Tight House, Fresh Air: Cost-Effective Means of Ventilating a Well-Sealed Home
Do you ever get that not so fresh feeling when you’re breathing in your energy-efficient home? A ventilation system can help bring the freshness back to your home, but with so many options, which offers the best bang for your buck? Read on.
A tightly sealed house offsets the effects of outdoor temperatures, keeps your home more comfortable, and reduces your heating and cooling costs. However, a well-sealed home may not be properly ventilated, allowing the air inside to get stale with chemical off gassing form carpeting, plastics, paints and more or smelling of old cooking odors, chemicals, moisture or perhaps dirty socks, among other things.
Installing a ventilation system that moves fresh air into your home while retaining, as much as possible, the indoor air temperature is one of the best ways to make sure your home breathes as well as you smell. Many solutions exist and depending on where you live you may also need to install either a humidifier or dehumidifier to help regulate humidity in your home.
To help homeowners and builders avoid this problem, The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) established a mechanical ventilation standard (Standard 62.2) for residences. To meet the standard, residences must be able to move air at a rate of 1 cubic feet per minute (cfm) for every 100 square feet of livable space and for each resident an additional 7.5 cfm must be moved. So, to meet the standard, a 2,000 square foot house occupied by three people needs 42.5 cfm of ventilation to meet the standard.
Simply opening a window isn’t the cheapest way to get stale air out of your home, especially in the winter or summer months. Depending on your needs, better, more cost-effective methods of home ventilation include:
Exhaust-only, pushing air out through leaks in the home envelop. This can be accomplished either with a continuos or intermittent exhaust fan;
Supply-only, a fan pushes outside air into the home, slightly pressurizing it and forcing stale air out through any leaks in the building; and
Balanced ventilation, this is the most expensive, it uses one fan to bring fresh air into the home and another remove stale air from the home, keeping the amount of air in the home balanced. They generally can provide a more equal distribution of of fresh air throughout the home.
These systems may be coupled with a heat- or energy-recovery ventilator system to help reduce any heating or cooling losses associated with the system.
The DOE Berkeley National Laboratory’s report, “Energy Implications of Meeting ASHRAE 62.2”, examined the cost-effectiveness of different ventilation methods in different U.S. climates. In addition to evaluating the cost-effectiveness of the venting methods themselves, the report looked at heat gains and losses associated with the types of building envelops.
The results of the study showed that the most energy-efficient means of providing mechanical ventilation was through the use of an intermittent exhaust fan. According to the study, most ventilation systems used between 800 kilowatt/hours to 1,700 kWh per year or between $50 and $100 in electricity costs per year, “for the most efficient options, which typically represented about 5% of the heating and cooling energy” used in the home.
Additionally, except for those systems that distributed air throughout the home, energy usage of such systems are directly associated with the “space conditioning” they provided for the home.
The second most cost-effective means of providing ventilation for the home was through a continuous-exhaust fan. Exhaust fans come in various sizes and powers to meet your needs, they start at around $100 and can be found at most hardware stores.
The study also found that homes with air leaks suffered from severe energy-usage penalties to regulate temperatures, without “necessarily providing more ventilation then a house with a better envelope and mechanical ventilation.”
Supply-only systems, which consist of a fan blowing air into the house, weren’t as effective. That’s because they can only blow so much air into a home and a well-sealed home doesn’t allow the air that’s inside the home out easily. Exhaust-only systems, on the other hand, work because any air lost will come in through outside leaks or whenever you open the door or a window.
However, both supply-only and exhaust-only systems suffer to a certain extent because they are not able to help distribute the air throughout a home. This can leave some areas of the home with more stale air than other parts.
If you’re worried about this, than you should look into a balanced-air ventilation system. Such a system utilizes the existing ductwork of a forced-air heating or cooling system and a motorized damper, along with a fan to bring fresh air into the home. These are more expensive systems to install and to operate, but can provide superior ventilation throughout your home.
Balanced-air systems can also be coupled with a heat recovery system or a energy recovery system to make sure outdoor air temperatures don’t change the temperature inside the house. However, these add some additional cost and complexity to the system and aren’t considered a cost-effective investment in most U.S. climates.