan for the possibility that the limits will apply to propane after the exemption ends.

The Federal Efficiency Standard for Electric Water Heaters

The U.S. Department of Energy sets minimum efficiency standards for water heaters sold nationwide. Under its current rule, residential water heaters manufactured on or after May 6, 2029 must meet higher efficiency levels.

The biggest change is for electric tanks. Electric storage water heaters larger than 35 gallons and up to 120 gallons will need heat pump technology to meet the standard. The common 40 and 50 gallon electric tank that heats with resistance elements will be replaced by heat pump models in those sizes.

A few details keep this from being as sudden as it sounds:

• The standard applies to units made on or after the compliance date, not to units already installed. Your existing electric tank can stay in service for its full life.
• Units manufactured before the compliance date can still be sold and installed after it.
• Gas tankless water heaters were excluded from this rule. The Department of Energy adopted separate standards for them, but Congress disapproved that rule and it was withdrawn in 2025, so no new federal minimum for gas tankless units is currently scheduled.
• Gas tank water heaters also face higher efficiency minimums under the same rule.

Federal efficiency rules can be revised or delayed, so confirm the current status with your plumber or the Department of Energy before you make a decision based on the compliance date.

Denver Building Rules and Single Family Homes

Denver adopted building code changes that push gas heating and water heating equipment toward electric alternatives. These rules have generated headlines, and they are often misread as a ban on gas water heaters in homes. They are not.

When the city adopted the code changes, the Denver City Council chose not to require single family homeowners to electrify. The rules that do exist focus on commercial and multifamily buildings, including requirements for new construction and for replacing gas equipment in existing buildings. Separately, the Energize Denver program sets energy performance targets for buildings of 25,000 square feet or more.

Denver has also begun updating its energy code for new and renovated small buildings, including single family homes and duplexes. Those proposals focus on efficiency and electrification readiness, and they had not been adopted when this article was last reviewed.

If you own a single family home in Denver, you can replace a gas water heater with another gas water heater, as long as the new unit meets the state emissions law and passes permit and inspection. If you own or manage a larger multifamily or commercial building, talk with your plumber about Denver's current requirements before your equipment fails. Those requirements include planning steps that are much harder to complete in an emergency.

Permits and Inspections

Replacing a water heater requires a permit in Denver. Most surrounding cities and counties in the metro area require one too. The permit is filed by the licensed contractor, and an inspector checks the finished installation.

The inspection protects you. An inspector confirms the details that make a water heater safe:

• Proper venting of combustion gases on gas units
• A correctly installed temperature and pressure relief valve with a discharge pipe
• Gas line connections and shutoff valves
• Thermal expansion control where the plumbing requires it

Skipping the permit causes problems later. An unpermitted installation can complicate an insurance claim after a leak or a fire. It can also become an issue when you sell the home and the buyer's inspector asks for records. The Electricians and Plumbers pulls the permit on every water heater replacement.

Incentives for Heat Pump Water Heaters

Heat pump water heaters cost more to buy than standard electric tanks. They use far less electricity because they move heat from the surrounding air into the water instead of creating heat with resistance elements. Incentives help close the gap in upfront cost.

Incentive programs change often, so this section describes how they work rather than listing amounts that may change.

• Federal tax credit. The federal tax credit for heat pump water heaters ended for equipment installed after December 31, 2025. There is no federal credit for new installations.
• Colorado state tax credit. Colorado offers a heat pump tax credit that covers heat pump water heaters. It works through registered contractors, who pass at least one third of the credit to the customer as a discount at the time of installation. The state has a built-in schedule that lowers the credit again in tax year 2029.
• Utility rebates. Xcel Energy offers rebates on qualifying heat pump water heaters for its Colorado customers. Other utilities in the state run their own programs.
• Regional programs. The Denver Regional Council of Governments runs Power Ahead Colorado, a multi-year program that offers rebates and energy advisors for heat pump projects across the Denver metro area. Its rebates currently cover cold climate heat pumps for space heating rather than heat pump water heaters, so check the program's current rules before you count on it for a water heater project.

Ask your contractor which programs your installation qualifies for and who handles the paperwork. Some incentives require preapproval before the work begins.

Plumbing and Electrical Work for a Heat Pump Water Heater

A heat pump water heater is a plumbing project and often an electrical project. Many models need a dedicated 240 volt circuit. Some homes need electrical panel work to support one. Some newer models run on a standard 120 volt outlet, which can make a switch from gas simpler.

The unit also needs enough surrounding air to work efficiently, a condensate drain, and a location where its fan noise and cool exhaust air are acceptable. Basements and garages are common choices in Colorado homes.

The Electricians and Plumbers is licensed for both plumbing and electrical work, so one team can evaluate the water heater location, the plumbing connections, and the electrical capacity together.

How to Check What Applies to Your Home

You can answer most of these questions in a few minutes by looking at the rating plate on your current water heater. It is the label on the side of the tank or on the front of a tankless unit.

1. Find the fuel type. The plate lists natural gas, propane, or electric. If both gas types appear, look for which one is checked or which conversion kit is installed.
2. Find the capacity. Tank size in gallons determines whether the federal heat pump standard applies to an electric replacement.
3. Find the input rating. For gas units, the BTU per hour rating shows which emissions category applies.
4. Find the age. Most manufacturers encode the manufacture date in the serial number. A plumber can decode it if the format is unclear.
5. Know your building type. Single family homes are outside Denver's electrification requirements. Multifamily and commercial buildings are not.

Write this information down or take a photo of the plate. If your water heater fails, having it ready speeds up the replacement and helps your plumber confirm a compliant model is available before arriving.

Planning Ahead Instead of Replacing in an Emergency

Most water heaters are replaced after they fail. That is the worst time to sort through rules and options, and it often means accepting whatever compliant unit is available that day.

If your water heater is approaching the end of its expected life, a planned replacement gives you time to compare gas and heat pump options, confirm incentives, and schedule any electrical work. Our guide to the signs you need a new water heater covers how to tell when that time is close.

A planned replacement is not the same as a rushed one. No rule described here requires you to replace a water heater early. Be cautious of any sales pitch that claims otherwise.

Sources

• Colorado General Assembly: HB23-1161, appliance emissions standards
• Colorado General Assembly: SB26-002, including the propane exemption
• Colorado Department of Public Health and Environment: Air Pollution Control Division
• U.S. Department of Energy: consumer water heater standards
• Internal Revenue Service: Energy Efficient Home Improvement Credit
• Colorado Energy Office: Colorado heat pump tax credits
• Xcel Energy Colorado: residential programs and rebates
• DRCOG Power Ahead Colorado: rebate program overview
• Denver Community Planning and Development: permits and building code