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| Smokey Fires and Creosote Prevention | |||||||||||||||||||||
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The main reason for the formation of creosote and excessive wood smoke is due to low operating temperatures caused by any of the following:
1. Wet Wood SupplyIt is normal practice to air dry wood outside for at least a full summer season. Correct drying will take 6-12 months depending on local conditions. The wood should be cut to length, split, piled loosely or stacked and covered in a protected shelter or under plastic to keep the wood out of contact from the elements. Several weeks before Fall a supply of this seasoned wood is normally brought into a heated space to insure that the wood has optimum moisture content. Some individuals will install a dehumidifier in the same heated space to promote drying.
2. Fire Box Loading The firebox can be loaded up to a maximum ¾ the height of the brick liner with 2” of protective ash left in the bottom of the firebox after cleaning. The initial wood load and fire should insure that a good bed of coals is established and the heating system is fired up to a temperature above 600 F . This will give the firebricks, metal heat exchanger and the venting system optimal radiant, convection and conduction heating characteristics. Normal steady state operating temperatures should fluctuate around 400 F depending on draft, combustion air supply and remaining wood fuel supply in firebox.
Notes:
1.
Stack thermometer probe should be inserted into breech at chimney base
2.
Non approved fuel sources such as manufactured fire logs, gasoline, naptha, crankcase oil, tires, creosote or treated timber, saltwater debris, disposable diapers and plastics from household garbage should not be burned. These materials can have extreme burning temperatures as well as corrosive action on the metal heat exchanger. Poisonous or carcinogenic substances such as dioxins can be generated in flue gases from the burning of plastics.
3.
It is common practice to operate the Forced Draft Fan when reloading firebox.
4.
A heat loss calculation will accurately size required furnace output and model.
5.
Non grated models recommended when burning wood only.
3. Combustion Air and the Forced Draft Fan Both the Forced Draft Fan and its Slide Draft control regulate the amount of Combustion Air entering the firebox. Combustion Air flow is what sets the burn rate of the wood in the firebox. The final control setting should provide an optimum burning rate and should not be set below the Minimum position.
The Wood thermostat located in the main living space will automatically control the operation of the Forced Draft Fan above the fire door. By forcing extra Combustion Air into the firebox with the Forced Draft Fan the burn rate of the wood will be increased. The faster the burning rate the higher the stack temperatures of the flue gases which will minimize creosote formation. Forced Draft Fan is located above the Firedoor The Forced Draft Fan (FDF) above the furnace firedoor is automatically operated by the Solid Fuel (Wood or Coal) Thermostat.
1.
Initial Set Up of Furnace Controls
a.
The Solid Fuel thermostat should be set at a normal room temperature of 21C (70F). With dual fuel operation set the back-up thermostat (oil or electric) to a lower setting of 15C (60F).
b.
The slide damper beside the FDF should be at Maximum setting. Over the heating season this can be moved towards the Minimum position to extend burn time of each load of firewood but carefully monitor for smoky fires or creosote build up. The final setting should provide satisfactory burn time and space heating without smoky fires or creosote build-up (See section 2).
Note: The firedoor slide damper is normally closed. In GRATED models the door slide damper is located in ash door. Remember that the ash pan needs to be cleaned DAILY to provide unrestricted Combustion Airflow into firebox and prevent grates from warping.
2.
Heating Cycle and FDF Operation
a.
If room temperature is below the Solid Fuel Thermostat setting of 21C(70F) the FDF will turn ON.
b.
The FDF will push extra Combustion Air into the firebox and accelerate the burn rate. This will heat the plenum on top of the furnace. The Fan/Limit control will then engage to automatically turn on the circulating blower inside the furnace and move heated air through house duct system (See Sections 6&7). Note: Blower will run for varying lengths of time depending on heat output of fire.
c.
When room temperature reaches 21C(70F) the Solid Fuel Thermostat is satisfied and the FDF will turn OFF. The fire will still burn due to the natural draft of the hot chimney pulling Combustion Air into the firebox through the opening in the FDF (See sections 4&5).
d.
When room temperature drops below the 21C (70F) the Solid Fuel Thermostat will again turn ON the FDF.
The FDF will keep running until one of the following occurs:
1.
Existing wood supply in the firebox is sufficient to reheat living space.
2.
Firebox is reloaded and a new heating cycle initiated to reheat living space.
3.
Room temperature drops until back up heating system starts at 15C(60F).
4.
Manual Toggle Switch on FDF is turned OFF.
5.
Solid Fuel Thermostat is set below existing room temperature.
Note: The FDF can run for extended periods of time and motor will be hot to touch. Whenever opening the firedoor the FDF should be running to prevent smoke from entering furnace room.
4. Chimney Draft Poor draft will cause a fire to smolder. The recommended draft setting for Newmac wood burning furnaces is between –0.03 to – 0.05” W.C. The recommended flue sizing for Newmac solid fuel furnaces is normally 8 “ or 7 ” diameter. The amount of dilution air entering the Barometric Draft Regulator should be minimized to prevent cooling of flue gases
Notes:
a.
Seven things to increase draft are colder outside air temperatures, higher chimney, greater wind velocity, higher atmospheric pressure, higher flue gas temperatures, closed draft regulator and special chimney caps.
b.
Use approved ‘solid fuel rated’ high temperature chimney only.
c.
Single wall flue pipe should not exceed 10 feet and have not more than two (2) 90 degree elbows. Combination furnaces can mount the blower section on either the left or right hand side to minimize flue pipe length.
d.
The horizontal run should slope at least ¼” rise per 1 foot run up towards the breech at the base of the chimney.
e.
Flue pipe connections must be secured with at least 3 metal screws.
f.
Code requires the flue pipe to be crimped end down toward furnace with flue pipe INSIDE smoke pipe of wood furnace.
g.
The chimney must be absolutely smoke tight throughout its entire length and must extend three feet (3’) above a flat roof or two feet (2’) above the ridges of peaked roofs.
h.
Flue Pipe – The conduit ( piping) connecting the smoke pipe (or flue collar) of the furnace to the chimney breech must be constructed of steel with a melting point no less than 1100 C. Galvanized flue pipe can not be used.
i.
Galvanized Draft Regulators are approved for Newmac solid fuel furnaces.
j.
New flue pipe may give off odours or smoke for the first few fires.
k.
Use approved sealing methods around the breech to chimney and install fire stops between floors for inside chimneys. Liners should be properly sealed at both top and bottom. Check both chimney installation codes and manufacturer requirements for details.
5. Combustion Air For new home construction it is necessary by installation codes to design Combustion Air for any fossil fuel burning appliances such as oil, wood, propane, or natural gas. Any age home may need to install Combustion Air. Combustion Air is normally supplied by an insulated pipe of either 5” or 6” connected to an outside permanently open air inlet hood. a. Symptoms of tight home construction can be a smoldering fire, odours and smoke back drafting into basement. b. Three (3) types of air systems to be designed for modern home construction are : Combustion Air , Ventilation Air for Human Health and Make-up Air for any exhaust fans connected to the outdoors. c. For enclosed furnace rooms there needs to be ventilation air for heating equipment cooling. d. Size of furnace room or open basement has no connection with providing outside Combustion Air in tight home construction.
6. DuctworkMetal plenums and duct system are to be installed for safety and correct operating set up. Airflow is important across any heat exchanger to provide safe operating temperatures and correct operation of the Forced Draft Fan. The size of the ductwork and the return air grills should be installed to provide correct airflow to the furnaces for a CSA certified 85 F temperature rise across the heat exchanger. Ductwork should work to the following recommended sizes:
Furnace Model Supply Return Nominal Grill Size WB/WG100 180 Sq.In. 250 Sq.In. 12”x30” (steel truss)
WAO/GAO 180 Sq.In. 250 Sq.In. 12”x30”
CL86/96 C/G 180 Sq. In. 250Sq. In 12”x 30”
CL115-170 C/G 220 Sq. In. 250Sq. In 12”x 30”
CL155 C/G 240 Sq. In. 280 Sq. In 12”x 30”
CL 170 C/G 260 Sq. In. 300 Sq. In 12”x30” + 6”x10”
(See App C.) 1. For solid fuel furnaces there are specified safety requirements for ductwork that require 6” clearance for 6 ft. from the supply bonnet. Labels on furnace casing clearly indicate MINIMUM installation requirements. Also 6 ft and 6” clearance required for Return ductwork on WG/WB. 2. The installation of ductwork for any wood burning furnace should be properly designed to provide gravity feed during power failure. It should be correctly sized with proper transitions and sloped to assist ‘gravity’ operation during power failure. See operation manual for correct safety procedures. 3. Recommended minimum plenum height is 24”. 4. Both Supply and Return air ductwork has to be fully enclosed . ie NO JOIST PANNING 5. Blockage in ductwork or over return air grills can cause unsafe operating conditions. 6. Insure installation of Return Air grill(s) maintains free area requirements. 7. It is normal practice to locate Return Air Grills on main floors of living space and not in basement area where furnace is located. 8. Do not install Return Air Grills directly on plenum. 9. Do not install Return Air Grills in an enclosed furnace room. 10. Size insulated air conditioning ductwork to maintain free area in table above. Avoid
a.
Excessive Heat Loss on parts or all of duct system. According to accepted design practice any ductwork located in unheated areas such as a garage, basement or crawl space should have sealed joints and insulated.
b.
Open Ended Ductwork where by the return air is taken from a different area than the supply air to living space. Both supply and return need to be installed to the SAME heating space to give a Close Looped System. For example: An incorrect installation may get its return air completely from an unheated garage space with no supply leads into this space. This would cause the operator to fire the heat exchanger above an 85 degree temperature rise. For a properly designed forced air system the return air temperature should be no lower than 55-60 F to maintain certified temperature rise of 85F across the heat exchanger. Proper sized and installed Return Air grills are important to the safe operation of any forced air system but especially with solid fuel furnaces.
When installing Return Air grills they are normally situated centrally on each floor of the main living space. When branches are installed the SUM of each of the return air branches should equal the MINIMUM recommended Return Air requirements as stated on the certification labels. It is better to oversize Return Air ductwork and grills.
The Free Area of each grill should be matched to the cross section area of the ductwork connecting to it. Typical trussed steel Grill Sizes are:
All Return Air ductwork should be fully enclosed and of metal construction. Any ductwork connecting to Return Air grill between joist space should be designed to maintain minimum requirements.
Proper Joist Space Installation Maintaining Free Area Requirements
· Blockage in ductwork or over return air grills can cause unsafe operating conditions · Do not install Return Air Grills directly on plenum. · Do not install Return Air Grills in an enclosed furnace room. · Slope both supply and return air ductwork to promote gravity feed during power failures. · Refer to installation manual for complete installation recommendations
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