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Tank Vs Tankless electric DHW consumption

asked 2022-01-18 15:58:35 -0500

ZapplingZane's avatar

updated 2022-02-22 13:19:45 -0500

Doing a consumption study using BEopt and when comparing a Standard Electric water heater Vs an Electric Tankless water heater there is only 59 kWh difference? They are both being modeled in a 3rd story 2BR apartment. I know that tankless water heaters are way more efficient then what BEopt is saying. Any ideas or tips would be great.

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answered 2022-01-18 19:05:39 -0500

updated 2022-01-18 19:07:26 -0500

The BEopt result seems reasonable to me.

The difference between electric tankless and tank water heaters is not that great, just look at their respective Energy Factors, which differ by ~5 percentage points. As electric tank water heaters can be insulated quite well, there aren't high tank losses that can be eliminated by going tankless.

Contrast that with gas tankless water heaters, which are significantly better than gas tank water heaters, with Energy Factors that can differ by up to 30 percentage points. This is because gas tank water heaters have multiple penetrations (gas line, flue), so they have high tank losses even when insulated well. By eliminating these tank losses, there is a large benefit to going tankless for gas water heaters.

Thus, gas tankless water heaters generally save a lot of energy while electric tankless water heaters provide marginal benefit. It's also pretty uncommon to install/use electric tankless water heaters because they have huge power draws. Thus, heat pump water heaters are a more common solution to improving on a conventional electric tank water heater. (One could alsofocus on reducing hot water usage via low flow fixtures, hot water pipe insulation, drain water heater recovery, etc.)

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Great answer! I'd also like to add that in general electric tankless water heaters can't provide as high of a temperature rise as gas ones can at relatively high flow water flow rates (5+ gpm). This is mostly an issue for northern climate zones.

Jeremy's avatar Jeremy  ( 2022-01-19 11:18:29 -0500 )edit

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Asked: 2022-01-18 15:58:35 -0500

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Last updated: Jan 19