Hearth Venting Manual Mechanical Venting of Fireplaces
Published by ENERVEX Inc. 1685 Bluegrass Lakes Pkwy. Alpharetta, GA 30022 First Edition - 2005 Second Edition - 2007 Third Edition - 2009 Fourth Edition - 2011 Fifth Edition - 2014 Hearth Venting Manual, Fifth Edition Copyright © 2014, 2011, 2009, 2007, 2005 by ENERVEX Inc., Alpharetta, Georgia 30004. All rights reserved. No part of this book may be reproduced, in any form or by any means, without permission in writing from the publisher. Requests for permission should be made to ENERVEX Inc.
Table of Contents INTRODUCTION.................................................................................................................... 1. VENTING IN GENERAL................................................................................................. 1.1 Designing Venting Systems..................................................................................... 1.2 Gravity vs. Mechanical Venting................................................................................ 2.
Introduction The primary purpose of this manual is to provide more detailed guidance on gravity venting and mechanical venting of decorative wood- or gas-fired heating appliances than can be found in the codes or in the appliance manufacturers’ instructions.
1. Venting in General 1.1 Designing Venting Systems Gravity venting uses the difference in gravity of cold vs. warm air to create draft for the heating appliance. Gravity venting is very sensitive to the temperature of the products of combustion, the ambient/outdoor temperature, the barometric pressure and wind. It is difficult, if not impossible, to adjust the draft to changing conditions.
2. Venting Problems and Possible Solutions As mentioned earlier, a well-designed and well-functioning venting system is more important for successful wood and gas burning than a good stove or fireplace. The surface of the pipe is also important. A corrugated or rough surface causes more flow resistance than a smooth surface. For a venting system to work properly, the draft MUST exceed the flow resistance. Otherwise there will be no movement of flue gases.
2.1.1. Problems associated with the venting system Problem Description Can Occur when.. Possible Solutions The chimney flue is too small. A chimney may be severely restricted if the inner diameter of the flue is too small. The velocity of the flue gas reaches a point where the flow resistance is so substantial that the flow resistance exceeds the draft. • A chimney is relined and the diameter thus reduced. • Redesign and rebuild the chimney to meet the draft requirements.
Problem Description Can Occur when.. Possible Solutions The chimney is too high. Increasing the height of a chimney increases the draft. Draft increases in proportion with chimney height but only to a certain point. At some point, additional height gives the flue gases more time to transfer heat to the flue walls and cool off. This will cause a reduction in the available draft.
2.1.2 Problems associated with the heating appliance The chimney is not the only culprit. The heating appliance itself can be the problem and cause spillage or improper combustion. Heating appliance problems depend on the appliance type. Fireplaces and stoves experience different problems: Problem Description Can Occur when.. Possible Solutions Oversized fireplace opening Generally speaking, there should be a 1:10 relationship in the cross-sectional area between flue size and fireplace opening.
Problem Description Can Occur when.. Possible Solutions The appliance is a seethrough fireplace Among critical fireplaces is the so-called “see-through” fireplace – a fireplace that is open into two rooms. The fireplaces must capture the air in the same way as an exhaust hood, which requires good draft in order to maintain a high velocity over the fireplace opening. Very often turbulence can be experienced inside the smoke chamber, and smoke problems can occur.
2.1.3 Problems associated with the building/house In the past, heating engineers often used high indoor pressure to keep cold air from infiltrating. When houses were leaky (before energy awareness), it was thought better to force warm air out through cracks to prevent cold air from infiltrating. In current homes and buildings, pressurized conditioned air is being pushed through walls and ceilings.
Problem Description Can Occur when.. Possible Solutions Stack effect created inside the building Stack effect is a symptom primarily experienced in multistory buildings. The stack effect in itself is not a problem. It is a very common phenomenon in high-rise buildings where it is ‘enhanced’ by the existence of elevators that constantly change the pressure when ascending and descending.
2.1.4 Problems associated with the building’s environment Problem Description Can Occur when.. Tall trees surrounding the building It doesn’t take much to • Trees are growing and affect the draft. A tall tree in getting taller over the years the vicinity of the chimney can create turbulence that, at times, may cause spillage in the heating appliance served by the chimney.
Problem Description Can Occur when.. Possible Solutions The wind is creating a downdraft Wind induced downdraft is a common draft problem – and often it’s only occasional. It may only occur on a windy day when the wind is blowing from a certain direction. Wind induced downdraft is caused by “eddies” – or flow patterns around the building and the chimney. • The downdraft can be caused by windloading. This is a scenario where eddies, or flow patterns, create an unfavorable draft condition.
3. Venting Standards and Codes All types of venting of a heating appliance, whether this is wood or gas fired, are governed by a national or local code. It’s worth mentioning that according to the code, a smoking fireplace is in fact a code violation that requires a correction. The standards can be made by an independent organization, like National Fire Protection Association (NFPA) or by industry-related organizations.
(b) The mechanical draft system shall be listed in accordance with UL 378, Standard for Draft Equipment, for use with the type of appliance and range of chimney service appropriate for the application. The mechanical draft system shall not cause or permit blockage of the flue or electrical hazard after exposure to a chimney fire or over fire conditions.
5. A vent cap shall be installed to prevent rain from entering the vent system. 804.3 Mechanical draft systems. Mechanical draft systems of either forced or induced draft design shall comply with Sections 804.3.1 through 804.3.7. 6. The vent termination shall be located at least 3 feet (914 mm) horizontally from any portion of the roof structure. 804.3.1 Forced draft systems.
NFPA54 / ANSI Z223.1: (c) Industrial appliances as provided in 12.3.4. In this code the installation of a mechanical draft system must meet the following requirements: (d) Direct-vent systems as provided in 12.3.5. (e) Appliances with integral vents as provided in 12.3.6. 12.4.3 Mechanical Draft Systems. (f) Mechanical draft systems as provided in 12.4.3. 12.4.3.
The International Fuel Gas Code is also virtually identical to NFPA 54 when it comes to the venting termination: 503.6.4 Gas vent terminations. A gas vent shall terminate in accordance with one of the following: 1. Gas vents that are 12 inches (305 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate above the roof in accordance with Figure 503.6.4. 2.
A venting system that terminates in the sidewall of a structure shall terminate at least 3 ft (0.9 m) above any air inlet to the structure that is within 10 ft (3 m) of the termination point. Exception No. 1: This requirement shall not apply to the combustion air intake of a direct vent appliance. Exception No. 2: This requirement shall not apply to the separation distance between the circulating air inlet and the vent discharge of a listed outdoor appliance.
4. Venting System Design 4.1. Gravity Systems from 4 inch ID all the way up to 60 inch ID. Sizes up to 12 inch ID are often considered “residential” sizes while sizes larger than 12 inch are considered “commercial”. The size of a chimney affects its capacity and how much product of combustion it can remove. Each size has a specific usable area, which is called the “effective area”. This area, along with the chimney height, determines the chimney’s capacity. 4.1.
The figure below shows the effective area of different flue shapes: 4.1.2.3 Pre-fabricated wood or coal stoves Stoves are supplied without a chimney. Again the chimney must be supplied by the installer, unless an existing chimney is used for the venting. The manufacturers’ recommendations are limited to type of chimney, diameter, maximum number of elbows and height restrictions. 4.1.2.
of normal design cannot cope with mechanically induced reverse flow or shortages of combustion air. In such circumstances, a fireplace should include a mechanical draft system of sufficient capacity to overcome other mechanized air-consuming systems. it may be possible to recess the fan into the cavity of the chimney. The fan must have adequate ventilation available, so it cannot be completely enclosed.
5. Mechanical System Design 5.1 Design Guidelines for Mechanical Venting of Gas and Manually Fired Appliances Fireplace Type There are two ways to determine the chimney fan type and size for the specific application. One-sided Formula to determine opening size AxH One alternative is to calculate the flue gas volume and the flow resistance and then select the chimney fan that meets the calculated requirements. This is normally referred to as an “approved engineered method”.
Fireplace Opening (sq.in.) - Wood Example: A two-sided fireplace measures 24” x 36” on the largest size. The opening measures 864 sq.in. Multiply by 2 and the opening used for the selection table is 1,728 sq.in. Eff. Flue ID 400 5 6 Step 2 - Determine the size of the chimney opening For this method a chimney or flue opening must be expressed as the inside diameter in inches. For a round chimney or flue this is not a problem as the size is expressed as 9”ID, indicating the inside diameter is 9”.
Special applications Fireplaces with two flues: When a fireplace is served by two flues of identical sizes, two fans are recommended – one for each flue. To size up such a system, take the total area of the appliance opening and divide by two. Then select fans as if there are two fireplaces each with one flue. Step 4 - Select a fan from the sizing table Select fan from sizing table Opening in sq.in. Example: A wood-fired fireplace with 2,400 sq.in.
Wood-Fired Fireplace 6. Guide for Mechanical Draft Systems There are a number of different ways to use mechanical venting systems. The following presents a variety of these applications. System 1 Chimney Fan 6.1 Mechanical Draft System for Wood-Fired Fireplace with a Single Flue Junction Box Application This is the most common form of installation and is used in all jurisdictions where the 2000 or later edition of the NFPA211 has not yet been adopted. Sequence of Operation 1.
Wood-Fired Fireplace 6.2 Mechanical Draft System for Wood-fired Fireplace with Multiple Flues System 2 Application Chimney Fans This is used in the same situations as System 1, but where multiple fans are required to handle the heat load. It is a typical installation for large fireplaces where a single flue cannot handle the amount of exhaust gases generated. Junction Box Junction Box *For one fan serving two flues please refer to section 6.1 as the wiring diagram is identical.
Wood-Fired Fireplace 6.3 Mechanical Draft System for a Wood-fired Fireplace with Safety System per NFPA211/IMC-2000 edition (and after) System 3 Chimney Fan Application Junction Box with Control Unit In jurisdictions where the 2000 or later edition of the NFPA211 has been adopted, there are new requirements for the use of mechanical draft systems in conjunction with solid fuel. The installation requires a safety control such as the EFC 211 Fan Control. Sequence of Operation EFC211, Fan Control 1.
Wood-Fired Fireplace 6.4 Mechanical Draft System for a Wood-fired Fireplace with Manual Damper and Safety System per NFPA211/IMC-2000 edition (and after) System 4 Application MFD Automated In jurisdictions where theDamper 2000 or later edition of the NFPA211 has been adopted, there are new requirements for the use of mechanical draft systems in conjunction with solid fuel. The installation requires a safety control such as the EFC 211 Fan Control. MFD-S Manual Damper ADC100 Sequence of Operation 2.
Gas-Fired Fireplace 6.5 Mechanical Draft System for a Gas-Fired Fireplace with a single flue with Safety System per NFPA54/IFGC System 5 Application This is the simplest form of installation when used with a gas fireplace. The set-up can be used with virtually any type of gas-fired heating appliance. Sequence of Operation FSC Fan Speed Control 1. Turn the fan speed control on by turning the knob clockwise. A “click” indicates the control is turned on. Adjust the knob to the desired speed. 2.
Gas-Fired Fireplace 6.6 Mechanical Draft System (automated) for a Gas-Fired Fireplace with a Single Flue with Safety System per NFPA54/IFGC System 6 Application This is the most automated type of installation for a gas fireplace application. The ADC100 control monitors both operation and the safety system. No adjustments are necessary after the system is installed and commissioned. The ADC100 does not have to be visible and can be installed in the attic.
Gas-Fired Fireplace 6.7 Mechanical Draft System for a Gas-fired Fireplace with multiple flues with Safety System per NFPA54/IFGC System 7 Chimney Fans Application This is used in the same situations as System 5, but where multiple fans are required to handle the exhaust volume. It is a typical installation for large fireplaces where a single flue cannot handle the amount of exhaust gases generated. Chimney Probe This is a simple form of installation when used with a gas-fired fireplace.
Gas-Fired Fireplace 6.8 Mechanical Draft System for a Gas-fired Fireplace with multiple flues and Safety System per NFPA54/IFGC System 8 Chimney Fans Application This is used in the same situations as System 6, but where multiple fans are required to handle the exhaust volume. It is a typical installation for large fireplaces where a single flue cannot handle the amount of exhaust gases generated. Chimney Probe *For one fan serving two flues please refer to section 6.
Gas-Fired Fireplace 6.9 Mechanical Draft System for a Gas-fired Fireplace with Damper and Safety System per NFPA54/IFGC System 9 Application This installation shows a combination fireplace and damper system. The ADC100 control monitors fan and damper operation and the safety system. No adjustments are necessary after the system is installed and commissioned. The ADC100 does not have to be visible and can be installed in the attic. Proven Draft Switch is part of ADC100 control.
Gas-Fired Fireplace 6.10 Mechanical Draft System (automated) for a Gas-Fired Fireplace with Modulating Fan Speed and a Single Flue with Safety System per NFPA54/IFGC System 10 Application This is the most automated type of installation for MFD Automated a gas fireplace application. The ADC150 control Damper monitors both operation and the safety system. No adjustments are necessary after the system is installed and commissioned.
Gas-Fired Fireplace 6.11 Mechanical Draft System for a Gas-Fired Fireplace with Modulating Fan Speed, Damper and a Single Flue with Safety System per NFPA54/IFGC System 11 Application This installation shows a combination fireplace and damper system. The ADC150 control monitors fan and damper operation and the safety system. No adjustments are necessary after the system is installed and commissioned. The ADC150 does not have to be visible and can be installed in the attic.
Gas-Fired Fireplace 6.12 Mechanical Draft System for a Gas-fired Fireplace with Modulating Fan Speed and multiple flues and Safety System per NFPA54/IFGC System 12 Chimney Fans Application This is used in the same situations as System 6, but where multiple fans are required to handle the exhaust volume. It is a typical installation for large fireplaces where a single flue cannot handle the amount of exhaust gases generated.
7. Frequently Asked Questions Q. Does the fan always have to be on when I have a fire in the fireplace? A. The motor can only be cooled when the chimney fan is operating, thus the fan should always be on when you have a fire in the fireplace. Otherwise, you may reduce the longevity of the fan. You may, however, run it at a very low speed. Q. What if the chimney has a constant downdraft and odor when not in use? A. Leave the fan running continuously at a very low setting. Q. Is the fan noisy? A.
Appendix A: Design Theory Fireplaces with natural draft chimneys follow the same gravity fluid law as gas vents and thermal flow ventilation systems. One-sided fireplaces for solid fuel In a one-sided fireplace a total front velocity of 3648 FPM with a mean chimney temperature of min. 300°F should provide a good combustion and a wellworking fireplace.
Stoves and fireplace inserts - transition from firebox to flue Stoves are different from open fireplaces due to the fact that they have a small inlet for the combustion air. However, the worst-case scenario occurs when the door is open, so this is the situation the sizing should be based on. In addition there are “external” factors influencing the resistance: - internal building pressure - external building pressure Again, use the airflow formula with a recommended frontal inlet velocity of 36-48 FPM.
Component resistance Example: ASHRAE has set up a range of k-values for different types of components in a chimney system. Chimney and stack manufacturers have set specific values for their own products. A list of component k-values can be found in Appendix C. Theoretical draft, Dt - 0.138 “WC Static Pressure Loss, Ps + 0.100 “WC Available draft, Da - 0.
5. Determine available draft Da = -Dt + Ps = -0.091 + 0.039 = -0.052”WC The available draft is negative so the system should work. If the draft is positive, adjustments can be made to the system to make it negative. There are two ways to solve this problem: increase the chimney height or increase the chimney diameter. Analyzing other factors If the fireplace and chimney seem to be sized correctly, but there is a smoke problem, other information may be needed.
Appendix B: Conversion table from rectangular to round flues B A Equivalent Diameter (ID) (inch) A B 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 4 4 4 5 5 5 6 6 6 6 6 6 6 6 6 7 7 7 5 4 5 5 6 6 6 7 7 7 7 7 8 8 8 8 8 8 6 5 5 6 6 7 7 8 8 8 8 8 9 9 9 9 9 9 7 5 6 6 7 7 8 8 9 9 9 9 10 10 10 10 10 10 8 5 6 7 7 8 8 9 9 10 10 10 10 11 11 11 11 11 9 6 6 7 8 8 9 9 10 10 11 11 11 12 12 12 12
Sources and References: 1) 2008 ASHRAE Handbook, HVAC Systems and Equipment, 2000 2) International Fuel Gas Code, International Code Council, 2009 Edition 3) NFPA 211 Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2010 Edition. 4) 2009 National Fuel Gas Code (NFPA54/ANSI Z223.1), 2006 Edition 5) 2009 International Mechanical Code, International Code Council, 2006 Edition. 6) UL (1996). Standard for Gas Vents. UL441, Northbrook, IL: Underwriters Laboratories, Inc. 7) UL (2001).
The products RS Chimney Fan Made of high quality, recycled cast aluminum, RS Chimney Fans keep the perfect draft for a long time. The fan features a quiet, enclosed pre-lubricated motor and is recommended to be used with gas or oil fireplaces, stoves, ovens, furnaces, water heaters, BBQs, and pizza ovens. FSC variable Fan Speed Control comes standard with the fan. RSHT Chimney Fan The RSHT Chimney Fan is a high temperature exhaust fan used to maintain proper draft in a solid fuel chimney or stack system.
ADC150 Draft Control The ADC150 Control, for gas appliances, monitors the draft and will maintain the proper draft set-point by modulating the chimney fan speed whenever needed. When the user turns the fireplace or appliance off, the control leaves the damper open until all residual combustion products have been exhausted. EFC 211 Control Use the EFC211 control with wood-fired heating appliances to control the proper speed of the chimney fan. The EFC211 fan control features an audible and visual alarm.
ENERVEX Inc. 1200 Northmeadow Pkwy. Suite 180 Roswell, GA 30076 USA P: 770.587.3238 F: 770.587.4731 T: 800.255.2923 info@enervex.com www.chimneyfans.