A point-of-use water heater is a small tank or tankless unit installed at or near one fixture, like a sink far from the main heater. You need one when hot water takes too long to arrive, when a remote sink is past the code's 50 foot limit, or when a business sink needs hot water fast.
What types of point-of-use water heaters are there?
There are two main types, and they suit different fixtures.
| Type | How it works | Best for |
|---|---|---|
| Mini-tank | A small storage tank under the sink keeps water hot | Short bursts, like handwashing, where instant hot water matters |
| Point-of-use tankless | Heats water only while it flows, no storage | Steady low-flow use at one fixture, with no tank to keep hot |
Both are usually electric. A mini-tank is still a storage water heater. So it needs the same safety parts as a full-size tank. That means a temperature and pressure relief valve under Section 504.4 of the Phoenix plumbing code. It also means a pan under Section 504.7 where a leak would cause damage, such as a cabinet over a wood floor.
A point-of-use tankless unit is sized for one fixture. Stiebel Eltron sizes its small units by three things: the hot water temperature you want, "the temperature of the incoming ground water, and the flow rate at the fixture." One fixture needs little flow. The code limits a home bathroom faucet to 1.5 gallons per minute and a public one to 0.5.
You can estimate the power a tankless unit needs for one sink. Maricopa County's guide says "1,000 Watts (1kW) will heat 4.1 gallons of water at a 100°F rise" each hour, and it sizes for a 60°F rise. A public hand sink at 0.5 gallons per minute uses 30 gallons an hour. Warming that by 60°F takes about 4.4 kW, by our math from the county's figure. A home bathroom faucet at its full 1.5 gallons per minute needs about three times that, around 13 kW. Check the maker's chart for the exact model before you buy, since each unit lists its own flow at each temperature rise.
When does a home need a point-of-use water heater?
A home needs one when a fixture is so far from the heater that hot water takes too long. It also needs one when the pipe run breaks the code limit. Section 607.2 of the Phoenix plumbing code says the hot water piping from the source to a fixture "shall not exceed 50 feet." The code counts a recirculation loop as a source of hot water. So a loop is the other common fix.
Common cases in Valley homes:
- A casita or a far wing of a single-story house, where the water heater sits in the garage at the other end.
- A remodel that adds a bathroom or wet bar well away from the existing heater.
- An addition where running a new hot water line back to the garage would mean opening walls or ceilings.
Our pages on whether a recirculation pump is worth it and what size water heater you need cover the other side of the choice.
When does a business need a point-of-use water heater?
A business needs one when a sink must get hot water fast and the main heater is too far away. This is where point-of-use heaters do the most work in the Valley. Maricopa County is strict about hot water in food businesses.
The county's guide sets the heater at "at least 120ºF." It says hand sinks, dish sinks, dishwashers, and service sinks must get hot water "within 45-seconds at all times." It also caps the pipe run from the heater to a fixture at "60 feet for incorporated areas, or 50 feet in unincorporated areas of Maricopa County." Where that's hard to do, "the Department recommends installing separate point-of-use water heaters for remote fixtures or appliances."
The county's plan review list adds that "Hot water or tempered water (100ºF to 110ºF) is required at all sinks." For big buildings, the guide also suggests a separate hot water system for the food side. It says a point-of-use system "can ensure a calculated and consistent supply of hot water to food service operations."
### Which sinks can use a small instant-hot heater?
Only single fixtures with low demand. The county says small under-sink "insta-hot" tankless units "are limited to approved single point-of-use applications due to their design limitations, such as hand-wash sinks, hot water beverage fill stations, etc." It adds that they are "not allowed to be installed for use at appliances or fixtures requiring a high hot water supply demand/flow volume rate, such as a service sink." And it notes that all tankless water heaters "require final onsite approval by the Department."
What temperature should a point-of-use heater deliver?
It depends on the fixture. For public restrooms, the plumbing code Phoenix uses requires tempered water, not hot water. Section 419.5 says "Tempered water shall be delivered from lavatories and group wash fixtures located in public toilet facilities provided for customers, patrons and visitors," through a temperature-limiting device that meets ASSE 1070. Section 607.1.2 sets that device to "not greater than 110°F."
Maricopa County's guideline narrows it for food businesses: tempered water "shall be maintained at a temperature of 100°F to 110°F," and "The recommended temperature for tempered water hand sink faucets is 100°F to 105°F."
| Where | Temperature rule |
|---|---|
| Public restroom lavatory (Phoenix code) | Tempered, limited to no more than 110°F by an ASSE 1070 device |
| Food establishment tempered water (county) | 100°F to 110°F |
| Food establishment hand sink (county recommendation) | 100°F to 105°F |
| Food establishment heater set-point (county) | At least 120°F, arriving within 45 seconds |
At home, the same scald logic applies. A small heater under a sink can deliver very hot water fast, so set it no hotter than the fixture needs.
Is a point-of-use heater worth it?
It's worth it when the alternative is a long wait, wasted water, or a failed health inspection. ENERGY STAR lists point-of-use electric heating among the approaches that, "Under the right circumstances," can save significant energy. It is not a whole-house solution, though. A point-of-use unit serves one fixture well and nothing else, so it works alongside a main water heater, not instead of one.
For restaurants, see our page on restaurant plumbing health inspection requirements and the guide to types of commercial water heaters. HQ Plumbing & Air installs point-of-use, tank, and tankless water heaters for homes and businesses across the Phoenix area. See our water heater service and commercial plumbing.
Small heater, right at the sink. It's the fix when the hot water is too far away.
The county recommends them for remote fixtures in food businesses; see the 45 second hot water rule and 60 foot pipe limit.