Restoration Guide: HVAC Air Quality

Editor's Note: This is article 7 of 16 in Chapter 8: The HVAC/Plumbing Guide of Old House Web's Home Restoration Guide. This guide was developed and edited for old homes from original materials in the U.S. Housing and Urban Development (HUD) Rehab guide.

7. INDOOR AIR QUALITY

Proper ventilation is usually not a problem for an old house that has never been restored. If anything, the opposite is usually true, you have too much outside air infiltration. However, once you have finished your remodeling to make your old house energy efficient, keeping the indoor air fresh and healthy is an important concern.

This article examines the importance of having clean indoor air in your old house, and discusses various methods you can implement during your older home restoration to help keep the inside of your home healthy.

Section 1--Indoor Air Quality Considerations During an Older Home Renovation

Old houses constructed in the 1700s and 1800s were not very energy efficient. They usually had single pane windows, lacked any type of insulation, and let in anything over a slight breeze inside the home. Building methods have changed a lot since those days, and the homes of today are almost airtight as builders strive to help homeowners save energy and shelter them from outside temperature extremes.

Unfortunately, making homes energy efficient has created another problem. Homes have become so airtight that they can't ventilate properly without help. Stagnant indoor air contains fumes from household products, can trap carbon monoxide and dust mites, and lead to mold and mildew. Appliances that remove air from a conditioned space without it being replaced can possibly lead to higher radon levels.

How much fresh air should be brought back into an almost airtight home is subject to debate, but just about everyone agrees that some fresh air is needed to help keep the inside atmosphere of your home healthy. While doing your older home restoration, keep in mind that in addition to all of the work you are doing to make your old house airtight, you should also plan on a way to maintain proper indoor air quality.

Section 2--Installing Ventilation Systems

Mechanical ventilation systems are the easiest way to help keep your indoor air quality healthy, and there are various systems available for your preservation project. If your old house is in an area that is very humid or very dry, you may want to also add a dehumidifier or humidifier to your ventilation system. You can even add an air cleaner to the system to help keep dust and pollen under control.

2.1: Add a Mechanical Ventilation System

Mechanical ventilation systems fall into three categories: supply, exhaust, and balanced. Supply and exhaust systems can cause possible problems inside your old house. They each use a single fan which either pulls fresh air into the home or exhausts interior air out of the home. A balanced system uses at least two fans which bring fresh air in and exhaust interior air. The most energy efficient of the balanced systems are the heat recovery ventilator and the air-to-air heat exchanger. These systems pre-heat fresh air brought into the system during the winter, and pre-cool it during the summer.

Adding one of these systems to your old house helps to keep the inside of your home healthy. There is a possibility that the ventilation system may increase your heating and cooling loads.

2.2: Add a Humidifier

Cold winter air can be much drier that summer air, and that can lead to the inside atmosphere of your old house becoming too dry. An interior humidity level of 35 percent to 50 percent is recommended during the winter, and an interior humidity level substantially less than that can lead to health problems. If you have a warm-air air furnace you can install a whole house humidifier, which works with the furnace system. Other options are pan, wetted-element, and steam humidifiers. Humidifiers require frequent cleaning to remove mineral deposits, unless there is an automatic flushing system attached. Most humidifiers are controlled by a humidistat. If you install a humidifier make sure it is set properly. Too much humidity in the indoor air can lead to excessive condensation.

2.3: Add a Dehumidifier

Excessive humidity in an old house can lead to its own set of problems. Too much humidity can cause health problems, can eventually cause an increase in the level of bacteria and mold, and may even lead to damaged building components. Bath fans and kitchen exhausts should be installed and checked for proper operation to remove humidity from those areas of the home. If your old house has a continual problem with high humidity, a dehumidifier should be installed.

2.4: Add an Air Cleaner

High efficiency air cleaners or filters can be added to your heating system to help reduce pollutants in your home. Air pollutants fall into two categories, gas or particulate, and there are filters designed for each. The most common type of filter is used for removing particulates such as dust, pollen, and mold spores, and there are high efficiency filters available which are rated at 90 percent.