In recent years the demand for energy efficient and comfortable living spaces has led to better insulated homes, or “tighter” homes. However, with tighter homes it is even more important that there be adequate quantity and quality of ventilation and airflow. Why would you want your house to be well ventilated?
- To provide enough fresh air to keep the occupants healthy
- To remove odors
- To dilute indoor pollutants
- To lower the indoor relative humidity
Most of these reasons are easy to understand. However, using ventilation to lower the indoor relative humidity can get problematic.
Ventilation and Humidity
To prevent moisture damage to a house, dry is always better than damp. However, some people begin to complain if the indoor relative humidity is too dry. Achieving a satisfactory balance can be a challenge.
Since cold air can’t hold as much moisture as warm air, ventilating a house helps lower the indoor humidity only when it’s cold outside, or on dry spring or fall days. In most parts of the U.S., ventilation during hot weather actually introduces more moisture into the house raising the humidity.
Most residential builders choose from one of three ventilation options: (1) an exhaust-only ventilation system; (2) a central-fan-integrated supply ventilation system; or (3) a balanced ventilation system using an Energy Recovery Ventilator (“ERV”) or a Heat Recovery Ventilator (“HRV”).
Increased ventilation has a greater energy demand and diminishing that cost is the purpose of ERVs and HRVs. Although they are expensive to install, ERVs and HRVs have the lowest operating cost of any ventilation option.
ERV and HRV - What do they do?
The purpose of an ERV or an HRV is to deliver fresh air to a home. Neither is designed to provide makeup air for combustion appliances or kitchen exhaust fans. They are not heating units, or energy-saving devices. But they reduce the amount of heating or cooling that your system must do to the fresh air that is coming into your home.
ERV and HRV - How do they do it?
The two fans in an HRV pull fresh air into a home while simultaneously exhausting stale air. Both the fresh air stream and the stale air stream flow through the core which allows some of the heat from the warmer air to be transferred to the cooler air. In winter, the HRV “recovers” some of the heat that would have been exhausted. This heat transfer occurs without any mixing of the two air streams.
An ERV does everything that an HRV does, plus it allows some of the moisture in the more humid air stream to be transferred to the dryer air stream. The moisture transfers with very little mixing of the two air streams. In the winter, this means that some of the heat and humidity of the indoor air is transferred to the cooler, dryer outdoor air that is coming in. And in the summer, some of the heat and humidity of the warm, moist outdoor air is transferred to the conditioned air that is being exhausted outside.
ERV and HRV – Which should I choose?
Here are some basic guidelines:
- Do you have a large house in a cold climate? Choose an ERV.
- Do you have a small, tight house in a cold climate? Choose an HRV.
- Do you live in a hot, humid climate? Choose either one, but the cost to run an ERV will be a little less than an HRV.
- In mixed climates, choose either appliance.
Remember, proper installation of either system is critical for maximum energy efficiency. If you go to the expense of purchasing an ERV or HRV you should insist on using a qualified and experienced contractor. You don’t want to put good money into installing either one if that installation is poorly done. So choose the right contractor to make your investment worthwhile. At GAMA Air we would be happy to provide you with a free quote to install an ERV or HRV. This could be part of an entire system replacement, or as an accessory to your existing system. Give us a call at (310) 651-6936 or use our online form to request an appointment.
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