What is a Deep Energy Retrofit?

A deep-energy retrofit is when a home undergoes extensive changes to cut its energy use by up to 90%.

While almost every homeowner probably longs to pay for only 10% of current energy use, a deep retrofit is only right for in certain situations, because of its high initial cost and long payback period (an upfront budget in the six figures and a payback period of 7 – 10 years is pretty standard.)  Still, understanding what it is and how it is done holds lessons for every homeowner.

At its core are the two fundamental goals of residential energy efficiency: use less energy to drive your home and make that energy as efficiently as possible.  For the average home, which uses about half of all its energy for heating and cooling, this means attacking the envelope of the building to make it as tight as possible and then re-engineering the HVAC system to be as efficient as possible.

As with most energy efficiency projects, the first step is an energy assessment, followed by weatherization.  The energy audit will reveal all of the areas that are leaking air, whether it’s heated air being lost in the winter or cooled air being lost in the summer.

In a deep energy retrofit, the process of weatherization is precise and perfect, with even the tiniest crack or opening found and sealed tight.  This can be done manually, using caulk, weatherstripping, canned-foam or other materials.  Also, this air sealing could be part of the insulation process, using foam insulation.

Super-Insulated Home

Next comes insulation.  And when we say insulation, we mean a lot of it.  In many ways this is what separates a deep energy retrofit home from an average home: it is likely that a retrofit home has 2 to 3 times the typical home insulation.  For example, if the building code requires roof insulation to be in the R-20 range, one would expect a retrofit home to have roof insulation in the R-60 range or above.

The effect of this is not just a home that stays warm during the winter, and cool during the summer, but also a home that requires a much smaller heating and cooling system than its less-insulated neighbor.  And a smaller system means less energy used.

In fact, one of the biggest reasons for an overly large energy bill is a heating and cooling system that is too big for the job that it needs to do.  This is always a difficult concept to get your head around. Right-size is best, too big is bad and wasteful.  So doing a super job on insulation means you can have a smaller HVAC system, which in turn means a lower energy bill.

Heating and Cooling Options

So what HVAC system would you see with a deep energy retrofit?  It could be an alternative energy system such as a geothermal system that is 400% more efficient than the average home’s system.  Or it could simply be an high-efficient gas or oil boiler or furnace.  With either case, you could see efficiencies in the 90% plus range.

The effect of super-insulation, and a smaller and more efficient HVAC system would result in the cost of heating and cooling your home dropping by somewhere in 75-90% range.

Behind the Walls
Innovation Center
One Broadway
Cambridge, MA 02142