Exhaust fan - controlled via humidity or temperature?

FarmerTy · Oct 9, 2014

I have a 210-gallon tank that I have finally been able to skin the stand and enclose the canopy all the way up to the ceiling. The back of the stand is open to be able to vent up to the canopy so that they all share the same airspace. I walled off the sides to enclose the airspace entirely for both under tank areas and above tank areas. The goal was to vent all heat and humidity from the tank outside via an exhaust fan. I think I have settled on a Panasonic vent fan from reading lots of feedback from larger tank builds.

My big question is, for those that have been venting their air outside, do you use temperature as the control for when it should vent, or humidity via a humidistat? I have an Apex controller and I currently have small clip on fans blowing across the sump and lights to cool the tank and it's linked to my tank temperature as the control. I have the option of directly controlling the vent fan via tank temperature with the apex or hooking up a humidistat to the apex breakout box and using that to control the operation of the vent fan with the humidity level.

My inclination is to use just the tank temperature to control the vent fan. I worry though that a small percentage of the time, perhaps the humidity may get higher in the enclosed tank but the temperature in the tank itself is low enough that it does not trigger the exhaust fan to turn on. I know this is more of a small concern as the lower temperatures generally prohibit as much water vapor in the air but part of me wanted real world experience with exhaust fan controls versus just my theoretical applications. Any input is much appreciated! Thank you!

FarmerTy · Oct 9, 2014

Just a thought as continued discussion... someone found this on my local club.

It seems to fit the bill nicely for control via temp or humidity level. Anyone use one if these?

http://www.amazon.com/gp/aw/d/B00336G1ME?vs=1

Odd, link is not redirecting. It is a Ventamatic duostat attic fan controller. It controls for temperature and humidity level.

Randy Holmes-Farley · Oct 9, 2014

I run a tiny vent fan in the top of my hood 24/7, but if I were to control it, it would be by temperature. I'm not sure, unless the fan is large or your ambient air is dry, that the humidity is going to be changing enough on a summer day to control well, and frankly, what humidity would you set it for?

AZDesertRat · Oct 10, 2014

I have found venting to the outside to be of limited value. You need to replace the air being forced out so you need an intake somewhere else in the house to allow exterior air back in if you live in a more modern well sealed home. In older homes there may be enough leakage around baseboards, windows and doors but you will still be drawing in hot air in summer months and cold air in winter months causing your homes AC or heat to run more frequently. You can only pull so much of a vacuum with fans until they do basically provide no air replacement. I have spent a lot of money and time sealing up my home to keep the 115 degree summer heat out so having to draw it in to replace the air I vent from the reef is counterproductive. I found a much cheaper alternative was converting to LED lighting and eliminating the 850 watts or MH and VHO and the 1/4HP chiller whch was another big source of heat in the house.

MarkDarnell · Oct 11, 2014

Application Errorhis is a wall box humidity stat, used for bathroom fans. You could mount this in a surface mount box. They sell for about $35 from a reputable electrical supply house.

MarkDarnell · Oct 11, 2014

Odd, the link didnt work. Just google "Leviton IPHS5-1LW"

FarmerTy · Oct 11, 2014

Thank you all for your inputs. It has helped me greatly to decide what I would like to try.

I've decided to go with a Panasonic Whisper vent fan with a "continous on" mode that I can set for a minimal 30cfm baseline to minimize water vapor buildup. I will set it to ramp up to 80cfm when the temp gets to be above a certain temperature in the hood or a certain humidity level (tbd) and that will be activated by the duostat I linked earlier. I will forgo any Apex integration at this time as it will not bring much value to me at this time to have it that way.

I don't have to deal with scorching heat here in Austin but it still does get very hot. I do have an older home so airtight is not a term I use often to describe my home. I will have to keep an eye on how often my AC cycles and note if it is doing it more once I start venting. I could see it being counterproductive in a well-sealed home or I exhaust too much air.