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Recirculation Loop Cost Calculator

What a hot water recirculation loop costs to run: delta-T corrected pipe loss, separate pump energy, and the annual total.

Inputs

The loop

Supply plus return, measured along the pipe, not the straight-line distance. Include the run from the heater to the furthest fixture and back.

The temperature held in the loop, normally the tank setting.

Attic, crawlspace, basement or slab. Winter air is what the loop loses heat to.

Contractor rule of thumb: insulated domestic hot water pipe runs near 10 Btu/hr per foot and uninsulated pipe roughly double that, at a 70 F water-to-air difference. Confirm with the insulation manufacturer's data or a measurement - this is the weakest input here.

Circulator and controls

Read it off the pump nameplate. Small bronze circulators run 15-45 W.

A loop on a 24-hour timer is hot all day. A timer or aquastat that shuts the loop down overnight cuts this line, and the pipe loss with it.

Usually the same as the loop hours. A demand-controlled pump runs less.

Changes the note you get back, not the arithmetic - the arithmetic follows the hours you entered above.

Energy price

All-in cents per kWh from the bill, since the pump and any electric heat the loop demands are both paid at the electric rate.

Result

Annual cost of the loop
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Annual energy for the loop
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Pipe heat loss rate
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Daily energy for the loop
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Share of the energy lost from the pipe
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—
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Where this stops applying
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Daily energy lost from the pipe
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Daily energy for the pump
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Calculation details
Water-to-air temperature difference
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Correction from the 70 F reference
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Actual loss per foot
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Pump energy as heat rate
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Combined loss rate
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What to check

  • Total loop length, supply plus return
  • Per-foot heat loss from the insulation manufacturer or a measurement
  • Hours the loop is hot and hours the pump runs

Standards referenced

Related calculators

Screening estimate only. The result panel lists the limits that apply to this calculation. Verify nameplate data, rates, groundwater temperatures and installer quotes before deciding, and have gas, venting and electrical installations checked against the local code by a licensed contractor.

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