14 - Friday, August 25, 1989 - North Shore Nev's

CHIMNEY LINERS

Match home's flue and furnace sizes as closely as possible

IF YOUR summer schedule in- cludes home renovation chores, such as adding insulation to your home, remember that energy con- servation can be hazardous to your health.

For instance, making a house air tight can result in improper venting of high efficiency furnaces and poorly. maintained chimneys, ac- cording to Jan Donnelly, president of a manufacturer of flexible and rigid chimney liners.

“Modern, efficient oil and gas furnaces give off cooler gases than their predecessors. if vented into an older, larger chimney, the chances of carbon monoxide poisoning and fire become much greater,’’ he says.

The problem is caused when to- day’s cooler exhaust gases enter older chimney flues where they ex- pand and cooi to their dew point before escaping from the chimney.

“One cubic foot of exhaust con- tains about two gallons of water,”’ says Donnelly. ‘‘During the winter, this water will freeze and thaw, causing the brick and mortar of masonry chimneys to crack and crumble. In addition, the conden- sation also contains sulphurous acids that eat away at the chimney.’

Flue gases must exit the chimney at 150°F to prevent condensation. The solution is to match fiue and furnace sizes as closely as possible, to keep exhaust fumes in a gaseous state. The most efficient way to do this is to down-size the existing chimney by installing a proper size Stainless steel or aluminum liner.

“We estimate that about one- third of all chimneys in the U.S. and Canada are experiencing some trouble releted to improperly sized venting units. This is largely the result of the shift to higher effi- ciency natural gas apgpiiances which burn at only about 650°F. Compared to solid fuel {i.e. coal and wood) which burns from 1,500°F to 2,100°F.

“Homeowners should be aware of the tell-tale signs of deteriora- tion: loose mortar, damp spots and flaking vrick, flue gas odors in the furnace area and blistering on walls where the chimney rises,’’ Donnelly says.

Crumbling brick from the chimney may fall inward, blocking the flue and causing exhaust fumes — including carson monoxide gas — to back up inside the house.

Wood stoves (and fireplaces) carry an additional potential danger in that creosote, a highly flammable residue, can condense in stove pipes and chimneys, in- creasing the risk of fire.

Over the past decade, home fires in which heating appliances were the source of ignition, increased to 10 per cent of the annua! total, from 8.4 per cent, according to Donnelly.

“The human cost of these fires was 352 injurics and deaths in Canada in 1437 (the most recent yeer for which statistics are avail- atle) and a further loss of $93.7 million in property.’’

Modern, efficiently burning heating units require a reduction in chimney size to effectively draw combustion air. Ironically, im- proper venting prevents the unit from operating at its optimum level, thus defeating its very pur- pose.

Furthermore, each appliance in the home should te vented sepa- rately, matching the type of ex- haust to a iiner of the preper size and material. “Under no cir- cumstances should you vent a solid fuel appliance together with a gas appliance,’* Donnelly says.

“Gas furnaces can be vented safely through aluminum liners, while oii and solid fuel units re- quire stainless steel.”’

Missing mortar and loose brick are obvious evidence of deteriora- tion. However, there are many other warning signs. Masons and heating/ventilating contractors are specialists in this field. They are qualified to repair any existing damage and to prevent further erosion by installing the most ap- propriate chimney liner.

To evaluate the state of your chimney, answer ihe following simple questions:

els the chimney adequately

supported?

Is the mortar and brick hard or can you push a knife blade into it?

eHas the chimney base deteriorated?

eis there deterioration below the roof line?

is there combustible material (i.e. timbers, wall members) within three to five centimetres (one to two inches) of the chimney?

Then, examine the flue by look- ing into it with a light and a mir- ror, through any available open- ings. Vertical and horizontal cracks in the brick — especially at offsets — can signal danger.

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