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Passive Solar House

NEW! Free ebook available at the bottom of this page for download! Did you know that you can heat up to 60-80% of your home without gas/electricity if you have a passive solar house? What does that mean exactly? It is actually quite a simple concept that has been used for millennia by peoples all over the world.

Interestingly, modern concepts of solar energy do not do it (the concept of “passive solar home design) justice. People to whom the thought of “solar energy” is uncommon to immediately think of a big array of solar collectors on the roof, or stuck outside in the yard by the house. But solar collectors for producing electricity are actually a hybrid system between passive solar and active solar. So then…

What IS the difference between Active and Passive solar?

ACTIVE solar implies using solar energy in a system with mechanical pumps and fans that will inevitably break down.

An example would be solar PV (photovolatic) cells/panels that generate electricity to run a fan that blows hot air (heated via gas/electric/solar/other) through ductwork into the rooms of your house.

PASSIVE solar is a system using solar energy where there are no moving parts whatsoever.

An example would be your rooms and bedrooms with big windows (and proper overhangs) facing towards the sun (usually south) to allow warmth to absorb into your floor (usually tile, rock/slate/etc., concrete, etc.), walls, and furniture, which becomes a heat sink to keep the house warm during the night after the sun has gone down.

In fact, you probably couldn’t tell a passive solar house was even “solar” orientated unless you had a good idea of window placement and where solar south is.

Although a passive solar house is designed for optimum energy efficiency, let me start by saying one thing…


Here is what a standard constructed house and a passive solar designed house have IN COMMON:

STANDARD HOUSE Roof with overhangsFloors with flooring materials
Insulated exterior walls
Windows and doors
PASSIVE SOLAR HOUSE Roof with overhangsFloors with flooring materials
Insulated exterior walls
Windows and doors

The difference being that a properly designed house will be warmer in the winter and cooler in the summer than those built by “standard construction” (this is where most house building contractors get it all wrong). A passive solar house can provide up to 60% of the heating requirements for your home, saving you up to 60% on your heating bills, not to mention saving on your cooling bills.

So what are the differences that make this incredible energy efficiency happen?

STANDARD HOUSE 1. Roof has improperly designed overhangs PASSIVE SOLAR HOUSE1. Roof has properly designed overhangs that keep the sun OUT in summertime and let it IN during winter to warm the house.
2. Floors with flooring tend to be NON-thermal mass (i.e. insulating) materials such as carpet, wood, or linoleum. 2. Floors have flooring materials that have thermal mass (i.e., conductive) qualities (tile, stone, brick, concrete, etc.) to store and release heat slowly into room for maximum comfort. Floors are the most direct/easy way to store the sun’s energy when it enters the house through a window.
3. Insulated exterior walls and interior insulation between rooms. 3. Insulated exterior walls, but interior walls may/should have thermal mass qualities to store additional heat (mass walls, brick/stone, adobe (like trombe walls), even water or concrete (stamped or colored, which is all the rage now). Walls are 4x more efficient for storing and releasing thermal mass into rooms compared to floors.
4. Windows and doors improperly placed for maximum sunlight exposure. 4. Windows and doors are placed on the proper sides of the house to eliminate unwanted sunshine (such as west windows in the hot afternoon summer sun that overheat) and allow it in during winter (such as larger south and east windows. Note: north windows do not gain sunlight but do lose heat, so are mostly avoided except for code requirements; skylights are also wasteful and are avoided).

Here is another difference, conceptually speaking, that explains why passive solar homes are more comfortable for those who live in them.

1. A passive solar house is designed to be in tune with nature (excellent design).
2. A standard constructed house is NOT necessarily in tune with nature (poor design).

So does it have to do with having more insulation? It could, but not necessarily.
Better, more efficient heaters and air conditioners? Not really.
More cost into building the home than a standard house? No, not necessarily that either (although they can cost about 10-15% more, depending).
Then what exactly are the differences?

inefficient house design

Standard Construction

The key is knowing how to let the sun IN to help warm the house in the wintertime and keep the sun OUT in the summer, as well as storing that sunlight as energy/warmth inside the house to help heat it passively (without pumps/fans/moving parts).

How is this little trick done? Well, before I tell you…

Let me give ask you something…

Do you have one of those windows in the home you live in now that faces west? Do you find that in the summer, alter an already hot day, that the sun is shining straight through that window making your air conditioner work even harder because it is heating up your house even more? If so, I can almost bet that you live in a building built under “standard construction” methods.

The key to letting the sun in a passive solar house is where THE HOUSE BECOMES THE SOLAR COLLECTOR in an efficient way.

direct gain

Passive Solar House

In the northern hemisphere, the majority of the sun’s energy comes from the south. Since between 60 and 80 percent of direct sunlight is available to use as solar energy, large windows facing solar south can provide up to 60-80+ percent off a building’s heating needs when the windows are insulated during the night with tight-fitting shutters, insulated curtains, or some other exterior device that closes to trap the heat in.

Clerestory windows can be used for additional light to upper levels within the structure or to back rooms that would not normally receive direct sunlight.

Also, it is important to note that a passive solar house should have about 1 square foot of window area for every 3-5 square feet of floor area. Otherwise, you will be looking at either a cold house or a very overheated one.

In order to know which way to face your windows, you must be able to find solar south (not magnetic south-since the sun does not rise and set exactly due east and west). Finding the sun in the sky at any given time of the year is easy.

There are three different ways to find solar south:

1. Place a stick in the ground and draw a line on the shadow cast at sunrise. Then draw another line on the shadow cast at sunset. Directly in between the two shadow lines draw a third line (on the south side for the northern hemisphere). This indicates the direction that the sun sill be coming from exactly in the middle of the day (any time of the year), and which way your windows (double-paned) should face to receive the most ample amount of sunlight for your structure. This should be south-southeast for most areas of the U.S.

sun direction

Finding solar south

2. Watch the news on television, or check your Almanac and note the times of sunrise and sunset. At exactly in between these two times place a stick in the ground and draw a line where the shadow is cast. Facing towards south (where the sun is) is where the line should point. This is solar south.

3. Find your location and see what the compass deviation (or angle of declination) is by looking on a topographical map. Examples: For Lincoln, Nebraska solar south is 9 degrees east of magnetic south according to the deviation. Because of the latitude being at 41 degrees, the main solar heating hours for the Lincoln area are between 8AM and 2PM each day. For El Paso, Texas solar south is about 11 degrees east of magnetic south, and the peak solar hours are between 9AM and 3PM.

Since so many of the hours to receive direct gain are in the morning and noon hours, many people choose to have some windows on the east side as well as on the south. But beware, any windows facing more than 40 degrees off solar south (either way) start to lose efficiency at a rapid rate.

Another few pointers includes proper use of thermal mass (acts as a heat sink), the glass-to-mass ratio, insulating efficiently–on the exterior of that mass rather than the interior (standard stick-and-brick construction, where the brick (thermal mass) is on the outside and the insulation is on the inside)–and properly designed overhangs.

You can download my book on PDF (FREE ebook*) here:
How to Design a Passive Solar House (76 pages)

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*this e-book is a companion book to my new hard copy book DIY: How To Build Your Own Green Home


Also, my old version (v1) of the paperback book, Passive Solar Energy House Projects: A How-To Guide, which includes passive solar home design, and more, is still available for those who wish to purchase a copy. This book is also FREE for KindleUnlimited and Amazon Prime members!

See my blog post on “House Design Blunders” for more details on why the house you live in now may be costing you more in utilities than it should.

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