A tankless water heater heats water on demand instead of storing it, which saves space and can lower energy bills – but in San Diego it lives or dies by maintenance. Our hard water scales the heat exchanger fast, so the unit you’re buying may need descaling or already be damaged. Here’s what a home inspector actually checks.
Gas vs. electric tankless: what’s behind the wall matters
Most tankless water heaters in San Diego County are gas-fired, and for good reason. A whole-house electric tankless unit can draw enormous amperage – often requiring multiple dedicated 40-amp double-pole breakers and a 200-amp service to support them. Many older San Marcos, Escondido and El Cajon homes simply don’t have the panel capacity, which is why retrofits are usually gas.
Gas units bring their own demands. They need adequate gas supply, proper combustion air, and correct venting – none of which are visible once the cover is on. A general inspection is visual and non-invasive, so we evaluate what’s accessible and observable, then flag anything that needs a licensed plumber or the manufacturer’s authorized service tech to open up and verify.
Gas line sizing is the most common miss
This is where a lot of installations go wrong. A storage tank water heater might use 40,000 BTU; a whole-house gas tankless commonly runs 150,000 to 199,000 BTU. That’s a four- to five-fold jump in gas demand. If a contractor swapped a tank for a tankless and reused the existing half-inch gas line without upsizing it (or running a dedicated line), the unit can starve for fuel – causing error codes, lukewarm water, or short cycling.
An inspector looks at the apparent line size feeding the unit and whether the install looks like a like-for-like swap. We can’t perform a gas pressure or load calculation – that’s a job for a licensed plumber or your gas utility – but undersized supply is a frequent red flag worth raising before close.
Venting: the part people forget about
Venting is where gas tankless units get dangerous when done wrong. There are two broad types:
- Condensing units are high-efficiency and typically vent through PVC or polypropylene pipe, which can run horizontally out a sidewall. They also produce acidic condensate that must drain properly, often through a neutralizer.
- Non-condensing units run hotter exhaust and require category III stainless steel venting – never PVC. Using the wrong vent material on a non-condensing unit is a serious safety defect.
We check for correct vent material, secure connections, proper termination clearance from windows and doors, and signs of a botched conversion (a unit moved indoors to a closet or attic without sealed combustion and proper intake air, for example). Indoor installs that don’t draw outside combustion air are a common problem in converted San Diego garages and utility closets.
Hard water and scaling: San Diego’s tankless killer
This is the single biggest issue for tankless water heaters in San Diego. San Diego County water is notably hard – much of our supply is imported and mineral-heavy. Inside a tankless unit, water flashes across a compact heat exchanger, and dissolved calcium and magnesium precipitate out as scale right on that hot surface.
Scale acts like insulation. As it builds, the unit works harder to hit temperature, efficiency drops, flow weakens, and error codes appear. Left unaddressed, scaling can cook a heat exchanger years before its time. Most manufacturers require periodic descaling (flushing) with a circulation pump and vinegar or a descaling solution – in our hard-water region, that often means annually rather than the every-few-years guidance you’ll see in milder climates.
What we look for on the scaling front
- Isolation (service) valves – the pair of valves that let a plumber flush the unit. If they weren’t installed, descaling is far more difficult, which usually means it was never being done.
- A water softener or whole-house filtration system, which dramatically extends tankless life in our area. Its presence is a good sign; its absence is worth noting.
- Error codes or visible mineral crusting at fittings and the condensate drain.
- Inconsistent or weak hot water during the inspection, which can hint at a scaled exchanger or undersized gas.
We can’t open the unit or run a descaling cycle – that’s outside the scope of a visual inspection and into the manufacturer’s authorized-service territory. But the clues above tell us a lot about whether the previous owner maintained it.
Lifespan: tankless vs. tank
On paper, tankless wins. A well-maintained gas tankless unit is often rated for 20 years or more, roughly double a conventional storage tank’s typical 8-to-12-year service life. The catch is that “well-maintained” carries real weight in San Diego. A tankless unit that’s never been flushed in hard water can fail far earlier, sometimes underperforming a tank that would have just chugged along.
If you’re weighing the trade-off, our companion guide on water heater inspection and lifespan in San Diego walks through how we estimate remaining life on both styles and what age-related warning signs mean for your budget.
What a home inspector checks on a tankless unit
During a general buyer’s home inspection, the tankless water heater gets a focused visual review. We typically look at:
- Unit type, apparent age, and visible model/serial data.
- Gas supply line – apparent sizing and whether it looks like an unmodified tank-swap.
- Vent material, routing, slope, and termination clearances.
- Combustion air supply for indoor and closet installs.
- Presence of isolation/flush valves and a drip-leg/sediment trap on the gas line.
- Condensate drainage and any neutralizer on condensing models.
- Seismic strapping or secure mounting, plus T&P or pressure-relief provisions where applicable.
- Water flow and temperature at fixtures during testing.
- Visible leaks, corrosion, scaling, or error codes.
Anything beyond visual access – internal scale, gas load testing, exact remaining lifespan – we refer to a licensed plumber or the manufacturer’s authorized service. For older homes, this water heater review often pairs with our 4-point inspection, which insurers frequently request and which covers the plumbing, electrical, roof, and HVAC systems together.
So, should you go tankless in San Diego?
Tankless makes a lot of sense here: endless hot water, a smaller footprint, lower standby energy loss, and a longer potential lifespan. The honest caveat is that our hard water demands discipline – flush valves at install and regular descaling, ideally paired with a softener. A neglected tankless in San Diego County is a maintenance bill waiting to happen, not a savings story.
If you’re buying a home with an existing tankless unit, have it looked at as part of your inspection so you know what you’re inheriting. And always verify specifics with a licensed plumber and the manufacturer before committing to repairs or a replacement.
Questions about a unit in a home you’re buying? Reach out to The Real Estate Inspection Company at (619) 752-4399, or review our fee schedule to see what a full inspection covers. We serve all of San Diego County from our base in San Marcos.
