When having a heating system replaced with a high efficiency system. The new furnace vents directly through the wall to the exterior. The hot water heater is now the onlyappliance venting into the masonry chimney. The concern now becomes exhaust gas damage will be occurring inside your chimney. It isnow necessary to have a chimney liner installed

Venting of any fuel burning appliance is serious business. been checked by the furnace installer. Canadian building codes mandate that once modified or changed, all fuel burning appliance vents must be sized according to code.



The dynamics of drafting are complicated. Traditional masonry chimneys were designed and sized to vent very hot flue gases from old coal, wood burning, or low efficiency gas furnaces. Chimneys are like water pipes, they can only handle so much exhaust at a given pressure.


The column of cold, dense air inside the huge chimney could cause a portion of the exhaust gas to spill back into your basement.

Herein lies the problem. Your chimney's existing flue liner may be oversized for the orphaned hot water heater. This can, in some instances, create condensation problems inside of masonry chimneys. Water vapor is a byproduct of the combustion of natural gas. If the inside of the chimney cools down too much or there is too much cold air inside the chimney, the water vapor can condense and saturate the masonry inside the chimney before it can escape into the atmosphere. Sometimes the condensed water contains acids that can chemically attack poor quality mortars.

Before you installed your new furnace, your old low efficiency furnace cycled on and off frequently. This process kept the inside of the chimney warm. That heat source has been removed.

Sizing:
Improper chimney sizing is primarily an issue when venting appliances. A very common example of this is the fireplace insert or woodstove which is vented without a proper liner into the smoke chamber of a typical fireplace. This is a real problem. This type of installation is commonly referred to as a slammer. Slammers are notorious for creating dangerous messes of creosote which can ignite into a chimney fire. Chimney fires are very dangerous things. In addition to path through heat which can ignite the combustibles surrounding or adjacent to a masonry chimney, burning debris can exit the chimney and ignite a home from the roof down. The way to eliminate the problems created by a slammer type installation is to properly vent all appliances with a liner sized to each appliance. One may also want to consider updating any woodstove or fireplace insert which was not produced in the last 15 years. During that time incredible strides has been made in woodstove design making available woodstoves which when installed properly, burned properly, and cleaned annually are much cleaner and safer than those which produced larger amounts of creosote in the past.
Condensation Issues:

All natural draft chimney functions due to temperature differences between the outside of the home and the exhaust gases. The draft created by this temperature difference draws the exhaust gases produced by a fireplace or appliance safely out of the chimney. Most all fuels have as a by product of combustion elements which can condense when they come into contact with cooler surfaces. In the case of wood fired appliances and fireplaces, creosote is the condensing by-product. As shown in the picture to the right, creosote condensation can be substantial when conditions are right for condensation to occur. Creosote is the fuel for chimney fires. The best way to ensure a chimney fire will not occur is to not have the fuel for it in the first place. In the case of natural gas or propane fired appliances the primary condensate is water. This condensation can speed up water damage to a chimney via the freeze / thaw cycle. Permanent damage to a chimney can be cause cracks in the structure of the chimney leading to structural failure or exhaust gases seeping into living space. The key to a condensation problem One of these conditions relates both to proper sizing of a vent system and its proper design and construction. This condition is a cool or cold flue. A cold flue which does not heat up properly is a surface ready to hold condensation.



Servicing Maintenance
Many gas utilities offer a maintenance service (often through contractors) that includes an annual furnace inspection, cleaning, and adjustment, if necessary. This type of annual checkup is highly recommended for both efficiency and safety measures, particularly for the newer mid- and high-efficiency equipment, in which case the electronic controls and safeguards should be checked periodically. These tasks cannot be done by the householder.
Some of the other tasks that should be performed by a serviceperson during regular maintenance are as follows:

inspecting the inside and outside of the vent pipe and stack

checking the condition of the furnace heat exchanger

checking the safety controls for the exhaust system

checking the other safety controls

checking the condition of all fan wheels—circulating, exhaust (induced draft fan) or forced (burner)—and cleaning, if necessary

cleaning or replacing the air filter for forced-air systems
Separately, many gas utilities or dealers may also offer a parts replacement plan, which, for an annual fee, covers repair, adjustment, or replacement of controls, motors, and parts. As well, they will alter appliances, equipment or piping and turn on gas service, if the pilot light has been shut off.

Furthermore, most utilities offer the following services at no charge: emergency services (such as investigating suspected gas leaks or carbon monoxide spillage); estimates for repairs, replacements, and alterations; verifying gas meter operation; and finding the location of buried gas lines.

If the furnace’s pilot light has been shut off during the summer to conserve fuel, relighting should be done carefully and in accordance with the manufacturer’s instructions, which are usually on a metal plate near the furnace burner or gas controls. Shutting off the pilot light for the summer is cost-effective only if you plan to shut it off and relight it yourself. If it fails to relight, you should contact the gas utility and have the relighting done by a qualified serviceperson. A fee is normally charged for this service. While the serviceperson is in your home, ask for instructions on properly relighting the pilot light. You could also ask for a brief inspection of the equipment.


Owner Maintenance
There are a number of maintenance tasks you can do yourself to keep your system working well. But even if you do these properly and regularly, you should still have your system serviced annually by an expert heating contractor or gas utility.
Routine Chimney Care

Other than the high-efficiency condensing models (which have special venting requirements) and certain mid-efficiency furnaces, all gas furnaces and boilers must be vented with:

a double-walled, prefabricated metal B-vent with an aluminum lining

a properly sized masonry chimney lined with a clay flue tile

a masonry chimney lined either with a B-vent or an approved stainless steel liner
Although a gas furnace vent (chimney) rarely, if ever, needs to be cleaned, it should be checked occasionally for signs of deterioration due to condensation or corrosion. You can check it simply by inserting a mirror in the cleanout opening at the bottom of the chimney on a bright day.

Look for a broken or flaking flue liner, or rusting or bending of the metal liner. Water streaks from the cleanout door or the base vent T can also indicate chimney condensation and other potential problems. Such as a cracked heat exchanger.

Take a look at the outside of the chimney as well. White or yellow efflorescence on masonry chimneys or deteriorating or flaking brick or mortar can indicate condensation problems in a masonry chimney. Don’t forget to look at the outside of metal chimneys as well. Rust marks could indicate the onset of serious corrosion.

The advantage of high-efficiency condensing furnaces is that they eliminate the need for a chimney and are thus vented out the side wall of the house through an effectively non-destructible PVC or ABS pipe. Make sure that the pipe always slopes upwards from the appliance to the outside, and ensure that the outside vent terminal is kept free from obstructions, including ice formation.

Certain types of gas-fired systems have special needs that may require your attention. Check your owner’s manual or discuss this with your installer or serviceperson.


Why do I need a chimney cap on my chimney?
An uncapped chimney:

Says "come on in, make yourself at home!" to birds and animals.
Allows rain and snow to enter your chimney, which leads to moisture damage and expensive repairs.
Creates a fire hazard as burning embers and sparks escape through the open chimney and land on your roof or in your yard.
 

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