Energy Savings vs. Home Air Quality
We can't only look at energy savings without looking at indoor air quality.
For example, have you ever been in someone's home in the winter (maybe your own) and you can feel how dry the air is - your skin may even be cracking.
Humidity is just one indoor air factor.
Indoor Air Quality Factors
The following factors have an impact on how comfortable you are in your home:
At what temperature are you most comfortable in your home? Well, you will likely get a different answer from different people. I, myself, like a cooler temperature in my home while my wife would like an indoor temperature of 2-3 deg C (4-6 deg F) higher. In our home we typical select the temperature that will save the most energy (in the winter I get the cooler temperature and in the summer my wife gets the higher temperature).
Ideal indoor relative humidity levels are 35% in the winter and 50% in the summer. Relative humidity levels below 25% lead to increased discomfort and drying of the mucous membranes and skin.
Low relative humidity also increases static electricity, which causes discomfort (shocks) and can hinder the operation of computers and other electrical equipment.
High humidity levels can result in condensation (water vapour in the air condenses into water droplets) which can lead to the development of moulds and fungi.
The velocity of the air circulating in your home affects your comfort level / home air quality. The more air movement the cooler you feel (this is due to convection which is explained on the home heat loss page). In the winter you want to minimize drafts, while in the summer good air movement has the desirable effect of cooling you down.
Temperature of Surfaces
As you will learn on the home heat loss page heat transfers from hot surfaces (say a warm ceiling in the summer) to cold surfaces (your body). This has the added effect of warming you up when the temperature may be fine.
Clothing and Activity Level
The warming (insulating) effect of clothing is straight forward. If you love to walk around your home in your pajamas you will likely be cold at times. You may raise the indoor temperature so you can. Conversely, if you love sweaters, you may lower your indoor temperature.
When our activity level increases our bodies pump blood faster and we warm up. Your activity level may lead you to adjust your indoor temperature settings if you operate a home aerobics class or something similar. If you are like most people you will just sweat after your home workout (may not like most people if you actually work out) and return to your normal body temperature without adjusting the room temperature.
The number and size of occupants will have an effect on your home energy and home air quality. The average adult dissipates approximately 106 W (360 Btu/hr) when functioning in a quiet, seated manner. So with 10 adults in a room, that is equivalent to over 1 kW of heating!
Next time you are in a large auditorium or stadium, think about the heat being dissipated by all the occupants.
Carbon dioxide (CO2) is exhaled by humans. CO2 is not a problem in itself, but levels of CO2 give you a good idea how effective the ventilation system is. If CO2 levels are high, it is likely levels of other more harmful gases are high as well.
Carbon Monoxide (CO) is a by-product of incomplete combustion. Unvented furnace, water heater, and vehicle exhausts are sources of CO. CO is highly toxic (near 15 ppm and higher) so we should be careful to vent all potential sources properly. Note that the effects of CO can be cumulative, meaning they add up over time.
Please ensure that your furnace vent is not located near any air intakes or open windows. All homes should have carbon monoxide detector to ensure indoor air quality.
Volatile Organic Compounds result from combustion sources, pesticides, building materials and finishes, cleaning agents, and plants and animals. Most oven VOCs occur in levels that are below the recommended standards.
Certain types of molds are alleged to have toxic effects. It is best to take care of mold problems immediately when they are found and take care to prevent their formation. High home humidity and water leaks are the primary sources of mold formation.
Potential particulate matter within the air includes dust, fibers, soot, smoke, decayed plant and animal matter, lint, mold spores, bacteria, pollens, and other living materials.
These items can cause heath problems as infectious organisms can exist and even multiply under certain conditions. In addition, particulate matter is likely to affect those with allergies.
The best way to limit particulate matter in your home is to have adequate air filters. Be sure to replace / clean your furnace filters regularly. Filters on outdoor air intakes are also a good idea.
The number of air changes per hour (ACH) is an important factor of home air quality. One air change is defined as replacing the volume of air in a space with new air. So a room that contains 5 cubic meters of air undergoing 2 ACH will have received 10 cubic meters of fresh air in the hour (and vented the same amount)
Without fresh air exchange, moisture may be trapped in a home, molds may form and grow, and other allergens and excessive dangerous gases can remain in the home.
Generally speaking, rooms in your home should get approximately 15 litres per second (30 cubic feet per minute) of fresh air.
As homes become more and more energy efficient they have become more air tight. Less efficient homes are typically drafty and naturally bring in fresh air. Newer, more efficient homes require specific equipment to control the rate of the fresh outdoor air entering your home.