JBI
REGISTERED
Sealed combustion units provide their own combustion air through the intake. Most solid fuel appliances have air intake ports for combustion air. Many 'gas log' type appliances have air intake ports. Why not stoves?
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Combustion Air
- Thread starter conarb
- Start date
Sandman
Bronze Member
ConArb,
Since 2005 I have enjoyed these discussions with you no matter where I was or what identity I assumed at the time. There were a few times when I enjoyed just rattling your cage a bit. In a few days I have to go back to 60-84 hour work weeks in Iraq and/or Afghanistan so my participation in this forum will end again. Below is my tutorial on Combustion Air and Makeup Air.
Combustion Air
Gas ranges and gas dryers would require additional combustion air if the volume of space in which the appliance is installed is LESS than 50 cubic feet per 1000 Btu/h of the aggregate input rating of the equipment (definition of a CONFINED space).
In most situations, the volume of space in which the appliance is installed in addition to rooms communicating with that space is greater than 50 cubic feet per 1000 Btu/hr (definition of UNCONFINED space, IRC M1702.2, UMC 701.2.1).
For example, a homeowner wants a Viking model DGCU155-6B, 45-inch, 6 burner gas ceramic cook top installed in her kitchen. The kitchen is 15' x 15' with 10' ceilings (2250 cu.ft.) and opens to a dining room 10' x 15' with 10' ceilings (1500 cu.ft) and a living room 18' x 14' with 10' ceilings (2520 cu.ft.). Total volume of space = 6270 cu.ft.
The manufacturer specifications with the burners set to high for this model are
12,000 BTU , 8,000 BTU , 10,000 BTU ,14,000 BTU ,8,000 BTU ,6,000 BTU for a total aggregate input of 58,000 Btu/hr. 58,000 Total Btu/hr/1000 x 50 = 2900 min. cu.ft. required. So, 2900 cu ft is required for combustion air and 6270 cu. ft is provided. There is sufficient air for combustion for this appliance in this space. If a gas range is present in the same space, then the aggregate input of that appliance must be added to the cook top and must be less than 6270 cu.ft.
In a building of ORDINARY TIGHTNESS, all combustion air may be from inside the space and adjacent spaces. In a building of UNUSUALLY TIGHT CONSTRUCTION defined by the IRC as having plastic film vapor retarders with a rating of 1 perm or less with all openings gasketed or sealed, heavy caulking and sealing around all window and door frames, between sole plates and floors, between wall-ceiling joints, between wall panels and at all penetrations with less than 0.5 air changes per hour, combustion air must be provided for from the outside. The only residential construction that I have been involved with that came close to meeting this definition was in Alaska.
Makeup Air
M1503.4 (new to the 2009 code): “Exhaust hood systems capable of exhausting in excess of 400 cfm shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.”
Since the cook top must be ventilated, the homeowner wants a Viking 48" Wide Chimney Wall Hood - VCWH, model VCWH4848. The VCWH4848 requires 1200 cfm in 10-inch duct with a max. run of 50 feet. Since 1200 cfm exceeds 400 cfm per M1503.4, makeup air must be provided by gravity or mechanical means or both. To comply with the code, one way is to wire the wall hood ventilator motor, model DEV1200, to a motorized damper in the 10-inch makeup air duct (to be approximately equal with the exhaust). The motorized damper must operate simultaneously and at the same speeds as the wall hood ventilator. The makeup air ductwork can come into the space anywhere convenient, soffits, ceilings or high in an exterior wall.
So, the wall hood ventilator removes cooking odors and moisture generated by the cook top at a rate of 1200 cfm and the makeup air duct work replaces the air removed at a rate of about 1200 cfm (since the wall hood ventilator creates a slight negative pressure, makeup air is permitted to be equal or slightly less than the amount of the exhaust air). This action only occurs when the wall hood ventilator is switched on. In a typical household, I would suspect these motors would be operating less than two hours a day.
Since 2005 I have enjoyed these discussions with you no matter where I was or what identity I assumed at the time. There were a few times when I enjoyed just rattling your cage a bit. In a few days I have to go back to 60-84 hour work weeks in Iraq and/or Afghanistan so my participation in this forum will end again. Below is my tutorial on Combustion Air and Makeup Air.
Combustion Air
Gas ranges and gas dryers would require additional combustion air if the volume of space in which the appliance is installed is LESS than 50 cubic feet per 1000 Btu/h of the aggregate input rating of the equipment (definition of a CONFINED space).
In most situations, the volume of space in which the appliance is installed in addition to rooms communicating with that space is greater than 50 cubic feet per 1000 Btu/hr (definition of UNCONFINED space, IRC M1702.2, UMC 701.2.1).
For example, a homeowner wants a Viking model DGCU155-6B, 45-inch, 6 burner gas ceramic cook top installed in her kitchen. The kitchen is 15' x 15' with 10' ceilings (2250 cu.ft.) and opens to a dining room 10' x 15' with 10' ceilings (1500 cu.ft) and a living room 18' x 14' with 10' ceilings (2520 cu.ft.). Total volume of space = 6270 cu.ft.
The manufacturer specifications with the burners set to high for this model are
12,000 BTU , 8,000 BTU , 10,000 BTU ,14,000 BTU ,8,000 BTU ,6,000 BTU for a total aggregate input of 58,000 Btu/hr. 58,000 Total Btu/hr/1000 x 50 = 2900 min. cu.ft. required. So, 2900 cu ft is required for combustion air and 6270 cu. ft is provided. There is sufficient air for combustion for this appliance in this space. If a gas range is present in the same space, then the aggregate input of that appliance must be added to the cook top and must be less than 6270 cu.ft.
In a building of ORDINARY TIGHTNESS, all combustion air may be from inside the space and adjacent spaces. In a building of UNUSUALLY TIGHT CONSTRUCTION defined by the IRC as having plastic film vapor retarders with a rating of 1 perm or less with all openings gasketed or sealed, heavy caulking and sealing around all window and door frames, between sole plates and floors, between wall-ceiling joints, between wall panels and at all penetrations with less than 0.5 air changes per hour, combustion air must be provided for from the outside. The only residential construction that I have been involved with that came close to meeting this definition was in Alaska.
Makeup Air
M1503.4 (new to the 2009 code): “Exhaust hood systems capable of exhausting in excess of 400 cfm shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.”
Since the cook top must be ventilated, the homeowner wants a Viking 48" Wide Chimney Wall Hood - VCWH, model VCWH4848. The VCWH4848 requires 1200 cfm in 10-inch duct with a max. run of 50 feet. Since 1200 cfm exceeds 400 cfm per M1503.4, makeup air must be provided by gravity or mechanical means or both. To comply with the code, one way is to wire the wall hood ventilator motor, model DEV1200, to a motorized damper in the 10-inch makeup air duct (to be approximately equal with the exhaust). The motorized damper must operate simultaneously and at the same speeds as the wall hood ventilator. The makeup air ductwork can come into the space anywhere convenient, soffits, ceilings or high in an exterior wall.
So, the wall hood ventilator removes cooking odors and moisture generated by the cook top at a rate of 1200 cfm and the makeup air duct work replaces the air removed at a rate of about 1200 cfm (since the wall hood ventilator creates a slight negative pressure, makeup air is permitted to be equal or slightly less than the amount of the exhaust air). This action only occurs when the wall hood ventilator is switched on. In a typical household, I would suspect these motors would be operating less than two hours a day.
Dr. J
Silver Member
Excellent post Sandman. One picky item:
I bet a lot of people neglect to consider the volume of the space a gas range is installed in. Although most kitchen layouts should have sufficient volume, particularly since many floor plans are open to the kitchen, a large range in a small "pantry kitchen" could be an issue.
I do not believe there is any requirement for the cooktop to be ventilated, so the better statement would be "Since the design includes ventilation for the cooktop...". The requirement for make up air is dictated because the owner CHOSE to have a hood over 400 cfm.
I bet a lot of people neglect to consider the volume of the space a gas range is installed in. Although most kitchen layouts should have sufficient volume, particularly since many floor plans are open to the kitchen, a large range in a small "pantry kitchen" could be an issue.
conarb
REGISTERED
Fantastic post Sandman, probably the best answer to a question ever on this or the former ICC Bulletin Board. Have a good time in your 60-84 hour work weeks in Iraq and/or Afghanistan !
Daddy-0-
REGISTERED
I have enjoyed reading this thread even though it is slightly over my head. Thanks for all of the great answers and debate. I have a feeling that this type of problem is only the beginning with some of this energy stuff.
Sandman. Keep your head down and stay safe. I will miss your participation in this forum.
Sandman. Keep your head down and stay safe. I will miss your participation in this forum.
Jobsaver
REGISTERED
Same as Daddy-O. Great questions, great answers, though over my head sometimes. Thanks for the effort. Protection and blessing and safe return to Sandman at war!