Tankless Water Heater Installation & Replacement in Mill Valley, CA
Navien, Rinnai and Noritz installs in Mill Valley's hillside and canyon homes. We size the gas line, plan the vent and the condensate drain, file the permit, and give you a free written estimate before any work starts.
Serving Mill Valley, Homestead Valley, Tam Valley, Almonte, Alto and Strawberry from our San Rafael base · Our Mill Valley plumbing page
Why a Mill Valley tankless job is more than a swap
A tank keeps 40 or 50 gallons warm on a small flame. A whole-house tankless unit fires hard for a few minutes at a time: Navien's NPE-A2 condensing models are rated from 150,000 to 199,900 BTU per hour. That's why most of a Mill Valley install happens behind the wall.
Proven on paper
When a tankless heater replaces a tank, the City of Mill Valley wants a gas pipe sizing worksheet with the permit: pipe material (iron or CSST), sizes, run lengths and the BTU load of every appliance on the line. The pipe that fed an old tank was sized for that tank, not for a burner several times bigger, so we do the math before we quote.
Direct vent, planned for the hillside
Condensing units pull air in and push exhaust out through 2" or 3" PVC, CPVC, polypropylene or stainless pipe. On a sloped lot the obvious wall is often above a deck or a stair, so we settle the termination point and clearances before install day.
Where an old tank never belonged
Mill Valley doesn't allow a non-direct-vent heater in a bedroom, a bathroom, or a closet that opens into one. A sealed-combustion tankless unit can often go where an old atmospheric tank was grandfathered in, or move outside altogether.
Crawlspaces, attics & garages
Mill Valley's hillside streets are tied together by historic public steps and lanes, and plenty of heaters live under the house. The City wants attic and under-floor heaters to have a floored path, a 30" work space, and a light and outlet. In garages, the flame must sit 18" up and be protected from cars. Wall-hung units clear the floor entirely.
Condensate, recirculation & soft water
A condensing tankless produces a steady trickle of acidic water. We send it through a neutralizer to an approved drain, and add a small condensate pump when the heater sits in a crawlspace or a garage below grade.
If the heater is at one end of the house and the main bathroom is at the other, you wait for hot water. Navien's A2 models have recirculation built in, or we add a separate pump.
Marin Water is soft (about 3.5 grains per gallon from the Mt. Tam reservoirs, 6.5 from the Sonoma supply), so scale builds slowly. We still fit isolation valves on every install so the yearly descale is quick. Why annual tankless service matters.
Homes and neighborhoods we see
Downtown, Cascade, Blithedale & Old Mill
The median Mill Valley home was built in 1958, and water heaters ended up wherever there was room: under the house, in a closet, at the back of a garage. On these jobs the gas sizing worksheet usually sets the scope.
Homestead Valley
A Mill Valley address, but County of Marin permits. Homes here tend to be older than in Strawberry, so we look closely at where the heater sits and how far it is from the bathrooms.
Tam Valley & Almonte
Median build year 1966 for Tam–Homestead Valley: mostly mid-century homes with garages and crawlspaces, where a wall-hung tankless frees up floor space.
Strawberry & Alto
Newer stock (Strawberry's median home dates to 1971), often with a tank in a hall closet or garage. Moving to a wall-hung or exterior tankless can give that space back.
Near the Arroyo Corte Madera
Mill Valley sits in Flood Control Zone 3 with Warner and Coyote creeks, and Miller Avenue has closed for flooding near Montford and Camino Alto. A wall-hung tankless keeps its burner and controls off the floor, unlike a tank on the slab.
City or County?
Inside city limits, the City of Mill Valley permits the job and reviews the gas sizing. Homestead Valley, Tam Valley, Almonte, Alto and Strawberry share the 94941 ZIP but are permitted by the County of Marin.
Signs it's time to replace, or finally go tankless
Tank leaking into the pan
Usually: tank corrosion. Not repairable.
We replace it and price tankless, tank and heat pump side by side.
Tankless ignition or flame error
Usually: a dirty flame rod, gas supply too small at full fire, or venting.
We test gas pressure at full fire before condemning the unit. Navien error codes.
Shower goes cold when a second tap opens
Usually: flow sensor, a clogged inlet filter, or an undersized unit.
We clean, test flow, and size to your fixtures.
Long wait at the far bathroom
Usually: a long run from an under-house heater.
We add recirculation, built-in or with a pump.
An older tankless that was never serviced
Usually: scale, worn parts, and no history to go on.
We quote repair and replacement side by side, like our April 2026 Noritz job below.
Soot, pilot outages or a burnt smell
Usually: a draft or combustion problem on an old tank.
We run a combustion and draft check first.
Thinking about tankless in Mill Valley?
A recent Mill Valley job: indoor tank to exterior tankless (July 2026)
Tank out of the house, tankless on the outside wall
The old heater was a gas tank inside the house. The new one is a tankless unit hung on an outside wall, which meant moving water, gas and power to a spot that had none of them. Four pieces of work made it happen:
- New water lines through the attic
We ran new water lines about 20 feet through the attic, from the old tank location out to the new unit. - New gas line from the meter
The tankless went close to the gas meter, so the new gas line from the meter to the unit was only about 4 feet long. - An outdoor outlet
A tankless unit needs power for its fan and controls, so we added an exterior outlet for it. - Expansion tank and neutralizer
We installed a thermal expansion tank on the water side and a condensate neutralizer so the acidic drain water is treated before it goes down the drain.
None of that shows up in a unit price on a website. It depends on the house, and it is the reason our tankless quotes come after a site visit.
Unserviced Noritz replaced with a Navien NPE-240A2
A Noritz tankless was failing, and it had never been serviced. At that age and with no service history, replacement was the better choice than repair, so we put in a Navien NPE-240A2. See our Navien tankless page.
How we decide
We look at the unit's age, the error history, whether it has ever been descaled, and what the failed part costs against a new heater. If a repair makes sense, we say so. If it doesn't, you get both options in writing.
What it costs in Mill Valley
Tankless is priced on site, because the number depends on the house. What moves it: the gas sizing result, where the unit goes (inside wall, attic, crawlspace or outside), vent length and exit point, new water lines, a new outlet, a condensate pump, hand-carrying up stairs, and recirculation.
2026 pricing. Every home is different, and the estimate is free and in writing before work begins.
Gas tankless vs. heat pump: our honest take
Gas tankless fits when…
- The heater lives in a crawlspace, closet or tight garage wall, or can go outside
- You need back-to-back showers or a big tub
- The gas line can be sized for it and there's a clean vent route
- You want a gas replacement that stays on the Air District's later timeline
A heat pump water heater fits when…
- You have a garage or basement with room air (or ducting) and a drain
- Your panel has capacity, or a 120V plug-in model will do
- You'd rather go electric now than at the next replacement
- You qualify for MCE's rebate of up to $675
Is gas tankless being banned?
Not yet. As of October 2026, here is where the Bay Area Air District's Rule 9-6 stands:
- 2027 tier: ordinary gas tanks (75,000 BTU/hr and below). Any built after January 1, 2027 must meet the zero-NOx limit, unless the amendment passes and the date slides a year to 2028.
- 2031 tier: this is where tankless sits, along with bigger heaters and residential gas boilers. A whole-house Navien NPE-A2 is well over 75,000 BTU/hr, so its cutoff is equipment manufactured after January 1, 2031, or 2033 if the proposal passes.
- Existing equipment: the standard only kicks in at sale or installation, so a heater that works can stay in service.
- Vote: the Board takes up the changes on November 4, 2026.
More in our 2027 gas water heater rule guide. We install heat pump water heaters, not heat pump HVAC; see our heat pump water heater page.
Rebates in Mill Valley
Mill Valley is in MCE's service area. MCE lists a rebate of up to $675 on a qualifying heat pump water heater (checked on MCE's site September 29, 2026), filed by a participating contractor, and Local Plumbing is one. TECH Clean California is on a waitlist, the HEEHRA program closed in February 2026, and the federal 25C credit ended for equipment installed after 2025. Check current terms at mcecleanenergy.org.
What a tankless installation looks like
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Site visit
We trace the gas line from the meter to the heater, find the vent route, and plan the condensate drain and power.
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Gas sizing & estimate
We run the numbers on every gas appliance in the house and hand you a free written estimate, with any upsizing spelled out.
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Permit
We file with the City of Mill Valley (with the sizing worksheet) or the County of Marin for unincorporated areas.
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Install
Old heater out. Wall-hung or exterior unit, venting, neutralizer, expansion tank, isolation valves, required pipe insulation and bonding in.
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Startup
Gas pressure checked at full fire, combustion check, recirculation set up if you chose it.
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Walkthrough
We show you the controls, the service valves, and when the first descale is due.
Mill Valley tankless FAQ
What does tankless installation cost in Mill Valley?
We price tankless on site with a free written estimate, because the gas line, the location, venting, water lines and power vary so much from house to house. For comparison, a 40–50 gallon gas tank runs $3,500–$6,500 installed.
Is a permit required to put in a tankless heater in Mill Valley?
Yes. The City of Mill Valley requires a permit for every water heater replacement, and a tankless replacing a tank also needs a gas pipe sizing worksheet. Homestead Valley, Tam Valley, Almonte, Alto and Strawberry are permitted by the County of Marin. We file it either way.
Will my existing gas line work for tankless?
Sometimes. A whole-house unit can draw close to 200,000 BTU per hour, several times what a typical tank uses. We calculate your line against every gas appliance before we quote. On our July 2026 job, the unit went near the meter and needed only about 4 feet of new gas line.
Can a tankless water heater go outside?
Often, yes. Our July 2026 Mill Valley conversion moved the heater from inside the house to an exterior wall, with new water lines through the attic, a new gas line and an outdoor outlet for power.
Is gas tankless still allowed in Mill Valley after 2027?
Yes. Whole-house gas tankless units fall under the Air District's January 1, 2031 tier (a proposal would move it to 2033), not the 2027 tank date. The Board votes on November 4, 2026.
Old tankless acting up: fix it or replace it?
It depends on age, service history and the part that failed. In April 2026 we replaced a Mill Valley Noritz that had never been serviced with a Navien NPE-240A2, because at that age replacing it made more sense than repairing it.
Do you service Navien, Rinnai and Noritz units you didn't install?
Yes: descaling, flame rods, flow sensors, fans and error codes. See our tankless water heater and Navien tankless pages.
We install tankless water heaters throughout Mill Valley (Downtown, the Old Mill area, Cascade and Blithedale canyons, Scott Valley and Sycamore Park) and in Homestead Valley, Tam Valley, Almonte, Alto and Strawberry. See our Mill Valley plumbing page. Hot water from a boiler or combi? See boiler replacement in Mill Valley.
Ready for tankless?
Tell us where your water heater is now and where you'd like it. We'll come out, check the gas line and give you a written estimate.
