hi-eff furnace combustion air ?

[dmfv]

I have been wondering this the last week or so. For combustion air is it necessary to have it piped to the outside? I have been to a few houses that it is getting the air from the furnace room, other it is piped outside. I have my G3 and am taking the G2 test in a month but I cannot find in the modules where it says specifically what is needed. Is it the type of furnace or is it the size of the furnace room?

I ask this as one house I was in the pipe was around 50 feet to outdoors and the furnace was not starting for lack of air. Im thinking a next in the middle of the pipe, the basement was roughly 1000 sq/ft very large but yet the pipe is going outside. others were very small but the water tank had a air intake. Does it depend on manufactures intructions or is this something that with experience will come with knowledge?

thanks

[acefurnacefixer]

as long as the area that the furnace is drawing air from is large enough, then its ok. But outside air is always best.

[Admin]

It depends on what appliances are installed and what kind of structure they are installed in, but usually you need to make provisions to supply your gas appliance(s) with outdoor combustion air.
All the answers are in Section 8 of the B149.01-05.  Download the B149.1-05 Quick Code Reference - Here

For example, the Lennox G61V is a Category IV High Efficiency furnace and can be installed as either a direct vent or non direct vent appliance.  Direct vent means there is an exhaust vent and an intake vent pipe installed to the outdoors.  Non direct vent means there is only an exhaust vent installed to the outdoors.  Other models like the Lennox G71P only allow direct vent installations.  You have to read the installation manual to see what's approved.  Here in Ontario most homes already have a 4" combustion air vent connected to the outdoors that supply air into the furnace room, in which case I prefer to single pipe my installations as non direct vent.  It saves having to make a second hole to install the intake vent, and it prevents nuissance no heat calls, caused by the direct vent intake being plugged with snow.

(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 is saying you must install outdoor combustion air unless, you have a direct vent (2 piped) appliance, or a non direct vent Category IV appliance installed in a non R2000 home in an open basement.  If the non direct vent appliance happens to be installed in a secondary room within the non R2000 house then Sections 8.2 through 8.5 do apply.

The following Clauses 8.2.1 and 8.2.2 apply to R2000 homes;

(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.

(8.2.2) ...If an appliance with a draft-control device and an appliance without a draft-control device are installed within the same structure or enclosure, the required free area of the air-supply opening shall be the greater of
(a) that required by Table 8.1, using the total input of only those appliances have draft-control devices; or
(b) that required by Table 8.2, using the total input of all appliances.

The following Clauses 8.2.4 and 8.2.5 apply to non R2000 homes;

(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).

(8.2.5) ...If an appliance with a draft-control device and an appliance without a draft-control device are installed within the same structure or enclosure, the required free area of the air-supply opening shall be the greater of
(a) that required by Table 8.3, using the total input of only those appliances have draft-control devices; or
(b) that required by Table 8.4, using the total input of all appliances.

One exemption to the combustion air requirements is found in Clause 8.2.3;

(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.

When you have appliances venting up a chimney you have to be aware of possible down drafting, negative air problems, caused by things like kitchen fans, bathroom fans, dryers ect;

(8.1.5) When an appliance other than a central-heating appliance or domestic water heater is installed in a location where there is insufficient air for combustion, provisions shall be made to provide an air supply sized in accordance with Table 8.1 or 8.2

[dmfv]

thanks for all the info..