Restoration Guide: HVAC Distribution Systems

Editor's Note: This is article 3 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.

3. DISTRIBUTION SYSTEMS

Heat distribution systems became common in homes over the last century, but an old house constructed in the 1700s or 1800s often relied on a central source of heat, and distribution was handled with openings from floor to floor. An older home restoration can often involve installing a new distribution system, or rehabbing an antiquated existing system.

This article examines the different types of heat distribution systems found in old house, including possibilities for updating old distribution systems and options for adding new systems.

Section 1--Options for Heat Distribution Systems in an Old Home Restoration

The age and location of an old house often dictates the type of heat distribution system found in the home. Colonial homes relied on fireplaces for heat, and eventually stoves using wood and coal came into use. The first designed heat distribution systems used hot-air, hot-water, or steam, and these systems are found in homes built during the early 1900s. Modern systems use four primary methods of distributing heat throughout a home:

• Steam, These systems use a boiler to produce steam which is piped to radiators located throughout the house. Steam systems use one or two pipes to circulate steam and allow condensation to return to the boiler.
• Air, Older air systems used a gravity method of circulating air, heated air would rise as it was distributed, and cold air would fall and be reheated. Due to the uneven air exchange of gravity air systems, and the increased availability of electricity, forced air systems gradually replaced the gravity method of air distribution. Forced air systems use electric fans to push heated air out into the rooms, and pull cold air in to be reheated. Changing a gravity system over to a forced air system usually involves installing a new system of ductwork.
• Water, A water distribution system uses a series of pipes and radiators throughout the home, similar to a steam system, but does not have the safety issues that a steam boiler can sometimes have. Older water systems used gravity to operate, heated water expanded and moved to the radiators forcing condensed water through return piping back to the boiler. Modern hot water distribution systems use a pump to move the water through the piping, and the radiators are often along room baseboards. As the air is heated, it circulates up into the room.
• Electric Resistance, this is not really a distribution system, as the heat is not being distributed from a central location. Electric resistance usually consists of a heat source for one location, such as electric baseboard heating, or a wall mounted heating unit within a single room.

If the old house you are remodeling has one of these heat distribution systems, there is a good chance that it may be in need of extensive repair to operate at peak efficiency, and it could be less costly to replace the system. Depending on the age of the old house, there is also a possibility that asbestos insulation was used in ductwork or around piping. An asbestos abatement contractor should be called in if you suspect that is the case.

Section 2--Restoration Options

2.1: Restoration of an Existing Forced-Air Distribution System

Rehabbing an existing forced-air distribution system involves checking the return and supply ductwork for possible leakage. Ductwork can be sealed with mastic, and if access is limited, aerosolized mastic may be a solution. All ductwork passing through unconditioned space, such as a crawlspace or attic, should be insulated. Registers and grills should be checked for proper operation, and registers that are not adjustable should be replaced. One downside to restoring an existing forced-air system is that the only way to correct a poorly designed system may be to replace it.

2.2: Restoration of Existing Water and Steam Distribution Systems

Rehabbing an existing water or steam distribution system during your older home renovation involves checking all supply and return piping for rust or leaks. Defective piping should be replaced, and any piping which passes through unconditioned space should be insulated. Foam pipe insulation can be purchased at most hardware and home improvement stores.

Valves and vents on radiators should be checked, and repaired or replaced. Many times a defective valve can be repaired, but you may wish to replace vents with a different speed to suit your heating needs. Radiator vents are available in very slow, slow, fast, very fast, and variable, depending on the level of output you desire. If you are installing new radiator vents, you may want to go ahead and replace the valves as well.

2.3: Restoration of an Existing Electric Resistance System

As previously discussed, an electric resistance system usually provides heat to a single area in an old house, and consists of an electric baseboard or wall mounted heater. Rehabbing the heater involves cleaning it, and straightening any bent heating fins, but it might be easier and safer to simply replace the unit.

An older home restoration involves making decisions concerning using existing systems or materials, or installing something new. In examining your existing heat distribution system, keep in mind that restoring it may still not provide modern comfort levels, or the energy efficiency of today's designs. Of course, the decision to install a new heat distribution system may be easy if your old house does not have any designed method of distributing heat.

One consideration when replacing a heat distribution system during an old home renovation, or installing a system in an old house which never had a system, is where to locate ductwork or piping in a home. Take some time to figure out the least intrusive method of supplying each room with heat, and it may help to get an HVAC professional involved. It might be possible to supply heat to the first floor from a basement or crawlspace area, and the second floor may be able to be accessed from an attic. Corners of closets can sometimes be used to install ductwork or piping from floor to floor.

Section 3--Installing New Distribution Systems

3.1: Installing a New Forced-Air Distribution System in Your Old House

A new forced-air distribution system should be designed by an HVAC professional so that it can be customized for your house. Proper sizing of supply and return ductwork is critical for the distribution system to operate at a peak level, and provide appropriate comfort levels efficiently. A professional can locate supply registers in places that promote proper heating and cooling for your old house's interior configuration. Forced-air distribution systems can be used for both heating and cooling.

3.2: Installing a New Mini-Duct Distribution System

Mini-duct distribution systems are old house friendly, as the ductwork is small and flexible, and can be installed fairly easily in a home which has never had a heating distribution system. Due to the smaller size of the ductwork, the air is delivered at higher velocities, and the air is delivered at different temperatures than a conventional forced-air system. Heating air is warmer than with a conventional system, and the cooling air is normally cooler. Mini-duct systems can be used for both heating and cooling.

3.3: Installing a New Water Distribution System

There are several types of hot water heat distribution systems in use today. The most common residential type is the single pipe radiator heat distribution configuration. A single pipe runs from a boiler to make a loop to radiators throughout the house. Depending on the size of your home, a drawback to this system is that the water cools the farther it travels from the boiler. A solution to this issue is to install larger radiators at the outer points of the water loop, or to install a couple of loops, each with its own water pump or zone valve. This allows each zone's temperature to be regulated. Hot water heat distribution systems can only be used for heating.

Radiant hot water heating systems are becoming more popular in homes. The systems consist of a series of small pipes or tubing that can be installed under the floor while remodeling. There are also heat panels which may be mounted at the baseboard or on the wall. As the water circulates through the piping, the air in the room is heated. Radiant cooling systems are also available, and use the same piping as the hot water systems, but they are usually used in conjunction with another cooling system.

Section 4--Installing a Zonal System in an Old House

A zonal system is similar to an electric resistance system in that there is no distribution system, but rather a source of heat for each main room. This is a good system for an older home restoration where preservation of the original configuration of the home is important. There is no ductwork to add, and unless you choose natural gas as a fuel, no piping either. Another advantage of zonal systems is that the heat can be regulated in each room that contains a heater.

Zonal systems may use baseboard or wall mounted heaters, and they usually use electricity or natural gas as a fuel, but heaters using gas may need to be mounted on outside walls. Most zonal systems only provide heat.