# Hvac



## terky (Oct 31, 2011)

Hello,

I am going to throw some good info up here so people can understand HVAC a little better.

I have attached a good duct sizing chart. Use this when thinking about exhaust.

Now for some rules for efficiency.

keep three times the diameter of straight pipe before and after the fan. This allows the air to organize itself to go through the fan.

When running flex duct, make sure it is pulled tight, hung straight, as in it doesn't droop down between hangers. Hangers should be every four feet.
Hangers on flex are supposed to be 1.5" wide. Either metal strap or vinyl strap. When taking corners with flex try to make nice smooth turns with long radius.

I recommend using R8 insulated duct. Flex is good because its already insulated. If you use metal you should insulate it with the silver backed insulation.

Technically, if a room is only moving 300 CFM or less you dont need an intake. There should be enough air leaks around to pull air in, unless you sealed that thing up well.

I have found 600W lamps need 80 - 100 CFM to stay at room temp. Maybe more for 1000W.

I think the best way to use a carbon filter is in the duct, before the fan but after the lights. This way all air is filtered and you can easily expand your duct system without worry. I have attached a pic. I would use a duct that has AT LEAST 3" all around the filter. 

The pic I attached shows duct coming off the filter box to the hoods. You can do that or put the inlet on the *** end of the pipe with duct ran to your room and branch ducts off of that.

You should have dampers on the taps that go to your light. That way you can adjust the system to equalize the air movement through the hoods.

Seal everything with duct seal. Duct tape should never be used on duct. Fasten flex with panduits (giant zip ties) if possible. One on the inner lining and one for the outer jacket.

Remember the goal is to move volume. You can hook a huge fan to small duct, and inside the duct there will be huge negative pressure. Once that pressure hits the room it looses all of its "umph." You want high volume in the duct so that the room has a negative pressure.

Now with all that negative pressure in your room you could start pulling in dust, water and bugs from outside. If you have an intake put a filter over it. Really you want a building to have positive pressure so that you wont have leaks, but most of us are doing this as a hobby and are not going to get a supply fan

That's all I can think of right now..... Post questions if you have them. 

View attachment FIELDDUCTSIZINGCHART.pdf


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## terky (Oct 31, 2011)

Dudes,

I install semi truck size HVAC equipment.

I put filters on the inlet of the hoods....

You can take it or leave it.


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## The Hemp Goddess (Oct 31, 2011)

What works for "semi truck size HVAC equipment" may not work for a grow room.  I am a master plumber, but not everything I do in homes or commercial properties translate into good grow room practices--much of it is overkill.

I have never found that I can keep a 600W light cool with a 80-100 cfm fan unless the intake air is really really cold. Also, if you are moving 300 cfm without any intakes, IMO, your room has far too many air leaks. This probably also translates into light leaks.  When running anything in series, it is important to have all your ducting and bends the same otherwise one of the lights will be pulling more air than the others.   I'm a little confused by this--are you advocating negative air pressure or positive air pressure?

"You want high volume in the duct so that the room has a negative pressure."

"Really you want a building to have positive pressure so that you wont have leaks, but most of us are doing this as a hobby and are not going to get a supply fan"



"


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## terky (Oct 31, 2011)

The Hemp Goddess said:
			
		

> What works for "semi truck size HVAC equipment" may not work for a grow room.  I am a master plumber, but not everything I do in homes or commercial properties translate into good grow room practices--much of it is overkill.
> 
> I have never found that I can keep a 600W light cool with a 80-100 cfm fan unless the intake air is really really cold. Also, if you are moving 300 cfm without any intakes, IMO, your room has far too many air leaks. This probably also translates into light leaks.  When running anything in series, it is important to have all your ducting and bends the same otherwise one of the lights will be pulling more air than the others.   I'm a little confused by this--are you advocating negative air pressure or positive air pressure?
> 
> ...


The room should be negative to the rest of the building but positive to atmosphere.

And no, I don't have light leaks.

You people are funny.

 I have been doing hvac since I got out of high school. Everything from houses to hospitals, radio stations that cannot have any noise travel through the duct, boiler venting.

I am only posting my expirience in my trade. I can go right now to 4 hvac shops and have a job. I know 3 of those shop owners and they all respect my work.

I am union trained and know what im talking about.


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## The Hemp Goddess (Oct 31, 2011)

My point was that ventilation for grow rooms and for regular home and commercial applications can be really quite different. This is true of all the trades--HVAC, plumbing, electrical...I am not trying to take anything away from your HVAC experience.  Like I mentioned, I am a master plumber and have been for many many years.  Applications for homes and businesses don't always have the same requirements as a grow room--we are creating quite a different environment in a grow space than the rest of a living space.  Far different rules can apply.


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## terky (Oct 31, 2011)

I did not claim to be an expert. I only claim that I design and install HVAC 5 days a week.

Puffin, those pics are just about how I have my duct. The pic I posted earlier is 3 different rooms. All using one fan and filter. So I think there are less parts. I put my filter last just in case there is a leak in the system. I would rather not have odors escape.

THG, I understand different requirments on different jobs.

Like I said, I am only sharing my expirience. Isn't that what the forum is for?

50 posts in 2 or 3 years. I don't speak unless I know what im talking about.

I respectfully post my opinion.
Take it or leave it.


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## Old_SSSC_Guy (Oct 31, 2011)

i've used that same sizing chart for years.  good stuff.

one thing about "HVAC in the Grow" is for sure - you always need more diameter ducting than you think.  i see these folks talking about running 240 CFM Dayton fans using 4" flexiduct and can only shake my head...

mondo years ago i asked a HVAC-shop-owning buddy what size duct work i needed to vent a 240 CFM fan.  he said i needed 10" minimum and if i was smart i'd use 12".  i thought he was crazy and i used 4" dryer duct instead; at the time i thought i was slick.  i was only being really dumb.

myself, i thought Terky's advice was cool...  

i only use the carbon filters on recirculating air, not on exhausted air.  i pull an input duct from outside and suck it through with a massive Vortex fan which then vents outside.  the air which is cooling the light systems never mixes with room air at all.  never thought it should...


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## terky (Oct 31, 2011)

here is a pic of the filter i just built. Its as sturdy as a tank and weighs as much.

Should last a long time.

Thats an 8' ladder.


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## Old_SSSC_Guy (Oct 31, 2011)

holy smokies there Terky!  how many pounds of charcol does that hyperberic chamber-lookin thing use?


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## terky (Oct 31, 2011)

Dunno, I got the $250 filter from the hydro shop. I am guessing the whole thing weighs about 75.

The metal only cost 70.


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## Old_SSSC_Guy (Oct 31, 2011)

so your big tube is only acting as a manifold, with the grow shop filter inside it?  it is only a manifold, why make it round?

maybe i'm misisng something...


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## FA$TCA$H (Oct 31, 2011)

appreciate the info, and the pdf reference, thanx!


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## terky (Oct 31, 2011)

Old_SSSC_Guy said:
			
		

> so your big tube is only acting as a manifold, with the grow shop filter inside it?  it is only a manifold, why make it round?
> 
> maybe i'm misisng something...



I dunno, guess it doesnt matter. 

Round pipe is cheaper, faster to install and in my opinion easier to hang. Just habit at this point.


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## BBFan (Oct 31, 2011)

Good post Terky.  Interesting read.  Thanks for sharing.


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## NorCalHal (Nov 1, 2011)

imho...thats friggin crazy.

Way too much work for no gain. Why envelope the filter?? What size fan you rocking? Are you going for a sealed room? 
I gotta agree with the others man, If your gonna use the filter at all with the lighting, have the filter before.

Not knocking your hvac experience man, but I have alot of grow experience and the K.I.S.S. method is allways the best.


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## NorCalHal (Nov 1, 2011)

terky said:
			
		

> Now with all that negative pressure in your room you could start pulling in dust, water and bugs from outside. If you have an intake put a filter over it. Really you want a building to have positive pressure so that you wont have leaks, but most of us are doing this as a hobby and are not going to get a supply fan
> 
> That's all I can think of right now..... Post questions if you have them.


 
I'm not understanding if you are shooting for positive or neg pressure? Allways neg in a growroom right?

Again, not knocking your skills man, not at all. In fact, I have some questions about AC's I think you could help me with.


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## terky (Nov 1, 2011)

NorCalHal said:
			
		

> imho...thats friggin crazy.
> 
> Way too much work for no gain. Why envelope the filter?? What size fan you rocking? Are you going for a sealed room?
> I gotta agree with the others man, If your gonna use the filter at all with the lighting, have the filter before.
> ...



My fan is a 6" 500 CFM fan . Hooked to my duct it actually moves close to its rated capcity. I enclose the filter because I can now attach 20 lights (or more) to that filter. I always plan for next year. I could easily rip out my fan, plug in a 12" 2000 CFM fan and be ready to rock.

That's the thing, its really easy for me and I have all necessary tools. That filter took more time for me to get the parts than to actually build and hang it. It is now 5' 6" off the ground. I can walk under it. I just think its cool I can use what I have learned in my trade for my hobby. Like the auto mechaninc with a supercharged car, why not, right?

You want a room to have negative pressure compared to the building, the building positive to the atmosphere. To do it right you would have your exhaust fan pull 500 CFM.  Then you would have a supply fan at the other end of your house pushing at least 525 cfm. More air in the building than is going out. All that air spreads through your structure. Once it hits the grow room it is sucked out. So the grow room has negative pressure compared to the house but the whole house is pressurized at 25CFM. But most people are not going to install a supply fan.....

Make sense? I am a mechanical mechanic, not an english major at all.

Orangesunshine, I will chew on your info and respond in the morning.


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## terky (Nov 1, 2011)

Orangesunshine,

Are you in a garage? In the pic of the filter it looks like I can see the bottom of a roof or something.

What kind of lights are in the veg room?

Is it just one lamp in the flower room?

And what climate are you in? I am in the NW so AC is not really needed with sufficient ventilation. From your name I assume your in Cali. If you are then your pretty much gonna need AC.

And I would recommend getting insulated flex duct from home depot. In my last room, which was in a house, I struggled with the heat until I switched everything to insulated duct. I even insulated my hoods. That simple change dropped my temps 20 F degrees.


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## NorCalHal (Nov 1, 2011)

I don't think a 6" fan will cool 4 lights, let alone 20 man. NO way will it cool 20. I push an 8" 675cfm  thru 5 lights (1000w)in a straight shot and it barely keeps them cool. Maybe it will work for 600's??

In my grow space, I have a 25' x 25' x 12' room. Pretty big. This sits in a 1500 sq/ft main room. I run a whole house fan (5000 cfm) for the exhaust in the main room to exhaust all the heat that the growroom produces.
This gives me a neg pressure in the main room. If I didn't push that air out, the main room would heat up silly stlye from all the light exhaust.

the ghrowroom has no exhaust at all. Only the lights get exhausted, but the air is pulled from outside the growroom and pushed thru the lights, then exhausted back into the main room., so no air from the growspace is EVER exhausted. I run multiple filters as scrubbers inside the room.

For cooling, I use a goodman 5 ton AC. I installed the airhandler/furnace inside the room with unistrut. No ducting whatsoever. Wide open baby. 2000cfm of 42 degree coolness. I love it. Only the AC part is running right now.
Pic of it below.

My question is I was told I could hook up propane to the furnace and it would operate as a heater also. Is this correct? Is this something I can do myself with a little reading? I havn't really got into it yet, but I would like that option.

Also, when I braised the copper, there was a small pinhole I assume and it has a supersmall leak. I cannot braise it closed because it is under pressure, so I guess I will have to pump it down and rebraise it?? PITA for sure, because I hired a crane and had the condensor placed on the roof of my building.


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## terky (Nov 1, 2011)

NorCalHal said:
			
		

> I don't think a 6" fan will cool 4 lights, let alone 20 man. NO way will it cool 20. I push an 8" 675cfm  thru 5 lights (1000w)in a straight shot and it barely keeps them cool. Maybe it will work for 600's??
> 
> 
> My question is I was told I could hook up propane to the furnace and it would operate as a heater also. Is this correct? Is this something I can do myself with a little reading? I havn't really got into it yet, but I would like that option.
> ...



Yes my fan will cool them. Its not just the fan but appropriately sized duct. Did you use 8" duct from your fan to the hoods? If so that is insufficient for that fan. Refer to the chart I posted. 8" will only move 150 - 200. hooked to that powerful fan you may be pulling up to 300CFM. Like I said in my first post, 100CFM per light. the reason it doesnt cool is because they are all in a line. You are only going to pull so much heat per CFM. I have formulas for CFM per watts of light, electrical equipment, and expected people in a room. It is not as simple as it sounds. When they engineer a building they calculate the heat loads to cooling required. East and west sides of buildings need more ventilation because the sun shines on the walls and heats them up. You need more CFM near windows because thats where heat is gained and lost depending on the weather.

I would run 14" duct from your fan to a 10"- 10"-14" Y. Then drop it to 8" at your first light.

Let me explain air movement in a duct. The air moves fastest in the center, It drags on the sides of the duct. This drag pulls energy away from your fan, making it less efficient. The bigger the center of the pipe the easier it is for a fan to pull air. There is also a maximum footage of pipe you can use. The chart I posted is good for about 100' of duct BUT!!! every fitting, elbow, change in elevation causes some drag. One 90 degree elbow is equal to 15' of duct drag. This is called "system effect." If you reach the maximum footage you have to use bigger duct to get the same airflow.

Call a local HVAC shop and get a propane conversion kit (if you have a natural gas furnace). If you feel comfortable about your mechanical skills then you should be able to swap the orifice. Basically like changing a jet in a carburetor. EDIT: make sure your venting is correct! If you use single wall vent you must be 6" from combustibles! If you use double wall vent you can get to 1" of clearance.

I dont think you have a leak. Could be wrong but I dont think it would work if it was leaking. There is minimum pressure requirements for the refrigerant. The computer would shut it down if it was leaking. EDIT: I am not a service guy I am an installer. But I know that if your refer lines arent to long you can shut the outlet on the compressor and use the compressor to evacuate and store the refrigerant. then close the inlet on the compressor. you now have empty refer lines. Just make sure to use an evacuation pump if you break the seal on the pipes. DO NOT DO THIS IF YOU ARE NOT COMFORTABLE!!!!!!!!!


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## terky (Nov 1, 2011)

orangesunshine said:
			
		

> yes---and yes---booths are in a garage---teams are LA Dodgers---LA Lakers---near the coast so OD temps are mostly high 70's if it ain't foggy---1k hps in the veg---2k hps in flower---with the space as tight as it is (very short runs of ducting) not sure changing it out for insulated stuff is gonna make much of a difference here---but---if i don't replace the portable a/c with a mini-slit i will have to get insulated duct for the exhaust cause that portable POS puts out a lot of heat---got the same filter set up in flower---the air in flower is pushed in from veg and pulled thru filter, 2 lights, and pulled out into the garage---i have negative pressure in both rooms



I have not built a sealed room yet. So this is what I THINK should be done

I dont know if you would even benefit from ventilation. Once the outdoor temps get too high its not gonna do anything. Ventilation would work in the winter but not in the summer. If you want the same environment year round I would get the biggest mini split heat pump you can or a full size heat pump. Hook that exhaust fan to a timer to change the air however often the peeps with sealed rooms recommend. Install back draft dampers on your exhaust and inlet.

Then your ready for CO2 anyway.

That is what I would do in a warm climate. Right now I am worried about keeping my temps up at night when the lights are off.

I just think that running duct in your space would be a waste of money.


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## NorCalHal (Nov 1, 2011)

It's starting to click in my head.
I understand that the way you are usuing your fan and ducting in the utmost efficient manner.

So lets talk sealed room. The air going thru the lights must be pulled and pushed from outside the grow area.

Usuing 8" hoods. My 8" fan is mounted directly to the flange of the first light. The light strings have 6, 1000w lights connected together. The room has 3 of these strings, for a total of 18 lights.,
 Pics I think, let me see. I was a little baked on the last post (like I'm not baked now haha), and forgot to post the pic of the ac up.

So, from the pic, I pull air from the left and push thru mu hoods, exiting the last light with 8" duct straight up and out of the room. So, it is a straight shot from the intake and 1 90 elbow out on the last light.

So, to have it better, I would change the intake of the blower to a 14", reduced down to the 8", and then change the exhaust end to the same 8"-14" out?

I think building a box like you have your filter in is more efficient but not feasable in my situation.
Mind you, I move my lights often for the first 4 weeks or so so adjustability is a must.

I have given it quite some thought, but with my limited knowledge, the straight line with the 8" mounted to the hood worked.
I thought about putting another 8" on the end to pull also, but not sure if that would be cool or not.

Cost is a factor too. Big factor. I know changing iit up would be some loot, but I am allways open to learn and make things better.


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## terky (Nov 1, 2011)

NorCalHal said:
			
		

> So lets talk sealed room. The air going thru the lights must be pulled and pushed from outside the grow area.
> 
> Usuing 8" hoods. My 8" fan is mounted directly to the flange of the first light. The light strings have 6, 1000w lights connected together. The room has 3 of these strings, for a total of 18 lights.,
> Pics I think, let me see. I was a little baked on the last post (like I'm not baked now haha), and forgot to post the pic of the ac up.
> ...



Your setup sounds good. The only thing I would change would be moving the fan as close to the outlet as possible. Have the outlet be at least 12", and the duct down to the hoods at least 10". BUT like you said, at this point your setup is working. The only benefit would be that your AC would not run as much. Not really worth the trouble. 

At my old place I originally had 6" duct running to my manifold. when summer hit it was just not good enough. I brought home an air measuring device. At my manifold I was only moving 200CFM. That's when I upgraded the duct to 12" R8 insulated. I remeasured the system and was pulling 450 CFM. more than doubled with minimal cost. I am just trying to point out to people struggling with heat that up sizing duct may be the cheapest route. That simple change dropped my temps from 96 to 76.

Big duct is cumbersome and the only reason I did mine this way is because I just bought a house with a shop. I am trying to do as much as possible with the equipment I have. I will probably tear it all down and build sealed rooms this summer. One step at a time. 

On a side note, my shop has a chimney. I plugged my fan in to that. Super stealthy.


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