A tankless water heater does not store hot water. When you open a faucet, a flow sensor inside the unit detects the draw and fires a gas burner or electric element. Water passes through the heat exchanger and comes out hot on the other side. Close the faucet and the unit shuts off. There is no 40- or 50-gallon tank reheating water you are not using, and the unit cannot run out mid-shower the way a tank can when the household draws faster than the tank recovers.
That said, tankless is not automatically the right choice for every Phoenix home. The unit's rated flow, measured in gallons per minute, has to cover your peak simultaneous demand, and that number shifts with the temperature rise the heat exchanger has to produce. Phoenix inlet water runs around 65 degrees in winter, so a unit rated at 11 GPM on the spec sheet delivers closer to 7 or 8 GPM at a 55-degree rise to reach 120 at the tap. Run a shower, a dishwasher, and a bathroom sink at the same time and you will feel the limit if the unit is undersized. Phoenix hard water, 12 to 20 grains per gallon depending on your water district, also means the heat exchanger collects mineral scale faster than it would in a softer market, and annual descaling is real maintenance, not optional. We walk through all of this during the assessment so you are choosing tankless with your eyes open, not because someone sold you on the idea of endless hot water without mentioning the tradeoffs.
We install Navien condensing gas units for most whole-home applications because the dual stainless-steel heat exchangers hold up well in hard water and the built-in recirculation pump eliminates the cold-water sandwich that cheaper units produce. When tankless is the right fit, it is genuinely good: a well-sized gas unit cuts water-heating energy use by roughly 8 to 14 percent over a standard tank, lasts 15 to 20 years with proper maintenance, and mounts on a wall instead of occupying floor space in the garage. Call 602-560-8989 for a free in-home assessment. We will size the unit to your actual demand, quote a flat rate before any work starts, and give you an honest answer on whether tankless makes sense for your household or whether a standard tank replacement is the better call.
What We Handle
Our Process
Size the Demand
We count fixtures, estimate your peak simultaneous draw, read the incoming water temperature, and check the existing gas line size and electrical capacity. A tankless unit that is undersized for the household produces lukewarm water under load, and one that is oversized wastes money on capacity you will never use. The assessment answers both questions before you spend anything.
Quote the Job
You get a flat-rate price that covers the unit, venting, gas line work if needed, and disposal of the old heater. If the assessment shows tankless is not the best fit, we will say so and quote a tank option instead. The decision is yours, and the price is the price before we start.
Install and Vent
Gas tankless units need dedicated venting to the outside, either direct-vent with a two-pipe intake and exhaust, or power-vent with a fan-assisted exhaust. Many tank-to-tankless conversions also need a larger gas line to feed the higher BTU burner. We handle the venting, the gas work, the mounting, and the water connections as a single scope so nothing falls through the cracks between trades.
Test and Walk Through
We run every hot-water fixture in the house, verify the temperature rise at the tap, check for error codes on the control board, and confirm the gas pressure is within spec. We also walk you through the unit's display, explain what the annual descaling involves, and set a reminder for your first flush so the heat exchanger stays clean.
Frequently Asked Questions
It depends on the household. A tankless unit eliminates standby heat loss, which is the energy a tank spends keeping 40 or 50 gallons hot around the clock. The DOE puts realistic savings for a gas tankless at 8 to 14 percent on water heating costs, not the 30 to 40 percent some marketing claims. The bigger payoff is lifespan: a well-maintained tankless unit lasts 15 to 20 years versus 8 to 12 for a tank. Over that span the energy savings and avoided second tank replacement add up, but only if the unit is properly sized and descaled annually in Phoenix hard water. There is a fuller comparison on our tank vs tankless page.
Descaling means circulating a vinegar or food-grade acid solution through the heat exchanger to dissolve mineral scale. Phoenix water runs 12 to 20 grains per gallon, and that calcium and magnesium deposits on the heat exchanger walls every time hot water passes through. Left alone, scale insulates the exchanger, forces the burner to run harder, and eventually restricts flow enough to trigger error codes. Navien and most manufacturers recommend descaling at least once a year; in the harder parts of the Valley, twice a year is better. A whole-home water softener slows the buildup but does not eliminate the need for flushing entirely.
The unit's GPM rating is measured at a specific temperature rise, and that rise changes with the season. A unit rated at 11 GPM at a 35-degree rise delivers around 7 to 8 GPM when Phoenix inlet water drops to 65 degrees in January and the unit has to produce a 55-degree rise to reach 120 at the tap. We size to the winter condition, not the summer one, because that is when the unit works hardest. For a typical three-bathroom Phoenix home running a shower, a dishwasher, and a sink at the same time, a condensing gas unit in the 199,000 BTU range usually covers it. Larger homes or homes with guest casitas may need two units or a recirculation loop.
Most can, but it usually involves more than just swapping heaters. A gas tankless burner draws significantly more BTUs than a standard tank, so the existing gas line from the meter to the unit often needs to be upsized from 1/2-inch to 3/4-inch or larger. The unit also needs dedicated venting to the outside, either a two-pipe direct-vent or a fan-assisted power-vent, which a tank water heater that shares a B-vent flue does not have. Electric tankless units skip the gas and venting but may require an electrical panel upgrade to handle the amperage. We evaluate all of this during the assessment so there are no surprises on install day.
Scale buildup on the heat exchanger is the most common issue in Phoenix. The unit's error codes usually point to the cause: ignition failure means the burner is not lighting, often from a dirty flame rod or a gas supply issue; a flow sensor fault means the unit is not detecting enough water movement to fire; and an exhaust blockage code means the vent run is obstructed or too long. Many of these trace back to deferred descaling. When scale coats the heat exchanger, it restricts flow, changes the temperature readings the control board sees, and can trip faults that look electrical but are really mineral buildup. Our water heater repair page covers the diagnosis side in more detail.
Phoenix hard water is harder on a tankless heat exchanger than it is on a standard tank, because every gallon passes directly over the exchanger surface instead of sitting in a tank where most of the scale settles to the bottom. A water softener reduces the grain count reaching the unit and slows scale formation, but it does not eliminate it, and the softener itself needs salt and periodic service. Whether a softener is worth it depends on your water district's hardness and how many hot-water appliances you are protecting. We cover the full picture on our water heater cost page, including what the long-term maintenance looks like.