Tankless Water Heater Gas Line Upgrades in La Vernia and San Antonio

Why the burner is so much bigger

The National Fuel Gas Code's annex estimates 35,000 BTU an hour for a 30- to 40-gallon automatic tank and 50,000 for a 50-gallon one. A tankless unit heats water as it flows, so it needs a big flame; federal efficiency criteria count gas models as residential below 200,000 BTU. A 199,000 BTU heater, with natural gas at roughly 1,000 BTU per cubic foot, burns close to 199 cubic feet an hour, about four times a 50-gallon tank.

Half-inch branches, small meters and long runs

Tank heaters are usually fed by a half-inch branch. The International Fuel Gas Code table for natural gas in steel pipe at normal house pressure gives half-inch about 172 cubic feet an hour over 10 feet and just 65 over 60 feet. At 60 feet, three-quarter-inch carries 137 and one-inch 257; at 100 feet one-inch drops to 195, and inch-and-a-quarter moves 400.

We size by the code's longest-length method: measure from the meter or regulator to the farthest outlet, total every appliance's rating as if all fire at once, and size each section from that row. A 199,000 BTU heater 60 feet out needs its own one-inch branch, and the trunk it shares with the furnace and range often grows too. On natural gas acreage, with runs past 100 feet, the heater alone can need inch-and-a-quarter; propane runs at higher pressure and has its own tables. A starved line shows up as flame errors or lukewarm water when a second fixture opens.

CPS Energy owns the meter and sizes it to everything that might run together. Its standards describe a residential-size meter rated at 175 cubic feet an hour, less than a big tankless unit can draw alone. Only CPS can set a larger one, after permit releases, so we total the load early. The same standards set 2 psi delivery for homes piped in flexible stainless (CSST), with a customer-installed regulator downstream, which lets long runs use smaller pipe.

Venting, and a drain for condensing units

Tankless exhaust is fan-driven, and the maker's instructions set vent material, diameter and maximum run, so the old tank flue rarely stays. Non-condensing models typically use Category III stainless steel. Condensing models pass exhaust through a second heat exchanger, leaving it cool enough for PVC.

The cooled exhaust sheds water that code commentary warns can be acidic. The fuel gas code wants corrosion-resistant drain pipe no smaller than the heater's condensate outlet, falling an eighth of an inch or more per foot to an approved fixture; some makers also require a neutralizer. The unit needs a 120-volt outlet too, and outdoor models need power for freeze protection.

Hard water and descaling

SAWS says its water's hardness occurs naturally in the Edwards and Trinity aquifers; private wells around La Vernia vary. In a tankless unit that mineral bakes onto a small, hot heat exchanger, cutting flow and causing error codes. Service valves at the heater let a pump flush descaling solution through without cutting pipe; follow your manual's interval, and see hard water and softeners.

Permits, pressure test and inspection

In San Antonio, the limited service and repair permit covers a water heater only when it is swapped for the same type in the same spot; tank-to-tankless is excluded and needs a general plumbing permit with DSD inspections. La Vernia requires a permit, inspection and contractor registration to replace a gas water heater or to add, replace or repair a gas line. Rules elsewhere differ by town and county, so we look up yours. The plumber doing the work pulls the permit.

1. Model and route. The rating plate sets the size; we measure the longest run.
2. Rough-in. New pipe, a dedicated shut-off and a drip leg at the heater, plus vent and condensate piping.
3. Test. The capped piping must hold on a gauge with the meter isolated, since CPS warns test pressure can damage its meters, and an inspector checks it where a permit applies (gas pressure test).
4. Light-off. Air is bled out, every joint gets a leak check, and the heater fires with several taps running.

Part of a full tankless install

Water connections, the relief valve and old-tank haul-away are on water heater installation and replacement; compare types on water heaters. We do this work around La Vernia and in east San Antonio, Cibolo and Schertz, Floresville and Seguin. Coupons that fit: $150 off a new water heater installation, 10% off for seniors, first responders, healthcare workers and military, and $50 off for new customers (terms on the coupons page).

Questions about tankless gas lines

Size the line before you buy

Phone (830) 475-2604 once you've picked a model. We'll look over the pipe, meter or propane setup and vent route, and schedule the job for a time that suits you. If you ever smell gas, leave the house first; after that, call at any hour and we send our on-call plumber right away.

Office hours 8 AM–11 PM daily · 24/7 emergency service