How Water Heating Works

Keep water hot and use less energy with Heat Pump Water Heaters.

If yours is one of the 750,000+ homes in Maine, New Hampshire, and Massachusetts that heats domestic hot water (DHW) with an oil-fired boiler, it’s hard to ignore the roar in your basement as the boiler fires up to make hot water while sunshine pours down onto your roof, especially in the summer.

drew-wyman-hpwh.jpgThis is a terribly inefficient (and therefore environmentally harmful) way to make hot water, but the good news is you can save hundreds of gallons of oil per year by switching to a heat pump water heater, and powering it with solar. Using the same refrigerant process as an air source heat pump, heat pump water heaters efficiently leverage the ambient air of your home for water heating.

How super efficient water heating works:

  1. Instead of making heat, solar hot water heaters simply move it from one place to another, which is much more efficient than conventional electric water heaters, or other ways to make hot water.

  2. They produce hot water 200-600% more efficiently than resistive electric tanks.

  3. While they move heat, they also help dehumidify the space around them.

  4. They are highly insulated, meaning the energy you do use for hot water is not wasted in ‘standby losses’ as the tank sits idle.

  5. They are available in large tank sizes, which means that you can easily meet the needs of a 4+ person household with a heat pump water heater.

All of this efficiency translates to savings, with bonus basement dehumidifying! Plus, many states offer cash rebates for installing them.

We currently use Stiebel Eltron Accelera heat pump water heaters for a number of reasons. We are very familiar with the brand, having used Stiebel Eltron’s equipment in rooftop solar hot water installations for years, and appreciate their excellent quality and long warranty (10 years). Due to its much lower electric consumption, a heat pump water heater needs only about 1/3 of the PV modules to generate the electricity for domestic hot water compared to a resistive electric tank.

Watch our video to learn how heat pump water heaters work:

Heat Pump Water Heater with Solar PV

  • Very simple and straightforward installation, can usually be done same day as Solar PV install

  • Excellent balance of efficiency and cost

  • Dehumidifies basements

  • Long-lived tank with 10-year warranty

  • Superior to ‘hybrid’ water heaters sold in big box stores, avoids using backup electric element whenever possible

Water Heating That’s Right for You

Whether it’s an electric option, or ‘true’ solar hot water, getting your oil boiler turned OFF this summer is a great goal. And if you’re burning propane or keeping an old electric water tank alive, there is still plenty of savings to be had by finding a better way.

Typical Yearly Water Heating Costs for a Family of 4*
Heat pump water heater powered by grid $413
Heat pump water heater powered by solar $165 **
Electric water heater powered by grid $1,238
Electric water heater powered by solar $495
On demand electric powered by grid $1,022
On demand electric powered by solar $408
Oil boiler (oil at $1.99/gal) $647 ***
Oil boiler (oil at $2.99/gal) $971
Propane water tank $1,539
On demand (tankless) propane $432

* Load calculations use 65 gallons a day of hot water for a 4-person household or 16.25 gallons per person. To calculate consumption for a different number of people, or different consumption, just do the math!

** Grid electricity priced at 25 cents per kilowatt-hour, solar at 10 cents per kilowatt-hour (roughly the 20-yr cost of solar PV for an average 5kw system), propane at $3.50/gallon.

*** Oil and propane tanks calculated at ‘average’ efficiencies. There are a few different ways of using oil and propane to heat domestic hot water (direct fired, indirect tank, tankless), this chart uses an average.