Restoration Guide: HVAC Fireplaces and Chimneys

Editor's Note: This is article 9 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.

9. FIREPLACES AND CHIMNEYS

Section 1--Overview

A fireplace can create an attractive atmosphere in your old house on a cold winter evening, and it can also be a good alternative source of heat. But it can be a health and safety hazard if not given a thorough inspection and any defects corrected prior to use.

This portion of the HVAC/Plumbing section discusses fireplaces & chimneys found in old houses, and addresses possible safety concerns, restoration methods, and options for making your fireplaces and chimneys more energy efficient.

Section 2--Options for Rehabbing and Improving Old House Fireplaces and Chimneys

A large percentage of old houses have a fireplace and chimney, and if you have a very old house, it could have numerous fireplaces and chimneys. When fireplaces were used as a main source of heat for a home they were often a fixture in most of the main rooms of the house. Over the years many of these fireplaces have been covered over, either because they were no longer needed, or because they were no longer functional.

All fireplaces in a home should be inspected prior to ever being used. If the fireplace and chimney are old, there is a good possibility that the chimney could be partially blocked, or might need cleaning. Chimneys which haven't been used in years may not even extend beyond the roof any longer and using them could cause a house fire. Even if a fireplace and chimney appears to be in good working order, it should still be inspected to make sure it adheres to modern building codes. Many old fireplaces had poor designs and caused excessive smoke while burning.

Masonry fireplaces can usually be repaired by a brick or stone mason, or you may choose to install an alternative or addition to the fireplace that can offer a more efficient source of supplemental heat during your home restoration.

2.1: Hire a Mason to Rebuild or Repoint the Chimney

A fireplace does not function properly unless the chimney is in good shape. All loose mortar between bricks should be removed and replaced, this is called repointing. The same type of mortar that was originally used when building the chimney should be used for repointing so that it has the same characteristics as the remaining original mortar. If the chimney is leaning or all of the bricks seem to be loose, the chimney should be taken down by a qualified mason and rebuilt. In most cases the original brick can be reused.

2.2: Place a Chimney Cap on Top of the Chimney

Many old chimneys were built without a chimney cap. A chimney cap helps prevent rain water from entering the chimney and mixing with the soot which can create contaminants. A cap with a screen helps prevent birds from nesting in your chimney.

2.3: Reline Your Chimney to Help Prevent Unwanted Fires

Chimneys built prior to the early 1900s used mortar to line the inside of the chimney, and there may be cracks or missing mortar which can allow heat to cause a fire. Even if the chimney has a tile liner they may be cracked or broken, and a new liner should be installed. New building code requires that all chimneys have a liner. Three approved methods for relining a chimney are:

• Use sections of metal piping which are available from heating supply distributors and some home improvement stores. Stainless steel should be used if the chimney is being used as a vent for a gas fired appliance. This is not a recommended method of relining if the chimney already has a weak draft.
• Use tile to line the chimney. This is required by some building codes if the chimney is being used for a wood burning fireplace.
• Line the chimney with a cement mix. There are companies which can pour a cement mix around an inflated hose which is removed after the cement dries. This method can also reduce the draft of a chimney, and cause further problems for a fireplace that does not draft properly.

2.4: Add an Exterior Air Supply to Your Fireplace for Combustion and Draft Air

A wood burning fireplace draws conditioned air from the room it is located in. This is one of the reasons fireplaces are not considered very energy efficient. An exterior air supply allows the fireplace to draw unconditioned air from the outside for its combustion needs. After installing an outside air supply you should install glass doors on the fireplace to keep conditioned air in the room, but this also reduces the radiant heat produced by the fireplace from entering the room.

2.5: Add an Environmentally Friendly Grate to Your Fireplace

An environmentally friendly grate is constructed of stainless steel, and is connected to a fan which blows air through holes in the grate. This results in a much hotter burning fire and reduces harmful emissions. The grate also has a heat reflecting shield which helps send more of the fire's radiant heat into the room.

2.6: Add a Gas Log Set or Fireplace during Your Home Restoration

Gas log sets can be placed in an existing fireplace, and can be vented or unvented. Vented log sets use a chimney flue to exhaust gases and are about 20 to 30 percent efficient. Unvented gas log sets exhaust their emissions back into the room, and are more efficient as no heat is lost through the chimney. Unvented gas logs sets are not approved in all states.

Gas fireplaces consist of an entire firebox with a gas log set inside. Some gas fireplaces are available in direct vent models which eliminate the need for a chimney. The unit is vented to the outside much like a clothes dryer. Gas fireplaces have glass doors on the front, and can be 60 to 80 percent efficient. They are also available with built in fans which allow them to provide convection heat along with their radiant heat. Gas fireplaces can not use existing masonry chimneys.

2.7: Add a Wood Stove, Fireplace Insert, or Advanced Fireplace during Your Home Restoration

You may not want to settle for the 10 percent efficiency that your wood burning fireplace provides. A wood stove without controls can provide 20 to 30 percent efficiency, and an advanced wood stove can produce heat up to an amazing 75 percent efficiency. Wood stoves can use existing chimneys with some modifications.

A fireplace insert is a contained firebox which sits inside an existing fireplace and can provide more efficient heat than a conventional wood burning fireplace.

Some states prohibit the use of traditional wood burning fireplaces and the emissions they can produce. Fireplace companies seeking to meet the guidelines of all states have produced fireplace models which meet the Environmental Protection Agency's (EPA) standards for wood stoves. These units are airtight and can produce heat with the same efficiencies as advanced wood stoves.