What are the three methods to ventilate a house?
- Exhaust only
- Supply only
- Balanced
For supply-only ventilation systems, what is the ideal location for supply registers?
High level supply, 12 inches from ceiling
For a balanced ventilation system, how is fresh air introduced into a house?
- Its own dedicated duct system
- Into the cold air return plenum of the furnace
What is the average energy efficiency of a balanced ventilation system?
70% average (55-85% energy efficient)
What is the recommended air changes per hour with a balanced ventilation system?
1/3 ACH
List the components of a HRV
- Cabinet
- Heat exchanger
- inlet & exhaust fans
- duct system
- Flow measuring stations
- Controls
- Air filters
- Condensate system
- Defrost system
What are the different arrangements for the defrost system of a HRV?
- Supply preheated air with an electric duct heater
- Warm exhaust air is recirculated through the supply side (no fresh air during this time)
- Exhaust fan stops & supply intake blocked with a damper
- Supply fan turns off & exhaust fan moves warm air through HRV
Do all HRVs have a condensate system?
No. Some HRVs may transfer moisture to supply air
What are the control options for a HRV?
- Thermostat
- Humidistat
- Dehumidistat
- Manual switch
- Timers
- Fan speed controls
Where are flow measuring stations installed on a HRV?
On both the supply & exhaust warm side ducts, 12 inches away from the dampers
How should the supply intake termination be located on the exterior of a house?
- 6ft away from the exhaust termination
- 3ft away from gas meters
- 3ft away from other exhaust vents
- 18 inches above grade
- 40 inches away from corners of buildings
- Away from driveways & garages
Where are the cold side ducts located on a HRV?
- Exhaust duct from the HRV to the outdoors
- Supply duct from outdoors to the HRV
How should cold side ducts be installed?
- Short & straight
- If flex ducts are used, they should be supported every 3ft
- Exhaust ducts should be sloped downwards to allow condensation to discharge
How should warm side ducts be installed?
- uninsulated
- rigid metal construction
How much ventilation is needed for a roof?
- 1 sq ft of ventilation per 300 sq ft of attic floor
- 1 sq ft of ventilation per 150 sq ft of attic floor when no soffits and air barrier below insulation
What are the disadvantages of turbine vents?
- Don’t work without wind
- Can depressurize the attic on windy days
- Noisy
- Prone to seize & leaks
- Can cause bulk water leakage
How much ventilation is needed for crawlspaces?
1 sq ft of ventilation per 150 sq ft of crawlspace floor
What are the different types of heat exchangers in a HRV?
- Flate plate
- Rotary wheel
- Concentric tube
- heat pipe
- capillary blower
- heat pump
What are some clues that insulation has been added to flat roofs?
- plugged:
- holes in roof coverings
- holes in ceilings
- fascia boards
- vents added to the roof
- extra thickness to roof
- lower ceiling height than expected
What are some clues of moisture problems in flat roofs?
- sagging or spongy roof surface
- sagging ceilings
- mold or mildew on ceilings
- rusted nail heads on ceilings
What types of insulation are suitable for below grade?
- rigid fiberglass
- mineral wool
- polystyrene boards
What happens when the HRV is not interlocked with the furnace fan?
short-circuiting of airflow
Can a HRVs condensate drain discharge directly outdoors?
Not in cold climates; may freeze
Define “hydgroscopic”
Materials with the ability to absorb large amounts of water (i.e. wood)
If water absorbed > max capacity = rot develops
If water absorbed < max capacity = will dry out as temp rises
