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DANGER

SOLVENT CEMENTS AND PRIMERS ARE HIGHLY
FLAMMABLE. PROVIDE ADEQUATE VENTILATION AND DO
NOT ASSEMBLE NEAR HEAT SOURCE OR OPEN FLAME. DO
NOT SMOKE. AVOID SKIN OR EYE CONTACT. OBSERVE ALL
CAUTIONS AND WARNINGS PRINTED ON MATERIAL
CONTAINERS. FAILURE TO FOLLOW THESE GUIDELINES
MAY RESULT IN FIRE, EXPLOSION OR AS-PHYXIATION
CAUSING PERSONAL INJURY OR LOSS OF LIFE. 

WARNING

THIS FURNACE AND ANY OTHER FUEL BURNING
APPLIANCE MUST BE PROVIDED WITH ENOUGH FRESH
AIR FOR PROPER COMBUSTION AND VENTILATION OF
THE FLUE GASES. MOST HOMES WILL REQUIRE THAT
OUTSIDE AIR BE BROUGHT TO THE FURNACE AREA.
FAILURE TO DO SO CAN CAUSE PERSONAL INJURY, OR
DEATH FROM CARBON MONOXIDE POISONING. 

NON-DIRECT VENT FURNACE
INSTALLATIONS 
(USING INDOOR COMBUSTION AIR) 

The furnace, although designed as a direct vent type
appliance, may be installed with the intake vent inside 
the structure. Non-direct vent installations require only an
exhaust vent pipe. 

Non-direct venting may be desirable when:

Using outdoor combustion air is not practical

The furnace is in a garage or attic 

Provisions are not made for routing of combustion air

The outdoor environment may contain contaminants
undesirable for combustion

Connecting a Non-Direct Vent to the Furnace 

When using indoor air or the non-direct vent
configuration, the combustion air inlet to the furnace must
be protected from blockage. Use a double elbow
arrangement if supplying combustion air through the top,
or a downward pointing single elbow if supplying
combustion air through the side.

WARNING

READ AND FOLLOW ALL INSTRUCTIONS IN THIS SEC-
TION. FAILURE TO PROPERLY VENT THIS FURNACE CAN
CAUSE CARBON MONOXIDE POISONING OR AN EXPLO-
SION OR FIRE RESULTING IN PROPERTY DAMAGE, PER-
SONAL INJURY OR LOSS OF LIFE.

If the furnace is to be installed in the vicinity of other
fuel burning appliances, adequate combustion air
must be available for the non-direct vent appliances.
See Section 10 of this manual, “Determining
Combustion Air.”

IMPORTANT

IN CANADA 

In addition to the general guidelines, in Canada, the non-
direct vent exhaust shall not terminate: 

• Directly above a paved sidewalk or paved driveway

which is located between two single-family dwellings
and serves both dwellings; 

• Less than 7 feet above a paved sidewalk or paved

driveway located on public property; 

• Within 6 feet of a mechanical air supply inlet to any

building; 

• Above a meter/regulator assembly within 3 feet

horizontally of the centerline of the regulator; 

• Within 6 feet of any service regulator vent outlet; 

• Less than 12” above grade level or anticipated snow

level; 

• Within 12” of any door, window, or non-mechanical air

supply inlet to any building; 

• Within 12” of the combustion air inlet of any other

appliance; 

• Underneath a veranda, porch or deck, unless (a) the

veranda, porch or deck is fully open on a minimum of
two sides beneath the floor, and (b) the distance
between the top of the vent termination and the
underside of the veranda, porch or deck is greater 
than 12”. 

IN THE U.S.A. 

In addition to the general guidelines, in the United States,
the non-direct vent exhaust shall be installed in accordance
with the following: 

• The clearance from the bottom of the terminal to grade
shall be 12” or increased to maintain 12” above the antici-
pated accumulated snow level. 

• The vent shall not terminate over public walkways or
over an area where condensate or vapor could create a
nuisance or hazard. 

• The vent terminal shall be installed 4 feet below, 4 feet
horizontally from, or 1 foot above any door, window, sof-
fit, under eave vent or gravity air inlet to the building. 

• The vent terminal shall have a minimum horizontal clear-
ance of 4 feet from electric meters, gas meters, regulators
and relief equipment. 

• Locate the vent terminal 3 feet above any forced air inlet
located within 10 feet. Any fresh air or make-up air inlet,
such as for a dryer or furnace area is considered a forced
air inlet. The vent terminal should be located no fewer
than 6 feet from an inside corner formed by two exterior
walls; a 10 foot distance is recommended. 

Recommended clearance from overhangs is a minimum of
1 foot vertically for each foot horizontally up to 6 feet. 

22

Summary of Contents for HG95E054

Page 1: ...ture reference USER S INSTRUCTION GUIDE INSTALLATION OPERATION AND MAINTENANCE MANUAL Model Serial Number Date of Purchase For future reference write down the model serial number and date of purchase Use these numbers in any correspondence or service calls concerning your furnace Keep these instructions for future reference CATEGORY IV NATURAL GAS AND LP GAS WARM AIR FURNACE LOCATED AFTER PAGE 43 ...

Page 2: ...ing Piping Length 18 Pipe Using A Concentric Venting Kit 19 Exhaust Vent 20 Exhaust Vent 21 Non Direct Vent Furnace Installations 22 Direct Vent Piping Termination 17 CONDENSATE DRAINS 25 Drain Hose Installation 25 Condensate Drain Installation 27 GAS SUPPLY 28 Gas Piping 28 Leak Testing 28 High Altitude 29 CONVERSIONS 29 Natural to L P Gas 29 to Natural Gas 29 Conversion Steps 29 HIGH ALTITUDE AI...

Page 3: ...he furnace Furnace for heating the home located in the attached garage for example 8 A gas fired furnace for installation in a residential garage must be installed so that the burners and ignitor are no less than 18 inches above the floor The furnace must be located or protected to avoid physical damage by vehicles 9 THIS FURNACE IS NOT TO BE USED FOR TEMPORARY HEATING FOR BUILDINGS UNDER CONSTRUC...

Page 4: ...SING BIRTH DEFECTS AND OTHER REPRODUCTIVE HARM UL AND CUL RECOGNIZED CO DETECTORS ARE RECOMMENDED FOR ALL BUILDINGS EQUIPPED WITH FOSSIL FUEL BURNING APPLIANCES ALL CO DETECTORS SHOULD BE INSTALLED IN ACCORDANCE WITH THEIR MANUFACTURER S INSTRUCTIONS AND APPLICABLE LOCAL BUILDING CODES WARNING THESE INSTRUCTIONS ARE INTENDED AS AN AID TO QUALIFIED SERVICE PERSONNEL FOR PROPER INSTALLATION ADJUSTME...

Page 5: ... wall horizontal vented gas fueled equipment It shall be the responsibility of the property owner to secure the services of qualified licensed professionals for the installation of hard wired carbon monoxide detectors a In the event that the side wall horizontally vented gas fueled equipment is installed in a crawl space or an attic the hard wired carbon monoxide detector with alarm and battery ba...

Page 6: ...l be required 4 Existing ductwork should be assessed for its air handling capabilities For residential applications the recommended air velocity of a supply air trunk duct is 700 feet per minute fpm and should not exceed 900 fpm The recommended air velocity of a supply air branch run is 600 fpm and should not exceed 900 fpm These values are slightly lower for flexible ducting The recommended air v...

Page 7: ...mpounds Polyurethane and similar derivatives fumes Printer s inks paint removers furniture strippers varnishes varsol toluene etc Water softener salts and chemicals LOCATION of UNIT General 1 The furnace is not weatherized Select a dry indoor location 2 Select a location where the exhaust and combustion air piping can be routed between the furnace and their terminations with a minimum of lengths a...

Page 8: ... OTHER COMBUSTIBLE MATERIAL EXCEPT WOOD INSTALLATION ON COMBUSTIBLE MATERIAL CAN RESULT IN FIRE CAUSING PROPERTY DAMAGE PERSONAL INJURY OR DEATH DANGER COMBUSTIBLE MATERIAL MUST NOT BE PLACED ON OR AGAINST THE FURNACE JACKET PLACEMENT OF COMBUSTIBLE MATERIALS ON AGAINST OR AROUND THE FURNACE JACKET CAN CAUSE AN EXPLOSION OR FIRE RESULTING IN PROPERTY DAMAGE PERSONAL INJURY OR LOSS OF LIFE 0 0 0 LO...

Page 9: ... entraining combustion gases from an adjacent fuel burning appliance or entraining combustion air for this furnace 5 Ensure that there is adequate space and accessibility for the air filter 6 If an air conditioning evaporator coil is required position it on the top of the furnace Ensure that no air can bypass the evaporator coil 7 Connect the supply air plenum to the supply air outlet Flexible duc...

Page 10: ...ace cabinet to prevent twisting or sagging General Considerations When choosing an installation position the installer must consider the following connections Combustion air intake Exhaust vent Gas pipe Electrical wiring Condensate drain trap Also consider the air conditioning connections a c drain access to filter s and access to furnace and a c for repair The blower compartment should be complet...

Page 11: ...upling bands 12 Tighten the vent clamp and secure in place using the screws provided FIGURE A RIGHT INDUCER POSITION FIGURE B LEFT INDUCER POSITION SUGGESTED METHOD FOR SUSPENDING HORIZONTAL FURNACE ALLOW ENOUGH ANGLE IRON OVERHANG TO PERMIT OPENING THE BLOWER DOOR 3 8 INCH THREADED ROD 2 INCH ANGLE IRON JAM NUTS LOCK WASHER FLAT WASHER SUPPLY AIR PLENUM RETURN AIR PLENUM SUSPENDED INSTALLATION IN...

Page 12: ...nducer drain connector will angle toward the front of cabinet with the second nested inside directed towards the top panel The 108 000 BTUH will require an extension between the inducer and the first elbow that is not provided If exhaust vent exits the left side panel the pipe can be routed straight outside the cabinet If exhaust vent exists the right side panel the inducer requires rotation The e...

Page 13: ...ide of the cabinet WARNING WHEN INSTALLED IN THE DOWNFLOW POSITION ON A COMBUSTIBLE FLOOR SUBBASE KIT IS REQUIRED FAILURE TO INSTALL SUBBASE KIT COULD RESULT IN FIRE DEATH OR SERIOUS INJURY The opening in the floor must provide adequate clearances to the combustible material A half inch of clearance will be required between the plenum and the combustible material If installed on a non combustible ...

Page 14: ...bow that is not provided If exhaust vent exits the left side panel the pipe can be routed straight outside the cabinet The pipe exiting the cabinet in any installation should be long enough to install the vent clamp on the outside of the cabinet Horizontal Right Installation In the horizontal left installation the combustion air and exhaust vent may exit through the top or right side of the cabine...

Page 15: ...r area from which the combustion and ventilation air will be drawn negative pressure could be a problem if natural infiltration from the outdoors does not match the rate at which air is exhausted IMPORTANT If planning to use the inside air of an unconfined space remember to test for proper furnace operation as well as other fuel burning appliances located within the unconfined space with respect t...

Page 16: ...ng salons Antistatic fabric softeners used in clothes dryers Carbon tetrachloride Chlorinated cleaners and waxes Chlorine and bromine based swimming pool chemicals Deicing salts or chemicals e g rock salt etc Dry cleaning fluids such as perchloroethylene Fumes from curing polyurethane and similar substances Halogen based refrigerants including R 12 and R 22 Hydrochloric acid muriatic acid and othe...

Page 17: ...ED TO THE FURNACE WITH SHEET METAL SCREWS TAPE THE SHEET METAL SEAMS IN THE VICINITY OF THE FURNACE WITH DUCT TAPE OR SIMILAR MATERIAL WHEN THE FURNACE IS MOUNTED ON A PLATFORM WITH RETURN AIR THROUGH THE BOTTOM IT MUST BE SEALED AIR TIGHT BETWEEN THE FURNACE AND THE RETURN AIR PLENUM THE FLOOR OR PLATFORM MUST PROVIDE SOUND PHYSICAL SUPPORT OF THE FURNACE WITHOUT SAGGING CRACKS OR GAPS AROUND THE...

Page 18: ...FOLLOW ALL VENTING GUIDELINES MAY RESULT IN ERRATIC FURNACE OPERATION FREEZE UP OF THE VENTILATION AIR PIPING OR SOOTING OF THE FURNACE DANGER SOLVENT CEMENTS AND PRIMERS ARE HIGHLY FLAM MABLE PROVIDE ADEQUATE VENTILATION AND DO NOT ASSEMBLE NEAR HEAT SOURCE OR OPEN FLAME DO NOT SMOKE AVOID SKIN OR EYE CONTACT OBSERVE ALL CAUTIONS AND WARNINGS PRINTED ON MATERIAL CONTAINERS FAILURE TO FOLLOW THESE...

Page 19: ...er location or installa tion can cause structural or exterior finish damage to the building Caulk all cracks seams or joints within a 6 foot radius of the termination Direct Vent Piping Termination General Guidelines The external portion of the piping in all cases is to consist of 2 pipe If 3 pipe is used between the furnace and terminal transition to 2 within 18 or less of the exterior wall When ...

Page 20: ... overhangs is a minimum of 1 foot vertically for each foot horizontally up to 6 feet As a protection against freezing do not expose a 3 x 2 reducing coupling to outdoor ambient temperatures Any adjacent painted surfaces should be in good condition no cracks peeling paint etc If wooden surfaces that may be periodically exposed to flue gases are present consider treating with a sealer Calculating Pi...

Page 21: ...entric vent terminal there must be a minimum of 12 clearance to grade or antici pated snow level There are no means available to raise the terminal externally If planning to use this terminal kit see The concentric vent termination kits may also be used in the vertical position A B C D E A B D F A A B B G E E D A A B B G VENT COMBUSTION AIR MAINTAIN 12 CLEARANCE 18 FOR CANADA ABOVE HIGHEST ANTICIP...

Page 22: ...to use one the screen may actually encourage the formation of rime ice which could cause the intake to become blocked in certain weather conditions Horizontal Exhaust Vent Termination Horizontal vents should pass through the exterior wall Figure 8 shows a standard horizontal vent detail Terminate the vent approximately 8 or more from the wall If it is not possible to obtain proper clearance to gra...

Page 23: ...equired if venting vertically through a roof The end of the exhaust pipe must be 12 higher than the entrance of the combustion air intake terminal The exhaust pipe extending through the roof must extend a minimum of 18 above any obstruction within an 18 horizontal distance VERTICAL TERMINATION OF COMBUSTION AIR AND EXHAUST VENT A B C TOP VIEW INTERIOR EXTERIOR C D J A B I A B E D C F H A A C D E E...

Page 24: ...ANT IN CANADA In addition to the general guidelines in Canada the non direct vent exhaust shall not terminate Directly above a paved sidewalk or paved driveway which is located between two single family dwellings and serves both dwellings Less than 7 feet above a paved sidewalk or paved driveway located on public property Within 6 feet of a mechanical air supply inlet to any building Above a meter...

Page 25: ...r appliances 10 000 Btuh 4 ft 121 cm below or to side of supply inlet to building or the 3 kW 12 in 30 cm for appliances opening 1 ft 30 cm above combustion air inlet to any other 10 000 Btuh 3 kW and 100 000 Btuh opening appliance 30 kW 36 in 91 cm for appliances 100 000 Btuh 30 kW K Clearance to a mechanical air supply 6 ft 183 cm 3 ft 91 cm above if within 10 ft inlet 305 cm horizontally L Clea...

Page 26: ...l air 6 in 15 cm for appliances 10 000 Btuh 6 in 15 cm for appliances 10 000 Btuh supply inlet to building or the 3 kW 12 in 30 cm for appliances 3 kW 9 in 23 cm for appliances combustion air inlet to any other 10 000 Btuh 3 kW and 100 000 Btuh 10 000 Btuh 3 kW and 50 000 Btuh appliance 30 kW 36 in 91 cm for appliances 15 kW 12 in 30 cm for appliances 100 000 Btuh 30 kW 50 000 Btuh 15 kW K Clearan...

Page 27: ... clamp to approximately 1 8 from the end of the hose 5 Fasten each drain hose to its inlet by tightening the hose clamps 6 Cut each drain hose near the blower division panel at the point where kinking is able to occur 7 Slide a hose clamp over the ends of the hose connect ing to the vent drain and condensate drain 8 Insert an end of the plastic elbow supplied into each hose 9 Cut hose lengths from...

Page 28: ...HORIZONTAL FLOW RIGHT CONDENSATE TRAP CONDENSATE TRAP HORIZONTAL FLOW LEFT UPFLOW DOWNFLOW CONDENSATE CONDENSATE TRAP TRAP FIGURE 11 FIGURE 12 FIGURE 13 FIGURE 14 26 ...

Page 29: ... Secure the condensate drain trap to the side of the fur nace using the mounting holes that were just drilled 5 Install one rubber grommet provided into each of the drain holes and then insert the 90 degree black drain tubes so that they extend down into the top of the drain trap Inside the top front cover connect the drain tubing from the flue connector to one of the drain pipes that were just in...

Page 30: ...HUTOFF VALVE AND GAS VALVE DURING ANY PRESSURE TESTING THAT EXCEEDS 1 2 P S I G 3 45 KPA w c 12 inches w c is recommended These pressures must be maintained while all other gas fired appliances are operating at maximum conditions exceed 10 5 inches w c inlet pressure with NG The gas valve has an adjustable internal regulator for controlling burner manifold pressure Burner manifold pressure is list...

Page 31: ...ace if applicable 1 Shut off electrical power to the furnace if applicable 2 Remove the upper front door to expose the gas train and burner assembly 3 Unfasten the ground joint union between the gas valve and gas supply piping if applicable 4 Unfasten the burner manifold pipe from the burner assembly It is held in place by 2 screws on either end of the manifold pipe 5 Remove the existing orifices ...

Page 32: ...5600 1 95mm 1 20mm 2000 3000 79200 75240 51480 48906 1 90mm 1 15mm 90 000 3000 4000 75600 71820 49140 46683 1 90mm 1 10mm 5 4000 5000 72000 68400 46800 44460 1 85mm 1 10mm 5000 6000 68400 64980 44460 42237 1 85mm 1 10mm 0 2000 108000 102600 70200 66690 1 95mm 1 20mm 2000 3000 95040 90288 61776 58687 1 90mm 1 15mm 108 000 3000 4000 90720 86184 58968 56020 1 90mm 1 10mm 6 4000 5000 86400 82080 56160...

Page 33: ... manifold first examine the gas piping system to ensure that it is correctly sized Pipe sizing is specified in ANSI Z223 1 NFPA 54 in the U S or the B148 Natural Gas and Propane Installation Code in Canada SETTING THE SUPPLY GAS PRESSURE 36G Valve Pressure Check Kit 1 Back inlet pressure test screw inlet outlet pressure boss out one turn counterclockwise not more than one turn with a 3 32 inch All...

Page 34: ...s are rated 120 VAC 60 Hz 1 phase The amperage rating is indicated on the furnace rating plate Each furnace requires a dedicated overcurrent device either a circuit breaker or a Type D time delay fuse It is permissible to connect furnace accessories such as humidifier transformers condensate pumps and electronic air cleaners If adding accessory equipment to the furnace circuit ensure that the comb...

Page 35: ... the main burners directly See the lighting instructions on the furnace To Start The Furnace 1 Remove the burner compartment access door 2 Shut off the electrical power to the furnace and set the room thermostat to its lowest setting 3 Ensure that the ignition system control switch on the gas valve is in the ON position 4 Replace the burner compartment access door 5 Restore electrical power to the...

Page 36: ...drops causing the room thermostat heating contacts to close 2 If pressure switch contacts are closed and have failed to open since the last cycle all subsequent steps will fail to occur 3 The induced blower begins a prepurge cycle of 15 seconds A momentary loss of gas supply flame blowout or a 4 The pressure switch contacts close The pressure switch contacts must close within 30 seconds If they fa...

Page 37: ...ce determine the air temperature rise of the furnace Insert a duct thermometer in the supply air duct The ther mometer should be placed as close as practical to the fur nace but out of the line of sight of the heat exchanger so to prevent a false reading due to radiated heat Ensure that the thermometer is within the duct air stream Avoid locations such as the inside radius of an elbow etc Insert a...

Page 38: ...nded that the heating airflow be set for the Nominal Plus setting when the furnace is matched for this cooling capacity Furnace is set at the factory for maximum cooling capacity and DIP switches must be field configured to match the cooling system 3 0 2 5 2 0 1 5 A B C D A B C D A B C D A B C D 2 5 2 0 1 5 1 0 Cool 3 0 2 0 2 5 1 5 Cool 5 0 3 5 2 5 1 5 4 0 3 0 2 0 1 0 Cool 5 0 3 5 2 5 1 5 4 0 3 0 ...

Page 39: ...commended that the Plus temperature rise is between 35 and 65 degrees F Heating Make adjustments to the controller with the electrical power off WARNING front blower shroud from furnace How To Remove The Blower 1 Disconnect power from furnace 2 Remove thermostat wiring from the integrated furnace control 3 Remove L1 Neutral and Ground connections between the integrated furnace control and the Furn...

Page 40: ...Y OR LOSS OF LIFE MAINTENANCE This is a critical connection Small amounts of corrosion can significantly increase the internal resistance of the connection A relatively small increase in resistance can result in a large decrease in flame signal Induced Blower The induced blower motor should be inspected and cleaned if necessary Clear any dust buildup from the ventilation ports Circulating Fan The ...

Page 41: ...TION WARNING heat and make a retrial for high every 5 or 10 minutes switch does not pull in the controller will continue in low finished and during the trial for ignition the high pressure If there is a demand for high heat low heat firing period is The fourth scenario heat the gas low the flame noise sounds deceptively like high heat should free it Note When the inducer is in high and gas valve t...

Page 42: ......

Page 43: ... limit trips 1 hour lockout Too many low pressure switch trips after ignition 1 hour lockout 1 hour lockout Reset by cycling power or thermostat CHECK and REPAIR 1 Replace Integrated Furnace Control 2 Rollouts or Fan failure see 5 Red Flashes 1 Pressure switch failure 2 Pressure switch tubing and wiring 3 Obstructions in air intake or exhaust flue system that prevent proper combustion air flow 1 P...

Page 44: ... ignition period If main flame is not sensed during trial for ignition system will shut off HSI element and main gas flow then go through another purge period and initiate another ignition trial A total of 4 ignition trials will be attempted before the system goes into lockout 1 Line voltage to L1 terminal of integrated furnace control must be 120 volts with reference to furncace chassis 2 Furnace...

Page 45: ...3 5 7 0 187 67 1 21752 8720 7 67 57 7 7 5 0 187 6 2 217 18286 2 7 23 5 7 21 7 7 5 0 187 6 2 217 18286 2 7 23 5 7 21 25 0 187 67 1 25 6 1 67 7 50267 7 803 5 1 6 72 6 7 72 0 187 725 8 7 6 77 1 8720 7 67 1 86 7 7 2 67 7 21752 3529 6 029 803 5 72 6 7 7 1 8720 7 43 7 50267 7 ...

Page 46: ...CE DO NOT TOUCH ANY ELECTRICAL SWITCH DO NOT USE ANY PHONE IN YOUR BUILDING LEAVE THE BUILDING IMMEDIATELY IMMEDIATELY CALL YOUR GAS SUPPLIER FROM A PHONE OUTSIDE THE BUILDING FOLLOW THE GAS SUPPLIER S INSTRUCTIONS IF YOU CANNOT REACH YOUR GAS SUPPLIER CALL THE FIRE DEPARTMENT INSTALLATION AND SERVICE MUST BE PERFORMED BY A QUALIFIED INSTALLER SERVICE AGENCY OR THE GAS SUPPLIER DO NOT USE THIS FUR...

Page 47: ... must be in place during normal furnace operation Attempting to operate the furnace with missing doors or panels could lead to the creation of carbon monoxide gas 4 If the furnace is installed in a confined space or if you intend to build a furnace room where insulation is present be aware that some insulating materials are combustible Do not allow building insulating materials to come into contac...

Page 48: ... valve Ensure that the Gas Valve Control is in the ON position see Figure 3 at right 9 Replace the burner access door ensuring that it is properly in place 10 Restore the electric power to the furnace 11 Adjust the thermostat to the desired setting If the thermostat also controls an air conditioning system ensure that the thermostat system switch is in the HEAT or AUTO mode If this is the first ti...

Page 49: ...e 2 Pull the filter out the front 3 Replace with a fresh filter and reconnect power to the furnace The filter will have an arrow indicating proper airflow direction DO NOT OPERATE YOUR FURNACE OR AIR CONDITIONER WITHOUT AN AIR FILTER FIGURE 4 AIR FILTER The furnace should be well supported on a level floor or by the means used to suspend the furnace in a horizontal configuration Base support shoul...

Page 50: ...ntioned in the sequence of operation points 5 and 9 will be ignored The furnace achieves its mid efficiency in two general areas First there is no wasteful standing pilot The furnace consumes no gas in between cycles Secondly the furnace is designed to allow very small amounts of excess air in the combustion process Older furnaces had heat exchangers that were commonly 40 larger than necessary for...

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