Outdoor Air Supply Confusion

[Admin]

Enbridge inspectors in Ottawa require an outdoor air supply for any water heater over 50,000 BTU's.  This can be problematic if the Energy Star rating of the home is jeopardized by an outdoor air supply.  We have been contracted to install 76,000 BTU GSW Enviro-Sense Power Vent water heaters.  According to the definitions in the code it is a Category IV appliance.  It is a non direct vent appliance.

(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.

Clause 8.1.2 (b) is clear, Category IV appliances installed in a non R2000 home and in an open basement are not subject to the air supply requirements of Clauses 8.2 through 8.5.

(8.2.1) An outdoor air supply sized in accordance with Clause 8.2.2 shall be provided for an enclosure or structure in which an appliance is installed when the enclosure or structure
(a) has a vapor or air barrier with joints continuously sealed by taping or caulking in all thermally insulated walls, ceilings and floors, or
(b) has an equivalent leakage area of 78 in² or less at a differential pressure of 9.00144 psig as determined by a recognized Canadian fan depressurization test procedure.

Our water heaters are not installed in an enclosure, but in a wide open basement.  Our basements do not comply with Clause 8.2.1 (a), and Engineers have performed fan depressurization tests that prove our homes exceed 78 in² of leakage, and that the homes do not comply with Clause 8.2.1 (b).

(8.2.4) An outdoor air supply sized in accordance with Clause 8.2.5 shall be provided for an enclosure or a structure in which an appliance is installed when the enclosure or structure is neither constructed as described in Clause 8.2.1(a) nor complies with Clause 8.2.1(b).

For arguments sake, let's go ahead and follow the outdoor air supply requirements of Clause 8.2.4, since we have proven our homes do not fall under the requirements of Clause 8.2.1.  Our water heater has no draft control device, so Clause 8.2.5 instructs us to use Table 8.4 to size our outdoor air supply.  Our smallest basement is 500 ft², which gives us a volume of 4000 ft³.  In Table 8.4, if we follow the 100,000 BTU line @ 3000 ft³, our required outdoor air supply would be 0".  

(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.

To be clear, a standard Power Vent water heater is not a Category IV appliance.   It also may have a draft control device, in which case Tables 8.1 or 8.3 would be used, and most likely require an outdoor air supply, unless the water heater was less than 50,000 BTU's.  Keep in mind even a standard Power Vent water heater, 50,000 BTU's or less, would have to follow Clause 8.2.6, if installed in an enclosure.  I rarely see the required louvres installed that communicate with the rest of the structure.

(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 homes also satisfy the GSW Envirosense Power Vent installation manual.  The installation instructions pg. 12 also defines an unconfined space as needing no less than 50 cubic feet per 1000 BTU's.  At 76,000 BTU's we need at least 3800 cubic feet of volume.  The volume of our smallest basement would have 4000 ft³.