Tankless water heater service in Cypress, TX for Rinnai, Navien and Rheem units

How does a tankless water heater work?

A tank heater keeps 40 or 50 gallons hot all day. A tankless unit keeps nothing hot. When you open a hot tap, water moves through a flow sensor, the burner lights, and the water picks up heat as it passes through a heat exchanger. Close the tap and the burner shuts off. The U.S. Department of Energy describes it simply: tankless units heat water instantly without a storage tank, using a gas burner or an electric element.

Because no stored water sits and cools, a tankless unit avoids standby heat loss, which is the heat a tank loses to the garage or attic around it. The Department of Energy puts the efficiency gain at 24% to 34% for homes that use 41 gallons or less of hot water a day, and 8% to 14% for homes that use around 86 gallons a day. In plain terms: smaller households gain more on energy, and big households gain less, though they still gain endless supply.

The trade is capacity. A tank gives you a big burst and then runs out. A tankless unit never runs out, but it can only heat so many gallons per minute. The Department of Energy says typical units deliver 2 to 5 gallons per minute, and gas units deliver higher flow rates than electric ones. That is why sizing matters more on a tankless install than on any tank we put in.

Condensing and non-condensing units

Most units we install in Cypress homes today are condensing models. They pull extra heat out of the exhaust, which cools the exhaust enough to form water. That acidic condensate needs a drain line, and Pacific Northwest National Laboratory guidance recommends a neutralizer on it. The upside is that condensing units can vent with PVC. Non-condensing units run hotter exhaust and need corrosion-resistant vent pipe, such as Category III stainless steel.

Tankless with a small buffer tank

Some models carry a small built-in tank. Navien’s NPE-A2 series, for example, includes a built-in buffer tank and recirculation pump. That buffer helps with the “cold water sandwich,” a short slug of cold water that can pass through before the burner relights between back-to-back uses.

How do you size a tankless water heater by GPM and temperature rise?

Every tankless unit is rated by how many gallons per minute it can heat at a given temperature rise. Temperature rise is the gap between the water coming into the house and the temperature you want at the tap. Size wrong and you get the most common tankless complaint we hear in Cypress: a great shower until someone starts the dishwasher.

1. Add up what runs at the same time

   List the hot water fixtures you use at once on a busy morning. The Department of Energy uses examples of a faucet at 0.75 gallons per minute and a showerhead at 2.5 gallons per minute. Two showers and a kitchen faucet at those rates is 5.75 gallons per minute. If you are not sure what a fixture flows, time how long it takes to fill a bucket.

2. Find your incoming water temperature

   The Department of Energy says to assume 50 degrees F incoming water unless you know otherwise. We would rather know. We measure the cold water at a tap in your house, and we plan for the cooler months, because winter is when a marginal unit falls short.

3. Pick your target temperature

   Most homes set 120 degrees F. The Department of Energy notes that a dishwasher without its own heater may call for 140 degrees F, and warns that temperature carries a scalding risk.

4. Subtract to get the rise

   At 50 degrees F in and 120 degrees F out, the rise is 70 degrees F. At 140 degrees F out, it is 90 degrees F. The bigger the rise, the fewer gallons per minute any unit can deliver.

5. Match the rating chart

   Read the manufacturer’s chart at your rise, not the headline number on the box. The headline number is usually measured at a small rise.

Here is what that looks like on a real spec sheet. These are Navien’s published flow ratings for its NPE-2 series, in gallons per minute at three temperature rises.

Source: Navien NPE-2 Quick Facts. Ranges at 67 degrees F reflect the A2 and S2 versions. Rinnai and Rheem publish similar charts for their models.

Notice what happens at a 67 degree rise. Even the largest unit in that line drops to under 6 gallons per minute. Our example morning of two showers plus a kitchen faucet, at 5.75 gallons per minute, fits the biggest model and not much else. That is why a four-bedroom house in Bridgeland or Towne Lake with three full baths sometimes ends up with two units piped together. The Department of Energy notes that two or more units can be installed for higher demand, at added cost.

Minimum flow matters too

Big flow is one end of the sizing problem. Small flow is the other. Navien lists a minimum flow of 0.5 gallons per minute for its NPE-2 units. PNNL guidance points out that washing hands or rinsing a dish can call for less than 0.5 gallons per minute. If your faucet aerators are very restrictive, the burner may not light at all on a gentle trickle, and you get lukewarm water at the bathroom sink.

What gas line and venting does a tankless heater need?

This is where most tankless jobs in Cypress get decided. The heater itself is the easy part. The gas supply and the vent path are what take time, and they are what a cheap install skips.

Gas line size

PNNL’s guidance says tankless gas heaters typically have burners of 120,000 to 200,000 BTU per hour, roughly 3 to 5 times a typical tank burner. It also says most tankless gas heaters need at least a 3/4 inch gas line from the street, and that branch lines may need upsizing too. Navien’s NPE-2 units have a 3/4 inch gas inlet and call for natural gas supply pressure between 3.5 and 10.5 inches of water column.

Gas pipe sizing is a calculation, not a guess. PNNL notes that sizing has to account for every other gas appliance on the line and the length of the pipe, using the NFPA 54 method. A home with a gas furnace, gas range, gas dryer and a fireplace may already be close to what its meter line can carry. Add a 199,900 BTU burner and the far appliances starve. Symptoms include the tankless throwing ignition codes when the furnace kicks on, or the range flame dropping while someone showers. When the line needs work, our gas line plumbers handle the resize and pressure test, and we pull the permit.

Venting

Tank heaters in older Cypress homes usually vent through a metal flue meant for that kind of appliance. A condensing tankless unit cannot reuse it. Navien’s NPE-2 units vent with 2 inch or 3 inch PVC, CPVC, approved polypropylene or stainless steel, and Navien’s literature advertises vent runs up to 75 feet. PNNL strongly recommends sealed combustion appliances, which pull combustion air from outside through a second pipe or a concentric pipe-in-pipe.

Local code also sets how far the intake must sit from the exhaust, and how far terminations must be from windows, doors and other openings. On a two-story house with the heater in the garage, that can mean routing the vent up through the garage ceiling and out the roof, or out a side wall that is far enough from the neighbor’s window and your own.

Power and condensate

Gas tankless units still need a 120 volt outlet for the controls, fan and spark ignition. Navien lists a maximum draw of 200 watts, or 350 watts with an external pump. Condensing units also need a condensate drain line to a proper drain. In a garage install, that is usually simple. In an attic, it takes planning.

What is involved in converting from a tank to tankless?

Most of our tankless work in Cypress is a conversion. The house was built with a 40 or 50 gallon gas tank in the garage or attic, and the owner wants endless hot water, more garage space, or a heater that does not leak into the ceiling. Here is how we plan it.

Isolation valves deserve their own mention. PNNL recommends installing flush-kit valves during installation so the unit can be isolated and flushed later. Without them, every descaling becomes a cut-in job. We put them on every unit we install, because in hard water areas the unit will need them.

Old tank heaters often sat on a pan, with a T&P discharge line and maybe an expansion tank. A wall-hung tankless frees that floor space. The garage spot where the old 50 gallon tank stood is often where a second refrigerator or a shelf ends up. In attics, getting the old tank out through the access is part of the job. If you are weighing a new tank, an attic unit or a heat pump hybrid instead, our water heater replacement page covers those options in detail.

What do tankless error codes mean?

Every brand uses its own code list, so a “10” on a Rinnai does not mean the same thing as a code on a Navien or a Rheem. We read codes from the manufacturer’s service literature for your model. What helps you as a homeowner is knowing the three families most codes fall into, because each family points to a different kind of fix.

Code meanings above come from Rinnai’s diagnostic code guide and maintenance care guide. Always confirm with the manual for your exact model.

Ignition codes in Cypress homes

When we get an ignition call, the first thing we check is gas, not the heater. An undersized line is the classic cause: the unit fires fine for a sink, then fails when the shower and the furnace run together. A gas meter that was never upsized after a tankless install will do the same. Ignition faults also show up after storms when vents take in water or debris, and in garages where a car runs near the intake.

Flow complaints

Lukewarm water at one faucet but not others usually means that fixture flows below the unit’s minimum. Low flow everywhere points to the inlet screen or scale inside the heat exchanger. A cold burst in the middle of a shower when someone else turns off their tap is often the cold water sandwich, which a buffer tank or recirculation setup can help with. For a heater that is dead, leaking or tripping, our water heater repair team works on tank and tankless alike, 24/7.

Why does annual descaling matter so much in Cypress?

Hard water carries dissolved calcium and magnesium. The U.S. Geological Survey explains that heating hard water can form calcium carbonate scale, and that scale shortens equipment life and raises heating costs. A tankless heat exchanger is made of narrow passages with water moving fast past a hot burner, which is exactly where scale forms and where it does the most damage.

Navien recommends descaling at least once a year, and more often with higher mineral content, a higher temperature setting or heavier use. Rinnai recommends flushing at least once a year and says the interval depends on your home’s water quality. Rinnai’s maintenance guide also says to flush before a year if the controller shows an LC, 00 or LC0 to LC09 code.

What scale does to the warranty

Navien’s NPE-A warranty excludes damage caused by local adverse conditions, including hard water deposits and lime or mineral buildup. Rinnai’s diagnostic guide is just as direct: hard water must be treated to prevent scale buildup, or damage to the heat exchanger will occur. Skip the flush and you can end up paying for a heat exchanger out of pocket.

How we descale a tankless unit

• Shut off power and gas, close the cold, hot and main water valves at the isolation kit.
• Open the purge ports to relieve pressure, then connect hoses and a small pump.
• Circulate the descaling solution through the heat exchanger. Rinnai’s guidance calls for 4 gallons of undiluted white vinegar and says the flush may take up to 45 minutes.
• Flush with fresh water. Navien says to flush with fresh water for at least 10 minutes after the descaler.
• Clean the cold water inlet screen, check the vent and air filter, and run hot water for a few minutes to clear air before we leave.

Is surface water changing this?

Partly. MUDs inside the North and West Harris County Regional Water Authorities are shifting from well water toward treated surface water under the Harris-Galveston Subsidence District’s targets. WHC MUD 10, which is converting to North Harris County Regional Water Authority surface water, told residents in 2026 that its incoming surface water would be softer than its previous groundwater, with fewer water spots and less lime scale. Softer is still not soft, and many homes mix sources through the year, so we still recommend a yearly flush. Our water softener installation page explains how to read your MUD’s water report and when a softener makes sense in front of a tankless unit.

Not everyone needs a yearly flush in every water type. One writer at Green Building Advisor ran a Rinnai for seven years before descaling and suspected annual descaling is mostly needed in very hard water. He also noted his unit lost flow by that point. Our view is simple: with Cypress groundwater history and warranties that exclude scale damage, a yearly flush is cheap insurance.

Does tankless work with hot water recirculation?

Yes, and in big Cypress floor plans it is often the best upgrade you can add. A tankless unit gives endless hot water, but it does not make hot water reach a far bathroom faster. In a two-story home where the heater sits in the garage and the primary bath is on the opposite end, waiting for hot water can take a while, and that cold water goes down the drain.

Built-in recirculation

Some units carry their own pump. Navien’s NPE-A2 models include a built-in buffer tank and recirculation pump, with a 3/4 inch recirculation inlet and a ComfortFlow mode. Navien sells a NaviCirc valve that can create a loop without a dedicated return line, and push-button accessories so you can call for hot water on demand.

Dedicated return line or crossover valve

Some homes, often larger custom builds, have a dedicated hot water return line. If yours does not, a crossover valve under the far sink can send cooled water back through the cold line. It works, though your cold tap may run warm for a moment.

The cold water sandwich

PNNL explains that when a recirculation pump reaches temperature and shuts off, the burner shuts down too, which can let a small amount of cold water pass before the burner relights. The usual fix is a small electric storage tank of 5 to 10 gallons, or a model with built-in minimal storage. We size recirculation and buffering together so the system does not fight itself.

Tank vs tankless vs hybrid: which is right for your house?

There is no single right answer in Cypress. A retired couple in a 1990s Longwood Village home and a family of six in a new Bridgeland build have very different needs. Here is how the three main options compare on the points that matter here.

Efficiency, lifespan and installation figures are from the U.S. Department of Energy. Tank lifespan reflects our local experience range.

A note on hybrids in Cypress: the Department of Energy says heat pump water heaters cool the space they sit in and need to stay between 40 and 90 degrees F year-round. A garage often qualifies most of the year. An unconditioned attic in August, when IAH averages a 94.9 degrees F high outside, is a harder fit. Our replacement team handles hybrid installs and can tell you if your space works.

What happens to a tankless heater during a power outage?

A gas tankless water heater stops making hot water when the power goes out. It needs electricity for its controls, fan and spark ignition. Cypress has seen what that means. Hurricane Beryl in July 2024 left more than 2.2 million CenterPoint customers without power, and the May 2024 derecho knocked out power to more than 900,000. During Winter Storm Uri in February 2021, rolling outages hit the region at the same time pipes were freezing.

• Backup power. PNNL notes that an uninterruptible power supply can keep a tankless unit running during outages. A small battery unit sized for the heater’s draw is one option.
• Generator circuit. If you have a standby or portable generator with a transfer setup, the heater’s outlet can be on the backed-up circuit. Navien lists a maximum draw of 200 watts for its NPE-2 units, or 350 watts with an external pump.
• Freeze protection. Any electric freeze protection built into your unit stops working when the power is out. In a hard freeze with the power out, drain the unit using the isolation valves, or call us and we will walk you through it.

What drives the cost of a tankless water heater in Cypress?

We do not publish a flat price for tankless installs, because two houses on the same street can need very different work. We give you a written price before anything starts. These are the factors that move that number up or down, so you can compare quotes on equal terms.

When you compare quotes, ask each company to list the unit model, the gas line size they plan to run, the vent material and route, and whether isolation valves and the permit are included. A quote that leaves those blank is not comparable to one that spells them out. Our homepage has a section on how we price work if you want to see how we build a written estimate.

Operating cost matters too. The Department of Energy notes that tankless units cost more up front but can offset that through lower energy costs over time, and that most last more than 20 years compared with 10 to 15 for storage units. That long life depends on regular descaling.

Who does a tankless water heater suit in Cypress?

Tankless makes the most sense for some houses and some owners. Here is how we see it across the neighborhoods we work in every week.

New and newer builds: Bridgeland, Miramesa, Dunham Pointe

Bridgeland began development in 2004, and new construction continues across its villages. Communities near the Grand Parkway, like Miramesa and Dunham Pointe, are newer still. Buyers here often ask whether to upgrade to tankless at contract or wait. If the builder offers a tankless option with the gas line and venting already sized for it, it is usually simpler to do it then than to retrofit later. If you are retrofitting, check where the gas meter is and how far the line runs to the garage.

Towne Lake and Cypress Creek Lakes

Towne Lake is fully built out, and Cypress Creek Lakes was built in the mid-2000s by Perry Homes and David Weekley Homes. With tank heaters typically lasting about 8 to 12 years, many of these homes are on their second tank or about to need one. That replacement moment is the natural time to ask about converting. Large floor plans with far-off baths are good candidates for tankless with recirculation.

Established areas: Fairfield, Coles Crossing, Longwood Village, Cypress Mill

Fairfield began in 1988, and Coles Crossing was built mainly from 1998 to 2008. Homes here may have original gas lines sized only for a tank, a furnace and a range. A conversion often means upsizing the gas line, so plan for it. Homes in Longwood Village and Cypress Mill, built in the 1990s to early 2000s, often have the heater in the garage, which makes venting easier.

Who should probably stay with a tank

• Homes where the gas line upgrade would be long and costly and the household uses little hot water.
• Owners who will not descale yearly and have hard water without treatment.
• Homes where losing hot water in a power outage is a real problem and no backup power is planned.

What buyers, sellers and landlords should check

• Buyers: Ask for the install date and any flush records. Look for isolation valves on the unit. Note any code on the display during your inspection.
• Sellers: A recent descale receipt and a clean controller help at inspection. Fix any vent or condensate issues before listing.
• Landlords: Put annual descaling on the calendar. Tenants rarely notice scale until the unit throws a code or the hot water runs lukewarm.

Every plumber who touches your gas line or heater should hold a current Texas license. You can check any plumber for free on the Texas State Board of Plumbing Examiners website. For more on what to check when buying or selling, see our property guide.

Questions Cypress homeowners ask about tankless water heaters

Related plumbing services in Cypress

Cypress neighborhood guides for this service: plumbing in Miramesa, plumbing in Dunham Pointe, plumbing in Blackhorse Ranch.