Every day, I am presented with the argument that a home can not be sealed tight because it must breathe. A long time ago, a friend and colleague of mine answered this comment by asking,“Have you ever seen a house with lungs?” Of course, the answer to this is no, but many people still believe that their house must get fresh air to breathe.What you must remember is that it is not the house that needs fresh air, but the occupants of the home. Also, you have to realize that everything we put in a house doesn’t need to be there, so we need to get it out. You may ask, “Isn’t this basically the same thing as the house breathing?” The answer to this is yes and no. Currently, many builders believe that fresh air needs to enter the home, but don't really care how or where. This can be a real energy buster for you if your home gets too leaky! What you want to do is control how much and where the fresh air enters - and let’s not forget about getting rid of the stale air.
You do this by creating a tight home that has few uncontrolled air leaks or air changes. Air changes are the number of times the air in your home is exchanged with fresh air over a given period of time. Typically, this is figured over an hour. Often times, air exchange rates are amplified for measurement purposes. This is done with a blower door that decreases the pressure in a home, and is usually measured at 50 Pascals. Most new homes that I see range between 5 and 8 air changes per hour at 50 Pascals (ACH50). However, there are the exceptions in which they have leakage below and above this range. I like to see homes around 3 ACH50, with controlled ventilation. The most efficient homes that I see are in this range and will typically have ERV’s or other means of air changing. (An ERV is an additional piece of equipment for your HVAC that can exchange and condition air.)
Once the home is tight, you need to get air in and air out. Building codes may state how much air you need to bring in and out of a home, so check there first! They may also limit the amount that can be brought in by natural means, such as leakage or passive ventilation. Once you have checked with someone who knows about the codes, you will want to get someone who is knowledgeable about exchange rates and how to achieve them. This is done by various means, and each has its own pros and cons. You may see the use of any of the following types or a combination of them:
1. Passive ventilation
This is ventilation that operates on natural forces and is most commonly seen in crawlspaces and attics; however, you may see it on exterior of walls as well. This is used to lower temperatures and humidity levels in these areas.
2. Spot ventilation
This is used to remove contaminants/stale air from a central location. An example of this is bathroom exhaust. Spot ventilation is very important to remove unwanted moisture in bathrooms and kitchens, but it can produce a negative pressure on the home. Just make sure you don’t go overboard on the size of the fan.
3. General Ventilation
This is simply the ventilation of the entire living space using fans. It may be broken down into sub categories or considered supply only or dilution ventilation, depending on the source. Dilution ventilation is achieved by only pumping in air to dilute stale air, and it can create a positive pressure on the home. The exhausting of air is not controlled. It can be achieved via a standalone unit or through the HVAC.
4. Exhaust Only Ventilation
Exhaust can be sub category of general ventilation, and it is achieved through exhausting of air only. This may seem like spot ventilation, but it is for the whole house and not just a certain location. It can be achieved through an exhaust fan in a central location, the HVAC unit, or through a bathroom fan that is designated to permanently stay on. This can cause a negative pressure on the home, because the intake of air is not controlled. A negative pressure can cause back drafting.
5. Balanced Ventilation
This is also called supply and exhaust ventilation. The air taken in will typically equal the air exhausted. This is often achieved with piece of equipment, such as an ERV or HRV. It keeps a balanced pressure in the home, and both sides of the air exchange are controlled and possibly conditioned to help lower heating and cooling loads.
There are several systems and variations on the ventilation types mentioned above. If you are building a home or just working to better your current one, talk to your contractor or someone knowledgeable about ventilation to work out a system that best fits your home, needs, and budget.
Install Energy Star Appliances
Since we are taking the time to talk about ventilation this week, I thought I would just mention Energy Star appliances. Many people will probably say that they already know about this, yet wouldn't understand its connection with ventilation. Many people don't realize that there are appliances and fixtures approved by Energy Star other than the typical dishwasher and refrigerators!
In respect to the topic on ventilation, there are Energy Star ventilation fans. When looking at a system that may be using one of these fans to provide ventilation, it is a good idea to have one that will save you energy.
So next time you’re looking for a new appliance or fixture, check to see if there is one that is Energy Star approved, because you just may be surprised by what you find!
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