Proposed solutions for heat stratification

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HVAC Project Summary - Hot Air Exhaust System

Property Details

• Location: 3-story home in Pittsburgh, PA
• House Orientation: Front faces West, Back faces East
• Roof Type: Hip roof (no gable ends available)
• Architecture: Brick exterior with dormer on 3rd floor

Current HVAC Setup

• Basement: New AC unit installed
• 1st Floor: Adequately cooled by basement AC
• 2nd Floor: 4 bedrooms, only 3 wall registers, inadequate cooling
• 3rd Floor: 2 bedrooms (converted attic) with separate mini-split units in each room
• Above 3rd Floor: Small uninsulated attic space (~4 feet high)

The Problem

Heat Stratification Issue:

• Hot air rises from 1st floor but can no longer escape to 3rd floor (doors stay closed for mini-split efficiency)
• Heat gets trapped at 2nd floor level, especially at stairwell landing
• Cold air from 2nd floor registers falls immediately down stairwell to 1st floor
• 2nd floor overheats while 1st floor overcools

Proposed Primary Solution: 2nd Floor Exhaust

Location: North Wall at Stairwell Landing

• Specific Position: Above existing small window on north wall at stairwell landing (halfway point between 2nd and 3rd floors)
• Why This Location:
  • Captures hot air trapped where 3rd floor doors block natural circulation
  • North-facing avoids afternoon sun heat and prevailing wind issues
  • High placement for optimal hot air capture
  • Creates beneficial suction to pull cold air up from registers before it falls downstairs

Fan Specifications

• Capacity: 1,200-1,500 CFM
• Control: Thermostat-controlled, activate at 78-80°F
• Damper: Motorized or gravity damper to prevent backdraft
• Speed: Variable speed preferred for efficiency

Secondary Solution: 3rd Floor Bedroom Exhaust

Bedroom Details

• Bedroom 1 (East side): Moderate heat load, mini-split on south wall
• Bedroom 2 (West side): High heat load due to afternoon sun, mini-split on south wall
• Both rooms: Ceiling fans, doors must stay closed for privacy

Fan Placement Strategy

• Location: North wall in each bedroom (opposite mini-splits)
• Bedroom 1: 150-175 CFM exhaust fan
• Bedroom 2: 200-250 CFM exhaust fan (higher due to west sun exposure)
• Control: Thermostat-controlled, staggered activation (west room at 76°F, east room at 78°F)

Replacement Air for Closed Doors

• Door undercuts: 1-2 inches off bottom of doors
• Transfer grilles: High-mounted (8+ feet) above doors for privacy
• Sizing: 1 square inch opening per 10 CFM of exhaust capacity

Installation Considerations

• Electrical: New electrical runs needed for all exhaust fans and thermostats
• Masonry Work: Through-wall penetrations in brick exterior
• Weatherproofing: Critical for all exterior penetrations
• Permits: Verify if required for exhaust fan installations

Expected Outcomes

• Eliminate 2nd floor heat buildup
• Improve effectiveness of basement AC system for 2nd floor
• Maintain optimal mini-split performance on 3rd floor
• Create proper air circulation throughout house

Questions for Contractor

1. What CFM capacity do you recommend for the primary stairwell exhaust fan?
2. How will you handle the brick penetration and weatherproofing?
3. Do you handle electrical work or should we arrange separately?
4. Can you provide examples of similar heat stratification solutions?
5. What warranty do you provide on installation and equipment?
6. What's your timeline for completion?