Tankless water heaters in St. Paul, MN

How a tankless unit works

A tankless water heater has no storage tank. When you open a hot tap, cold water runs through a heat exchanger and a gas burner heats it on the spot. When you close the tap, the burner shuts off.

Because nothing is kept hot between uses, a tankless unit avoids the standby heat loss of a storage tank. The trade-off is that it can only heat so many gallons per minute. The Department of Energy says tankless units typically deliver 2 to 5 gallons per minute, and gas models generally deliver more than electric ones.

Sizing for cold Minnesota water

A tankless unit is sized by two numbers. The first is flow rate: add up the fixtures you expect to run at the same time. The Department of Energy’s sizing guide uses a shower at 2.5 gallons per minute plus a faucet at 0.75, for a total of 3.25.

The second is temperature rise: the difference between the water coming into your home and the temperature you want at the tap. DOE suggests assuming 50°F incoming water if you don’t know it. Heating that to 120°F is a 70°F rise. In a Minnesota winter, incoming water can be colder, so the unit has to add more heat and its usable flow drops.

That is why we size for the coldest months, not the average. A unit that keeps up in July may fall short in January if two showers run at once. Our tank vs. tankless guide for Minnesota covers this in more depth.

Venting and gas supply

A gas tankless unit needs its own venting to the outdoors, and the vent type and route must match the manufacturer’s instructions. The old chimney or vent from a tank heater often can’t be reused as is.

Tankless burners use a lot of gas while they run. Many homes need a larger gas line or a new run from the meter to supply one. We check your gas piping and venting before recommending a unit, and the gas and venting work is done under a permit. If you smell gas at any time, leave the house and call 911 and Xcel Energy at 1-800-895-2999 from outside. If another company supplies your gas, call the number on your gas bill.

Descaling in hard water

Hard water leaves mineral scale inside the heat exchanger. Scale cuts efficiency and flow, and it can trigger error codes. Many Twin Cities suburbs and private wells have harder water than St. Paul’s softened city supply.

The Department of Energy notes that periodic maintenance keeps a tankless unit efficient and extends its life, so follow the owner’s manual. In practice that means flushing the heat exchanger with a descaling solution on the schedule the manufacturer sets and cleaning the inlet screen. A water softener can reduce scale if your water is hard.

Pros and cons vs. a tank

• Efficiency: DOE says tankless units can be 24% to 34% more efficient than storage tanks in homes using 41 gallons of hot water a day or less, and 8% to 14% more efficient in homes using about 86 gallons a day.
• Lifespan: DOE says most tankless units last more than 20 years, compared with 10 to 15 years for a storage tank.
• Endless supply, limited flow: You won’t run out of hot water, but running several fixtures at once can outpace a single unit.
• Cost: The upfront cost is higher than a tank, though lower energy costs can offset some of it over time.
• Ignition: DOE recommends models with an intermittent ignition device rather than a standing pilot light, which wastes gas.

Still deciding? Compare options on our water heaters page, ask about financing on qualifying installations, or request an estimate.

Signs a tankless unit needs service

• Hot water runs lukewarm when more than one fixture is on
• Water temperature swings during a shower
• The unit shows an error code or shuts off mid-use
• Flow from hot taps is weaker than from cold taps
• It has not been flushed or descaled on the manufacturer’s schedule
• You hear new noises from the unit while it heats

Common questions

Sources

• U.S. Department of Energy — Tankless or Demand-Type Water Heaters
• U.S. Department of Energy — Sizing a New Water Heater
• Saint Paul Regional Water Services — About Your Water