Boulder All-Electric Remodel Requirement: What Triggers It

For a gut remodel of the rooms you already live in, Boulder's 2024 energy code usually decides the all-electric question on one line of the plan: whether the furnace, the air conditioner or the water heater gets replaced. The share of the house the work touches matters too, but on its own it never triggers the requirement.

That matters if you own a City of Boulder house and plan a gut remodel or an addition, or you're buying one and counting the project into what it's worth to you. If the rule applies, the heat source, and possibly the electrical service, become part of what the project costs.

The short answer: In the City of Boulder, a remodel carries the all-electric requirement only when three things happen together: the work exceeds 50 percent of the home's floor area, at least half the thermal envelope is altered, and the heating or cooling equipment or the water heater is replaced. Then the code requires primary space and water heating to be all-electric or non-fossil, and the City says the old gas unit may stay as a backup; where only one piece of equipment is replaced, the City's energy-code staff are the ones to say how that applies. A remodel of existing living space that replaces no heating, cooling or water-heating equipment carries no all-electric requirement, however large; turning a garage or other unconditioned space into living space falls under the addition rules instead. An addition on its own counts as new construction, so new equipment serving it has to be electric. Two building permits for the same home applied for within 24 months count as one. Unincorporated Boulder County, including Niwot, runs its own code.

What triggers Boulder's all-electric requirement in a remodel?

Three conditions, and all three have to be true at once. The rule is Section R503.2 of the 2024 City of Boulder Energy Conservation Code, which the City adopts by reference in Chapter 10-7 of the Boulder Revised Code and which applies to building permits applied for since Dec. 1, 2024.

The third row is where the size-based summary goes wrong. The mechanical condition has no size at all: it's met when equipment is replaced, and "space conditioning" in the code covers cooling as well as heat. The City's energy code FAQ gives "a replacement of an existing furnace, A/C, heat pump, etc." as its examples, so a gut remodel that swaps a tired air conditioner can meet that condition while the furnace stays. What the rule then asks of that furnace is one of the two questions at the end of this page.

Turned around, the same row is the useful fact. A remodel that replaces no heating, cooling or water-heating equipment doesn't meet the third condition, so the all-electric requirement doesn't apply, whatever the square footage. The code says unaltered parts of a house aren't required to comply "unless triggered by a higher level of alteration," and the staff memo to City Council in May 2024 was blunt about it: "when a level 3 alteration does not include replacement of HVAC equipment, there is also no requirement that electric equipment be installed." That project still owes the energy rating in the last row, because every Level 3 does. One exception sits outside the equipment rule: R501.2 says "Changes where unconditioned space is changed to conditioned space shall comply with Section R502," the addition rules, so new equipment serving a converted garage or other unconditioned space has to be electric.

Before anyone plans around keeping the equipment, check how old the furnace, water heater and air conditioner are. A gut remodel can end up replacing equipment for reasons that have nothing to do with the code: age, a relocated mechanical room, a system resized for the new envelope. In a remodel that meets the other two conditions, that replacement is the trigger. An owner can ask whoever services the furnace and water heater how old each one is. For a buyer, those ages show up in a home inspection in Boulder County. Keeping an old furnace to stay under the rule has a cost of its own: a house finished on the surface with its systems left old is the middle position the half-measure note argues usually costs the most.

The Energy Rating Index is the scale behind the familiar HERS score: 100 is the code's reference house, 0 a house that nets out to zero energy use. For a Level 3, the first report the City asks for is a baseline rating of the house as it stood before the work (R503.2.2.1), so the rater has to see the house before anything comes out. Ask your architect or builder early who will do that rating, and put it on the schedule ahead of demolition. Whether a given project is a Level 3 at all is the City's determination, made on the plans.

This is the City's code, and it stops at the city limit. Unincorporated Boulder County, including Niwot and the county side of Gunbarrel (which splits parcel by parcel, so confirm which side an address is on before planning around either code), runs its own building code, and neither the county's 2025 code amendments nor its BuildSmart guide requires additions or remodels to be all-electric; Boulder County Community Planning & Permitting answers for a specific project. What the county does cap, across most of its residential and rural zoning, is how big a house can get, which Boulder County's home size limit sets out.

Two permits in 24 months are one permit

Phasing a remodel doesn't split it for the code. Section R501.2.1 reads: "Any two or more building permits for the same dwelling unit that are applied for in any 24-month period shall be considered as one permit for the purpose of determining and meeting the requirements of Section R501.2." Section R501.2 is what sends a project to the addition rules or the alteration rules, so it's the combined scope that gets measured.

Picture a kitchen and basement one spring, then new siding, new windows and a furnace replacement the next. If both years' work is on building permits, for the code that's one permit, measured as one scope against the 50 percent lines, so two modest-looking jobs can together meet all three conditions. Whether a stand-alone trade permit, such as one for a furnace alone, counts with the rest is for the City to say.

For a buyer, one detail in R501.2.1 matters: it's keyed to the dwelling unit and says nothing about a change of owner, and it counts permits by when they were applied for, including one that was never finished. Before your Inspection Termination Deadline, pull the City's permit records on the address (anyone can search them by address from the City's records resources page) and ask the seller about any permit applied for in the last two years. Don't count on the City answering how that work counts toward yours inside that window: its energy-code staff say conceptual and hypothetical questions aren't one of their core services, so ask once you can describe the real project.

Can you keep a gas furnace in a Boulder remodel?

In most City of Boulder remodels, yes. In one that meets all three conditions, the City's FAQ says old gas equipment can stay as a backup. Outside a remodel that meets all three conditions, a working gas furnace or water heater can stay. R501.1.1 opens: "Except as specified in this chapter, this code shall not be used to require the removal, alteration or abandonment of, nor prevent the continued use and maintenance of, an existing building or building system lawfully in existence at the time of adoption of this code." The chapter does specify two things short of all three conditions: the energy rating for any Level 3, and electric-ready wiring when gas equipment is replaced. Neither requires a working furnace or water heater to come out. Replacing a failed one on its own doesn't carry the requirement either; the same Council memo said "there is no requirement for the replacement equipment to be all-electric unless that replacement is part of a substantial level 3 alteration." That's the catch in the plan owners reach for next, remodeling now and replacing the furnace on its own later: a replacement permit applied for within 24 months of the remodel's permit application may be measured with it, so ask the City how it would count before you plan around it.

Inside a remodel that meets all three, the code requires the primary heating and hot-water equipment to be electric or another non-fossil source, and the old gas equipment can stay behind as a backup. Where both are being replaced, that's straightforward; where only one is, the code doesn't say, and that's the second question below. The City's FAQ puts the backup rule this way: "The existing equipment could remain as backup if desired but could not be replaced like for like."

Even in a remodel that meets all three, a gas range, a gas dryer and, per the City's FAQ, a gas fireplace can still be replaced with gas. R503.2's electric requirement reaches "primary space and water heating," so a range or dryer isn't part of it, and the FAQ confirms: "You can still replace a gas range or fireplace in a Level 3 alteration that includes substantial mechanical and envelope alteration."

One consequence of going electric belongs in the budget: electric heat and hot water draw on the panel and the service, and the code says alterations "shall not … overload existing building systems" (R503.1). On an older house, ask your inspector to note the electrical service size, and ask an electrician early whether it needs an upgrade, which involves Xcel Energy, the utility. Neither the equipment nor the upgrade has a price that holds from one house to the next, so get both quoted while the design is still open.

What the Boulder energy code asks of an addition

New space is treated as new construction. Section R502.1 says additions "shall conform to the provisions of this code as those provisions relate to new construction," and the new-construction rule, R403.1, requires the systems for heating, cooling, water heating, cooking and clothes drying to be "all-electric or fueled by other non-fossil fuel derived energy sources." So for an addition on its own, the new equipment serving it must be electric, a new water heater included (R502.5 and R403.6). The City's FAQ adds two specifics: gas service lines can't be extended into an addition for gas equipment, and a new gas range can't go in the addition, though it could replace the existing range in the kitchen.

Size changes the paperwork. An addition over 1,000 square feet of conditioned floor area must use the energy-rating route, which rates the whole house: R502.2.2 requires showing that "the existing building plus the addition achieves a maximum ERI of 50 or a 30% reduction from the existing building ERI," which starts with a baseline rating of the existing house "prior to construction." A smaller addition can take that route or a prescriptive one, which still requires an air-leakage test of the addition plus the existing house. Additions also owe at least five efficiency credits from the code's menu unless an exception applies (R502.7); the exceptions include an addition that grows the home's conditioned floor area by less than 25 percent.

An accessory dwelling unit built as an addition, or carved out of a garage, follows the addition rules above; what a lender will count of its rent is an underwriting question, not a code one. A scrape-and-rebuild is new construction outright, so the new-construction rule above applies to the whole house; the North Boulder guide covers the demolition review that can come first. And the Council memo's proposed roadmap for new construction shows rating targets tightening in the 2027 and 2030 code cycles, so the permit's application date decides which rules apply.

What if the project is an addition and a remodel, or replaces just one system?

Neither case is settled by the code's text, so the answer has to come from the City.

The first is a project that's both an addition and a remodel. R501.2 says: "Where both additions and alterations are included in the scope of work, the larger portion of work will govern the direction (R502 or R503) for compliance." It leaves open whether new equipment serving the addition still has to be electric when the remodel is the larger portion and wouldn't trigger the requirement on its own. The City's FAQ gives this very shape as an example, saying a 1,500-square-foot Level 3 alteration with a 500-square-foot addition "should proceed as if it were a Level 3 alteration in terms of energy code compliance," but it doesn't say whether that frees new equipment serving the addition from the electric requirement, and the Council memo doesn't take the question up.

The second is a gut remodel that replaces one piece of equipment. The mechanical condition is met when "the space conditioning equipment or service water heating equipment is replaced." If only the water heater, or only the air conditioner, is replaced in a remodel that meets the other two conditions, what the rule then requires of the furnace that stays isn't settled by the text.

Put both to the City's energy-code staff in writing before the design is final, describing the real project: the floor area the work touches, the envelope work, each piece of equipment to be replaced, and the address. The City's energy code page lists an email request through Inquire Boulder as the quickest route, plus a phone line (303-441-1880) and appointments, and its booking page notes that "providing answers to conceptual design or hypothetical questions is currently not one of our core services due to the resources it would require." A described project gets a better answer than a what-if. Keep the reply with the plans.

If the house is inside Boulder city limits, the City's code governs, and the diligence list for the city's mid-century houses (radon, original systems, the sewer lateral) is in living in Boulder. If it's on the county side, none of the City's code applies, and the county's permitting office answers instead.

What's been permitted on the house in the last 24 months, and how old its heating, hot-water and electrical equipment is, can both be checked before you own it. We can pull the permit history and read the inspection report with you inside your Inspection Termination Deadline, so you have both before the design starts. If you already own the house and this project is the alternative to moving up, a read on what it's worth as it is now is the number to set against what the project will cost.

True North Boulder is a real-estate team with eXp Realty. This is general information about the City of Boulder's energy code for owners and buyers, not legal, engineering or financial advice. The City decides how the code applies to a specific project; confirm yours with the City's energy-code staff, and for advice on a particular property, talk to a licensed architect or a Colorado attorney.