Heat pumps for mid-century homes take more planning than heat pumps for a typical tract house. Eichler-style post-and-beam houses have no attic, many were built with radiant heat in the slab, and owners want to keep clean ceilings and uncluttered rooflines. Add the Bay Area's new rules for gas water heaters and furnaces, and it pays to understand the options before anything breaks.
This guide explains what the Bay Area Air District's appliance rules require and when, the heat pump options that suit houses without attics or ducts, how heat pump water heaters fit, what to check in the electrical panel, and how to place equipment so it doesn't fight the architecture.
Why mid-century houses are different
The National Register nomination for Palo Alto's Greenmeadow tract, built by Eichler Homes in 1954 and 1955, sums up the constraints. It says Eichler roofs do not have attics, that radiant heating systems were standard, and that the underside of the wood roof decking is the finished ceiling. Its evaluation criteria count readily visible air conditioning or heating ducts against a house's integrity.
In practice, that means a conventional ducted system has few places to hide. Ducts would have to run across the ceiling, inside new soffits or over the roof. That's why ductless systems and heat pumps that work with the existing radiant floor deserve a close look.
The Bay Area Air District rules, in plain terms
On March 15, 2023, the Bay Area Air District announced that its Board had adopted amendments to Regulation 9, Rules 4 and 6, requiring new natural gas furnaces and water heaters to meet zero-NOx emission standards. Here is how they work as of the Air District's building appliances page, updated November 4, 2026:
Water heaters. On November 4, 2026, the Board adopted amendments to Rule 9-6 that delay the zero-NOx compliance date for residential water heaters to January 1, 2028. The amendments also create exemptions for properties with significant electrical or space constraints, among others.
Furnaces. The Air District's current fact sheet lists 2029 as the compliance date for furnaces rated under 175,000 BTU per hour.
Later dates. The Air District says the November 2026 amendments also set January 1, 2033, for some categories, including hydronic units and large water heaters.
Only at replacement. The rules apply when a water heater or furnace is replaced after the compliance date. There's no mandate to remove or replace working appliances before they fail.
Not covered. Stoves, ovens and dryers aren't affected, and the Air District's FAQ says propane-fired equipment isn't covered.
What complies. The FAQ says the only commercially available appliances that currently meet the standards are electric, typically heat pumps.
If your house has a gas boiler feeding a radiant floor, note that Rule 9-6 covers gas-fired boilers as well as water heaters. The Air District's fact sheet on the amendments lists 2033 for water heaters and boilers rated above 75,000 BTU per hour. Ask the Air District or a licensed contractor which category your equipment falls into. Dates have already changed once, so check the Air District's page before you plan around them.
Space heating options without ducts
The U.S. Department of Energy describes heat pumps as able to provide both heating and cooling, delivering up to three times more heat than the energy they use. For a mid-century house, three approaches come up:
Ductless mini-splits
The Department of Energy describes ductless mini-split heat pumps as air-source units that can be installed in homes without ducts, with flexibility for zoning or heating and cooling individual rooms. In a house with glass walls, the challenge is placement: wall-mounted indoor units need solid wall space, and refrigerant lines need a route to the outdoor unit. Ask to see where every line set will run before you sign.
Air-to-water heat pumps with the radiant floor
If your radiant tubing is in good condition, an air-to-water heat pump can replace the boiler as the heat source. Technical guidance from a hydronics manufacturer explains that low supply water temperatures let an air-to-water heat pump operate at high efficiency, and that adding floor covering resistance raises the required water temperature and significantly reduces that efficiency. Thick carpet or pad over a radiant slab works against a heat pump. Have the tubing inspected before you invest in a new heat source.
Ducted systems
Ducted heat pumps are an option where ducts can be hidden, for example in an addition with a conventional attic. In the original post-and-beam spaces, visible ductwork is the trade-off the Greenmeadow criteria warn against.
Whatever you choose, California's 2025 Energy Code says altered or replacement space heating systems can't use electric resistance as the primary heat source, with exceptions when the existing system is already electric resistance. The code applies to permit applications filed on or after January 1, 2026.
Heat pump water heaters
Under the Air District's schedule, the water heater comes due first. The Department of Energy says heat pump water heaters can be two to three times more energy efficient than conventional electric water heaters. The Air District's fact sheet says that in many cases they can replace gas water heaters with only light electrical work, and that many newer models plug into a standard 120-volt outlet.
The 2025 Energy Code also sets conditions for a replacement water heater. A single heat pump water heater qualifies when, among other requirements, its storage tank isn't located outdoors and sits on a rigid insulated surface of at least R-10, and the unit has a qualifying communication interface. The code still lists a natural gas or propane system as an option; the Air District rule is what limits new gas water heaters after its compliance date. Ask your installer how both apply to your location in the house.
Check the panel before you buy equipment
The City of Palo Alto's utility advises having a licensed electrician evaluate the panel before electrification work. It says many fully electric homes may be able to operate with a 100-amp panel depending on usage and appliance choices, and it describes options such as circuit sharing and smart panels. The Air District's FAQ notes that lower-voltage heat pump water heaters and load-sharing plug devices can avoid the need for a panel upgrade in some homes. Plan the whole house at once: water heater, space heating, cooking and car charging all draw from the same service.
Placing equipment so it suits the house
Outdoor units: look for a side yard or rear location that keeps units out of the street view and away from bedrooms.
Line sets and conduit: route them along inside corners or under eaves, and paint covers to match the siding.
Indoor heads: place them on solid walls rather than over glass, and pick the slimmest units that do the job.
Roof: avoid ducts or equipment that change the roofline when seen from the street.
For how these choices fit into a full remodel, see our Eichler renovation guide, our overview of mid-century modern design guidelines and our page on materials and construction. Rules and incentives change, so confirm current requirements with your city, utility and a licensed contractor (California's C-20 license covers HVAC work), and ask a tax advisor about any credits.
Frequently asked questions
Do I have to replace my gas furnace or water heater now?
No. The Air District says the rules apply only when a water heater or furnace is replaced after the compliance date, and there's no mandate to replace working appliances. As of November 4, 2026, the date for residential water heaters is January 1, 2028.
Can a heat pump work with my radiant floor?
It can, if the tubing is sound. An air-to-water heat pump can supply the radiant system, and it runs more efficiently at lower water temperatures. Heavy floor coverings raise the temperature needed and reduce that efficiency, so factor in your flooring.
Do heat pump water heaters need a 240-volt circuit?
Not always. The Air District says many newer models can plug into a standard 120-volt outlet. Location and space still matter, so compare models with your installer.
Does the Air District rule cover my radiant heat boiler?
It may. Rule 9-6 covers gas-fired boilers as well as water heaters, and the Air District's fact sheet lists 2033 for boilers rated above 75,000 BTU per hour. Because rules and exemptions have been amended, ask the Air District or a licensed contractor how they apply to your specific boiler before you plan a replacement.
Related reading
Eichler Radiant Heat: Copper vs. Steel, Repair, Replace or Retire
Flat Roof Solar on Mid-Century Homes: Placement, Batteries, Billing
Planning an all-electric upgrade for a mid-century home, or buying one with older equipment? Call or text the Boyenga Team at (408) 373-1660 or (650) 383-8606, or contact the Boyenga Team and we'll help you think it through.
