Radiant Heating in Eichler Homes: Problems and Options

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Eichler homes are known for walls of glass, open beams and heat that comes up through the floor. That floor heat is a radiant system: water pipes set into the concrete slab, warmed by a boiler. When it works, it is quiet and even. When the original pipes start to leak, owners face a hard question, because there is no crawl space to run new pipes and often nowhere obvious to put ducts. This page explains how these systems work, what the sources say about their weak points, the warning signs of a slab leak, and the ways to keep an Eichler warm when the original system is failing.

It is part of our Bay Area Winter Heating Help Center. We want to be clear from the start about what we do and do not do. Repairing an original in-slab radiant system or its boiler is a specialty of its own, and we will tell you honestly if your problem is outside our scope. What we do is add heat pumps and ductless mini-splits to Eichlers and other homes without ducts, either alongside a slab system or in place of one.

How Eichler radiant heat works

The City of Palo Alto's Eichler design guidelines describe it simply: "Radiant heating is embedded in the concrete slab flooring, similar to Frank Lloyd Wright's techniques with his Usonian houses" (City of Palo Alto Eichler guidelines). A boiler heats water, a pump circulates it through tubing in the slab, and the warm floor gives off heat to the room and the people in it. The same guidelines note these homes were built on "foundations without crawl spaces," which is why a slab system is hard to get at and why adding conventional ducts is not a simple job.

Slab radiant heat also responds slowly. A thick concrete floor takes a long time to warm up and to cool down, so large overnight setbacks tend to leave the house cold in the morning rather than saving much.

Where Eichlers are in our area

The guidelines say Eichler "constructed over 11,000 homes during his career as a merchant builder," with "some 2,700" of them in Palo Alto. The Eichler Network lists Eichler neighborhoods in Palo Alto, Mountain View, Stanford and Los Altos; in San Jose, Sunnyvale, Cupertino, Santa Clara, Saratoga and Monte Sereno; in Redwood City and other Peninsula towns; and in Walnut Creek, among other places (Eichler Network). In Walnut Creek, Rancho San Miguel has 535 homes, "375 Eichlers, the rest standard ranches" (Eichler Network).

What the sources say about the original systems

Opinions on Eichler radiant heat are genuinely mixed, and it helps to see both sides.

• The case against the original installations. The Palo Alto guidelines list "radiant heating that is inefficient" among the typical deficiencies of Eichler homes, along with "single-pane glass" and "lack of insulation" (City of Palo Alto).
• The case for radiant heat in general. The U.S. Department of Energy's consumer guidance has said radiant heating is "usually more efficient than forced-air heating because it eliminates duct losses."

Both can be true at once. Radiant heat as a method avoids duct losses, while an original slab system heating a house with single-pane glass and little insulation may still feel costly and slow. Whether yours is worth keeping depends mostly on the condition of the pipes.

Copper versus steel pipes

This is the single most important fact about your system. As reported by the Eichler Network, "leaks in copper pipes are readily repairable. If the tubing in your system is steel, and it was not properly installed or maintained, the first leaks may signal the end of the system's useful life. Once corrosion in a steel system starts, it can spread to such a degree that repair is not a practical option" (Eichler Network). If you do not know which you have, a radiant specialist can usually tell you.

Warning signs of a slab leak

The hard part is that slab leaks usually hide. The contractors quoted by the Eichler Network say "most radiant leaks in the slab are not apparent by looking at your floor" and that "the water usually goes straight down into the ground" (Eichler Network). They also explain why a leak can go on for a long time: the system "is designed to automatically add water to keep up the pressure," and once it is leaking, "the oxygen in the fresh water will contribute to pipe corrosion." So a leak can quietly make itself worse.

What to watch, per the same article:

• Boiler pressure. Check the gauge on or near the boiler from time to time. The article gives a normal operating range of "between 10 to 20 lbs." A reading outside that range, or one that keeps drifting, is worth a call to a radiant specialist.
• A system that keeps taking on water. Because the fill is automatic, you may not notice. Ask a specialist how to tell whether yours is adding make-up water.
• A regular pressure test. The article recommends "a thorough inspection every one to three years," including "a pressure test to check for leaks."

If you do see damp patches on the floor or water near the boiler, turn the system off and call a radiant or hydronic specialist. Do not wait for a visible sign, though, since most leaks never show one.

Who to call for the slab and boiler

For leaks, pressure problems, the boiler itself, circulator pumps and zone valves on a radiant system, call a radiant or hydronic heating specialist. Before you hire one, it helps to ask:

1. Can you tell whether my slab tubing is copper or steel?
2. Will you pressure-test the system and give me the results in writing?
3. If there is a leak, can you locate it, and what repair options make sense for my type of pipe?
4. If the slab system cannot be saved, what would you suggest instead?

If your boiler is gas-fired, it is a fuel-burning appliance, so the house needs working carbon monoxide alarms under California law (Health and Safety Code 17926). Our gas smell and carbon monoxide page covers what to do if an alarm sounds: get out first, then call 9-1-1.

What Cool Aid can do: heat without ducts

Whether your slab system is working, limping or finished, a heat pump can give an Eichler reliable heat without tearing up the floor.

Ductless mini-splits, room by room

A ductless heat pump pairs an outdoor unit with slim indoor heads mounted on the walls, each with its own temperature control. No ducts and no crawl space are needed. ENERGY STAR says an air-source heat pump "can deliver up to three times more heat energy to a home than the electrical energy it consumes," and that certified models are tested for low-temperature performance "down to 5°F" (ENERGY STAR). See our ductless mini-split installation page for how a job is planned and heat pump vs mini-split for the difference between the two.

Supplemental heat alongside a working slab

If your radiant system still works but is slow or struggles in the glass-walled living area, one or two ductless heads can take the load in the rooms that need it most. That way you keep the warm floor and add faster heat where you want it. ENERGY STAR's advice for heat pumps fits the way slab heat works too: "pick a comfortable temperature and leave it there."

Heating and cooling in one system

Large single-pane windows lose heat in winter and let in sun in summer. A heat pump heats and cools, so the same equipment that replaces failing slab heat can keep the glass-walled rooms comfortable on hot afternoons.

Whole-home replacement

If a steel slab system has reached the end of its life, a multi-zone ductless system with a head in each main room is the approach we usually suggest for a home without a crawl space. Where a home has been remodeled with space for ducts, a ducted heat pump may also be possible, and we will look at that during the estimate.

Installing a new heating or cooling appliance requires a building permit in California, and for heat pumps the state Energy Code requires refrigerant charge verification in every climate zone (California Energy Commission). We handle permits as part of the job. For rebates that may apply, see our Bay Area heat pump rebates guide, and check any program's rules before installation, since some must be reserved in advance. For pricing, see mini-split installation cost in the Bay Area.

A sensible plan for this winter

1. Find the boiler pressure gauge and note the reading.
2. If you have not had one in the last few years, book a pressure test with a radiant specialist before the cold sets in.
3. Test your carbon monoxide alarms if the boiler burns gas.
4. If the slab system is unreliable, get a ductless heat pump estimate so you have a plan before a cold snap, not during one.

We work with Eichler owners in Palo Alto, Mountain View, Sunnyvale and San Jose, and across our Bay Area service area. If rooms are cold for other reasons, our guide to cold rooms and uneven heating may help.

Get a ductless heat pump estimate for your Eichler

Frequently asked questions

Written and reviewed by Jim McKinny, owner of Cool Aid Air Conditioning & Refrigeration — California C-20 and C-38 licensed, EPA Universal certified, second generation of a family business serving the Bay Area since 1966. Every job we complete is backed by our 1-year parts & labor warranty.