Wall furnaces // San Jose and Los Gatos
Williams Wall Heaters in San Jose and Los Gatos
Williams has built wall furnaces in Colton, California since 1916, and a lot of South Bay housing still runs on them. We service, size, and replace every current Williams line, and we will tell you straight when a wall furnace is the wrong answer for your room.
$99 residential diagnostic, waived if we do the repair on the same visit.
A real technician answers. Not a phone tree. Most weekday calls in San Jose and Los Gatos get seen the same day.
A Wall Furnace Is Not a Small Central Furnace
A wall furnace is its own category of equipment, and the difference matters when something breaks. A central furnace pushes conditioned air through ducts to the whole house. A wall furnace heats the room it is mounted in, and nothing else. No ducts, no attic air handler, no registers, no return. That makes it the cheap and sane answer for a space that never had ductwork, and a bad answer for a four bedroom house someone is trying to heat on the cheap.
The gravity models are the part people underestimate. A Williams gravity wall furnace has no blower and needs no electricity. Warm air leaves the top of the cabinet by convection and cold air feeds in at the bottom. When PG&E drops the Los Gatos hills in a January storm, that unit keeps running on a millivolt thermostat powered by its own pilot. Very little else in a modern house does that.
The tradeoff is efficiency. Williams gravity and counterflow units land between roughly 65 and 76 percent AFUE depending on the model, against 80 to 98 percent on a modern central furnace and better than that on a heat pump. On a single room that number is often irrelevant. On a whole house it is the whole argument.
Where they still earn their keep
- ADUs and garage conversions with their own gas stub and no room for ductwork
- Willow Glen and Cambrian bungalows where the original wall furnace is still the only heat
- Los Gatos hillside cabins that lose power before they lose gas
- Single additions and back bedrooms the central system was never sized to reach
- Vintage homes where a floor furnace has to be replaced in its original footprint
Williams Models We Size, Install, and Service
Williams builds five families that show up in South Bay homes. The sizes and efficiency figures below are the manufacturer’s current published ratings, not rules of thumb.
| Family | Cabinet height | BTU range | Distinguishing trait |
|---|---|---|---|
| Monterey Top-Vent Gravity | 59 in | 25,000 / 35,000 / 50,000 BTU | vents straight up through the roof |
| Direct-Vent Gravity | 45 in | 14,000 / 22,000 / 30,000 BTU | vents out through the wall behind it |
| Forsaire Counterflow | 51 in | 35,000 to 65,000 BTU | blows warm air out at the floor |
| High-Efficiency Direct-Vent | 28 in | 7,400 / 17,700 BTU | the small one, for a room that needs very little |
| Floor Furnaces | 24 in | 30,000 / 50,000 / 62,000 BTU | sits under the floor, you walk over the grille |
Williams model specifications
Monterey Top-Vent Gravity
Gravity wall furnaceThe classic. No blower, no electronics, no electricity. Recessed or surface mounted, standing pilot, and almost nothing in it to fail. This is the unit behind most of the wall grilles in pre-1970 San Jose houses.
- Sizes
- 25,000 / 35,000 / 50,000 BTU
- Efficiency
- 70 percent
- Electricity
- None required
- Venting
- Vertical, through the roof
Best fitOpen living areas where silence and outage tolerance beat efficiency.
Direct-Vent Gravity
Sealed combustion, no powerSame no-electricity gravity operation, but sealed combustion pulling outside air and venting straight out the back wall. No roof penetration to flash and no combustion air drawn out of the room.
- Sizes
- 14,000 / 22,000 / 30,000 BTU
- Efficiency
- 65 to 67 percent
- Electricity
- None required
- Venting
- Horizontal, through the wall
Best fitSmall ADUs, back bedrooms, and any room where a roof vent is not practical.
Forsaire Counterflow
Forced air, top vent or direct ventThe blower pulls air down from ceiling height and pushes it out at the floor, which is why a Forsaire warms a cold garage conversion far faster than a gravity unit of the same size. The highest rated wall furnace Williams builds. The top vent line comes in 35, 50 and 65, the direct vent in 40 and 60.
- Sizes
- 35,000 / 40,000 / 50,000 / 60,000 / 65,000 BTU
- Efficiency
- 75 to 76 percent
- Electricity
- 120V for the blower
- Venting
- Top vent or direct vent
Best fitGarage conversions, workshops, and larger rooms that need fast recovery.
High-Efficiency Direct-Vent
Small load, sealed combustionThe low profile option for a room that genuinely needs very little heat. The 7,400 runs on a self-generating millivolt thermostat off the pilot, so it keeps heating through an outage. The 17,700 adds a two-speed circulating fan and needs 120V. Undersizing is rarely the problem here. Oversizing is.
- Sizes
- 7,400 / 17,700 BTU
- Efficiency
- 72 percent at 7,400, 76 at 17,700
- Electricity
- None on the 7,400, 120V fan on the 17,700
- Venting
- Horizontal, through the wall
Best fitTight, small, well insulated rooms where a 25,000 BTU unit would short cycle.
Floor Furnaces
Original-footprint replacementWilliams is one of the last manufacturers still building these, which matters when a 1930s Los Gatos house has a dead floor furnace and the owner does not want to cut the floor open for something new. Natural convection moves the room air three to five times an hour.
- Sizes
- 30,000 / 50,000 / 62,000 BTU
- Efficiency
- Gravity convection
- Electricity
- Millivolt, none required
- Venting
- Through the crawlspace
Best fitVintage homes replacing a failed floor furnace in the original opening.
Gas Wall Furnaces Have an End Date in Santa Clara County
The Bay Area Air District adopted zero-NOx appliance rules that apply in Santa Clara County, so both San Jose and Los Gatos are covered. Nothing you own now has to be touched. What changes is which units can be built for this market, and therefore what we can still put in your wall later.
Jan 1, 2027
Gas storage tank water heaters rated 75,000 BTU per hour or less, manufactured after this date, have to be zero-NOx. Wall furnaces are not affected by this one.
Jan 1, 2029
Residential and commercial furnaces have to be zero-NOx, and that language covers non-central equipment like wall furnaces. The rule is keyed to when a unit was built, not when it goes in, so a gas wall furnace manufactured after this date cannot be sold or installed here. Units built before it stay installable until that stock runs out.
Jan 1, 2031
Commercial and multifamily water heaters between 75,000 and 2 million BTU per hour follow.
The rules apply to new appliances only. Nothing requires you to retrofit or remove a wall furnace that is already in the wall, and no inspector is coming to look at it.
Parts, service, and safety work on an existing Williams unit are not restricted by these rules at any of the dates above.
If your unit is failing, replacing it with another gas wall furnace is legal today and nothing in these rules makes it illegal later. The 2029 date applies to units built after it, so it governs what manufacturers can ship here, not what sits in your wall. You are not buying a stranded asset, you are buying a unit that will outlive the rule change by a decade.
Zero-NOx in practice means electric. For a single room that is a ductless heat pump or an electric counterflow unit. We would rather you hear that now than in 2030.
The Four Failures We See Most on Williams Units
A wall furnace has very few parts, so the failure list is short and most of it is cheap. The one expensive failure is worth knowing by name.
| What you see | What we measure | What it means |
|---|---|---|
| It lights, then goes out the moment you let go of the knob | Millivolt meterThermopile output under load. Healthy is 350 to 750 mV. Under 300 it gets replaced. Then manifold pressure at the valve. | Almost always a thermocouple or thermopile at end of life. On a millivolt unit we read the thermopile output in millivolts, and anything under about 300 open circuit is done. Cheap part, quick visit. |
| Lazy yellow flame, soot marks above the grille, a smell when it runs | Combustion analyzerCarbon monoxide in the flue and stack temperature, then a mirror and a light on the heat exchanger itself. | Yellow means incomplete combustion. Usually a blocked orifice, lint and dust in the burner, or combustion air being starved. We put a combustion analyzer on it rather than guessing, because this one can put carbon monoxide in the room. |
| The fan runs but the air coming out is cold | MultimeterVoltage at the gas valve terminals, limit switch continuity, and whether the thermostat call is actually reaching the valve. | On a Forsaire this is typically a failed limit switch or a gas valve that is not opening. The blower running is a clue, not the fault, because on these units the fan and the burner are on separate controls. |
| It fires, runs a few minutes, shuts off, and does it again all evening | Stopwatch and draft gaugeCycle length in minutes, vent draft at the hood, and spillage at the relief opening. | The unit fires, satisfies, and shuts off within a few minutes, over and over. Either the thermostat is sitting in the heater’s own rising warm air, or the vent is partly blocked, or the unit is simply oversized for the room. |
The expensive oneThe expensive one is a cracked heat exchanger. That is a hard stop and it means replacement, not repair. It is also the reason a gas wall furnace older than ten years is worth a combustion check once a year.
San Jose and Los Gatos Wall Furnace Work
We are based in San Jose off Noella Way. Los Gatos is fifteen minutes up the valley and about three hundred feet higher, which is enough to matter in January.
San Jose
Volume, ADUs, and postwar bungalows.San Jose runs on wall furnaces in two directions at once. On one side there is the old stock: Willow Glen, Cambrian, Rose Garden, and the Spanish revivals where a gravity wall furnace or a floor furnace has been the only heat since the house was built, and the grille in the hallway is the original. On the other side there is the ADU wave. A detached 400 to 600 square foot unit with its own gas stub is close to the perfect wall furnace application, and we size a lot of them.
- Willow Glen and Cambrian bungalows on original units
- Rose Garden and Naglee Park vintage stock
- Detached ADUs and garage conversions valley wide
- Slab-floor Eichlers with no crawlspace to work in
Los Gatos
Older, steeper, and more likely to lose power.Los Gatos is a different problem. The downtown and Almond Grove houses are older and often have original openings that a modern cabinet does not drop straight into. Up the hill toward the summit, the argument shifts entirely: those homes lose power more often than anywhere else we work, and a gravity unit that runs without electricity stops being a quaint old thing and starts being the reason the house stays above 50 degrees. We size for that on purpose up there.
- Almond Grove and downtown historic openings
- Hillside and summit homes that lose power first
- Cabins and second units on propane rather than natural gas
- Floor furnace replacements in original footprints
What it costs
A typical wall furnace replacement in San Jose or Los Gatos lands between $2,500 and $4,200 installed, depending on the model, the venting, and what the old unit left behind in the wall.
What happens when you call
A real technician picks up, not an answering service. Most weekday calls in San Jose and Los Gatos get seen the same day.
What it is doing, roughly how old it is, and whether you can smell gas. If you can smell gas we tell you to shut it off and leave.
Combustion analyzer, millivolt meter, draft check. You get the reading, not an opinion.
The repair price, or the replacement price, before anything is touched. The $99 comes off if you go ahead the same visit.
Most wall furnace repairs are done in the same visit. A replacement is usually a single day.
We leave the old unit gone, not in your side yard.
Book Wall Furnace Service
Call and a real technician picks up. If you are sending a message instead, these four things get you an accurate answer on the first reply.
- 1The model number off the rating plate inside the lower door
- 2Room dimensions and what the space is used for
- 3What it is doing now, or not doing
- 4A photo of the unit and the wall around it
San Jose, Los Gatos, and the rest of the county
We are based in San Jose off Noella Way, so Los Gatos is a short reach and same-day is the norm in both. We cover the rest of Santa Clara County and into San Mateo County.
Williams wall heaters, frequently asked
How long does a Williams wall heater last?
Do Williams wall heaters need ductwork or electricity?
What size Williams wall heater do I need?
Are gas wall heaters still legal in California?
Can you replace a floor furnace with a wall furnace?
What does a Williams wall heater replacement cost in San Jose or Los Gatos?
Should I just put in a ductless heat pump instead?
Do you service Williams units you did not install?
Wall furnace out in San Jose or Los Gatos?
Call Silicon Valley Comfort. We diagnose it with a combustion analyzer, tell you whether it is a thermocouple or a heat exchanger, and quote the whole job before we start.
408-691-5940Silicon Valley Comfort, 5158 Noella Way, San Jose, CA 95124. service@air.systems. Open 24 hours.