The Bay Area’s Gas Water Heater Rule: What to Plan for Now If You’re Remodeling in Marin or San Francisco

If you’re planning a kitchen, bathroom, whole-home, or ADU project in Marin County or San Francisco, there’s a regional rule worth building into your plans before any walls open. The Bay Area Air District has adopted a zero-NOx standard for new residential gas water heaters. In practice, that means the next water heater many homeowners buy will be a heat pump unit. Heat pump water heaters have different space, electrical, and drainage needs than the gas tank they replace.

The start date is currently in flux, which is part of why this is worth understanding now. The planning decisions it affects are easiest to make while a remodel is already underway, whichever date the rule ultimately takes effect.

Where the Rule Stands Right Now

Here’s a quick summary, based on the Bay Area Air District’s building appliances page as of late September 2026:

• The adopted rule. The rule adopted in 2023 sets a zero-NOx standard for new gas water heaters under 75,000 BTU/hour, which covers most residential tank units. The adopted start date is January 1, 2027.
• It applies at replacement. Existing water heaters aren’t required to come out.
• Proposed delay and exemptions. In July 2026, the Air District released draft amendments. They would move the start date to January 2028 and add exemptions, including for low-income property owners and for situations where electrical panel or physical space constraints make the switch impractical.
• Smaller tanks. Staff have also recommended a later date, January 1, 2031, for water heaters under 35 gallons.
• Timing of a decision. The Air District Board is tentatively scheduled to consider the amendments in November.

A separate rule covers gas furnaces on a later schedule. This article focuses only on water heaters.

Because the final language hasn’t been adopted, check the Air District’s page for current status before making equipment decisions. Nothing here should be read as a final interpretation of the rule for your specific property.

Why a Possible Delay Doesn’t Change the Remodel Math

Whether the rule starts in 2027 or 2028, it applies when your water heater is replaced. If your current unit is already several years old, its replacement will very likely fall under the new standard either way.

So the useful question for a remodel isn’t “Do I have to switch now?” It’s this: if you’re already opening walls, moving plumbing, or upgrading electrical, what would it take to be ready later, and what would that same work involve after the remodel is finished?

Preparing for a heat pump water heater after a remodel can mean opening new drywall to run a circuit, cutting in a drain, or reworking a closet you just finished. During a remodel, much of that work happens alongside rough-in trades that are already on site.

Four Things a Heat Pump Water Heater Needs That a Gas Tank Doesn’t

1. Air Volume

Heat pump water heaters pull heat from the air around them, so manufacturers specify how much surrounding air space the unit needs. The requirement varies. ENERGY STAR’s installation guidance notes that some 240V models need as little as about 450 cubic feet, while some 120V models designed to replace gas units need more than 700.

A small interior closet that held a gas tank for decades often won’t qualify on its own. Louvered doors or ducting can sometimes solve it. Those are design decisions, and they’re far easier to make on paper than after cabinetry is installed.

2. Electrical Capacity

Many heat pump water heaters are designed for a dedicated 30-amp, 240V circuit, which often means an electrician runs a new line when replacing a gas unit. Several manufacturers also make 120V models that can use an existing circuit and avoid new wiring, though they come with tradeoffs, including slower recovery. Which type fits depends on your panel and on everything else your project adds.

That last point matters in a remodel. A kitchen project may add an induction range, a more powerful range hood, or new appliance circuits. An ADU or addition adds its own load. The water heater belongs in the same electrical conversation, not in a separate one that comes up two years later.

3. Condensate Drainage

Heat pump units dehumidify the air as they run, which produces condensate. That water has to go to a nearby floor drain or be moved with a small condensate pump. In a garage or basement, this is usually manageable. In an upstairs interior closet, it can mean a new drain line routed through finished space.

4. Location and Sound

A heat pump water heater has a compressor and a fan, and it cools and dries the air around it. That can be a benefit in a garage or basement and a drawback in a closet next to a bedroom. Decide where the unit belongs before the floor plan is final.

What’s Different in Older Marin and San Francisco Homes

Older housing stock raises a few specific questions.

Where the water heater is now. In many older San Francisco homes, the water heater sits in a ground-floor garage or basement. Those spaces often have enough air, but headroom, access, and drain routing vary. In many mid-century Marin homes, it’s in a hall closet or under-floor area, and closets are the hardest fit.

Panel capacity. Many older homes have electrical service sized long before induction cooking, EV charging, and heat pumps. Whether your panel can carry another load depends on a load calculation by a licensed electrician. The number printed on the panel won’t tell you.

Shared venting. If your gas water heater shares a flue with another gas appliance, removing the water heater can change how that vent performs for the appliance that remains. A licensed professional should evaluate this as part of the scope, not after the fact.

Hot water distance. A remodel is also the moment to ask whether the water heater is in the right place at all. If the kitchen or primary bath is moving, the distance from the water heater affects how long you wait for hot water at the tap.

These aren’t the only surprises older homes can hold. Our look at what demolition often reveals in older Marin and San Francisco homes covers several more.

What to Decide Before Demolition, and What Can Wait

Decide before demolition:

• Where the water heater will live long-term, and whether that space meets the air volume and clearance the likely equipment requires
• Whether your electrical service can carry the remodel’s added load plus a future heat pump water heater
• Whether to rough in a dedicated circuit now, even if you keep the existing unit
• How condensate would drain from the chosen location
• Whether a vent or gas line serving the current water heater will be affected
• Whether the remodel changes plumbing runs enough to justify relocating the water heater

Can often wait:

• The specific brand and model, if your current water heater is healthy
• Whether you install the heat pump unit now or run the existing one until replacement
• Rebate applications, which depend on the equipment and timing you choose

Preparing the space and electrical during a remodel doesn’t commit you to replacing a working water heater. It means the eventual replacement is a swap instead of a second project.

These are the same kinds of choices covered in our guide to what to decide before demolition day. When they come up mid-project instead, they’re a common source of change orders.

Questions to Ask Before You Approve a Remodel Scope

1. Does the scope include an electrical load calculation, and does it account for a future heat pump water heater?
2. If a dedicated circuit, drain, or ventilation path is included, where does it appear in the scope? If it’s not included, is that a deliberate choice?
3. If the current water heater location won’t work for a heat pump unit, what are the alternatives, and what else do they affect?
4. What permits will the water heater and electrical work need in your city or county, and who’s responsible for pulling them?
5. If the existing water heater is near the end of its life, what’s the plan if it fails mid-project?

A proposal that answers these clearly is easier to compare against other remodeling bids. If one bid includes water heater prep and another doesn’t, you aren’t comparing the same scope.

If you’re planning an ADU, the water heater question sits alongside the permitting changes covered in our post on California’s 2026 ADU law changes.

A Note on Exemptions

It’s reasonable to wonder whether one of the proposed exemptions might apply to you. The draft panel and space exemptions are aimed at situations where the switch is impractical.

The language hasn’t been adopted yet, and how any exemption applies to a specific property will depend on the final rule. A remodel is also often the point when those constraints are easiest to solve. We’d suggest planning for the standard rather than around an exemption.

Frequently Asked Questions

Do I have to replace my working gas water heater?

No. The rule applies when a water heater is replaced. An existing unit can stay in service.

When does the Bay Area water heater rule take effect?

The adopted date is January 1, 2027. Draft amendments released in July 2026 would move it to January 1, 2028, and the Air District Board is expected to consider them in November 2026. Check the Air District’s site for current status before making equipment decisions.

Can a heat pump water heater go in a closet?

Sometimes. It depends on the model’s air-volume requirement, which varies by manufacturer. Small closets often need louvered doors or ducting to work. The manufacturer’s installation instructions are the deciding factor.

Will I need an electrical panel upgrade?

Not necessarily. It depends on your existing service, what else the remodel adds, and whether a 240V or 120V unit fits your situation. A load calculation by a licensed electrician is the way to find out.

Should I install a new gas water heater before the rule takes effect?

Under the current rule, installing a gas unit before the start date is allowed. It doesn’t remove the need to plan, though, because that unit’s eventual replacement will likely fall under the new standard. Weigh the unit’s age and your remodel timeline with your contractor.

Helpful Resources

• Bay Area Air District: Rules 9-4 and 9-6 Building Appliances: the official rule page, with current status, draft amendments, and FAQs
• Air District: Draft Changes to the Water Heater Rule (July 2026): the announcement of the proposed delay and exemptions
• Air District: Know the Facts: plain-language background on the building appliance rules
• ENERGY STAR Heat Pump Water Heater Installation Guide: space, electrical, and installation considerations

Where to Start

If you’re planning a bathroom remodel, kitchen remodel, or ADU or addition in Marin County or San Francisco, put water heater location and electrical capacity in the first scope conversation, not the last. During an initial site visit, we can look at where your water heater is now and what a future replacement would need, then build that into the proposal.