Air plays a big role in a home's comfort level and dependability of its components. Understanding a home's air can help in determining problems and their solutions. Since the Eighties, there has been a tightening of a home's thermal envelope to be more energy efficient for heating and cooling. The thermal envelope is the shell that surrounds the home and protects and separates indoor and outdoor air space. Envelope components commonly include exterior roofing, siding, insulation, wood framing, a polyethylene air vapor retarder, and interior ceiling, walls and flooring. This also includes window and doors. The quality of these materials and their installation will determine how much air will seep in or out of a home. Gaps by windows, doors, siding, and insulation allow penetration of cold and warm air into the thermal envelope. This can cause damaging moisture condensation on building components. Insulation can suffer loss in R-value when wet from moisture and wood frame member can rot. Mold and mildew will also develop from trapped moisture. This can aggravate allergies and cause other health problems. Good caulking and vapor barriers will reduce air penetration into the thermal envelope. Problems caused by moisture in walls is difficult to detect. Often the only visible hints will be missing areas of exterior caulking or moisture stains on interior surfaces.
Interior air humidity levels can change from family to family depending on cooking, bathing, laundry and similar activities. Plastered wall and ceiling surfaces often become cracked from changes in these different living styles. This can happen soon after a home is vacated or shortly after a home is reoccupied. On occasion we may get a call from one of our clients finding a crack that was not in our report., It is possible the crack may have just happened. Newer homes sometimes are too tight and have high air humidity. In extreme cases, whole house air exchangers have to be added to reduce humidity levels. Stains that are old in appearance and are dry may become damp again from seasonal insulation and ventilation problems or a change in humidity from a home's different family occupation. A poorly vented attic can cause several problems such as mold growing on the roof's decking from a crawlspace moisture problem or a high humidity from living conditions. Moisture on the under side of shingles causes them to curl and fail. In colder climates, heated air lost into a poorly vented attic will melt snow. This, in turn, will result in ice damming and shingle damage. Think of a home's thermal envelope as a balloon. If you poke a hole in it, air will leak out and collapse. Since a house is a bit more rigid than a balloon, air leaking out is replaced by air leaking back in.
Now think about the normal operation of a furnace. The furnace is called into action by the thermostat sensing a drop in temperature. House air is pulled into the burner and mixed with gas for combustion. The air / gas mixture burns in the heat exchanger and rises up the chimney to the outside. From the outside you can observe a large plume of air leaving the house. Consider that same volume of air seeping back into the house to replace what went up the chimney. Air is being sucked in every crack and crevice, loose fitting window and door, and even in through fireplace chimneys and kitchen and bathroom bath vent fans. The air, of course, is unheated so the interior temperature is cooled which starts the cycle over again. Newer heating system installations have combustion air which brings outside air into the combustion chamber. Combustion air can be added to any existing heating system using interior air for combustion to make the heating system more efficient. Fireplaces operate on the same principal. Often drafting problems are caused by a house being too tight. Usually the room with the fireplace is warmed from the fire but other rooms may even be cooler from air seepage around loose fitting windows that are replacing the air that has gone up the chimney. A thermostat should never be located close to a fireplace. Opening a window in the same room when operating a fireplace will usually resolve a poor drafting problem. Running kitchen and bath vent fans may cause a fireplace drafting problem. The operation of a fireplace could cause a furnace venting problem. Air could be pulled down a furnace's chimney. In this situation a furnace will not draft properly, seeping flue gas out of the burners and draft hood into the home's interior air.
Scorching is usually visible by the draft hood and burners; look for this in homes with fireplaces, for this is a dangerous problem. Remember to think of the house as a group of systems all working together. Air movement, humidity levels, insulation, ventilation, vent fans, fireplaces, and heating systems with chimneys.