Key Concepts

The “Whole House” approach

Every home is a unique mixture of systems (i.e. heating/cooling, insulation, ventilation, plumbing, electrical, etc) that work together using energy to make us comfortable.  If you change one system it will affect the others and, as much as possible, those consequences should be anticipated to avoid problems.  For example, adding insulation to your attic will likely change how often your heating system runs, which may affect operating efficiency, which may change how much fresh air you need for good indoor air quality, etc.  Therefore, it is VERY important that you consider the “whole house” so you get it right the first time.

Every home is as unique as the occupants.  What works for one home may not be the best solution for yours.  The concepts of energy efficiency are constant but your home should have its’ own specific plan.

Comfort:  Human “comfort” is hard to define and even harder to quantify, but should be considered in the planning process of making changes to your home.  The best known elements of comfort are temperature and humidity, but there are many more, including ventilation, lighting, etc., that are personal preferences and should also be considered.

Heat Loss:  50% of your home’s energy use

Houses lose heat in three ways:

1.  Conduction:

Hold a steel rod in a hot fire and you will quickly learn about conduction of heat through metal.  Your home loses heat (or gains heat during a hot summer day) through the walls, windows, and foundation by conduction.  R-value is a measure of resistance to thermal conduction.  All building materials have an R-value (wood = R-1/inch, cellulose R-3.5/inch) and generally speaking, higher is better.

Goals for Deep Energy Retrofits:

Location Effective R-value
Basements R-20
Walls R-30
Ceilings R-60

2.  Infiltration/Convection:

Heat moves with air movement.  When it’s cold outside the hot air in your house rises (chimney effect) and where it can escape around windows, attic hatches, etc., it will pull cold outside air in thru other leaks.  Good for fresh air, bad for heating bills.

Can a home be too air tight?  See Myth Buster #4, and Indoor Air Quality, below.

Goals for Deep Energy Retrofit:  Less than 0.1 ACH (air changes/hour) which allows you to precisely control your ventilation and recycle the heat you have already paid for with an air-to-air heat exchanger.

3.  Radiation:

Stand next to a fire or hot stove and you will feel heat moved by electromagnetic radiation.  Stand next to a cold surface (window or poorly insulated wall) and you body radiates heat towards the cold surface and cools you off.

Goal for Deep Energy Retrofit: Windows are a small portion of you home energy usage and your budget should reflect about 5-10% for window improvement.  Good news:  There are less expensive ways to improve window performance without buying new windows.  See Myth Buster #1.

VERY IMPORTANT – Where your home loses heat:

location % total heat loss
Conduction (walls, ceiling, foundation) 50-60%
Infiltration (air leaks) 30-40%
Radiation (windows, cold surfaces) 5-10%

*** So….. if energy efficiency is the #1 priority, then you should spend you time and $money$ increasing R-value of the envelope and reducing infiltration.  That is 90% of the solution.

What is “Effective” R-value and “thermal bridging?”

wall infrared image: 1

2 X 6 Wall with Fiberglass Insulation

Consider this infrared photo (click to enlarge).  Shot from above it shows a 2X6 inch stud wall 16 inches on center with the cavities filled with R-19 fiberglass.  The 14.5” wide cavity (purple) is R-19 BUT every 16 inches you see the 2X6 (red/green/blue) with an R-value of 5.5 acting as a “thermal bridge” and reducing the “effective” R-value of this wall to R-13.  So what we mistakenly consider a R-19 wall, is an effective R-13 wall.

Same Wall with 2" Foam Sheathing


Consider the next photo of the same wall with an added 2” of foam board sheathing.  Predicted R-value would be R-25 (R-19 glass + R-6 foam) and effective R- value would be 22 – almost double the R-value.  Eliminating or minimizing thermal bridging is an important concept for Deep Energy Retrofits and all R-values are in “effective” terms.

Indoor Air Quality

All homes and the humans inside need fresh air.  A national standard of .35 ACH (air changes per hour) by natural leakage is a recommended minimum.  The problem is that most older homes have too much fresh air leakage which wastes energy.  On the other hand, many newer homes built in the last 20 years are often too tight and suffer from indoor air pollution such as radon (think cancer), carbon monoxide (think poison), humidity (too high think mold, too low think dry skin and lungs).   What’s a sentient being to do???

Easy:  Make it very, very tight and ventilate it right!

Air-to-air heat exchangers can insure that your indoor air is fresh and save energy at the same time.  They pull stale air out of the house and replace it with fresh air pre-heated with 60-80% of the heat “recycled” from the stale air.  Yes, they use electricity but very little.  In our Deep Energy Retrofit example, the heat exchanger uses about 7 cents of electricity per day and saves $2 worth of heat!  That’s win-win!

Blower door

Blower door in action

Note:  ACH (air changes/hour) for your home can only be measured with a blower door test usually done by an energy auditor.  The test tells you exactly how much your house leaks and where those leaks are.  Testing should be repeated after the work is done to determine how much fresh air leaks in naturally and how much and how often your ventilation system should run.

Sealed Combustion

In Deep Energy Retrofit any appliance that burns fuel should have its’ own dedicated air supply.  This prevents the appliance from sucking warm air out of the house while pulling cold air in through leaks.  It also prevents the back drafting of dangerous post-combustion gases—such as carbon monoxide—into the living space.  The most common sealed combustion appliances in New England are the Rennai, Toyo Stove, and Monitor wall mounted heaters.  These have a single through-wall pipe that allows for both incoming fresh air and outgoing exhaust.  All new furnaces and boilers come with the option of sealed combustion and most older boilers and furnaces can be retrofitted.

Sealed Combustion

Sealed combustion heating system

The photo at left shows a sealed combustion boiler with fresh air inlet (far left) and exhaust pipe going to single thru-wall pipe.

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