Does your furnace kick on and off frequently? Is the blower fan loud? Are some areas of your home warmer or colder than others? Well, you’re not alone! HVAC design is a very complex process. It involves some serious thermodynamics and a complete understanding of air pressure and velocity. The Building Performance Institute estimates that anywhere from 30-40% of furnaces are oversized in the United States. This often leads to the furnace turning on and off frequently, which can lead to humidity problems and air quality issues.
The old rule of thumb was 1-ton of heating for every 500 square feet of conditioned living area. However, this really has nothing to do with the physics of the system. Today, HVAC systems should be sized using a Manual J calculation (developed by the Air Conditioning Contractors of America or ACCA). This calculation considers the amount of insulation for every wall, ceiling, floor, window, and door. It factors in where windows are placed relative to the Sun’s path where the home is built. You also need to know how “leaky” the home is, or how much air escapes the home relative to its volume. You need to know the climate where the house is located; how hot or cold it is and how much humidity there is. As you can see, the calculation involves a lot of data. Sophisticated software is used to input this data into thermodynamic equations to determine the amount of heat loss or gain for the home depending on the season (heating or cooling). In fact, our HVAC systems are actually designed for the 99% hottest or 99% coldest day of the year. This means the system can still perform on these extremely cold or hot days.
The old rule of thumb was 1-ton of heating for every 500 square feet of conditioned living area. However, this really has nothing to do with the physics of the system. Today, HVAC systems should be sized using a Manual J calculation (developed by the Air Conditioning Contractors of America or ACCA). This calculation considers the amount of insulation for every wall, ceiling, floor, window, and door. It factors in where windows are placed relative to the Sun’s path where the home is built. You also need to know how “leaky” the home is, or how much air escapes the home relative to its volume. You need to know the climate where the house is located; how hot or cold it is and how much humidity there is. As you can see, the calculation involves a lot of data. Sophisticated software is used to input this data into thermodynamic equations to determine the amount of heat loss or gain for the home depending on the season (heating or cooling). In fact, our HVAC systems are actually designed for the 99% hottest or 99% coldest day of the year. This means the system can still perform on these extremely cold or hot days.
That’s just the first part. Now you must select a fan that will move all of this conditioned air through a series of ducts to make sure every room is adequately heated or cooled. The duct design for an HVAC system is really important. You can lose a lot of energy (and therefore money) with bad duct designs. HVAC systems are also how we primarily control the humidity in our homes and the air quality. Unfortunately, air quality is often an afterthought. If you only have one filter, then you are probably not breathing in very clean air (especially if it’s only an inch thick!). I can tell you from experience that very few homes have a good duct design. Most are incorrectly sized and improperly insulated. Our home energy audits help identify problems like these and we can help you decide if upgrading your HVAC equipment is cost effective. It is amazing how much money you can save by upgrading your furnace or properly insulating and sealing your ducts!
Controlling moisture in your home is a huge part of maintaining a healthy home and avoiding costly repairs. Many homes are built to be “leaky”. This is measured by computing how often the total volume of air in the conditioned space of your home is exchanged with the outdoors. The standard measurement is Air-Changes per hour (ACH) and is measured during a depressurization of the home using a blower door. Most modern codes call for 3 ACH as the maximum allowed. To be certified as a “passive” home (high energy efficiency) you need 0.6 ACH! Many homes are around 7 or 8 ACH and can be as high as 15 or 20 ACH! The reason homes are built so leaky is to help control moisture levels within the structure. When energy was relatively cheap, this was a perfectly viable option. Now, however, the loss in energy coupled with the advancements in insulation and vapor barriers makes the leaky home quite obsolete not to mention expensive.
In Wyoming, this is perhaps best demonstrated in the crawlspace and the basement. Most crawlspaces are ventilated to control moisture. There have been many studies conducted across the country now that have challenged the traditional ventilated crawlspace design. Sealing the crawlspace and tying it into the conditioned space offers big savings on energy and improved comfort. Of course, it needs to be done by a competent contractor that understands how to properly seal a crawlspace. Moisture must be properly controlled, and all combustion appliances must be safely installed. Basements lose a lot of heat in the winter as well. Again, air sealing and proper insulation can go a long way.
In Wyoming, this is perhaps best demonstrated in the crawlspace and the basement. Most crawlspaces are ventilated to control moisture. There have been many studies conducted across the country now that have challenged the traditional ventilated crawlspace design. Sealing the crawlspace and tying it into the conditioned space offers big savings on energy and improved comfort. Of course, it needs to be done by a competent contractor that understands how to properly seal a crawlspace. Moisture must be properly controlled, and all combustion appliances must be safely installed. Basements lose a lot of heat in the winter as well. Again, air sealing and proper insulation can go a long way.
Recently, I have seen a lot of “misinformation” on spray foam insulation. People claim they cannot sell their homes with spray foam insulation installed. This is a real shame. Spray foam insulation was one of the crown jewels of the aviation and aerospace industry. It is some of the best insulation around. The problem lies in how it is used. Closed-cell spray foam insulation is a phenomenal air barrier. It can help seal up a home so that very little air escapes. That’s where the moisture problems can occur. However, by properly exhausting the air (possibly through a Heat Recovery Ventilator or Energy Recovery Ventilator), this can easily be managed. Spray foam can be used to make a home incredibly energy efficient and it really is a pity that poor installations and mismanagement have scared some people away.