Should Mill Valley switch to a heat pump?

Mill Valley is a place where a heat pump genuinely costs more to operate than the alternative. Against a like-for-like gas furnace and AC swap, going electric costs $1,000 more up front here (already netting out a $2,000 tax credit). The heat pump would cost about $3 more a year to run than the furnace it replaces — a premium with no payback. That's Mill Valley's own climate and rates talking, not a hedge or a caveat.

How cold Mill Valley actually gets

Mill Valley has a mild winter by US standards — 2538 heating degree days a year against a 65°F base — and summers rarely ask much of an air conditioner, at 78 cooling degree days. The 99% winter design temperature here — the cold snap equipment must be sized for, not the seasonal average — is 45.1°F, against a record low of 43°F. That puts the seasonal coefficient of performance at 3.54 for the recommended standard unit. Mill Valley's winters don't get cold enough to need the cold-climate premium — a standard unit holds up fine. Climate figures trace to the nearest NOAA station, RICHMOND, 7.9 miles from Mill Valley.

What it actually costs to run, year to year

Electricity use for heating alone comes out to about 1,815 kWh a year on the 2000-square-foot reference house; folding in cooling puts the electric bill near $618 a year. That compares with roughly 26 Mcf a year of gas at Mill Valley's 22.01 per-Mcf rate — about $615 a year — against a local electricity rate of 32.83¢/kWh. Priced as a standalone purchase rather than against a like-for-like replacement, equipment payback runs past the 15-year equipment life, for a 15-year net position $1,043 behind.

If your home heats with electric baseboard instead of gas

Not every home in Mill Valley has gas service. Against electric-resistance heat — baseboard or an electric furnace, both 100% efficient but still just resistance — the case for switching gets stronger here. Switching saves about $1,525 a year here — a heat pump moving heat rather than generating it needs far less electricity than resistance coils — so the extra $5,500 spent up front comes back in about 3.6 years.

How Mill Valley compares nationally

Mill Valley lands at position 2142 out of 3206 cities on heating severity (coldest is 1), and 2529 out of 3206 by population size (biggest is 1). That's the mildest third of cities covered, where utility rates carry more of the answer than climate does.

What to do with this number in Mill Valley

Mill Valley, California is home to about 13,904 people, and the figures above are the same ones a local HVAC contractor uses to size and quote a system — this site doesn't guess where a real quote would land, it just tells you whether it's worth asking for one. In Mill Valley, nothing is lost by holding off until the current equipment genuinely fails.

Line up a few local HVAC quotes before you decide.

Where Mill Valley's figure comes from

The methodology guide walks through exactly how Mill Valley's 3.54 seasonal COP and the rest of this page's numbers get built. Mill Valley is one of the cities where running costs land higher every year, not just slower to pay back — the guide to where this happens lays out why.