Thermal Imaging and Insulation

Around two years ago, we had a thermal imaging study done of our exterior walls and ceiling of our house. In a thermal imaging study, the walls are photographed using an infrared camera. Areas that are colder show up dark blue to purple, areas that are warmer show up light red to white. The study also involves a blower door test, where the house is otherwise sealed and a blower is installed on one door to exhaust air out of the house. Infrared photos are then made of areas where there might be air leaks, for example around light fixtures, plugs, etc. The study showed that our house had average insulation compared to other houses, with several areas where the insulation had failed or was not properly installed resulting in thermal holes. There were also numerous places where the blower door test showed extensive air leaks. "Average" sounds fine, except the baseline is very low. Most houses built before 1970 in California have little to no insulation. After all, the climate here is mild compared to the Midwest and East Coast. Of course, we get subfreezing temperatures in winter at night and 100 degree temperatures in summer periodically, but back in the 50's and 60's, energy was cheap and people who moved from the East Coast were happy with running the furnace.

I subsequently built a spreadsheet model of our house and calculated that we could get about a 30% improvement by doubling the insulating power (R-value) of the insulation  using closed cell foam. That prompted us to move forward with the current plans to seal up the thermal envelope of the house in order to reduce natural gas usage for heating. With the exception of a couple areas, the drywall and insulation are now off the inside of the house. The temperature inside is about twice as warm during the day as beforehand (and maybe twice as low at night). Just as for the solar hot water tank I measured last fall (reported on here), insulation does seem to make a real difference in temperature control. This is good news, since our primary effort on this job is to substantially increase the insulation.

Here's some pictures of the inside of our house without drywall. Here you can see the pellet stove and the fireplace without insulation around it:

The fireplace area was one of the worst areas in the thermal imaging study. There was essentially no insulation around the fireplace. This thermal image shows the area above the fireplace:

The colored bar on the side shows colors corresponding to temperatures. Further toward purple is colder,  further toward red is warmer. The horizontal  light green to yellow lines are the studs you see in the picture above with the drywall off. They are warmer than the cavities, which are the turquoise areas between the lines. Typically, in a well insulated wall, the cavities are warmer than the studs because the insulation material filling the cavities transfers heat much less efficiently than the studs.

Here is what the west wall of the family room looks like with the drywall off:

This shows the wall between the sunroom (protected from construction dirt by the plastic curtain) and the side door.

In the thermal image below, you can see that the insulation in the stud bay next to the door was either omitted or was so poorly installed that it collapsed:

In the thermal image above, you can see that the insulation along the header at the top and the stud in the middle has sagged away from the stud.

The thermal images point out a major problem with the most common form of insulation used in the US: fiberglass batting. Batting is very difficult to install correctly and even when installed, has a tendency to sag with age. Any areas where the batting detaches from the studs results in thermal holes or air leaks. In California, the likelihood that batting will sag is relatively high because of the high amount of ground movement (i.e. earthquakes). Even small movements can result in tears to the paper surrounding the fiberglass, eventually causing the paper to fail and the insulation to sag. Tightly packing the stud bays with batting, blown fiberglass or, even better, cellulose is a superior way to get the same amount of insulating power (R-3 per inch). Closed cell foam is yet better because it seals air leaks tightly and has twice the insulation power (R-6 per inch) but is more expensive. Open cell foam provides the same tight air seal but has the same insulating power as blown fiberglass or cellulose.

Air leaks cause even more heat loss than simple conductive transfer through the walls. In the picture below, you can see some insulation peeking out from under the drywall that was not removed from the area in front of the upstairs bathroom:

 In the thermal image below done with the blower on, you can see the air being pulled in around the light on the ceiling right outside the bathroom where the insulation above is at:

Notice how the pink fiberglass is discolored by black dirt? That is from 30 years of air flow entering and leaving the  house in winter when the heat is on (and taking the heat energy with it). The fiberglass acts as a filter, removing all the dirt from the air. While it is nice to have fresh, filtered air inside the house, pulling it randomly through the ceiling and walls doesn't seem the right way to do it.

Our plans for the system remodel are to seal the thermal envelope and instead ventilate the house through the heat recovery ventilation system. This will pull fresh air into the house and exhaust stale air  out in a controlled manner, through a heat exchanger which transfers heat from the inside air to the outside, so the heat doesn't get lost. It also filters the air so that the black dirt you see above doesn't end up on random inside parts of the wall, but rather on a removable filter that can be washed periodically.