Craftsmen of Homes

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Roanoke & Smith Mountain Lake, Virginia

Heat Pump Water Heaters

For a new home designed and built with energy-efficiency in mind, the water heating appliance decision likely has the single-greatest effect on overall energy savings.  True, space heating and cooling equipment is important; but an air-tight and well-insulated home just uses less energy for heating or cooling, and those 'loads' are sized accurately at the specifications phase of planning.  Also true, lights and other appliances as a group take up the largest segment of the energy-expense pie chart shown below.  But improvements to individual fixtures, lamps, and non-water-heating appliances have smaller, incremental impacts on the whole balance.  Therefore, at the outset, do as much as you can to reduce water heating costs by selecting the best water heating appliance your budget will allow.

For a recent home we designed and built here on Smith Mountain Lake, Virginia, the pie charts below compare the impact of a single decision:  do we install a new 50-gallon electric resistance tank water heater, or do we install a new 50-gallon electric heat pump tank water heater ?  Seldom do we see simple payback opportunity as short, as dramatic, as what we see here.  Clearly an opportunity not to be missed.

Energy efficiency of electric resistance water heating for Smith Mountain Lake Home designer builder Timber Ridge Craftsmen Inc.

Energy efficiency house Smith Mountain Lake Home designer builder Timber Ridge Craftsmen Inc. heat pump hot water heaters energy modelling analysis.

Comparing $414. annual energy cost for the electric-resistance water heater, versus $132. for the electric heat pump water heater, we see an expected annual savings of $282.  Even with normal variations from predicted energy use, it is common for simple payback periods on heat pump hot water heaters to be in the three-to-five-year horizon - well within the expected life of the appliance, and well worth the purchase decision.

Details matter, of course.  The Energy Factor (EF) of water heaters is an important efficiency metric to pay attention to, when planning this purchase.  A higher EF is better. New heat pump water heaters have listed Energy Factors of 2.5 to 3.1.  Storage tank capacity is important, depending on the daily utilization of hot water (showers, soaking tubs, teenagers, and so forth). Both 50 and 80 gallon tank sizes are common.  First Hour Rating is an important metric, especially if daily hot water usage is high. As is the ability to switch the water heater from heat pump to electric resistance mode if the need/ circumstance arises.  Selecting the right unit for your home is important, and can shorten the payback period when done well.

Heat pump water heaters need to 'breathe'.  Or rather, they rely on air passing over the coils to exchange heat.  For this reason heat pump water heaters have different space installation requirements than electric resistance tanks.  We prefer installing these in mechanical rooms no smaller than 10' x 12'.  Additionally, they should be installed with ample room for a service technician to access all sides, unobstructed.  Manufacturer installation guidelines for heat pump water heaters should be followed closely, or improved upon with greater room sizing and clearances.

Heat pump water heaters slightly cool the ambient air of the room they are installed in.  Which makes sense, since that is where the harvested heat comes from.  They may also slightly dehumidy the space.  In actual practice, we have not noticed either of these facts to be much of a help or hindrance.  

These units do make modest noise when running.  The fan(s) move more air, at higher velocity, than say a refrigerator does.  They can be noisier then, than a refrigerator.  Perhaps the best analog comparison would be a window AC unit, with fan speed running at medium or high speed.  Hence, in a quiet house it is common to hear this unit running (downstairs in a basement below, for example).  But to us it is the sound of energy savings compared to electric resistance units, and is therefore quite acceptable.  If operational noise would be a serious consideration for you, choose a model based at least in part on the manufacturer's decibel specification.  Or consider a gas-fueled tankless hot water heater instead.

Following are a few resources helpful in continuing you own research and edification on this important subject.

Resources

Updated 2015 Water Heating Appliance Requirements - Dept of Energy 

Helpful Energy Star Searchable Database - Heat Pump Water Heater Comparisons

Stiebel Eltron "Accelera" Line of Heat Pump Water Heaters