Furnace installation in Mill Valley is shaped by two facts: homes here heat for much of the year, and many were built long before modern equipment existed. Higher elevations stay cooler year-round, north-facing slopes and redwood-shaded lots get little sun, and older homes from the early 1900s to the 1960s often put the furnace wherever it fit: a crawlspace, a basement corner, a hall closet or the garage. A good replacement respects both. Whether your home sits high on the slopes of Mount Tamalpais or lower in town, we plan around the house rather than around a standard box.
Fitting the furnace to the space
Crawlspace installations. Many Mill Valley homes have a horizontal furnace under the floor. Access is tight, the ground is often damp, and the furnace should sit on a proper platform or hang from the framing, clear of soil and standing water. We measure the access opening before choosing a model, because some units will not fit through it.
Closets and basements. Upflow furnaces in small closets need correct clearances and combustion air. A closet that worked for a furnace from decades ago may need changes for a modern one, especially a condensing model.
Garages. Usually the simplest location, with room for a high-efficiency furnace, its vent and its drain.
80% or high-efficiency: venting decides
A condensing furnace (95% AFUE and above) vents through plastic pipe that can exit a side wall, and it makes condensate that needs a drain. In a crawlspace that usually means a condensate pump and a vent route under the floor to an outside wall, all planned before the quote. A standard 80% furnace uses the existing metal flue, as long as that flue is in good condition. Since furnaces here run so many hours, high efficiency often pays off; the venting route is what sometimes rules it out.
Sizing it right
Old furnaces were often oversized, and many houses have since gained insulation and new windows. We do a heating load calculation instead of copying the old furnace’s capacity. A right-sized furnace with a two-stage or variable-speed design runs longer, quieter cycles and keeps damp, cool rooms more even.
Ducts and air quality
A new furnace is only as good as the ducts it feeds. In a crawlspace we check that return air is drawn from the house, not from under it: a leaking return pulls damp, musty air into the living space. We seal the connections at the furnace and point out duct runs that are damaged or uninsulated.
Furnace or heat pump?
If you also want cooling, compare a furnace plus a new AC with a heat pump that does both; see heat pump installation in Mill Valley. Many homeowners here ask about Trane furnaces; we install and service all major brands.
How the installation runs
- Home assessment: your current furnace, its location, venting, gas line and ducts.
- Recommendation: options that suit the house and your budget.
- Detailed quote: the full price in writing, with no hidden costs; financing with approved credit.
- Installation: removal of the old furnace, a new platform, venting and drain where needed.
- Safety testing: gas pressure, combustion, temperature rise and a carbon monoxide check.
Installed prices typically run $3,500–10,000, depending mostly on the efficiency level and the work around the furnace. For more on equipment, see the furnace installation page; if your furnace might still be saved, see furnace repair in Mill Valley. The Mill Valley page covers our other work in town.