"Five Ways your Home Loses Heat"
Heat is lost to infiltration and air loss by over 3 times the amount it is lost due to ceilings. These categories generally stack up this way in terms of % heat loss in a home:

Infiltration / Air Leakage: 35%
Windows & Doors: 18%-20%
Floors & Below Grade Space: 15%-18%
Walls: 12%-14%
Ceiling/attic energy lost to conduction because of lack of insulation : 10%

(note: this last category of "ceilings" does not include leaks through microscopic cracks in the plaster, lifted drywall tape, moisture damaged disintegration, holes for light fixtures, leaks through penetrations for wires etc.)

The alternate EERE research shows similar air losses categorized differently

That is, put another way, insulation only insulates when air does not move through it.
Consider this example here of the green metal siding that obviously not only did not prevent air flow, it did not stop flying insects such as wasps from building their nests in the fiberglass "insulation" !
This insulation provided almost no benefit. Air filters for engines are sometimes made of fiberglass. Fiberglass provides no air barrier of its own.

Remember to compare these general percentages with the cost for each repair and keep in mind that blown cellulose insulation both insulates and reduces air leakage.
If a wasp can FLY into the insulation, you KNOW the air flows right through it - thus making the "insulation" worthless

If a wasp can FLY into the insulation, you KNOW the air flows right through it - thus making the "insulation" worthless

Insulation only works if there is an effective air barrier.

An Energy Audit is the key to finding the air leaks

An energy Audit is a detailed analysis of the hidden energy losses that can increase your monthly cost of living by as much or more than a car payment ! So ONE energy audit can save you many times the cost of a new car! Even more importantly, those air leaks sometimes exacerbate allergies to mold, vermin and dust as well as make you unecessarily uncomfortable.

An independent auditor is the best first investment during planning for building upgrades because that auditor works for YOU and not for a commission on a bigger heat pump or more expensive windows etc.

Some tips on getting started with your own lifestyle and building shell "tuneup" (audit).
Energy Star listing of "Common Problems" (most of which will be qualified and quantified by a thorough energy audit.
Energy Star on Audits

Dominion Home Energy Calculator

How much pollution does your energy consumption generate?

(note: to find how much pollution an alternative energy source would save, just plug in the estimated kWhrs of energy replaced by your alternative energy source instead)
Also this includes the power line losses (estimated for your location!)

Home Energy Saver - Do It Yourself audit guide

"Consumers don't want to buy electricity or fuel.
They want warm showers and cold beer !"

— Amory and L. Hunter Lovins, Rocky Mountain Institute

A Blower Door

...uses calibrated fans and meters to measure how MUCH your building leaks air. This give you the chance to see exactly how leaky or well sealed a house is. Then after work is done, can see how much the efficiency has been improved.
One caveat to remember is that this simulates a very windy day. There are some instances where a house can be leaky but if the leaks are protected from the wind, it will still hold heat. But a Blower Door is a great place to start with quantifying the effectiveness of your house for holding heat and AC in.

Any audits you get on your building should include the Cubic Feet per Minute and the calculated Air Exchange Rate that comes from using a Blower Door properly.
Did the audit include the CFM and air exchange rate (number of exchanges per hour.) ?

After the blower door has enabled us to both quantify as well as qualify the location, size and nature of the air leaks, bypasses etc., then we can consider controlling the three types of heat loss or gain.

Heat Transfer

Understanding some basics of heat transfer will help you save money and energy consumption.

Heat moves from a hot place to a cold place
Heat moves in proportion to the DIFFERENCE in temperature. So it costs more to heat a house on a 20 degree day because the heat moves more quickly out of your house.
Heat moves in three different ways that must be addressed differently

ConVECTion (with moving air) This is the most common way you lose heat (Ex: Hot air coming out of the duct leaks). Also a way to get hot air coming in during the summer.
ConDUCTtion (ex: The hot frying pan to your food)
Radiant (ex: The Sun shining on you and your house)

Any plan for efficiency, energy conservation and targeted alternative power must take all three forms of heat transfer into account.

Which finally leads us to ... (drum roll) ... the reason you came to this web page ... Insulation

The theory behind insulation is to slow heat transfer. This works regardless of the direction of the heat flow. Heat moves from hot to cold places in proportion to the difference in temperature. So in summer, your air conditioned house loses heat outward to the hot outside. Your house will get hot faster when its hotter outside. In the Winter, reverse the process. Insulation will work the same in either case.

Insulation slows heat transfer by impeding the three different way that heat moves (see heat transfer)
The most effective insulation is a vacuum. That is why we used to have "vaccuum thermos" containers before we came up with advanced closed cell foam that could be blown into shapes.
In a vaccuum, the heat cannot move by either convection or conduction.

The next most effective insulation is air. STILL air. If the air moves either through an area, then it is transferring the heat by convection, like in your oven. Air gaps that are too large can have "convection currents" that go in a loop to carry the heat from a cooler window pane to a hotter one. Or inside a wall gap. If there is a leak, then the air just carries the heat with it through the air gap. That is why leaks are so important to heat loss control.

So the goal is if you can't have a vacuum, to keep the air STILL. That is why double paned windows and foam and air barriers with fiberglass work better than single pane windows or fiberglass with no air barrier.
Fiberglass is used on engine air filters. Fiberglass does not stop air flow. So without an air barrier, fiberglass is nearly worthless, only slowing the heat loss slightly.

Closed cell foam works by trapping cells of air. Open cell foam also traps some air, but not as much. Styrofoam encapsulates tiny tiny air bubbles in plastic.
Storm windows work by slowing or stopping air flow.
Cellular shades work by trapping a cell of air.
Exterior insulation works by trapping air outside stone and mortar so the air inside can use the stone as a "thermal battery" and store heat.

Eventually entropy wins and everything ends up the same temperature. Insulation only slows that process down.

So insulation must control
Radiant Heat gain and loss
Conduction of heat from one object to another
Convection of that heat through the air currents

Cellular Shades

Cell shades are like adding a styrofoam panel to your window ... in-effect superinsulating your windows. They can also come with a track to block air from flowing around the shades.
BUT ITS BEAUTIFUL AND RETRACTABLE!

[Click here for a demonstration]

Cellular shades are especially helpful on the north side of a house where you do not get any solar gain in the winter and thus want to keep your heat in, but cellular shades can also help control excess heating from the Summer Sun and keep your AC inside and the Summer Heat out!

Commonwealth Solar can install cellular shades for maximum cost-effective window insulation.

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Ductwork

Heating and Cooling Ductwork is a MAJOR potential loss point for heating and air conditioning!

Air leakage through gaps in ducts. The heat is lost with the air moving (convection).
Air leakage through (convection) interface of duct to wall/floor/ceiling (registers)
Conduction of Heat through walls of ducts

Air leaks are the leading loss point for heating and air conditioning.
The first goal of any efficiency and conservation effort must include checking the ductwork for leaks.

Burying the ductwork where possible under cellulose insulation will help tremendously with both causes (conduction and convection) of heat loss from ductwork.

We have even seen very "affordable" installed ductwork that was LEFT WIDE OPEN, typically at the end of a house. We usually find those when the occupants complain that an end room seems to get little or no air flow from the registers.
But where the ducts are in the attic or even (horrors!) out in the outside air ... then proper testing, sealing and then insulating those ducts is vital.

If the house seems to be cheaper to heat with electric space heaters, this is a very important piece of evidence that your ductwork is hugely wasteful.

Two studies showed that ducted homes had 70 percent more air leakage and used 17 to 22 percent more energy for space heating.

Consider that the square footage of exposed air is often just as large in the ductwork as the entire ceiling of the building! The duct has four sides and travels the length and width of most buildings. In spite of this huge square footage of your conditioned air to the attic and/or outside air, most ducts have no insulation or only R3 for half an inch!

So putting ductwork in the attic is like adding another whole attic of heat loss in the winter or heat load in the summer. So a duct exposed to the heat and cold of an attic with no insulation or only R3 of an inch or fraction of an inch makes heating or cooling a house with ducts in the attic like heating and cooling an entire additional building. Is your wallet up to that?
The solution is to either place the ductwork in the conditioned space (not in the attic) if you are installing a new system from scratch for an upgrade of a historic house or building a new building.
If the ductwork already exists in the attic, then seal and insulate as much as absolutely possible. Check that ductwork periodically because often some of the sealing will fail over time.
Also pay attention to how well sealed the registers are to the wallboards, ceilings and floors especially because a leaky return register can draw in air from the inside of the wall or even outdoors which might include mold, illness causing irritants like fiberglass fibers, and vacuum air from the basement or crawlspace through the inside of the wall where holes in the base allow air to come up from below.

Oikos noted that one study showed that "by repairing 43 percent of the duct leaks, they cut infiltration by 63 percent." and that "heat loss from the average ducted air distribution system reduces the overall system efficiency by 30 percent."

An independent auditor is the best investment because that auditor works for YOU and not for a commission on a bigger heat pump or more expensive windows etc.

Foam outside wall that will keep out freezing air temperatures in the Winter as well as a air and vapor barrier for leak reductions

Exterior Insulation

Usually a brick or concrete foundation and/or walls are insulated inside. However when possible, its actually better to insulate on the OUTSIDE.

Exterior Insulation usually with foam panels provides a wonderful opportunity to use the "thermal mass" of your building to your advantage. Thermal mass is any heavy mass (like the thick walls of older municipal buildings, or a cave, for example) that change in temperature very slowly. Thus as you go into Summer, the cooler condition of the thick walls decreases your need for Air Conditioning. And then as you enter Winter, the left over heat from the Summer decreases the rate at which your house cools off.

Insulating the outside of a thermal mass, that is, a thick brick or concrete wall and/or foundation now means that effect is amplified because you have insulated your walls from the extreme heat of early Summer and the extreme cold of early Winter. As you run your Air Conditioning or Heating, it is now heating a wall that averages the outside temperature as well as absorbing as a kind of "thermal battery" your efforts to cool or heat your house to the temperature you want.

An added benefit is that in some cases there are many microscopic holes in the mortar that allow diffused air to be drawn through the brickwork!
So instead of "pointing" the joints in brick, another option that gives you energy efficiency benefit is to put on exterior insulation.
(For example, in one blower door test, we found a steady blast of air coming down a chimney. This was in spite of the fact that the top of the chimney was capped solidly. It turns out the mortar had failed to some degree, it needed pointing, and so the air was coming into the house through the mortar!)

Interior Storm Windows

Interior storm windows are very easily made of "clear" pine or other more attractive wood and slips into the inside of the window to create an air barrier for far less than a new replacement window. It also allows you to keep the historic windows but stop the air loss.
Also interior storms can be constructed for rental historic office or residences cheaply enough to save more than what was spent on the storm windows. There are also more permanently attached magnetic interior storm windows.

Interior storm windows stop the air leakage that accounts for MOST of the lost heating or air conditioning. Then shade cloth in the summer prevents too much radiant heat from the sun coming in. Cell SHades are like instant retractible insulation for your windows

Cell SHades are like instant retractible insulation for your windows

Cellular shades can insulate the windows from conducted heat lost in both winter (nighttime) and the summer (daytime).

Generally interior storm windows are made on a wooden frame sized to the window minus about 1/8th of an inch. Then weatherstripping is applied to the outside after PolyOlefin ("heat shrink") film is wrapped around that frame. That weatherstripping provides both the air seal and the friction to keep the interior storm window in place.

Commonwealth Solar can manufacture interior storm windows.

Interior Storm Window is a cherry frame with Poly Olefin (heat shrink) film wrapped around it

Interior Storm Window is a cherry frame with Poly Olefin (heat shrink) film wrapped around it

Lighting

Illumination makes up a huge part of any typical energy bill for a building.
Lighting is included in the insulation section because so often the heat of that light bulb PUMPS YOUR HOT OUT OUT THROUGH A BYPASS IN THE CIELING. As you can see in the graphic ...

Incandescent lights are essentially heaters that also make light since 90% of the energy goes into making heat. There are other ways to illuminate your work and play space.

The worst problem case are the recessed incandescent lights or halogens that are each a potential fire hazard and "smoke stack" that will pull heated or cooled air right out of your living space!

A professional energy auditor will pay a lot of attention to recessed lighting.

Many times there is no insulation or sealing on the recessed lighting containers and this becomes the equivalent of several wide-open windows!!!

Misconceptions that Misappropriate your Money

Example 1: Fiberglass insulation.

Fiberglass insulation only works when there is no air flow or air pressure

Commonwealth Solar provides the service of blowing cellulose insulation and simultaneously sealing your attic and walls after a proper audit

Building Science.com

foil bubble insulation can reflect heat back toward YOU

Example 2: Misconception: Radiators are inefficient.

Heat goes from a hot place to a cold place

pennies

Example 3: Solar Attic Fans.

install a ridge vent and/or
bury your ductwork in blown cellulose insulation and/or either
get a reflective roof such as TPO with insulation under the membrane or

seal the roof in something like the silver or white coating that also has the benefit of protecting your roof tiles, metal or membrane from the sun's UV and heat.
This will also reduce the heat load on whatever is inside your attic, such as your heat pump air-handler. The less your air handler has to fight, the less you pay and the longer it lasts.

Example 4: "Houses must breathe".

dry

Building Performance Institute literally wrote the DOE book on moisture

[More on energy wasted by ductwork
in the attic and how you can save that]

More On why a Professional Energy Audit
should always be a part of
purchasing or upgrading a house.

other