Code question regarding air supply

[livinisfishing]

Hello everyone my name is Jason, this is my first post kind of an introduction and a question at the same time. I  have been a gas tech for a few years now and still am amazed at what im constantly learning.

My question is in regards to air supply grill sizing. In the very few years I have been in the trade i have not had to size a grill always open basements. Well this job im on now has a furnace and a water tank in an enclosure. My company is replacing both.

The new furnace is a direct vent system and the water tank is a pv 50. What i need to know is when adding up the total btu's to size the grill opening do you include the direct vent appliance in the total btu input? I am saying no, my co worker is saying yes. The reason i am saying no is because it is direct vent and gets its own combustion air from outside. My other reason is that the code clearly states that a direct vent appliance does not adhere to section 8.2 to 8.5. My co workers argument is that the code also says you need to add up the total of all the appliances in the enclosure.

If i am wrong ill gladly admit it and be happy that i learned something.

Thanks

[Admin]

You're right in my opinion.  Ultimately Clause 8.2.1(a) says that Clause 8.2.6 does not apply to your direct vent furnace.

(8.1.2) The requirements of 8.2 through 8.5 inclusive do not apply to:
(a) direct-vent appliances, or
(b) Category IV appliances unless installed in designated R-2000 homes or in an enclosure.

Your direct vent furnace does not require any additional air supply but your power vented water heater would have to comply with Clauses 8.2 through 8.5.  

In your case we are exempt from any outdoor air supply requirements but because you're in an enclosure we need openings that communicate with the rest of the structure.

(8.2.3) An outdoor air supply shall not be required for a single water heater with an input of 50 000 Btuh or less within an enclosure or structure where there are no other appliances that require an air supply.  Except for direct vent water heaters, when the water heater is contained in an enclosure, permanent openings shall be provided as described in Clause 8.2.6.

I can see how your co worker could interpret Clause 8.2.6 to mean you have to add the furnace and water heater BTU's when sizing openings.  I don't believe that's the intent of Clause 8.2.6 even though Clause 8.2.6 (a)(i) says to use the total input of all appliances.

(8.2.6) When an appliance(s) is located within an enclosure and permanent openings sized and located in accordance with items (a) and (b) of this Clause are supplied to allow communication between the enclosure and the rest of the structure, the total volume of the structure may be used to determine air supply requirements, provided that the structure is not constructed as described in Clause 8.2.1 (a) and does not comply with Clause 8.2.1 (b).  Otherwise, the volume of the enclosure shall be used.  The openings shall be as follows:
(a) In all cases, an opening shall be provided that shall
 (i) have a free area of not less than 1 in² per 1000 Btuh of the total input of all appliances within the enclosure; and
 (ii) be located not more than 18 in or less than 6 in above floor level.
(b) When one or more appliances are equipped with draft-control devices, an additional opening shall be supplied having the same free air area as the opening required in item (a), and the opening shall be located as near the ceiling as practicable, but in no case lower than the relief opening of the lowest draft-control device.

Our water heater is non direct vent and installed within an enclosure where there are no other appliances that require an air supply.  Most manufacturers will interpret this for us.  The following is from the GSW 6G5076N water heater manual,

Appliances installed in a Direct Vent configuration that derive all air for combustion from the outdoor atmosphere through sealed intake air piping are not factored in the total appliance input Btu/hr calculations used to determine the size of openings providing fresh air into confined spaces.

Some PV water heaters have a draft control device (draft hood) and would need 2 openings.  Most of the models I see these days are FVIR compliant and have sealed combustion and no draft control device so you would use 1 opening.  You would also have to check the installation manual.  Some manufacturers have different requirements than the code when it comes to sizing openings and number of openings.  I would make sure I followed the more stringent requirement.

4.1.4 Where a conflict exists between the manufacturer's certified installation instructions and this Code, the most stringent of the two shall prevail.

And also keep an eye out for gas dryers that might be installed in the same enclosure.  You would have to consider the dryer when determining the combustion air requirements.

[livinisfishing]

thanks a lot for your response very informative! I am glad i found this site..lots of information directly related to our code and trade.

[lmetcalfe]

a direct vent appilance takes its own air from outside and exhaust from the same vent. there is no combustion air requirement for the direct vent.
clause 8.2.3 says a water heater 50,000 btu per hour or less will Not require  a combustion air supply as long as no other appliances with in the enclosure or structure require one. so you do not have a combustion air requirement.

if it is not a water heater than use table 8.1 for a appliance with draft control or table 8.2 for appliance without draft control for your combustion air requirement

if you have both pieces of equipment with in the enclosure you use table 8.1 for ONLY those with draft control then use table 8.2 with the total input of ALL the appliances and take the bigger size.

if you are taking the air from the structure to supply the enclosure follow clause 8.2.6 with is 1 in squared per 1000 btus (just knock off the 3 zeros). all the total input. Cut a lower opening that size 6 inches off the floor no more than 18 inches and if one of the appliances have draft control a second hole must be cut the same size as the lower opening as close to the ceiling as possible. (its for dilution air to feed draft control)

[Admin]

a direct vent appliance takes its own air from outside and exhaust from the same vent.

A direct vent furnace or water heater can also use 2 seperate vents.  What you have described is a concentric direct vent.

clause 8.2.3 says a water heater 50,000 btu per hour or less will Not require  a combustion air supply as long as no other appliances with in the enclosure or structure require one. so you do not have a combustion air requirement.

Clause 8.2.3 states no outdoor air supply is required.  Unless the water heater is direct vent you must follow the combustion air requirements in Clause 8.2.6.

if it is not a water heater than use table 8.1 for a appliance with draft control or table 8.2 for appliance without draft control for your combustion air requirement
if you have both pieces of equipment within the enclosure you use table 8.1 for ONLY those with draft control then use table 8.2 with the total input of ALL the appliances and take the bigger size.

Tables 8.3 and 8.4 could also be used for homes that are not built as described in Clause 8.2.1 (a) or (b).

if you are taking the air from the structure to supply the enclosure follow clause 8.2.6 with is 1 in squared per 1000 btus (just knock off the 3 zeros). all the total input. Cut a lower opening that size 6 inches off the floor no more than 18 inches and if one of the appliances have draft control a second hole must be cut the same size as the lower opening as close to the ceiling as possible. (its for dilution air to feed draft control)

It's important to note some manufacturer's have more stringent requirements than the gas code and Clause 4.1.4 says we must follow the more stringent requirement.

I don't agree with how Enbridge interprets the outdoor air supply rules.  See the thread on Outdoor Air Supply Confusion – Here