Rheem Tankless Water Heater Installation in Frisco, TX

Every capacity figure printed on a tankless water heater is meaningless without a temperature rise attached to it, and the reason homeowners get caught out is that the rise changes by more than a factor of two across a North Texas year. The governing equation is simple: usable flow in gallons per minute equals BTU per hour multiplied by efficiency, divided by the temperature rise in Fahrenheit multiplied by 500. The 500 comes from 8.33 pounds per gallon multiplied by 60 minutes multiplied by one BTU per pound per degree.

Run that for a 199,000 BTU condensing unit at 0.95 efficiency and you get about 378 divided by the rise. In August, when inlet water arrives near 80F and a 105F shower needs only a 25F rise, the arithmetic says fifteen gallons a minute, which is not a real number because the unit's maximum flow rate limits it long before that. In January, with inlet water at 50 to 55F and a 55F rise required, the arithmetic gives closer to seven, and the honest working figure after allowing for real-world derating is 5.5 to 6.0. That is the number to size against, because the January morning is the only one that matters.

This is why almost every complaint about a tankless unit not keeping up arrives between December and February, and why a unit that was described as handling three showers is suddenly handling two. Nothing has degraded. The inlet water got thirty degrees colder and the unit is being asked to do roughly twice the work per gallon. If capacity in winter is the priority, size on the January row and treat everything above it as headroom.

An outdoor-bodied unit removes three problems in one move: no vent run, no combustion air question, no indoor condensate route. On a house with no good interior location that can be the difference between a straightforward job and an expensive one, and we install them regularly. The caveat is specific and it is not about the equipment being poorly made.

Freeze protection on outdoor tankless units is electric - resistance heating elements, and on some models controlled burner cycling. It works well and it protects to temperatures far below anything Frisco normally sees. It also stops working the moment the unit loses power. February 2021 demonstrated that a multi-day hard freeze combined with extended outages is a real scenario in this region rather than a hypothetical one, and any honest conversation about an outdoor unit has to include what you will do if that happens again.

1. 1

   Insulate the exposed piping properly at installation

   The water lines to and from an outdoor unit freeze before the unit itself does. Closed-cell pipe insulation, UV-resistant jacketing on anything in sunlight, and insulation on the recirculation return if there is one.

2. 2

   Know where the isolation valves and drain plugs are

   You cannot drain a unit in the dark during an outage if you have never located the service valves. Ask for them to be pointed out at handover and photograph them.

3. 3

   When a hard freeze and a likely outage coincide, drain it

   Close the cold isolation valve, open a hot tap indoors to break the vacuum, open both service port bibs and remove the drain plugs so the exchanger empties. Leave it drained until power is restored.

4. 4

   Refill and purge before restoring power

   Close everything, open the cold valve, run a hot tap until flow is steady and air-free, then restore power and gas. Firing an exchanger with air pockets in it is an avoidable way to damage the unit.

5. 5

   Consider a small backup power source if outdoor is the only option

   The freeze protection draw is modest. A modest generator or battery backup on that circuit alone is a cheaper insurance policy than an exchanger replacement.

Tankless units ship with an adjustable setpoint and it is genuinely tempting to raise it, because a higher setpoint means less hot water is needed to reach a given mixed temperature, which makes the unit appear to have more capacity. It also raises the burn risk at every tap in the house, and the relationship between temperature and injury time is steeper than most people expect.

Children and older adults burn faster than those figures, because their skin is thinner. That is the argument for 120F as a default delivery temperature in a household with young children, and it is what we set unless there is a specific reason not to. The specific reasons do exist: some dishwashers perform better with a 140F supply, some laundry regimes want it, and a recirculation loop holding stored volume behaves better at a higher temperature.

Where a higher setpoint is genuinely wanted, the correct answer is to raise the source temperature and mix it back down at the point of distribution or at the fixture, rather than to distribute 140F water everywhere and rely on people being careful. A thermostatic mixing valve at the heater outlet blends stored or produced hot water down to a safe delivery temperature; point-of-use valves do the same at an individual fixture such as a bath. Both are inexpensive relative to the equipment and both are the difference between a considered design and an accident waiting to happen.

One point about Legionella, because it comes up. The classic risk case is a large volume of water stored for long periods in the lukewarm band, which is a storage tank problem rather than a tankless one - a tankless exchanger holds well under a gallon and does not stagnate. What reintroduces the concern is anything that stores or holds warm water: a buffer tank, and particularly a long recirculation loop sitting at an intermediate temperature. If you run a loop, run it at temperature rather than tepid, and do not lower the setpoint to save gas on a system with substantial held volume.

A gas tankless water heater needs electricity. The blower, the ignition, the controls, the flow sensor and the freeze protection all run on it, and the unit typically wants a dedicated 120 volt supply with a receptacle within reach of the cord or a hard-wired connection depending on the model. In a garage or an outdoor location, the receptacle needs GFCI protection. None of that is exotic, but it does mean an electrical item may appear on the quote where none existed for the tank being removed, because plenty of atmospheric gas tanks needed no power at all.

The consequence is the failure mode nobody expects: a power cut means no hot water even though the gas is still flowing and the house still has water pressure. Homeowners who kept hot water through outages with an old standing-pilot tank are sometimes genuinely surprised by this, and it is worth knowing in advance rather than discovering it on the third day of an ice storm. If your house has a standby generator, putting the water heater circuit on it costs almost nothing at the time the generator is installed and is disproportionately valuable.

• Dedicated 120 volt supply, GFCI protected in garage and outdoor locations
• Running current is modest in normal operation and rises when freeze protection engages
• No power means no hot water regardless of gas supply
• Worth including on a standby generator circuit if one exists
• A surge protective device on the circuit is cheap relative to a control board
• Wi-Fi coverage at the unit is a real constraint on connected models in detached garages and far attics

On connectivity, the useful applications are narrow but genuine: a push notification when the unit faults while you are away, remote setpoint adjustment, a vacation mode, and giving a technician the fault code before the visit rather than during it. What it does not do is monitor the things that actually shorten a unit's life. No app measures scale thickness in the exchanger, gas pressure under full fire, or the state of a neutraliser cartridge. Connectivity is a notification channel, not a maintenance programme, and it should not displace the annual flush.

Rheem's breadth of distribution through both plumbing supply houses and retail is a genuine convenience, and it introduces one thing worth understanding. Manufacturers across this industry commonly build differentiated model families for different sales channels. Units that look broadly similar can differ in specification, in included accessories, in the parts supply chain behind them and, importantly, in warranty terms. That is not a scandal and it is not unique to any one brand; it is how the industry is structured.

The practical implication is simply that you should read the documentation for the exact model you are buying rather than a general brand-level warranty summary from a web page. If you are comparing a bid against a unit you found yourself, compare the model numbers rather than the family names, and check whether the terms differ. We are happy to price a homeowner-supplied unit and we will tell you plainly if the model on the box is not the one you thought you were comparing.

We deliberately do not publish specific warranty durations here. They vary by model family and by revision, and a figure that was accurate when this page was written is not a figure you should rely on when you buy. Confirm the terms against the current manufacturer documentation for the specific model, and treat any contractor quoting warranty length from memory with mild scepticism, ourselves included.