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Discussion Starter · #1 ·
My HT is 14' x 17' with an 8' ceiling. It gets very warm during a movie, between the CRT PJ, and anywhere from 3 to 16 people in the room.


Is there a formula for figuring out how many BTU's of air conditioning I should have?
 

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Discussion Starter · #2 ·
If BTU's are British Thermal Units, does that mean I need more of these, or fewer if there isn't a Brit in the house?


Seriously, how does one calculate their room cooling requirements?
 

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Hi Diver,


I've used a formula that came up when I did my research on AC systems on the net. I have it written down somewhere but don't know where. So please forgive me if this is not spot on.


The formula is intended for a ceiling height of 8 feet. If I remember correctly you multiply your square footage by 20. In your case that gives you 4760 BTU. They said to add 300 BTU per person and also to adjust up to 10 or 15% if you live in a particularly hot place or if you have lots of windows.


If I remember correctly 10 000 or 12000 BTU is what in America is called a 1 ton unit. A 2000 sq.ft. home in Austin Texas uses a 2.5 or 3.0 ton unit.


At least that gives you a ballpark figure. I've read that you shouldn't oversize the AC capacity too much since that can create troubles due to short cycles.


Mine will be in a garage with no windows and good insulation. The garage is roughly 440 sqft. I will probably go with a 1 ton unit. A totally separate system from the one of the house. This way I can individually adjust which saves energy and I don't have noise coming through the vent system.


From my superficial knowledge there are two or three things to consider that I've read about.


Scroll compressors are more efficient and quieter than piston kind.

Flexducts are not as efficient as metal but quieter. There are inline noise absorbers and low noise grills for outlets and intakes.

Take a 10 Seer or higher, as those are more efficient. They cost more in the first place but you can offset the investment by lower utility bill and you do something good for the environment or at least not that much harm.

Usual compressor noise is around 70db. The quietest are around 50db.

I have not yet found measurements of ambient noise in hometheaters when only the AC is on.


If you or anyone else could tell me what their values are that would be great. In one of Dennis Erskin's posts he said the noise level in your listening room should be not more than 30db when there is not music playing. I hope I can get to that because what good is all the insulation if a fridge or AC makes to much noise afterwards?


I am very thankful for all inputs on that matter.


Till
 

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I do believe that 500 BTU's per person is suggested. In addition to the above you must consider the thermal dissipation of the equipment in the room. On average, we're finding 9000 to 11000 BTU's per hour. In essence, the same as a kitchen but with a 2 hour utilization cycle.
 

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I've actually considered (for the 2nd floor TV room) installing an 8,000 BTU Maytag special ($179) into the attic and building a cowling or hood to bring forced cooled air into the room, which is above the garage.


I figured that the attic is hot in the Summer anyways, and in the Winter its not a problem at all. Then again, in the Winter I suppose I could haul static attic air into the TV room directly and dump heated air pretty efficiently if the TV room gets too warm in the Winter.
 

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I too am interested in this subject. My house is 8 months old and very energy efficient. The downside of that is that once the temp. gets to a certain point in the house it takes a while to kick the AC back on. That means my theater is getting warmer while the rest of the house stays the same.


My theater is in our spare bedroom and the even with the equipment off it doesn't get as cool as the living room or the master bedroom. Even my kids' rooms stay cooler than this room.


What are my options? Could it be that the hot air is not able to escape? I have one register that delivers air, but no intake.


I am running a Panny PT L200 and two Kenwood receivers. I don't even dare use my PC as it just expels heat. I haven't even sealed the door with weatherstripping yet. I can imagine that that might make it worse.


In order to keep this room cool with the equipment I have to put the air at 75. Unfortunately that makes the rest of the house really cold.


Any suggestions would be appreciated.


Don
 

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Discussion Starter · #7 ·
Don,


You could use an exhaust vent, just above your projector, to draw warm air from the ceililng, and exhaust it out of the room.


You could then install a fan in the air duct to the theater room, and have this duct fan controlled by a thermostat in the theater room. When it turns on, I would think it would draw air from other registers in the house, which as you say, is already cooled by the air conditioner.


I couldn't tell you whether to size the exhaust duct so that it is the same, or smaller than the house HVAC duct to your theater room. Does anyone know for sure whether it is more desireable to have a positive pressure in the theater room, or negative?
 

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Diver, you are correct. I will be employing this idea in the bedroom closet (bredroom is converted for TV room) ceiling as the components will be stashed in the closet.
 

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Thanks for you suggestions Diver. I guess I need to go to Home Depot this weekend and check out what I need. My only concern is where does the air vent to? Is it safe to have it vent into the attic? Do the Bathroom vents do this or do they vent through the roof?


I think I need to climb up into the attic to find out. At least I'll finally get the cables off my floor and through the concuit I had put in for the PJ.


thanks,


Don
 

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Discussion Starter · #10 ·
You can duct the warm exhaust air to another room in the home (Not sure if this meets building code), or to the outside. I would not exhaust the warm air from your theater room into the attic. You want to eliminate any possibility of condensation issues leading to mold or mildew.


You could duct the exhaust to one of the vents under the eaves of your roof, or tap into an existing bathroom vent duct, if it passes through your attic.
 

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Anybody know of a good QUIET fan type? I am going to be building an exhaust duct for my equipment rack but wanted to make sure I didn't get a fan that sounded like a leaf blower.


Chet
 

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Discussion Starter · #15 ·
Wanman,


I'd use an in-line duct fan for both sources - Fresh air into the theater room, and also for exhausting warm air from the room.
 
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