One of the advantages of building a tiny house or small house is there is seemingly more time and more interest in building such a house with as little heat/air loss as possible. Through photos we have seen far more fuss and concern over insulation, joint tightness, ceiling framing and “sandwiching”, and overall attention to temperature detail then perhaps in larger sticks ‘n bricks. No matter how much care is given to the topic there is still a chance of heat/air loss/gain and that is typically found in the window areas. And while windows give our little homes light, warmth, ventilation, and even ambiance, they also play havoc with our energy efficiency. One way to reduce such energy costs is two-fold. The first method is to install energy-efficient windows or retro-fit your home with energy-efficient windows. The other method is a more simple and cost-effective one and also a more historical option.
The window quilt is a dateless tradition in heat retention and is a simple enough method of reducing up to 80% heat loss through window glass. In fact, in our first winter in the tiny house we realized that despite our ENERGY STAR windows with a significant rating the sub-freezing temperatures outside were no match for the glass or gas pocket within. We needed something more. That is when I remembered seeing a documentary – This Far By Faith – on PBS that covered The Quakers during the 17th century. Having settled in Pennsylvania they were forced to endure some rather unfortunate weather scenarios and turned to their own resourcefulness to solve the problem. Many of the small homes would use standard quilts made by the women to cover up windows and doors thereby stopping any unwanted drafts. So what exactly is the window quilt other than a blanket hung upright?
The Window Quilt
In the most simple of terms the window quilt is just that. It is a blanket (or quilt) that is hung on the inside of a window to reduce heat transfer through your tiny house windows. And while wall cavities vary in their insulating capacity (ranging from R12 to R40), windows, and especially older, aluminum ones, can be as ineffective as R2. In fact, the average window at a big box store is still only R4 to about R7 with the cost rising with each R-value. So a window quilt with its topping, filling (or batting), and backing can easily add another R8 to R10 insulating property to give your windows a total of (optimistically speaking) R10 – R12 which is pretty comfortable when considering the use of a proper indoor heating system as well. Adding another R5 (the quilt) is comparable to adding 1″ of styrofoam insulation.
How Do We Lose Heat Though
Very quickly, there are 3 ways windows lose heat from your house:
- Conduction. This is the transfer of heat energy by contact. Warm interior > window glass > cold exterior.
- Convection. Heat loss caused by moving air.
- Radiance. Loss of infrared energy using the windows as light energy.
A window quilt addresses all three loss methods by creating another layer between the interior air and the exterior air.
Conduction is the simple transfer of heat energy by contact from the warm air in the room, to the glass, to the cold air outside. (In the case of double glazed and triple glazed units, conduction losses are slowed by creating more layers to be crossed, including insulating layers of air or inert gas.) Convection is the loss caused by moving air. Radiance is the loss of infrared energy simply transiting the window barrier as light energy, to which the windows are fairly transparent. The quilt covering our window addresses all three heat-loss modes. It creates an additional boundary layer between the warm air in the room and the cold air outside – in fact, 4 layers of boundary, to reduce conduction loss. By hanging against the window frame, it prevents air from flowing from the room to the window surface, reducing convection loss. Finally, by including a radiant barrier within the quilt, it reduces radiant heat loss.
What we found was that hanging quilts (which was archaic in our approach….read: duct tape and clothespins) once the sun started dipping down everyday we would maintain our interior temperature more effectively while staving off the chill that came with nighttime. We would reverse the process in the morning and allow the sun to heat the house and do its job. And because we used quilts we really liked and because winter has that certain “feeling” our tiny house really was not just warm but also quite cozy.
What about you? Have you ever used window quilts or are they something you may see a need for now? Do you remember anyone in your family historically using them?