Passive heating can save energy with no or few operating costs.

We employ passive solar energy to reduce operating costs significantly.  Passive heating should be given high priority with your budget determinations as well.  For instance, windows can reduce the need for lighting during the daytime hours.  A well-insulated house will absorb lots of energy if the house has south facing windows.  Low-energy fans can transfer heat away from home spaces that are too warm and into spaces that need more heat.  Our AirScape fans can transfer much larger amounts of heat energy than they use in electric energy to accomplish that task. Passive heating of the shop has been very successful for us.  The shop requires very little active heating through most of the winter.

My wife and I built our home with a large shop/garage all along the north side of our home.  Structural Insulated Panels formed the separating wall to minimize the heat loss between the home and shop.  However, we also move surplus passive heat from the house to the shop on sunny afternoons.  The other three outside SIP walls reduce heat loss enough to further attenuate our need for any active heating.

Clothes driers can use tremendous amounts of energy.

A clothes drier performs a necessary mission of keeping us clothed in clean clothing.  However they do waste a lot of the energy generated to dry your garments.  We decided to try an old idea for using that waste exhausted heat to contribute to the warming of our shop.  I installed a dryer vent “T” connector in the duct before it exited the house to the outside.  The duct now extends about seven feet straight through the wall between the laundry room and the shop.  The end of the new duct extension feeds a simple lint trap purchased at a local big box store.

We block the short vent leading to the outside with insulation batting material for the cool months of the year.  Hence, the dryer vents into the shop and the lint trap prevents the escape of lint into the shop.  The wife and I both enjoy the pleasant fresh smelling odor that permeates the shop on laundry days all winter.

I move the vent blocking insulation from the short outside duct to the end of the duct in the shop.  This exchange causes the surplus heat to once again dissipate into the great outdoors.   Surplus summer heat only robs from our normally cool comfortable shop temperatures.


Savign surplus dryer heat is a form of passive heating.

Why waste surplus dryer heat? Heat the garage with it as a form of passive heating. 

Windows perform a big role in augmenting your passive heating function.

Windows might save more heat than any other participant (excepting ceiling and wall insulation) in the passive heating game.  We chose to purchase dual pane Low E windows from Marvin Windows.  The low fenestration specifications attracted our attention even more than the acceptable R values.  Fenestration levels give an indication of how much air penetrates the windows under a standard test conditions.  High speed cold Montana winds caused us concern about excessive air penetration.  Our choice confirmed our decision because these window do not show any signs of air penetration anywhere.

We took advantage of south facing windows to improve passive heating results.

Southerly views contribute greatly to our passive heating energy goals.


The Low E feature presented us with equally good benefits.  Low E coatings on modern windows block out high angle sunlight in the summer months.  However, they allow full penetration of the winter sunlight with the exception of destructive ultra violet wavelengths.  This feature provides useful winter heating while minimizing overheating from the summer sun.

We must block Thermal bridging around windows and doors.

I must add a note about thermal bridging around windows (and doors).  All windows find their support from adjacent vertical studs on each side which support a header above the window.  The header supports the roof in the absence of studs where the window resides instead.  The bottom of the window rests on a 2X6 support.  The 2X6 studs, header and lower support member present only an R2 resistance to the flow of heat through them.  Thus, we call them “thermal bridges” which are not a good thing!

We did attempt to overcome the deficiencies of the thermal bridging and I believe we were successful.  The first attack involved installing an R8 fiberglass foam board over all the inside OSB surface of any exterior SIP walls.  These foam boards totally covered all the inside surfaces of the thermal bridges surrounding all windows and doors.  Additionally, the EIFS (Exterior Insulation Finishing System) installers added four inches of foam over all thermal bridges.  Those additions added greatly to the total insulation factors of the thermal bridging areas of the house.  The minimum R factor increased from and R2 to a minimum of R26 which as they say “Ain’t bad”!  Simply stated, our changes reduced the conductive heat loss over those critical areas from 50% to 3.8%.


Passive heating gets a boost by covering the thermal bridging with good insulation.

Thermal bridging was going to be a big problem maintaining our passive heating.


Passive heating is assisted by R26 total insulation.

R26 total insulation over window and door thermal bridging areas.

Window shade insulation can contribute much to passive heating.

We stated above that our windows are dual pane and have an R (resistance) value of only R3.  A single pane of glass displays an R value of only R1.  Hence, everything else is compared to that benchmark, so that an R3 dual pane glass is three times as resistant to heat transfer as a single pane window.

We divide one by the R value of a material to get the amount heat loss compared to a single pane window.  Our R3 window therefore exhibits only 1/3 as much heat loss as a single pane window.  The Marvin windows reduce the heat loss by 67 percent (1 minus 33%) to be stated differently.

Let us examine window shades more as they relate to their R values.  We have chosen some triple honey combed Hunter Douglas Architella window shades that offer an R4 insulation value.  If we add 4 to the R value of the windows (3), we wind up with a total R value of 7.  These shades plus the windows will reduce your heat losses by 86% compared to non-shaded single pane windows.  When we try for further reductions, the extra costs will not justify the minimal improvements we can make.  That is an example of the principle of diminishing returns.


We installed this R5 shade to test for a passive heating loss test. A temperature gun showed much higher temperatures on the inside surface of the shade than the window.

Triple cell R5 insulated shades tested well in our passive heating loss tests.

Other window shade advantages.

We will enjoy another benefit to our shades when they get installed.  The black out version that we selected for our bedroom and den also has a circular reflecting Mylar layer in the middle.  The Mylar reflects radiated light and infra-red energy from the direction it came.  Thus, we will pull thee shades in the winter at night so radiated heat stays  inside where we want.  Conversely, the hot summer heat is reflected back outside before it can be absorbed by heat masses in the house.  Therefore, the window shades also contribute to summer passive cooling.

People often purchase window shades strictly for privacy and security issues.   They then discover  that shades also serve to reduce noise levels in the home.  Noise will really manifest itself when you have parties.  Sounds always reflect off hard surfaces such as floors, wood work and walls only to be amplified and made obnoxious.  You can lower your shades to a comforting level to stop glare from south facing windows.