Restoration Guide: HVAC Vents and Exhaust

Editor's Note: This is article 15 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.

15. APPLIANCE VENTS AND EXHAUSTS

Section 1--Overview

Appliance vents & exhausts can serve many purposes in an old house. They can vent combustion type appliances such as furnaces, boilers, and hot water heaters, or they can exhaust cooking devices, bathroom moisture, or clothes dryer heat and lint. Vents that are partially blocked or in need of cleaning can be a safety or health hazard, and should be cleaned or replaced. Vents that were sized for original appliances that have since been replaced during a previous home renovation can also cause safety issues.

Section 15 of Old House Web's edited version of the HUD Rehab Guide HVAC/Plumbing volume takes a look at the appliance vents & exhausts that you may encounter during your home restoration, and discusses safety and health considerations that you should be aware of while remodeling.

Section 2--Appliance Vents and Exhausts for an Old House

There is a possibility that your old house might not have any appliance vents & exhausts. The age of the home, the type of heating and hot water system, and whether the home has ever had any restoration work done in the past can determine whether vents and exhausts exist. Ventilation exhausts are a fairly modern innovation, and while some modern codes require them for safety and indoor air quality, many older homes still lack them. Appliance venting is necessary for combustion type devices such as gas or oil fired furnaces, gas fueled hot water heaters, or hot water boilers. If your old house has an electric furnace and hot water heater, you may not need to be concerned with appliance venting.

However, if your home has any appliance that requires venting, or your home renovation includes adding vented appliances, it should be a priority to inspect all new and existing vents. Existing vents may have been in use for many years, and could require a thorough cleaning to ensure safe operation. In addition, codes have changed as engineers have increased their knowledge of proper ventilation and exhausting procedures. Your existing vents may require modifications to allow the appliance to function at peak efficiency; vents that are sized too large can create as many problems as those that are sized too small. It is also possible that an appliance was replaced at some point in the past, and modifications to the venting system were never made to accommodate the needs of the new appliance.

You should also take a look at the other exhaust and ventilation systems in your old house. Examine existing kitchen exhausts and dryer vents. A kitchen exhaust can become a fire hazard if there is a buildup of grease inside it; proper operation also contributes to indoor air quality. Dryer vents can become a large fire hazard if there is a buildup of lint inside. Bathroom exhausts are not as likely to become fire hazards, but their proper operation contributes to indoor air quality, and helps to reduce the possibility of mold or mildew becoming a health hazard in your old house.

2.1: Adding an Exhaust for a Clothes Dryer during a Home Restoration

It is not unusual for an old house to be without a clothes dryer exhaust; not that long ago many homeowners dried their clothes on lines in the backyard and a clothes dryer was considered a luxury. There are codes that dictate the maximum length a dryer exhaust can be and bends in the exhaust reduce that maximum length. Some dryer manufacturers have models that allow the length to be increased, and code inspectors usually take that into account. It is also possible to use a power exhaust if you cannot meet exhaust length code due to the location of the dryer. Not following the dryer manufacturer's recommendations for installing the dryer exhaust, or exceeding the maximum length or number of bends allowed in the duct, can create safety and health issues.

2.2: Adding a Range Exhaust during a Home Restoration

Your local building code may or may not require a range exhaust, but even if it doesn't, it can be a good idea to add one while remodeling. There are two types of range exhausts--one exhausts to the outside and one recirculates indoor air through a filter and back into the kitchen. While both types can contribute to improving indoor air quality, the unit that exhausts to the exterior does a better job of removing contaminants created by cooking. Follow manufacturer's recommendations when installing a new kitchen exhaust; the length of the duct can affect the efficiency of the exhaust. Smooth ductwork usually works better for a range exhaust as it aids airflow and reduces the amount of sediment buildup.