top of page

The Power of Heat Loss

Updated: Apr 1, 2021

For any home the most important factor to consider when thinking about the comfort level of your home, is heat loss. Have you ever felt a draft when sitting in your friends kitchen or living room? Yep. That's called heat loss. Insufficient insulation. Good news is, it's fixable.

But, don't underestimate the power of heat loss.

Hot air rises - just like your energy bill will - if you don't pay attention to how heat leaves your home. A poorly insulated attic can result in 25% heat loss in fall and winter—that’s 25 percent of your average heating costs going toward energy that won’t even heat your home.

A poorly insulated attic can loose 25% of your heat. That's 25% of your average heating costs that are literally - going up and out into thin air.

Calculating Heat Loss & Cool Gain

A geothermal system is best when a detailed and accurate heat loss/cool gain is calculated. The Engineer Designer needs to know all sorts of things about the home to be accurate. At King Energy LLC, this is what Scot does really well. Firstly, a heated space needs to be defined. It may seem very basic, but it’s surprising how many people do not consider if they are going to finish off the basement, or that big space over the garage or they notice (after it’s built), their attic is big enough to have a game room. A homeowner may decide the three-season room needs to be fully heated. This type of "after the fact expansion" can cause many problems with the initial system design and the homeowner’s satisfaction with the end product.


Get a Home Energy Audit (HES) scheduled. These experienced technicians will offer energy saving improvements that can put money back in your pocket.

King Energy recommends calling Lantern Energy.

Defining the Heated Envelope

The basement and the attic are recurring areas of confusion. There are two ways to handle the basement. The ceiling can be insulated with R-25 fiberglass batts. Batt insulation is typically made of fiberglass or mineral wool (also called rock wool). It can be used to insulate floors, walls, ceilings and attic spaces. If the ceiling only of the basement is insulate, this puts the basement in unheated space. Any duct work in the basement will then need to be insulated to R-8 and heat transfers in the duct work are lost to the basement.

The other option is to insulate the foundation walls of the basement which puts the

basement inside the heated area of the home. In this case, and heat transfer from the

duct work are not lost to the outside but remain in the envelope.

The top of the house can be the insulated floor of the attic, which makes the attic unheated. Alternately, spray foam could be installed in the rafters and end gable walls to enclose the attic into the heated envelope. The designer needs to know which way this will be handled because this will change things similarly to the basement scenario.

Even well-installed ducts in an unheated attic have a heat loss/cool gain. Poorly air

sealed and insulated ductwork in a hot summer attic is a particularly onerous situation.

Both of these areas of the home need to be decided on, and that decision should not


Insulation Level and Type for All Exterior Surfaces

We see this decision is often put off or altered on the fly. Different insulation systems result in different R-values, and more importantly, different levels of air tightness of the structure. A common issue is many design for spray foam in the walls, but when the quotes come in, the homeowner backs down to cheaper conventional insulation.

Below is a quick overview of the different types of insulations. For detailed information

check out the Energy.Gov site:

  1. Blanket (batts & rolls) - offers a "do-it-yourself" opportunity and easily are fitted between studs, joists and beams.

  2. Concrete block insulation - requires specialized skills. Insulating cores increases wall R-values.

  3. Foam board (rigid foam) Interior must be covered with 1/2" gypsum board or other fire safety material. The exterior must be covered with weatherproof facing.

  4. Insulating concrete forms (ICFs) - these are foam board or foam blocks and are installed as part of the building structure. Insulation is literally built into the home's walls, creating an excellent high thermal resistance. ICF's are highly efficient and we love creating geothermal systems for an ICF home.

  5. Loose-fill & blown in. Usually of fiberglass or cellulose, this insulation is good for adding to existing finished areas and irregular areas.

  6. Reflective system - these are foil-faced kraft paper, plastic film or polyethylene bubbles. We're not a huge fan of this option, as it just is messy and too many unknowns. Our confidence level that it is done well remains low.

  7. Spray Foam-Used to enclose existing walls, open cavities and unfinished attic floors. Offers a good R-value for the price.

  8. Structural insulated panels (SIPs) - these are foam board or liquid foam insulation core. Upon construction, the walls are fitted together. Sip-built homes provide superior and uniform insulation compared to more traditional construction. My timber frame home contains SIP panels with a geothermal system. It's awesome.

Example of SIPs Here is Spray Foam and ICFs

Does (Window) Size Matter?

Short answer? Yes. And No. Windows, especially sliding doors, seem to have the habit of growing. Even if the plans call for a six foot slider, we are rarely surprised to find a nine footer was actually installed. Since the walls are R-25, and the slider is R-3, the extra glass area can affect the heat loss. A really nice view might be cause for the owners to expand the original window sizes. South facing glass is a net gain, so not all expansions of glass area are bad. Unfortunately, not all really nice views face south. Transom or half round windows are items that can show up after having been omitted in the plan and yes, they matter when we're talking about heat loss.

Even the most energy-efficient window must be properly installed to ensure energy efficiency and comfort. Some things to look for when considering windows are:

  • Seek out ENERGY STAR and NFRC labels.

  • U-Factors: Range is usually between .20 - 1.20 (HINT: look for a low number)

  • Solar Heat Gain Coefficient. Range is usually between 0 - 1. (HINT: look for a low number)

  • Visible Transmittance: Range usually is between 0-1 (HINT: look for a high number)

  • Air Leakage: Range is <0.3 (HINT: Look for a low number)

Ceiling Heights

The presence of vaulted ceilings are often not detailed on plans or are a late change, but they change the heating requirements by increasing the surface area and volume of the space. It is also more difficult to get high R-values in the more limited space of a cathedral ceiling. A vaulted ceiling may also change the duct layout to help de-stratify the air, or maybe a good spot to consider a ceiling fan. Ceiling fans can contribute a great deal in keeping your rooms with high ceilings cool in the summer. They improve air circulation.

It only takes a little common sense, not necessarily a thermal-dynamic engineer, to know that high ceilings will increase the workload of your geothermal system. But alas, common sense seems to be lacking in our society and in some home owners we run into. With cathedral ceilings you must consider where the duct work will go. The point here is to plan and to be knowneledgable about the facts. While high ceilings will create a spacious feel, they also place a higher demand on the heating and cooling system.


Skylights add the same concerns as windows. The associated light wells that often go with them change the volume and heat loss area similar to a cathedral ceiling. Skylights are not of much use for passive solar since they are at the same angle as the roof. This reduces their ability to collect lower angle solar rays in the winter but is more effective in collecting the sun’s higher angle rays in the summer (bad).

I love skylights. I have five in my home. I love them because they add natural light and I like the sun. We advise homeowners to be mindful of where they place skylights as we all know, that heat rises. And since skylights are placed on the roof, that means you loose heat in the winter and cool in the summer from this area. But there are tips to mitigate your heat & cool loss. Basically being smart about where they are placed; are their trees that can shade them in the summer? Some skylights offer tints, coatings and glazing (I am not a big fan of these, after all, isn't the purpose of a skylight to let light and sun in? Why diminish it, you might as well roof it then.) You can also slope the skylights based on your location to the sun. The slope of your skylight, relative to the position of the sun in the sky, is important because it determines how much heat is able to pass through into your home. Also purchase skylights that hold a strong R-value.

The good news is, you can have it all. As long as we know you are planning on skylights, we can add that into our calculations when we design your heating and cooling system.

By implementing your common sense (or seeking out the expert advice of professionals who you trust) your home can be maintained at that wonderful comfort temperature level you seek-no matter what the temperature is outside.

The power of heat loss is real, we simply ask, you keep us informed of your house design -taking into consideration of all the topics covered here -so we can design it once and do it right.

125 views0 comments

Recent Posts

See All


bottom of page