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Old 07-28-2010, 11:46 AM   #1
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Sizing Window AC For Open Room


I have a home theater/TV room that is not adequately being cooled in the summer. It's the farthest room from the furnace, and has a 6 foot archway that is permanently open to the kitchen. It can sometimes be 10-15 degrees warmer than the rest of the house.

There is cold air coming from the two registers in the room, but they're not supplying enough obviously. We have been able to make the room somewhat comfortable by putting fans in the kitchen blowing into the room, but the noise of the fans is bothersome, especially since the purpose of the room is for watching TV.

We recently had a return installed in the room hoping it would help. It does somewhat, but not enough to get rid of the fans. The A/C guy is recommending a mini-split system but we really can't afford that right now. So I was thinking of installing a window A/C that has a reputation for quietness (possibly a Friedrich Kuhl?) I know it will still make some noise, but I figure it will be much better than the floor fans I am using now.

My question is how to size it. The room is 12x18 or 216 sq. ft. Using the standard charts I should get a 6000 BTU model. But I also need to consider the fact that the room is open to the kitchen via a 6' archway, which in turn is open to the rest of the house via a 5' archway. Another factor is that the room was previously a garage that the former owners converted, and one of the 18' walls is an uninsulated exterior wall (north-facing). Can anyone tell me how much to up-size the unit based on those two criteria?

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Old 07-28-2010, 04:23 PM   #2
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Sizing Window AC For Open Room


If your going to keep the 2 supplies that the room has now. A 6000 BTU will probably be fine.

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Old 07-29-2010, 05:47 AM   #3
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Sizing Window AC For Open Room


If you can get to your ductwork I would install more registers or increase the size of the one's that exist now, that would be the cheapest and quietest way to go.
Sounds like you need better supply air than return air. If you install more airflow try to direct it to the perimeter at the windows and doors.
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Old 07-29-2010, 06:01 AM   #4
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Sizing Window AC For Open Room


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Originally Posted by COLDIRON View Post
If you can get to your ductwork I would install more registers or increase the size of the one's that exist now, that would be the cheapest and quietest way to go.
Sounds like you need better supply air than return air. If you install more airflow try to direct it to the perimeter at the windows and doors.
While that would be good while the system is running. When the system isn't running, the room would get hot again anyways. So they would need to set the thermostat lower to bring the system back on, and then over cool the rest of the house.

Plus, when the room wasn't being used, it would tend to get very cold.

In winter, it would then become a very hot room. While the register dampers can be closed in winter. They may become loud as air whistles through them.

A 6,000 BTU window unit is not expensive these days. And can be turned on only when the room will be used.

I prefer ductless splits for those rooms. They're quieter. But they aren't a cheap option.
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Old 07-29-2010, 06:30 AM   #5
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Sizing Window AC For Open Room


appleye1

If you get more CFM air flow in the room the room should be just fine and the system should operate normally as the rest of the house, airflow appears to be your culprit.

It would still be quieter, and cheaper, and more comfortable to run the A/C fan on the on position rather than have a window shaker using electric and be noisy plus take up window space.

I would first try increasing air flow before I ran out and bought a new window unit.

The cost of the unit and the electric you use will be incorporated into the cost of fan run time.
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Old 07-29-2010, 07:03 AM   #6
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Originally Posted by COLDIRON View Post
appleye1

If you get more CFM air flow in the room the room should be just fine and the system should operate normally as the rest of the house, airflow appears to be your culprit.
If the thermostat is in that room.
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Old 07-29-2010, 07:34 AM   #7
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Sizing Window AC For Open Room


If I recall he didn't mention the location of the thermostat. Besides if it was in the room it would be cooler because the thermostat being in that room would increase run time, which is good anyway for dehumidification.

Just for the record where is the thermostat location. Do you have a basement or attic that you can get to?
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Old 07-29-2010, 07:52 AM   #8
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Sizing Window AC For Open Room


As you said. If the thermostat was in the room. That room wouldn't be hot in the summer.

OP can verify.

And the rest of the house would get cold when he was using that room.

Theater rooms, and sun rooms are about the same as far as the heating and cooling needs are always different then the rest of the house. They gain(theater and sun rooms in the summer) and lose more heat(sun rooms in winter) quicker then the rest of the house.

Since he said the room is at the farthest from the furnace. Its doubtful he'll get an extra 80 CFM by adding another supply or 2. Contractors don't install duct systems sized for extra air to a room down the road.

He can try running the central fan while they use that room before he buys a window unit. It will help. But probably not as much as what adding the return did.

Its a heat generating room. So it will be warmer then the rest of the house without a supplemental cooling system.
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Old 07-29-2010, 08:12 AM   #9
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Sizing Window AC For Open Room


If the thermostat was in that room and the rest of the house got cooler he could always balance the system to decrease air flow to the rest of the house.

We do not know the design critiera for the house or the capacity of the system it's quite possible he has the extra BTU rating to get more out of the system depending upon where he installs the takeoffs.

The return is already in now and running the fan on , on is unknown at this time. It's worth a try.
We know it's a heat generating room by the post and we are only giving DIY information and different things to try, that's all I am saying.

Go with what you got before you start buying window shakers and using more electric and have a noisier room.

Another thing he can always do the extra duct runs himself without much expense and time if it's accessible.
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Old 07-29-2010, 08:43 AM   #10
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Originally Posted by COLDIRON View Post
If the thermostat was in that room and the rest of the house got cooler he could always balance the system to decrease air flow to the rest of the house.

So when the room was not in use. The rest of the house would get hotter. Since that room would cool so much quicker without the equipment on.

We do not know the design critiera for the house or the capacity of the system it's quite possible he has the extra BTU rating to get more out of the system depending upon where he installs the takeoffs.

Good chance the equipment is oversized. highly unlikely that the duct system is sized to handle more air to that room

The return is already in now and running the fan on , on is unknown at this time. It's worth a try.
We know it's a heat generating room by the post and we are only giving DIY information and different things to try, that's all I am saying.

I'm figuring that he is going to install teh window unit as a DIY project.

Go with what you got before you start buying window shakers and using more electric and have a noisier room.

Actually. Using the central system to cool the theater room, will raise his electric bill more then running a window unit in it. only when they are using the room.

Using the central system to cool that room, when its only 72 outside is a waste of electric.


Another thing he can always do the extra duct runs himself without much expense and time if it's accessible.
Then he has to readjust all the registers again when winter comes around, so the theater room doesn't roast.


While doing the supply runs himself will be economical. It still has the pitfalls of having someone else do it for him. uneven temps in the house.

Seen lots of people do what your saying. And it always ends up, that either the room is cool and the rest of the house cold, or the house is cool, and the room is hot. And the people either end up adding a window unit, ductless split. or making due. And not being completely happy with their entertainment room. Specially if they have company over.

He can add the extra supply/supplies. And then when it doesn't work. He can wish he hadn't spent the money or time on installing it/them.
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Old 07-29-2010, 08:53 AM   #11
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Sizing Window AC For Open Room


appleye1

Do what you like, hope you make out OK.

I am no longer in this discussion when the moderator and long time wizard of DIY starts answering me in RED I know I am doomed and will never get the last word in, if I answered from now till doomsday.

Must be nice to have that kind of control and power.
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Old 07-29-2010, 09:00 AM   #12
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Sizing Window AC For Open Room


I think you should have a professional come and determine what is needed to cool your room like the rest of the house. Maybe add a couple more registers, maybe do some balancing. There is no reason why your central AC can't do this.

Why should this room be cooled separately from your other rooms?

On another note, the first thing you should do is insulate that exterior wall. If you buy the cellulose insulation they will usually give you the machine to blow it in for free (Lowes, etc. does this). Pull off a piece of siding, drill a hole, fill the void.
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Old 07-29-2010, 09:02 AM   #13
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Quote:
Originally Posted by COLDIRON View Post
appleye1

Do what you like, hope you make out OK.

I am no longer in this discussion when the moderator and long time wizard of DIY starts answering me in RED I know I am doomed and will never get the last word in, if I answered from now till doomsday.

Must be nice to have that kind of control and power.
You can answer in red also. Being a mod has nothing to do with that.
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Old 07-29-2010, 09:18 AM   #14
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I think you should have a professional come and determine what is needed to cool your room like the rest of the house. Maybe add a couple more registers, maybe do some balancing. There is no reason why your central AC can't do this.

Why should this room be cooled separately from your other rooms?

Theater rooms. Are their own separate load, from the rest of the house. And their load varies by usage, and time of usage. The same as a sun room. So a separate unit to condition only that room. Instead of running a much larger central unit. Operates cheaper. And keeps the room comfortable, without having to readjust the registers each season.

On another note, the first thing you should do is insulate that exterior wall. If you buy the cellulose insulation they will usually give you the machine to blow it in for free (Lowes, etc. does this). Pull off a piece of siding, drill a hole, fill the void.
You dead on about insulating that wall.

On many calls that I get for theater rooms. I recommend that if a mini split is out of their price range(what I prefer to install). That they install a window unit, or a through the wall unit themselves(I push for the window unit, for down the road replacement ease).

Walmart(5200 BTU is less the 130 bucks as I recall) window units are inexpensive, quiet on low, and can be changed out in less than 30 minutes if it fails down the road.

Did you ever have a party in your house when it was 50 or 60 degrees out. And almost need to turn your A/C on, because of the number of people at the party. Same thing for this room. just its not only people, its equipment also.

With this room. No need to run a large central unit, to cool it down.



PS: Red typing in a quote, is to make the reply stand out so no one misses that there is a reply in the quote.
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Old 07-29-2010, 09:22 AM   #15
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Sizing Window AC For Open Room


More info!

The thermostat is at the other end of the house near the bedrooms. This is a ranch house with a basement. The thermostat is roughly above the basement furnace, which is also at the other end of the house. Like I mentioned, this room used to be a garage, and I think when the house was built 40 years ago they didn't really consider it part of the house as far as heating/cooling. In trying to get the theater cool, I have to make the rest of the house freeze.

Re: insulation. Exterior is brick. I could put in insulation via the inside walls, and plan to eventually, but I just haven't felt like going through the mess and inconvenience so far (this is one of our main living spaces.) At least it is a north-facing wall, so it doesn't get crazy hot like a south wall would.

Re: ductwork. The room is on a slab attached to the house (the rest of the house is above a basement) and the existing ductwork was run through a raised floor. I really can't get to it. The only part I can get to is the 8" line off the main plenum in the basement, that feeds the theater ductwork. According to my A/C guys increasing the size of that line probably wouldn't help. I suppose I could do something elaborate by running duct up through a closet from the basement and through the attic to the theater, but nobody professional has suggested that yet, and I personally don't think it would end up supplying much extra air. Balancing the existing ductwork is also problematic as the downstairs is finished and most of the dampers are now difficult to get to.

Thanks for the help so far. I'm open to additional suggestions! Like I said, my A/C guy thinks a mini-split is the way to go, but I can't afford that right now. To me, it seems to me like the cheapest and easiest option to try now is a good quality window unit. I just can't figure out if I need to add BTUs to compensate for the fact that the room is open to the rest of the house. Or does that matter since the rest of the house is already cooled?


Last edited by appleye1; 07-29-2010 at 09:31 AM.
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