Day and Night Fan controller

I just bought a VSC-DNe ( A day/Night variable fan speed controller ) I want to run a space heater to kick on at night to keep my night temps from getting too cold. The only prob with this device is that it turns the ventilation fans completely off when it gets cool at night. I want the vent fans to run at a min speed to keep a neg pressure in the room to keep smell from escaping the room when the heater is doing its thing at night. Has anybody heard of a device that will do the same thing except throttle the fan down at night instead of off? I have been racking my brain to accomplish this. Thanks guys.

It must have a thermostat ,some how bypass it.

I have a SMS fan controller that has a thermostat attached to it. Set minimal fans to lowest setting and keeps everything sweet lights off while running a electric fan heater. Yeh also keeps the tent neg pressure too. Great bit of kit.

Thanks guy but, I think I finally found the device I need. Its the
[h=3]Titan Controls Mercury 4 - Multi-Function Fan Speed Controller[/h]You can set the idle speed that the fans run when its below the set temp. Im going to set the idle lowest it will go. Im curious as to how low you can get the fans to idle. Going to store to swap it out today.

Temp-2V
http://aeroponicsnmore.com/climate-control-ventilation-c-23_5/temp-2v-fan-speed-control-variable-idle-setpoint-p-181

This controller has seperate settings for day/night, and it PERFECTLY controls my tent temps. I've used this controller for about 2 years now. No need to buy a Air Conditioner with this little bugger!