What do you think of these hood plans?

[menelaus22]

I'm thinking about creating a custom hood for my 20 gallong nano.

4 20w Coralife Mini PC's.
1 MH
2 Silent Computer Fans
1 LED Moonlight Strip.

I'm still debating which MH set-up to go with. Considering I'm already running 80w of combined PC, perhaps a 75w will do it? What's a good quality and QUIET ballast and bulb. I don't want to deal with any humming, etc.

What material should I use for the hood itself? Some people say dense particle board will hold up to the heat of the MH.

[Geoff]

looks good.

i would say skip the LED lights. if you want silent ballasts than electronic is what you will be looking for. as for what to build the hood out of. i used solid pine for mine. normal plywood would be a better choice. i would stay away from particle board though. it can absorb moisture and swell.

G~

[menelaus22]

I remember you have a thing against the whole moon light thing... ; ) But, for the wow factor, I think I might have to leave it in there. I probably won't have it on, but it'd be nice to have the option just to show off.

What can I do to make it fire retardant. The last thing I want is this sucker burning to bits.

[Doug1]

Particle board is so dense yet srtucturally week compared to plywood, and its a pain to seal well
For fireproofing, a metal reflector with 1/2" spacers to stand it off from the wood, as well as fans for air movement ought to di the trick

[menelaus22]

do you think two fans pumping air out from the top (like in the diagram) should be enough? I was thinking about relocating them to the sides, but heat rises, so it seems like it would work more efficiently on the top.

[Geoff]

Originally Posted by menelaus22

do you think two fans pumping air out from the top (like in the diagram) should be enough? I was thinking about relocating them to the sides, but heat rises, so it seems like it would work more efficiently on the top.

i like them blowing out on the top, for the same reason you have. i have found when you put them on the side you get annoying light leakage that can get in your eyes. when the fans are on top the light leakage is to the ceiling.

G~

[Horace]

I am told it is NOT a good idea to have fans blowing out. You should have the fans blowing air in. By blowing air out you are essentially removing moist air through the fan. This will shorten the life of the fan dramatically. Just a suggestion :P

[Geoff]

Originally Posted by Horace

I am told it is NOT a good idea to have fans blowing out. You should have the fans blowing air in. By blowing air out you are essentially removing moist air through the fan. This will shorten the life of the fan dramatically. Just a suggestion :P

yes, this is correct, but it is removing the heat from the tank more efficiently. fans are cheap, chillers are not.

G~

[wharyat]

I would consider putting colder air into the hood and pushing out the heat is more efficient. The only way pulling air would be as efficient is if the hood was completly sealed except for strategically placed intakes, or if you already had another fan opposite to it blowing in.

[wanareef]

I had built a hood like that with only a MH in it, using pine and two fans on the side. That thing was heavy after a while. If you can add a counter balance or something it'll be eiaser to open. I just used a pencil to prop it open when I need it up

[Geoff]

Originally Posted by wharyat

I would consider putting colder air into the hood and pushing out the heat is more efficient. The only way pulling air would be as efficient is if the hood was completly sealed except for strategically placed intakes, or if you already had another fan opposite to it blowing in.

why do whole house fans blow out?

if you try blowing cold air in, how is the hot air going to get out? you are forcing the air against what it wants to do. which direction do the fans in your computer case blow? there is a reason why your CD drives and floppy drives get completely covered in dust over the years. this is where the replacement air for the exhast fans come from. by blowing air into the hood you are keeping the hot/humid air in the hood. if you pull the air out then you are removing the hot/humid air and replacing it with colder outside air. there are few chances of creating eddies in the hood where hot air can stay.

G~

[yardboy]

Your plans look good. I'd suggest a 70W DE MH. The clearance is a lot lower, and you can fit it in amongst the PC's easier. I'm planning on a similar setup. Though I've got several size tanks, I think the 20L is one of the best sizes. That and a 10 gallon sump with an UrchinC in sump skimmer. (but I guess the consensus is skimmerless. I'd still do it.)

Also, why 20W PC's? 55-65's fit over a 20L with plenty of room to spare.
Oh yeah, I just noticed you're showing reflective mylar as a reflector. Is it heat-tolerent? I've been wondering about using it myself, but it's just plastic film, after all.

[wharyat]

Should have added that vents are needed to keep the air moving.

I have 3 fans that blow in and 3 that blow out on my computer case. The most efficient design would be to have and equal number of fans blowing in and out.

If you have a fun blowing air out it will not do what you want it to, which way does a processor fan blow? To cool something off you need to supply it with molecules that are holding less energy. Air will take the path of least resistance.

Easier to illustrate what I mean:

[Jeremiah]

I personally would skip the 20 watt mini pcs and get two 55/65 watt pc's or two 75 watt vho's in there. Those 20 watt mini pcs were garbage in my opinion compared to real pc's or vho's. They get hot, and watt for watt are far less efficient.


I would check out hellolights.com for reflectors and they have excellent prices on everything else you would need too.

[Geoff]

ok, another way to look at the whole fan thing. if you have 2 fans that can move say 75cfm each. if you have one blowing in and the other blowing out you are only moving 75cfm through the hood. if you have both fans blowing out you will be moving 150cfm through the hood.

G~