Wall and Floor Furnaces: Care, Safety and Replacement

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Some older Bay Area houses, from pre-war bungalows to early postwar tract homes, were built without ducts and heated by a gas wall furnace in the hallway or a floor furnace under a metal grate, and some of those heaters are still running. They are simple machines with their own hazards: a grate that can burn a bare foot, a standing pilot that goes out on a gusty night, and a vent pipe nobody has looked at in years. This page explains how they work, what you can safely check yourself, and how to decide between repairing one and replacing it.

It is part of our Bay Area Winter Heating Help Center. If you smell gas or a carbon monoxide alarm is sounding, stop here and follow the gas smell and carbon monoxide steps first.

How wall and floor furnaces work

Both are gas heaters with no ductwork. A burner fires inside a metal heat exchanger; room air warms as it flows over the outside, while combustion gases stay inside and leave through a vent pipe (the flue). Many older units have no blower: warm air rises out of the top of the grille and cooler air is drawn in at the bottom.

• Gravity wall furnaces sit inside a wall cavity, often in a hallway, with the vent running up inside the wall to the roof.
• Floor furnaces hang in the crawlspace under a large grate in the floor. Hot air rises through the middle of the grate and cooler room air sinks back down around the edges.
• Direct-vent wall furnaces are the newer style: mounted on an outside wall, they take combustion air from outdoors and vent out through the same wall.

With no ducts, the heat stays close to the heater, so far bedrooms run cool. That is how these systems behave, not a fault. If uneven heat is the main complaint, our page on cold rooms and uneven heating covers the options.

Standing pilots and thermocouples

Most older wall and floor furnaces use a standing pilot: a small flame that burns all the time and lights the main burner when the thermostat calls for heat. A thermocouple sits in that flame and, while hot, holds the gas valve open. If the pilot goes out, the thermocouple cools and the valve shuts off the gas. That little rod is the main safety device on these heaters, so it should never be bypassed. (Some models use a thermopile, which also powers the wall thermostat.)

The usual reasons a pilot will not stay lit:

• A worn thermocouple that no longer produces enough signal to hold the valve open.
• A dirty or partly blocked pilot, giving a small, weak flame that does not fully wrap the thermocouple.
• Drafts, such as wind coming down the vent or a strong draft across a floor grate.
• A gas valve that is starting to fail.

If the pilot has gone out and you do not smell gas, you can relight it by following the lighting instructions printed on the label inside the access panel. PG&E's advice is to "shut the gas off at the appliance's gas shutoff valve" and "always wait five minutes to let gas disperse before trying to relight" (PG&E gas safety). PG&E also offers free pilot relight appointments to residential gas customers (PG&E pilot light service). Our pilot light and ignition guide goes through the relighting steps in more detail.

Clearances: the grate and grille get hot

The grate over a floor furnace gets hot enough to burn skin and can scorch anything left on it, a real risk for toddlers, pets and bare feet at night. A wall furnace grille gets hot too.

• Keep rugs, furniture, curtains, laundry, toys and pet beds off the grate and away from the grille. Do not dry clothes on either one.
• Never cover a floor grate. The furnace needs that opening to move air, and a blocked grate can overheat.
• The exact clearances for your model are on its rating plate or in its manual. As a simple household habit, keep the same 3-foot clear zone that the U.S. Fire Administration recommends around space heaters (USFA heater safety card), and follow the label if it asks for more.

Using a portable heater in the back bedrooms? Read our space heater safety page too.

Venting and carbon monoxide

The vent is the part of these heaters that deserves the most attention. The U.S. Department of Energy's consumer guidance has said that floor furnaces "may have special venting problems because their vent connector exits the furnace close to the floor and may travel 10 to 30 feet before reaching a chimney," and that owners should check whether the venting or the furnace itself needs replacing. Wall furnace vents run hidden inside the wall, so a rusted or separated joint can go unnoticed for years.

Signs that the venting or combustion needs a look:

• Soot or dark scorch marks on the wall above the grille or around the grate.
• A lazy yellow or orange flame instead of a steady blue one.
• Headaches, dizziness, weakness, upset stomach, vomiting, chest pain or confusion, which the CDC lists as the most common symptoms of carbon monoxide poisoning (CDC), especially if they ease when you leave the house.

The CDC also warns that people who are asleep "can die from CO poisoning before they have symptoms," which is why an alarm matters more than symptoms. California requires a carbon monoxide device in every home with a fossil-fuel heater, a fireplace or an attached garage (Health and Safety Code 17926). Under the current building code as summarized by Santa Cruz County, alarms go outside each sleeping area, on every level, and inside any bedroom that has a fuel-burning appliance in it (Santa Cruz County). If your wall furnace sits in a bedroom or opens into one, that last point applies to you.

Newer direct-vent units can have problems too: in 2008 the CPSC recalled about 52,000 Rinnai EnergySaver direct-vent wall furnaces (RHFE-431 and RHFE-556, made 2000 to 2007) because a gasket could fail and leak carbon monoxide (CPSC recall notice). If you have one, confirm the recall work was done.

The CPSC recommends a yearly professional inspection of fuel-burning heaters, including "chimneys, flues and vents" (CPSC), and PG&E offers free gas appliance safety checks (PG&E).

What we check on a wall or floor furnace

We work on wall heaters and floor furnaces, including pilot assemblies, thermocouples, gas valves and venting. A typical service or repair visit covers:

1. Checking and cleaning the pilot and burner.
2. Testing the thermocouple or thermopile and replacing it if it is weak.
3. Checking the gas valve and gas connections.
4. Inspecting the heat exchanger and combustion chamber as far as the unit allows, looking for rust-through, cracks or scorching.
5. Checking the vent: connections, slope, rust, blockages and whether it is drawing properly while the heater runs.
6. Checking clearances and your carbon monoxide alarms.

You get a plain explanation before any work begins, and every repair carries our 1-year parts and labor warranty.

Repair or replace?

A wall or floor furnace with a sound heat exchanger and a safe vent is often worth repairing. Replacement starts to make more sense when:

• The heat exchanger or combustion chamber is rusted through or cracked.
• The venting cannot be made safe without opening walls or running a new flue.
• Parts for that model are no longer made, so every repair becomes a workaround.
• A floor furnace has been under water. After a winter storm floods a crawlspace, the CPSC's guidance is that gas control valves that have been under water "must be replaced," and that other submerged parts, including venting, need to be checked by a qualified technician (CPSC). Do not relight it first to see if it works.

We will tell you plainly when repair no longer makes sense on an old heater, and why. For a broader framework, see our furnace repair or replacement checklist and the hidden dangers of old heaters in Bay Area homes.

Replacement options

A new direct-vent gas wall furnace

The closest like-for-like swap. A sealed direct-vent unit does not depend on an old flue inside the wall, but it heats about the same area your old heater did. Installing a space-conditioning appliance requires a building permit in California (California Energy Commission), and we handle that as part of the job.

A ductless heat pump (mini-split)

A ductless heat pump pairs an outdoor unit with one or more slim indoor heads, with no ducts. It heats and cools, and a head can go in the bedrooms your wall furnace never reached. 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" (ENERGY STAR). Our ductless mini-split installation page explains how a job is planned, and mini-split installation cost in the Bay Area covers pricing.

What about the Air District's 2029 furnace rule?

The Bay Area Air District's zero-NOx rule for furnaces takes effect for units made after 1 January 2029, and it applies to new installations, not to heaters already in your home (BAAQMD appliance rules FAQ). The rule (Regulation 9, Rule 4) is filed under "fan-type residential central furnaces," and we found no Air District guidance on gravity wall or floor furnaces, so confirm before assuming either way. Our page on gas furnace rules and heat pumps covers the rule in detail.

We service wall and floor furnaces from Santa Clara across the South Bay, Peninsula, Tri-Valley and East Bay; see San Jose furnace repair or our Redwood City page for local details.

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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.