Residential Ventilation: An Introduction to the Part Nine Options

1993 Code Changes

The 1993 amendments to the Ontario building Code regulation, which include a new section on mechanical ventilation for housing, will be used for permits issued after July 1.

Why the Changes?

The 1990 ventilation requirements were causing a lot of confusion, and a wide variety of interpretations. There were suggestions that all systems should be designed to Part Six. In an effort to maintain some prescriptive ventilation alternatives in Part Nine, the Ontario New Home Warranty Program got together with the Heating Refrigeration and Air Conditioning Institute, Canada Mortgage and Housing Corporation, National Research Council, Ontario Home Builders' Association, Ontario Natural Gas Association, Ontario Ministry of Environment and Energy, Ontario Ministry of Housing, and Ontario Hydro. They researched what was actually happening in the field and what might be used instead. The new Section 9.32.3 with its straightforward requirements and look-up tables, is the result.

"Hope in the Wall" Option Was Not Popular

The basic 1990 Part Nine System relied on exhaust fans. Make-up air was required if there were any "spillage-susceptible combustion appliances" (furnaces, fireplaces, water heaters, etc. which used a natural draft chimney). A duct through the basement wall usually provided the make up air. Air coming in through that "hole" was cold - which raised two problems:

• Some municipalities demanded baseboard heaters to keep the basement at 16*C, which had a large energy cost.
• If an owner stuffed up the hole to keep the basement warm, there was a possibility of combustion appliances might back draft, spilling dangerous gasses into the home.

1993 Solutions:

a) Restrict Spillage-Susceptible Appliances - The 1993 Code spells out four new Options for ventilation systems that do not need Part Six design. It also spells out what combustion appliances can and cannot be used with them. Basically, this means you can't use a Part Nine ventilation Option if you have natural draft gas or oil furnaces or water heaters - or natural or induced draft gas fireplaces. Few natural draft gas furnaces (aka: atmospheric draft) are available any more in Ontario. However, even induced draft furnaces will be considered natural draft if they are con-vented to a natural draft chimney. Also, natural draft gas and oil water heaters and oil-fired furnaces are common, as are natural and induced draft gas fireplaces. Using any of them will mean the house ventilation system must be designed under Part Six.

b) HRV's can be Used "Off-The-Shelf" - The 1990 Code required Part Six design for systems using a balanced Heat Recovery Ventilator. Options 2,3, and 4 in the 1993 requirements spell out three different options for HRV's in Part Nine.

c) Wood Fireplaces Only Allowed with HRV and Co Detector - Solid-fuel burning appliances are not allowed with the basic exhaust-only system (Option 1). They can only be used in Option 2,3, or 4, which use a balanced HRV. Direct vent gas fireplaces are allowed in any of the four Part Nine systems, though. The carbon monoxide detector is intended to warn people if a smouldering fire starts to back draft. Opening a window may solve the immediate problem. Recurrent back drafting requires attention.

d) Ventilation Must Run at Two Levels - Essentially, this produces a "normal" ventilation capacity (principal exhaust fan), designed so owners could run t continuously if they wanted to, and a "high" level (when you add the supplementary exhaust capacity).

With an Exhaust-Only system (Option 1): The simplest system would use one principal exhaust fan in the basement, with a duct from inlets in bathroom(s) and/or kitchen (not range hood). Supplementary capacity would be point exhaust in other bathrooms/kitchen.

With an HRV (Options 2, 3 and 4): The HRV would be the principal exhaust fan. Supplementary exhaust capacity could be provided through:

• Individual fans exhausting directly to the outside or
• A "high" setting on the HRV

Look-up tables are used to calculate capacity in litres/second. This is a big advantage over 1990's performance standard of 0.3 air changes per hour, based on house volume.

Using 9.32.3. Mechanical Ventilation

1) Decide if you want to use the Part Nine Ventilation System Options. If you prefer to use Part Six, don't bother with this section.

2) Find out if the home qualifies for 9.32.3.:

• It's a Part Nine residential occupancy building, and
• The ventilation system will be self contained, serving only one dwelling unit, and
• It has four bedrooms or less, and
• Any gas fireplaces' are direct vent units, and
• Any gas or oil furnaces and water heaters' are direct vent or induced draft units.

Unless the home meets ALL these requirements, it must be designed to Part Six.

3) Next, find out whether the home is Type 1, Type II or Type IV. (Type III contains natural draft non-solid fuel fired appliances, natural draft or induced draft gas fireplaces, or both, and must be designed under Part Six)>

Type 1 - Has forced air heating system, and no electric space heating and no wood-burning fireplace.

Type II - A Type I house with a wood-burning fireplace.

Type IV - Has ANY electric space.

Option 1 - Exhaust Fans Only

Exhaust fans expel air from the house, which draws outside air in through the building envelope. No additional supply air required. Forced air heating system circulation fan distributes air.

Option 2 - HRV: Extended Exhaust

Heat recovery ventilator ductwork takes exhaust air from kitchen, bathrooms and/or other central location, and supplies pre-heated outside air directly to return air plenum of forced air furnace.

Option 3 - HRV: Simple Exhaust

Heat recovery ventilator takes exhaust air from, and supplies pre-heated outside air directly to, the return air plenum of the forced air heating system

Option 4 - HRV: Full Supply/Exhaust

Heat Recovery ventilator is fully ducted to distribute supply air to the various rooms of the house. Return ducting takes exhaust air from kitchen, bathrooms and/or other central location.

Other Considerations

Ventilation Capacity:

Tables are used to find out how much ventilation is required:

• Total ventilation capacity: Use Table 9.32.3.A

A typical three-bedroom house might need 65 litres/second.         65

• Principal Exhaust Fan Capacity: Use Table 9.32.B.

3-bedroom house must be able to provide 30 litres/second.          - 30

• Supplemental Exhaust Capacity: Subtract principal exhaust

fan figure from total ventilation capacity.                                    = 35

Ducts:

Ducts can be sized using look-up tables in Part Nine, as long as they stay below maximum lengths, number of elbows and fittings:

Principal exhaust ducts...........................................................see 9.32.3.4.(9)

Supplemental exhaust ducts...................................................see 9.32.3.5.(4)

Outdoor air supply and main trunk, for Option 4........................see 9.32.3.7.(5)

Branch Supply Ducts...............................................................see 9.32.3.7.(7)

Soil Gas:

Consideration must be given to providing make up air for exhaust devices if soil gas is deemed to be a problem.

Wood Fireplaces:

A carbon monoxide detector is required in the same room, hard wired to the house smoke alarm system, if there is any solid fuel-burning appliance. HRV required. HRV must be designed not to depressurize the house.

Fans:

Maximum sound rating for fans, which contribute to total ventilation capacity: 2.5 Sones in bathrooms, 3.5 Sones in kitchens.

Switches:

The principal exhaust fan must have a centrally located switch, labeled VENTILATION AIR. If a forced air heating system is used to distribute air, the circulation fan switch must be next to the ventilation switch. Switches are also required in each bathroom and kitchen to operate exhaust fan; manual override if necessary.

From CMHC