Attic Heat Harvester
attic heat harvester 1 floor installation

Differential Temperature Controller Technical Specification

attic heat harvester differential temperature controller

The Attic Heat Harvester Ltd. powerful microprocessor based Differential Temperature Controller is designed for applications that compare two thermistor derived temperatures to control external devices based on user pre-settable parameters and a predefined algorithm. The Differential Temperature Controller also calculates, displays and remembers system performance data.

In the Attic Heat Harvester guise the Differential Temperature Controller continually monitors an attic and a room sensor to determine whether a fan should be turned on to move solar heated attic air from the attic to one or more rooms.


System input power: 230vac 50Hz (default) or 115vac 60Hz. - voltage selection made using links.

Micro Processor: Microchip PIC16F1936

Clock rate 2 Mhz

Controller power consumption excluding relay output power - 1 Watt

1 - Attic thermistor
2 - Room thermistor
30K at 25C
30K at 25C


1 - 3 amp 230vac SPNO relay - provides 230vac (115vac) to power fan
2 - 0.05 amp max, 18-26vac SPCO relay - provides 24vac to open/close main air valve

Option: 3 - 1 amp 230vac SPNO relay - provides 230vac (115vac) to power attic cooling fan

2 line x 8 character 5.6 mm high LCD display with LED backlight

3 push buttons: 'MODE', '+', '-',


1 - +5vdc on -
2 - System running -

3 - Fan On -

Green LED
Yellow LED - flashes each second in normal operation flashes differently if system errors detected - see error codes


110 x 110 x 68mm (4.35 x 4.35 x 2.7 in) with clear polycarbonate lid
Fixing holes: 4 in a rectangle spaced at 95mm (3.75 in)
Weight 0.5kg (1.1lbs)

System Performance Parameter range:


Current Power (cPwr)

Current Efficiency (cEff)

Total Power (tPwr)

Total Efficiency (tEff)

Fan Hours (FHr)

Average Temperature Difference (AvTD)
-9.9 to 70°C in 0.1°C increments
18 to 160°F in 0.2°F increments

0 to 65.5kW in 0.1kW increments

0 to 99.9 in 0.1 increments
100 to 999 in increments of 1

0 to 999.9 kWhrs in 0.1 kWhr increments
1000 to 16609 kWhrs in increments of 1

0 to 999.9 in 0.1 increments

0 to 999.9 in 0.1 hr increments
1000 to 6553 (270 days) in 1 hr increments

0 to 25.5°C
or 0 to 45°F

System user pre-settable parameter ranges and initial default values
Range Default
Attic Temp - Room Temp (AtT-RmT)

Max Room Temp (MaxRoomT)

Fan Flow (Fan-Flow)

Fan Power (FanPower)

Max Attic Temp (MaxAticT)
0 to 25.4°C
0 to 42°F

5 to 30°C
41 to 86°F

0 to 5120 cmh
0 to 3060 cfm

0 to 255 watts

35 to 60.7°C
95 to 141°F


1400 cmh
820 cfm

90 watts