It never ceases to amaze me how the options for green building multiply from month to month and year to year.

When we started our projects at 394 Frederick St. and 173 Downey St., there was one manufacturer for recessed LED lighting (Permlight), one manufacturer for residential hot water heat pumps (Airgenerate – see AirTap heat pump at right, mounted on a standard hot water tank), and not even one manufacturer of FSC-certified wood windows.

Today those options abound.

Now, as we start up our projects at 1566 and 1436 Sanchez St., we’ve got dozens of LED lighting vendors we can work with, numerous choices for wood windows that have been FSC-certified, and now numerous hot water heat pump makers.

What is a hot water heat pump?

Well, we’ve talked about them here at eco+historical before, but in brief, they are hot water heaters that:

  • Are powered by electricity (not gas)
  • Have storage tanks (not on-demand, tankless units)
  • Are often called “Hybrid” since they can both
    • Heat water by extracting heat from the surrounding air and transferring (“pumping”) it into the tankOR
    • Heat water w/an electrical resistance coil (which is hotter and heats the water faster  – good when there’s high demand – i.e. multiple showers)

This process of extracting heat from the surrounding air (which doesn’t need to be hot) is about 2 to 3 times as efficient as even an on-demand tankless hot water heater, making it just about the most efficient way to heat your home water.

GE did a great 3D animation showing how this works for their GeoSpring hot water heat pump.

STEP 1: Extract Heat from Air using an Evaporator

STEP 2: Insert Heat into Water using Coils

STEP 3: If Needed, Add Heat with Resistive Heat Elements

When we were building our previous projects, we bought our hot water heat pumps as after-market add-on units for our existing hot water tanks.  What this means is that anyone with a storage hot water heater – gas or electric – can add on a heat pump unit and cut their energy use for hot water by as much as 50%-60%. Here’s a chart from Airgenerate that shows how efficient the heat pump hot water heater is by comparison:

We used the AirTap (about $500 – $600) at the Frederick and Downey projects and just mounted it on top of a gas hot water heater at one home and on an electric hot water heater at the other.  It’s quiet and efficient and after extracting heat from the air, it vents out cool “waste” air which you could, if you so chose, vent somewhere else in the home with a little custom sheet metal ducting to get some free air conditioning.

Some great options would be to vent into a wine room or perhaps, if you have a big audiovisual setup, to an AV closet or cabinet.

Now that there are great options from

Rheem A.O. Smith and GE

it’s only a matter of time before these products start achieving major sales volumes that will drive the prices down from their current $1500-ish level.

Once that happens, we’ll all be bathing and showering at 50% guilt discount.