Lochinvar recommends the installation of barometric dampers in the flue of each unit when they are commonly vented. Since draft varies seasonally with changes in temperature, the barometric damper ensures that the unit will always see a constant draft. If the draft remains below the maximum setting, the damper remains closed and does not have an effect on the venting.
Lochinvar recommends the use of Type “B” double wall vent material in all category I vent systems. Lochinvar products provide a high thermal efficiency and transfer a large portion of the heat from the combustion process into the water. As a result, the flue gas temperatures are reduced. The use of a double wall Type “B” vent material provides an insulating gap to reduce radiant heat losses from the flue. This helps to maintain the heat in the flue products to ensure that proper draft is maintained and the flue products are vented to the atmosphere.
A barometric damper is set by adjusting the weights on the chain that controls the opening of the relief door on the barometric damper. A draft gauge must be used to read the draft below the damper and above the unit’s flue outlet. The damper must be installed in the vertical flue pipe off of the unit’s flue outlet. The barometric damper must be installed 3 to 4 feet above the flue connection to the unit. Adjust the weights on the damper to provide a negative draft of 0.04 to a 0.05 when the unit is firing at full rate on a typical cool day. As draft increases above this level, the door on the damper will open and maintain a constant draft at the unit.
Yes, it is acceptable to use Category IV vent material on a Category II vent system. The manufacturers of vent pipe only produce vent material for Category I or for Category IV vent systems. Any vent system that is other than Category I must use the Category IV material. The use of single wall vent material in a Category IV vent system is acceptable when a condensate tee is installed in the vent system.
The KNIGHT Heating Boiler, TurboCharger & Power Direct Vent Commercial Water Heaters and DVN, LVN & PVN Power Vented Residential Water Heaters are the only products currently produced than can be vented with a PVC pipe. PVC venting material is used in full condensing products and those that add sufficient dilution air to the flue products to always keep the temperature of the flue products below the maximum temperature rating for PVC.
The Efficiency+ and Copper-Fin II models are available with a sidewall vent system that does not require a separate induced draft fan for operation. These vent systems require the installation of a Category IV vent system.
The limits in vertical and horizontal run can best be evaluated by using the venting tables in the National Fuel Gas Code. These tables rate each vent diameter for a capacity in Btu’s based on both the vertical and horizontal run of the vent. There are separate columns for atmospheric combustion units (NAT) and fan assisted combustion units (FAN). As a general rule, the tables in the National Fuel Gas Code are based on a maximum horizontal run of flue not be more than 1 ½ feet for each inch of vent diameter. Operation of a flue with this maximum horizontal run must include a vertical height noted in the venting tables to generate adequate draft in the vent system. Any time the 1 ½ feet per inch of diameter length in horizontal run is exceeded, there is a very good chance that you will experience problems with the venting system.
The negative pressure vent appliances should be located as close as possible to the point where the vent system turns vertical to the termination and the induced draft fan.
All Category IV vent systems are required to use the AL29-4C vent material. Many Lochinvar products operate in a near condensing level of efficiency with vent product temperatures above the acceptable limits for PVC. This is especially true for heating boilers operating at high temperatures.
A barometric damper is used to maintain a specified draft at the point of flue connection to a boiler or water heater. The weighted door on the barometric damper is adjusted so that when draft below the damper exceeds the maximum desired draft, the door opens and draws air from the mechanical room to break the draft above the unit.
As long as the units are all classified as Category I vent units, as many as six flues can be combined to a common flue as long as the minimum input of a single unit firing meets the minimum Btu/hr requirements of the flue as noted in the National Fuel Gas Code vent tables. Carefully review the input at minimum fire for a single M-9 boiler. The Btu/hr output of a single stage of burners firing on an M-9 boiler may not provide adequate heat to operate a large diameter common vent. This may limit the number of units installed in a common flue or the size of the common flue.
The flue pipe installed on the vent connection to a Lochinvar boiler or water heater should have a minimum of three to four feet of vertical rise before an elbow or barometric damper is installed in the flue pipe. This will give the flue products adequate to time rise and generate the required draft in the flue before the products are turned and asked to move horizontally.
The four vent categories define whether the flue products are cooled to the point where they may condense in the flue or are will maintain a temperature above their dew point. The vent category also defines if the pressure in the flue is positive or negative.
Category I – Negative draft stack with flue product temperature above dew point
Category II – Negative draft stack with flue product temperature at or below dew point
Category III – Positive draft stack with flue product temperature above dew point
Category IV – Positive draft stack with flue product temperature at or below dew point
Only Category I vents from multiple units can be combined without an engineered vent system. An engineered vent system requires a special vent system with an induced draft fan to mechanically control the movement of flue products.
A bull head tee is when flue products enter both sides of the run of a tee and all flue products must then turn into the rise of the tee. This type of piping causes a high restriction at the point where the discharges from two flue connections meet against one another. This can result in a restriction or possible spillage of flue products as they attempt to turn vertical into a common flue. A common flue header is best designed with wyes for connection of each individual unit into a common header.
The damper companies show it sitting right on top of the boiler. Lochinvar boilers and water heaters use a fan assisted combustion process. The 3 to 4 feet of vertical rise ensures that any velocity pressure from the fans is fully dissipated and the flue products are now rising due to the natural buoyancy of the heated products of combustion. A tee installed directly on the unit’s flue discharge or very close to the unit may allow some flue gas spillage until adequate draft is established therefore a minimum vertical height at the point of flue connections is recommended.
The white flakey material is generally a zinc oxide. This is a result of condensate in the vent system. Flue gas condensate is acidic and attacks the zinc coating on the steel vent pipe. Sustained operation of a vent that is condensing will result in serious degradation of the flue pipe. When the protective zinc coating is reduced, the condensate will attack the steel base metal causing rust to appear. Sustained operation will result in holes rusting in the vent and the possibility of spilling gas flue products into an occupied living space. The vent system problems must be corrected before a hazardous vent condition occurs.
The draft should be measured in the vertical stack rising form the units flue connection. A hole should be drilled approximately 3 to 4 feet above the flue outlet and below an installed barometric damper. All draft measurement must be made with a draft gauge while the boiler is firing to properly evaluate vent performance.
The common vent must be installed in a Category IV AL29-4C vent material with a properly sized IVS fan and accessories.
The IVS system uses a variable speed motor to maintain a constant draft eliminating the need for a barometric damper in the vent system.
The flue connections from appliances of different vent categories can only be combined with the Lochinvar IVS engineered vent systems. All requirements for this type of vent system must be submitted to Lochinvar for review to ensure proper application.
The manufactures of vent material only produce Category I and Category IV vent material. A vent requiring a Category II vent system must use a Category IV vent material.
A barometric damper is set by adjusting the weights on the chain that controls the opening of the relief door on the barometric damper. A draft gauge must be used to read the draft below the damper and above the unit’s flue outlet. The damper must be installed in the vertical flue pipe off of the unit’s flue outlet. The barometric damper must be installed 3 to 4 feet above the flue connection to the unit. Adjust the weights on the damper to provide a negative draft of 0.04 to a 0.05 when the unit is firing at full rate on a typical cool day.
It is best to consult the installation and operating instruction for each specific model to determine the specific vent material requirements. Generally, all Category I negative draft appliances will be vented with Type “B vent material. When ever an optional vent system is selected there may be specific material restrictions for each product. Any vent system that is classified as a direct vent system will require a Category IV AL29-4C vent. This same AL29-4C material is also required on all Intelli-Fin and Power-Fin products.
As a general rule of thumb, as long as the vent is not more than two vent sizes larger it will generally work but you should always consult the vent tables in the National Fuel Gas Code (NFGC) to ensure proper operation. This especially true for fan assisted combustion units. The FAN column in the NFGC vent tables lists a minimum and maximum Btu/hr rating for each flue diameter. It is possible that a new fan assisted boiler may stage fire at a low input below the minimum required for a larger existing stack. In this case the flue products would not have enough heat to ensure a proper draft. This can result in flue gas condensate and flue gas spillage. Both are potentially dangerous so a careful review of the vent capacity must always be made to ensure safe operation.
The pressure sensor for the IVS system should be placed at the far end of the common manifold above the multiple units. Balancing baffles are installed in the discharge from each of the positive pressure flue to balance the draft from the IVS to each of the installed boilers.
The ANSI Z21.13 Low Pressure Steam and Hot Water Boiler Standard contains a test to determine vent category for heating boilers. The boiler is operated at a steady state condition. A stack with two 90° elbows and four feet of vertical flue pipe is installed on the vent of the boiler. A temperature measurement grid and multiple pressure points are installed in the discharge of this vent pipe. Based plotting of the temperature of the flue products as they relate to the CO2 concentration on a vent category curve contained in the ANSI standard and the pressure in the flue (negative or positive) the vent category is determined.
A draft gauge must be used. A small ¼” hole should be placed in the stack approximately 3 to 4 feet above the unit’s flue outlet and below any installed barometric dampers. Insert the tube from the draft gauge just into the flue and measure the draft on the scale as the unit is firing.