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Pre-Installation Application Guide

MFC Series Boiler

Vent and Combustion Air Guide

Applies to Models 3000 through 10000

Exhaust venting, combustion air and piping

requirements for MFC Series boilers

Other documents for this product include:

OMM-0104 GF-148 MFC-Series User Manual

OMM-0108 GF-148-IN MFC-Series Installation Manual

TAG-0077 GF-148-E MFC-Series Electrical Power Guide

TAG-0078 GF-148-G MFC-Series Gas and #2 Oil Supply Guide

TAG-0081 GF-148-B MFC-Series Boiler Application Guide

Disclaimer

The information contained in this manual is subject to change without notice

from AERCO International, Inc. AERCO makes no warranty of any kind with

respect to this material, including, but not limited to, implied warranties of

merchantability and fitness for a particular application. AERCO International is

not liable for errors appearing in this manual, not for incidental or consequential

damages occurring in connection with the furnishing, performance, or use of

these materials

TAG-0080_OG • GF-148-V • 3/29/2023

 MFC Series Boiler Vent and Combustion Air Guide 
 
 
 TAG-0080_OG •GF-148-V •3/29/2023 Technical Support •(800) 526-0288 •Mon-Fri, 8 am - 5 pm EST Page 2of 

Table of Contents 
General .............................................................................................................................3 
Approved Vent Materials...................................................................................................3 
Code Required Vent Terminations....................................................................................4 
Combustion Air Supply......................................................................................................5 
1 Combustion Air from WITHIN the Building..................................................................6 
2 Combustion Air from OUTSIDE the Building..............................................................7 
3 Two-Permanent-Openings Method (USA Only).........................................................7 
4 One Permanent Opening Method ..............................................................................9 
5 Opening a Louver Through the MFC Series Boiler....................................................9 
Direct Vent/Ducted Combustion Air ................................................................................10 
1 Optional Air Intake Adapters ....................................................................................10 
Exhaust Vent and Combustion Air Systems ...................................................................12 
Gross Natural Draft .........................................................................................................12 
Acceptable Pressure Ranges..........................................................................................12 
Exhaust Fans ..................................................................................................................12 
Corrections for Altitude....................................................................................................13 
Manifolded Systems........................................................................................................13 
Elbow Quantity and Separation.......................................................................................13 
Exhaust Muffler And Air Inlet Attenuator Guidelines.......................................................13 
Vent and Combustion Air System Design Requirements................................................14 
Condensate Removal......................................................................................................14 
Individually Vented Systems ...........................................................................................15 
1 MFC Series Pressure Drop Calculation Example..................................................15 
Manifolded Ducted Combustion Air.................................................................................17 
Common Vent Breeching (Manifolded)...........................................................................19 
Pressure Drop and Draft Data Tables.............................................................................21 
 
 

MFC Series Boiler Vent and Combustion Air Guide

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1. General

The AERCO MFC gas-fired or fuel oil-fired (backup) boiler is a high efficiency, forced draft,

hydronic-heating unit with unique venting capabilities. All MFC venting options (which include

horizontal and vertical discharges, direct vent, and manifolded vent breeching), typically exceed

the capabilities of competing combustion equipment. These and other features enable MFC

boilers to provide extremely high thermal efficiencies and optimum temperature control under

widely varying conditions. It is therefore critical that the flue gas vent and combustion air system

be designed to maintain these objectives.

MFC’s high efficiency is achieved through air/fuel modulation and the release of energy from

the moisture condensing in the combustion products. Because condensation can occur in the

exhaust vent system, means must be provided to remove the moisture accumulation. Each MFC

model is fitted with a condensate removal trap, as indicated in Figure 1, which illustrates the

vent connection and condensate removal connection for the MFC 3000, MFC 4000, MFC 5000,

MFC 6000, MFC 8000, and MFC 10000 models.

The design guidelines in this bulletin provide broad latitude while meeting the objectives of

safety, longevity and optimum performance.

2. Approved Vent Materials

The MFC boiler is a Category II, III, and IV appliance, which requires special attention to exhaust

venting and combustion air details. The exhaust vent MUST be UL listed for use with Category II

and IV appliances. The following materials are allowed:

The MFC 3000, 4000, 5000, 6000, 8000, and 10000 boilers can use only AL29-4C venting

materials. Polypropylene, PVC, and CPVC are NOT allowed.

TABLE 1: Flue System Requirements –Minimum Thickness for AL29-4C

DIAMETER

WALL

THICKNESS

DIAM.

WALL

THICKNESS

DIAMETER

WALL

THICKNESS

0.015"

0.020"

20"

0.024"

0.015"

10"

0.020"

22"

0.024"

0.015"

12"

0.020"

24"

0.024"

0.015"

14"

0.020"

26"

0.034"

0.015"

16"

0.020"

28"

0.034"

0.015"

18"

0.024"

30"

0.034"

Proper clearances to combustibles must be maintained per UL and the vent manufacturer

requirements. The UL, National Fuel Gas Code (ANSI Z223.1/ NFPA54)1, NFPA 31 Standard for

the Installation of Oil-Burning Equipment, and CSA B149.1-10 guidelines are often the basis for state

and local codes. AERCO's recommendations follow the guidelines of these agencies, unless

more stringent codes govern the installation site. The venting and combustion air systems must

meet all applicable code requirements. AERCO will not be responsible for failure of the system

design to meet code requirements.

All Canada installations must comply with CSA B149.1 installation code.

MFC Series boilers have the capability to condense on #2 fuel oil if the fuel oil has a low sulfur

content (<15 ppm) and return temperatures are no less than 140 degrees Fahrenheit. For

applications which shall take advantage of this capability, please be sure to utilize the appropriate

venting specified above that has been approved for oil fired equipment and condensing on fuel

oil.

MFC Series Boiler Vent and Combustion Air Guide

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3. Code Required Vent Terminations

The guidelines provided in this bulletin should be followed to comply with AERCO, UL, NFPA 54

(National Fuel Gas Code, ANSI Z223.1), NFPA 31, and in Canada: CSA B149.1-10

recommendations and regulations.

Vent terminations should be at least 4 feet below, 1 foot above or 4 feet removed horizontally

from any window, door or gravity air inlet of a building. Such terminations should extend beyond

the outside face of the wall by at least 6 inches.

Figure 1: Location and Piping of the Two Condensate Drain Ports

The bottom of the vent termination should be at least 12 inches above both finished grade and

any maximum snow accumulation level to avoid blocking the vent or air intake. The vent

termination should be least 3 feet above any forced-air building inlet within 10 feet. Design must

prevent flue gases from recirculating through the boiler air intake.

Vents should not terminate over public walkways or areas where condensate or vapor could

create a nuisance or be detrimental to the operation of regulators, meters or related equipment.

Discharges should not be located in high wind, wind-blocked areas or corners, or be located

directly behind vegetation. Discharges in these locations may cause the flue pressures to fluctuate

and result in flame instability. As a general rule, designs should minimize wind effects.

Wall and roof penetrations should follow all applicable codes and the vent manufacturer's

instructions. Vents should never be installed at less than required clearances to combustible

materials, as enumerated in UL, NFPA, CSA B149.1-10 or local codes "Double-wall" or “Thimble”

assemblies are required when vents penetrate combustible walls or roofs.

Vertical discharges should extend at least 3 feet above the roof through properly flashed

penetrations, and at least 2 feet above any object within a 10-foot horizontal distance.

Vertical and horizontal discharges should be designed to prevent rain from entering the vent.

Large-mesh screens can be applied to protect against the entry of foreign objects but the 'free

area' should be at least equivalent to the flue cross-sectional area when unrestricted.

CONDENSATE TRAP

VENT OUTLET

CONNECTION

MFC BOILER

TO DRAIN

UNDER SIDE OF EXHAUST CHAMBER

SHOWING THE TWO CONDENSATE PORTS

CAUTION! PORTS MUST BE PIPED

TOGETHER BEFORE THE TRAP.

DRAIN

PIPING

CONDENSATE

DRAIN PORTS

MFC Series Boiler Vent and Combustion Air Guide

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If the vent system is to be connected to an existing stack, the stack must be UL listed for Category

II and IV appliances (capable of 350F, positive pressure and condensing flue gas operation).

Masonry stacks must be lined, and the vent penetration must terminate flush with, and be sealed

to, this liner. Vents may enter the stack through the bottom or side. All side connections must

enter at a 45-degree connection in the direction of flow and must enter at different elevations, with

the smallest vent connection at the highest elevation. MFC vents must not be connected to other

manufacturer’s equipment.

The exhaust vent must be pitched upward toward the termination by a minimum of ¼ inch per

foot of length. Condensate must flow back to the MFC unit freely, without accumulating in the

vent.

4. Combustion Air Supply

The MFC boilers require the following combustion air volumes when operated at full capacity.

TABLE 2: Required Combustion Air

Volumes (at Full Capacity)

UNIT

VOLUME

MFC 3000

700 SCFM

MFC 4000

935 SCFM

MFC 5000

1170 SCFM

MFC 6000

1400 SCFM

MFC 8000

1870 SCFM

MFC 10000

2335 SCFM

These flows MUST be accommodated. Air supply is a direct requirement of NFPA, CSA B149.1-

10 (Canada) and local codes that should be consulted for correct design implementation.

In equipment rooms containing other air-consuming equipment ― including air compressors and

other combustion equipment ― the combustion air supply system must be designed to

accommodate all such equipment when all are operating simultaneously at maximum capacity.

Combustion air intakes must be located in areas that will not induce excessive (>0.10" water

column (W.C.)) intake air pressure fluctuations. Designs should take into account equipment

blowers and exhausts when using room air for combustion.

Intakes should be located to prevent infiltration of chlorides, halogens or any other chemicals that

would be detrimental to the operation of combustion equipment. Common sources of these

compounds are swimming pools, degreasing compounds, salts, plastic processing and

refrigerants. When the environment contains these types of chemicals, the air MUST be supplied

from the outdoors using direct-vent/ducted-combustion ductwork.

Air intakes must not be located in the proximity of garages, industrial and medical hood venting,

loading docks or refrigerant vent lines. Boilers should not be installed in the proximity of activities

that generate dust if that dust can enter the boiler intake. Boilers should be located to prevent

moisture and precipitation from entering combustion air inlets.

When a boiler is used, temporarily, to provide heat during ongoing building construction or

renovation, accumulated drywall dust, sawdust and similar particles can:

•Accumulate in the unit’s combustion air intake and block combustion air flow.

•Accumulate over the burner surface and restrict flow of air/fuel mixture.

MFC Series Boiler Vent and Combustion Air Guide

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In these situations, AERCO recommends that a disposable air intake filter be installed,

temporarily, above the boiler combustion air inlet. Air filters may be required year-round in

instances in which dust or debris can enter the combustion air tube. Consult the boiler Operations

and Maintenance Manual for details.

Combustion air temperatures as low as -30°F can be used without affecting the integrity of the

equipment; however, the combustion settings may require adjustment to compensate for site

conditions.

4.1 Combustion Air from WITHIN the Building

Where combustion air will originate from within the building, air must be provided to the equipment

room from two permanent openings to an interior room (or rooms). Openings connecting indoor

spaces shall be sized and located in accordance with the following:

•Each opening shall have a minimum free area of 1 inch2per 1,000 BTU/hr (2,200

mm2/kW) of total input rating of all appliances in the space, but not less than 100 inch2

(0.06 m2).

•One opening shall commence within 12 inches (300 mm) of the top of the enclosure, and

one opening shall commence within 12 inches (300 mm) of the bottom. (See Figure 2).

•The minimum dimension of air openings shall be not less than 3 inches (80 mm).

Figure 2: All Combustion Air from Adjacent Indoor Spaces through Indoor

Combustion Air Openings

INDOOR

COMBUSTION

AIR OPENINGS

MFC Series Boiler Vent and Combustion Air Guide

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4.2 Combustion Air from OUTSIDE the Building

Outdoor combustion air shall be provided through opening(s) to the outdoors in accordance with

the methods described below. The minimum dimension of air openings shall not be less than

3 inches (80 mm). The required size of the openings for combustion air shall be based upon the

net free area of each opening. When the free area through a louver, grille, or screen is known, it

shall be used to calculate the opening size required to provide the free area specified. For

additional details, consult NFPA 54, or in Canada, CSA B149.1-10, paragraphs 8.4.1 and 8.4.3.

4.3 Two-Permanent-Openings Method (USA Only)

Two permanent openings shall be provided; one commencing within 12 inches (300 mm) of the

top of the enclosure and one commencing within 12 inches (300 mm) of the bottom. The openings

shall communicate directly ― or by ducts ― with the outdoors, or spaces that freely communicate

with the outdoors, as show on the following pages:

•When communicating directly with the outdoors, or when communicating to the outdoors

through vertical ducts, each opening shall have a minimum free area of 1 inch2per

4,000 BTU/hr (550 mm2/kW) of total input rating of all appliances in the space (see Figures 3

and 4).

Figure 3: All Combustion Air From Outdoors - Inlet Air From Ventilated Crawl

Space and Outlet Air to Ventilated Attic

MFC Series Boiler Vent and Combustion Air Guide

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Figure 4: All Combustion Air from Outdoors - Through Ventilated Attic

•When communicating with the outdoors through horizontal ducts, each opening shall have a

minimum free area of 1 inch2per 2,000 BTU/hr. (1100 mm2/kW) of total input rating of all

appliances in the space (see Figure 5).

Figure 5: All Combustion Air from Outdoors through Horizontal Ducts

OUTDOOR OPENINGS

TO HORIZONAL AIR

DUCTS

MFC Series Boiler Vent and Combustion Air Guide

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4.4 One Permanent Opening Method

One permanent opening shall be provided, commencing within 12 inches (300 mm) of the top of

the enclosure. The appliance shall have clearances of at least 1 inches (25 mm) from the sides

and back of the appliance, and a clearance of 6 inches (150 mm) from the front. The opening

shall communicate with the outdoors directly or through a vertical or horizontal duct to the

outdoors or spaces that freely communicate with the outdoors (as shown in Figure 6) and shall

have a minimum free area as follows:

•1 inch2per 3,000 BTU/hr (700 mm2/kW) of the total input rating of all appliances located

in the space.

Figure 6: All Combustion Air from Outdoors through Single Combustion Air

Opening

4.5 Opening a Louver Through the MFC Series Boiler

A louver can be opened using the auxiliary relay contacts, part of the MFC burner controls. These

contacts are provided by a single pole double throw (SPDT) relay that is energized when there is

a demand for heat and is de-energized after that demand is satisfied. The relay contacts are rated

for 120 VAC at 5 amps, resistive.

NOTE:

Do NOT power the louver directly using the Auxiliary Relay. An external relay (supplied by

others) must be employed for this purpose. The boiler power cannot support external

accessories.

MFC Series Boiler Vent and Combustion Air Guide

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If the louver features a proof-of-open switch, it can be connected to the boiler’s Enable/Disable

terminals. The Enable/Disable terminals must be closed for the unit to fire. If the proof-of-open

switch does not prove within the programmed time frame, the boiler will shut down.

For wiring connections and further details regarding the auxiliary relay and limit circuit, refer to

the MFC Series boiler Operations and Maintenance manual.

If an AERCO supplied sequencing panel is being used to manage a multiple boiler installation,

the louver can be opened using the System Start relays. Refer to the MFC Series Operations and

Maintenance Manual, GF-148, for wiring connections and further details.

5. Direct Vent/Ducted Combustion Air

The MFC is approved for direct vent installation; i.e., it can draw all combustion air from the

outdoors through a metal or PVC duct connected between the MFC unit(s) and the outdoors. This

configuration is useful for situations in which room air is insufficient or otherwise unsuitable for

combustion. The minimum ducted combustion-air duct sizes for the MFC boilers are as follows:

•MFC 3000 = 10-inch diameter

•MFC 4000 = 12-inch diameter

•MFC5000 = 12-inch diameter

•MFC 6000 = 14-inch diameter

•MFC 8000 = 16-inch diameter

•MFC10000 = 16-inch diameter

In many installations, the combustion air duct can be manifolded for multiple unit applications.

The length and restriction of the ducted combustion duct directly impact the size, length and

restriction of the discharge venting. The direct vent air intake should be located at least 3 feet

below any vent termination within 10 feet.

A screen with mesh size not smaller than 1” x 1” must be installed at the inlet of the ducted

combustion air duct.

5.1 Optional Air Intake Adapters

The following Air Inlet Adapters are available from AERCO:

Air Inlet Adapters

MFC Model

Riello Burner

Part Number

3000 Dual Fuel

RLS 120

201044004

NOTE:

Rectangular to circular transition piece shall be field-fabricated.

Adapters for other Riello burners shall be field-fabricated.

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