Tankless water heater installation

What changes when the tank goes away

A tank stores hot water and keeps it hot. A tankless unit stores nothing and heats water as it passes through, which means it has to produce in seconds what a tank has all day to accumulate. That single difference explains everything else about the installation.

Enormous instantaneous input. A whole-house gas tankless commonly needs 150,000 to 199,000 BTU, against 40,000 for a typical tank. That is not a detail; it is why the gas line is the first thing that gets checked.

Flow, not volume, is the limit. A tankless is rated in gallons per minute at a given temperature rise. You never run out of hot water; you run out of simultaneous fixtures. Two showers is usually fine. Two showers, a dishwasher and a washing machine in a cold February is where sizing shows.

Temperature rise is seasonal. Texas groundwater sits around 75 °F in late summer and can drop to the mid-50s in winter. The same unit delivers noticeably fewer gallons per minute in January than in August, and sizing is done for January.

There is a minimum flow to fire. A trickling tap may not activate the burner at all. Modern units have low activation thresholds, but the behaviour is different from a tank and worth knowing about in advance.

The three prerequisites that decide the price

Gas supply. The existing half-inch line that fed a 40,000 BTU tank will not feed a 199,000 BTU tankless. Most installs need three-quarter inch from the meter, sometimes larger, and occasionally a meter upgrade from the utility. This is measured properly, total connected load, developed length, and every appliance on the same run, not estimated. An undersized gas line is the most common cause of a tankless that short-cycles, throws error codes, or simply never delivers what it promised.

Venting. A tankless cannot share a flue with anything and cannot use the old water heater's vent. Condensing units vent in PVC, usually horizontally through an exterior wall, which is why they generally end up on an outside wall rather than where the tank was. Non-condensing units need stainless category-III venting, which is expensive. The venting decision drives the location decision.

Condensate. A condensing unit produces acidic condensate that needs a drain and, in most jurisdictions, neutralisation before discharge. It needs somewhere to go that will not freeze and will not damage what it lands on.

And a fourth, unofficially: hard water. Texas hardness scales a heat exchanger faster than anything else in the system. A tankless in untreated hard water without a maintenance plan is a warranty claim in waiting. Softening, or at minimum a scale-inhibiting treatment plus annual descaling, belongs in the plan rather than being discovered later.

Where it goes, and why not where the tank was

Owners expect the new unit to hang where the old tank stood. Sometimes it does. Frequently the better answer is elsewhere, and the reasons are practical rather than aesthetic.

Venting wants an exterior wall. A short, direct horizontal vent through a side wall is cheaper, more reliable and easier to service than a long run through a roof.

Condensate wants a drain. A location with no nearby drain means a condensate pump, which is another component that can fail.

Gas wants to be near the meter. The longer the run, the larger the pipe has to be. A location on the meter side of the house can be substantially cheaper.

Distance to fixtures costs you wait time. Moving the heater further from the bathrooms adds seconds to every draw, and a tankless already has a short delay of its own before hot water arrives. On a long run, a recirculation loop is worth discussing at install time rather than retrofitting later.

Outdoor models exist and work in most of Texas, but they need freeze protection and reliable power, and the Panhandle and North Texas see hard freezes that make an indoor or garage location the safer choice.

Setting expectations honestly

Endless hot water is true. The tank never runs out because there is no tank. Long baths, back-to-back showers, and a guest bathroom in use all evening are genuinely solved.

Instant hot water is not true. The water still has to travel the pipe, and the burner takes a second or two to reach output. A tankless is typically slightly slower to first hot water than a tank in the same location, not faster. Recirculation is the fix, and it costs something.

The cold-water sandwich is real. Turn hot off and back on within a few seconds and a slug of unheated water arrives between two hot ones. Modern units with a small buffer tank reduce it. It is a minor annoyance most households stop noticing.

Running costs drop, but not dramatically. The saving is standby loss. The energy a tank spends keeping water hot for nobody. Real, worth having, and not usually enough on its own to justify the conversion cost. Go tankless for the endless supply, the wall space, or getting stored water out of an attic. Treat the efficiency as a bonus.

Lifespan is longer, with a condition. Twenty years is realistic against a tank's ten, if it is descaled. Untreated in hard water, a heat exchanger can be compromised in five.

When we will tell you not to

Not every house should convert, and it is cheaper to hear that before the work than after.

When the gas infrastructure makes it disproportionate. If the install needs a new meter, forty feet of upsized pipe and a re-route, the number frequently exceeds what the household will ever get back.

When the heater is electric and staying electric. Whole-house electric tankless needs service capacity most Texas houses do not have, often multiple dedicated double-pole circuits and a panel that can carry them. Point-of-use electric is a different and reasonable product; whole-house electric tankless usually is not.

When demand is small. One or two people in a single-bathroom house are well served by a modest tank. The conversion cost has nothing to buy.

When nobody will maintain it. A tankless is an appliance with a service interval. If an annual descale is not going to happen and the water is hard, a tank is the more honest recommendation.

When the tank failed this morning. Converting under pressure with no hot water in the house leads to compromises. If tankless is genuinely what you want, plan it. If you need hot water tonight, replace the tank and revisit the conversion when the next one is due.