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Ideas for fish room ventilation please?

Trevor Pleco

21 Oct 2012
Cape Town
I’m trying to work out what I need to sort out the ventilation for my fish room, it's approximately fifty cubic meters containing about about 2000L of water. Being winter here with cold nights I’m getting major condensation problems on the windows and water collecting on the ceilings and then raining droplets. To try and reduce heat loss the room is pretty well sealed so adding to the problem. I also have installed a small wall panel heater to reduce the power consumption of the tank heaters at this time of the year.

It seems I have three options.. either a ceiling mounted exhaust fan, a wall ventilating fan or a dehumidifier, so what do I get...?

The ceiling mounted exhaust fan with a ball bearing motor is nice and quiet compared to the other options, however I have an almost flat roof with minimal space above the ceiling so have concerns it will draw the moisture up and then dampen the IBR roof sheets from underneath. It would presumably also suck out the precious warm air from the room, so more work for my heaters and pushing my winter electricity bill up further.

The wall ventilating fan is noisy and does not seem that efficient as have the same thing in my bathroom and shower. It’s also a mission to plumb requiring a large hole through the exterior wall and a vent outside.

The dehumidifier is fairly costly and then the most expensive of the three to run, it also makes quite a noise and would presumably have its work cut out with continuously not just sucking the moisture out the air but indirectly also out the tanks… or would it ?

Any guidance or wisdom appreciated !
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I think I'm going to need to see some pictures of this epic fish room...
lol, not too epic, mainly dominated by veil ancistrus raising tanks as usually have about 1000 fish in stock and by default now seem to supply the local trade, but at least it pays the fishy bills. My main 760L scaping tank is in the lounge, will post some pics post IAPLC :)
Depends on your budget but add number 4 to the list, HRV. Low running costs and recovers most of the heat leaving. It's as if it was designed for a fish room :D

I'd personally rule out No2 and No3. The de-humidifier would be working over time and as you've said would cost a lot to run and buy. We have/had a fan in the bathroom too, until I disconnected it and packed it out with polystyrene. The heat lost during the winter was ridiculous. I'm sure there are better, more insulated models around though, gap in the market if there isn't :lol:

Have a look into heat recovery anyway, pretty perfect really.
My mate used to keep the filtration and other stuff for his marine tank in a "shed" attached to the house and yes condensation in colder times is a major issue.

He got round and/or reduced by

- Making the roof as high as possible, thus easier to ventilate and/or stir the air.
- Using as much insulation as possible in the roof.
- Large diameter extractor fan (so quiet) connected to a temperature compensated humidistat. Needs to be temperature compensated or else once you set humidity trigger level in summer comes on 100% time in winter or if you set in winter never comes on in summer.
- Air circulating ceiling fan will prevent condensation, again off a thermostat/humidistat.
- Dehumidifier in winter when fans have less effect. Have to be careful as most dehumidifiers don't work below 5C, so might need heating to keep room above 5C.
ok thanks for all this info, perhaps it's just a simple solution and using a standard air fan to circulate the room will help as you suggest.. There is one already installed for cooling down things in Summer so perhaps I'll will try it on low on a timer and see what gives ..

Have been investigating HRVs they seem scarce and costly on this side..
Do you guys get a reduced rate electricity overnight? If so I'd run a dehumidifier over night with the tank lids closed. That should be most effective, or maybe get them to turn on via a humidistat.

Some sort of HVLS fan if you could rig one up would pressurise the room enough to push out damp air of a vent maybe
I have an insulated shed kept at 23C and just use a circulation fan 24/7 to keep air moving. I dont get much condensation in the winter except where one of the joints in the insulation needs repair. Some of my tanks don't have cover glasses. Of course it will also depend on the efficiency of your insulation, if the temperature gets very low outside you might find the cracks around your door fill with ice, can make it difficult to feed the fish:-/

Try this as the cheap option first.
Thanks good call, just trying this with a simple wall mount fan, but the damn thing won't operate off a timer, as you need to manually engage one of the speed setting knobs to get it in motion, tried to open it up and hot wire the switch, but foiled again as it has odd triangular head shaped screws which I can't open, seems I need to buy another fan ...!

Coldest we get is about 8'C
Ok just to report back, just for starters I've tried the simple wall fan to keep the air moving, as Jolt suggested, it helps a little, but I still have a major condensation problem mainly after cool nights on windows, walls that face outside and the ceiling is a mass of water droplets !

Suggestions still most welcome ?
I don't think you'll ever really overcome this without properly insulating it and providing some sort of outside ventilation.

I'm not sure if the fish house is part of your house, or a shed against the house. If it's a shed, you could replace the glass window with ply and insert a fan there. Like you/I've mentioned though, you can lose loads of heat through these. There has to be a some sort of sealed version available though surely. One which air only escapes when you want it to.

If battening the room out and adding insulation is out of budget, the only other thing I can think is to simply cover the walls/ceiling with polythene. It won't solve the problem, but at least the condensation is not going to damage or rot away your house and fish room. You'd obviously have to do the floor too though.

I think we need some pics though to get a proper idea :thumbup:
Are you heating the room or just the tanks? You need to get the walls warm or you will have condensation. insulation, and the more the merrier, will reduce the size of your heating bills. If you have lights these will also act as heaters if the air is circulating. Extraction will remove the air in the room which contains moisture but you will then have further evaporation from the tanks so you are fighting a losing battle. Insulation and circulation will reduce cold spots but it depends on circumstances, how you design your fishhouse is a compromise between cost and what you want to keep in it, and how long you expect to be using it for fish.
If you have a fan heater wire it into a room stat and set it at 15C and blast the air up to the ceiling and see if that helps with the condensation, if it does you can work on insulation later.
My mate that suffered severe condensation in his house due to no intervening door between kitchen and rest of house and no trickle vents on windows, bought one of these installed up stairs of the house to keep condensation at bay. Had to add external drain as kept on filling up all the time, especially in the winter.

He got one of these as they are silent and can be left running 24/7 as they don't make any noise.
Any way he cured the source of the problem now, kitchen extension with door and better kitchen ventilation and new windows with trickle vents, so no longer needed the dehumidifier and flogged on Ebay for almost as much as he paid for it.
Apologies, have been away from the forum for a while ! Many thanks for all this new feedback and ideas.. things seem to have improved quite a bit with simply covering most the tanks with perspex and pool solar blankets on the bigger volumes of water and continuously running a wall fan.

To answer some questions -
@NC10, "I don't think you'll ever really overcome this without properly insulating it and providing some sort of outside ventilation''.That's part of the dilemma, as with introducing outside ventilation so I loose the room's insulation and require my heaters to work over time. Increase the insulation and the condensation increases. I'm still looking for the magic "sealed version' as you put it. It's a room inside my house 5m x 5m.

@ian_m, I was trying to avoid the humidifier given that others felt it will be continually sucking water out the tanks and given the expense of running the machine.

@Jolt, I'm currently just heating the tanks, when I heated the room for a short period at the start of winter the condensation increased given the contrast of the temp outside. A fan heater is an option to try thanks, but presumable these use a lot of power so would have to be on a timer ?
Hi again, the way I have my fishhouse is partioned off part of a sectional concrete garage and it is insulated with 2" rigid polyurethane board. Used a lot in construction now. I heat the room with two tubular heaters, 120 watts total I think, its a long time since I installed them, and gave a blower pushing the air over the heaters and around the room. The heaters are wired through a room stat so go off when they reach the required temperature. In the bad winters we had a couple of years ago the room dropped to around 16C on the bottom row, which is ok for some if my killifish. I also have 6 fluorescent lights which also give some heat and 2 tanks have internal heaters. As I have already said I don't see much condensation.
You haven't said if you have any insulation or what your walls are made of.
I suggested a fan heater as a trial, uf you do use one keep it on a very low heat setting and high fan speed. DONT leave it for a long time or rely on it, they are unreliable and thermostat could fail leaving you with dead fish and a large electricity bill.
If you try it for a few days and it seems to reduce the condensation you can look at setting up a permanent fan or consider insulation.