Indiana homeowner pegs near-instant hot water at about $127 per year, not counting pump electricity

"For the joy of having nearly instant hot water, a little over $10 a month is money very well spent."

An Indiana homeowner shared detailed calculations on Reddit’s r/Homeowners forum after asking what it really costs to run a dedicated, insulated hot-water recirculation loop with a tankless water heater.

What the homeowner calculated

In the thread, the original poster said they use a Rinnai RXP199iN tankless water heater connected to a 90-foot dedicated recirculation loop.

They wrote that they had gotten into a debate with a friend about the actual cost of a recirculation loop for a tankless water heater, noting that they had seen claims online that the expense could run from $35 to $65 per month for a loop operating around the clock.

Using a pipe heat-loss calculator, the homeowner estimated annual costs at $127. Their math used 624 Btu per hour of loss, gas priced at $0.024 per cubic foot, and 1,030 Btu per cubic foot, which came out to 5,466,240 BTU over a year.

On that basis, they said the system would cost a little more than $10 a month to operate, far below the monthly figures they had seen elsewhere online.

The homeowner also pointed out several limits to the estimate: it assumed 100% water-heater efficiency even though the real figure is closer to 97%, treated pump costs as zero, and did not account for any water savings from spending less time waiting at the tap.

Still, the homeowner’s conclusion was clear: for nearly instant hot water, a little over $10 a month felt worth it.

When another commenter asked about electricity for the pump, the homeowner said that cost had not been included. They added that internet searches suggested the unit draws 78 to 98 watts while running and that, at $0.1375 per kilowatt-hour, 24 hours of operation would be about 35 cents, or a little over $10 a month. Even so, that figure may be overstated if the pump does not run continuously.

Another commenter said their own system, even when set to run continuously, only switches on every 30 minutes or so for about five seconds.

Commenters also noted that the loop’s heat loss is not always a net loss. During winter, it can help warm the house, while in the cooling season it can put extra load on the air conditioner.

What homeowners can do

For anyone planning a remodel or repipe, installation details can make a significant difference. In this case, the homeowner said a fully insulated loop and 1-inch PEX helped reduce resistance and avoid major pressure loss even with several fixtures running.

For homeowners considering an upgrade, Cala offers customizable smart heat pump water heaters designed to lower energy bills by heating water only when needed.

That focus on timing reflects one of the main themes in the Reddit discussion, where pump runtime was a major factor in the total cost. Rather than treating hot-water demand as constant, Cala’s smart heat pump water heaters are built around household usage patterns and customization. Buyers weighing convenience, efficiency, and operating cost may want to compare recirculation controls with options from Cala.

Related stories

These stories look at similar trade-offs involving recirculation loops, tankless heaters, and long waits for hot water.

• A homeowner learned the right recirculating setup can cut daily waits and reduce water waste.
• Another homeowner found tankless recirculation would save little if the shower still lagged.
• In Georgia, a homeowner found the recirculation pump never shut off, leading to repeated error codes.