# Solved: A/C BTUs



## jp1203 (Jul 21, 2005)

Hey All-

I'm pretty much fed up with the heat in my "office." I plan to buy myself a window air conditioner in the relatively near future. Currently, it's 77 in here and I just can't stand it!

I'd like suggestions on BTUs. The room is 12X14 feet, has two computers, a rather large CRT monitor, and an A/V receiver (at least that's all I can think of that would generate a lot of heat). The ceilings are 8 feet high.

Reguarly, I'd be the only one in the room, besides two parakeets. Saying that, though, I bet if this room had A/C a friend would end up being here a lot with his laptop to keep out of the heat.

There is a single window (2X3 feet) facing west (the one I'd put the Air conditioner in), and there's a double window (4X3 feet) facing north.

Attached to the room is a relatively large closet (6X4 feet) that is frequently open.

The walls are 1 inch thick wood (not sure what type, but it's real wood paneling. Behind that on two sides are interior walls and two sides are exterior walls with wood siding on the outside of the house.

The floors are wood (same type as the walls I think) with no insulation beneath them to the basement.

I thought about a 5200 BTU, but I think that would be far too weak for this room. I've tried all kinds of calculators and they come up with 6000-7000. Based on your experiences, what do you all think is the best bet?


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## JohnWill (Oct 19, 2002)

77F? I normally set my A/C to 78 for the summer! Are you trying to create a cold storage room, or air-condition a living space?


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## jp1203 (Jul 21, 2005)

A living space 

We keep the house set to 62 during the winter, so anything over 72ish really starts to bug me.

It's currently 86 outside and 79.7 in here...not to mention it's very very humid. I'd like to keep it in the upper 60s even on the hottest days.

Calling for 93 tomorrow as well...normally in the summer we'll get about 1/2 hot days and 1/2 reasonable days.


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## JohnWill (Oct 19, 2002)

We keep our winter temperatures at 68, and I have setback thermostats on all three units, and they only keep it warm when we expect to use the area. I can't imagine keeping the temperature at 62, my wife would disown me!


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## jp1203 (Jul 21, 2005)

Generally, people don't keep their heat much higher than 66 up here, especially on the mountain. Although, I remember my great aunt used to keep her heat set to the max on her thermostat all the time and complained it was too cold. It was usually at least 100. I really doubt too many people are like that though. Her furnace must have never shut off!

We heat with wood a lot too to help the furnace on frigid days. Heats up the floors very nicely. The furnace is an old Armstrong from '73 that runs 80% efficient still. Granted, it'd fill a small bedroom, but it does its job well.


Almost no one has central air here, although I'm told where you are, it's odd not to have it. My goal is to have one for my "office." The rest of the house can go without.

Of course, I have to wait a bit until I replace this casement window. Won't be long at all though, two need to be replaced on this side that gets all the weather. They're somewhat warped. I will replace it with a normal one so I can have A/C.


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## buck52 (Mar 9, 2001)

Howdy JStergis

I'm in eastern mass and hate the heat...

My modest home office is 10x14 with a 6x3 closet...full of girlfiends clothes... ... anyway... I am quite well insulated ...2 exposed walls that are framed 2x6 and the floor and ceiling are well insulated also...2 windows with insulated glass... I bought a 5000btu AC for it because I have to keep the door closed...my cat just loves to eat ethernet and printer cables... 

low cool and low fan speed keep the room very comfortable... if I go to medium cool you could need a sweatshirt...

All that said... sorry to bore you... I would go with 1 size bigger that you calculate/think you need .... I firmly believe the unit will perform better if not run at full capacity all the time...

My thought is that as you stated , in the 6 to 7 thousand btu range should do the trick...

buck


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## jp1203 (Jul 21, 2005)

buck52 said:


> Howdy JStergis
> 
> I'm in eastern mass and hate the heat...
> 
> ...


I'd say I have to agree. A 5000 might have to work hard in my office cave. Mine is very well insulated, which is why it's tough to cool it down once it's warm. Not much gets through 1 inch thick wood panels on the wall I don't think.

Actually, I won't be on much until the power comes back. Know that big storm that went through last night? I don't know if it went out your way, but in Eastern Berkshire Co. it hit very hard. We've had no power since 10 last night and no one has come to look despite our complaints. There's 4 houses on our road without power in a 1/4 mile section, but the rest of the road is perfectly fine. There was a big crack and it was gone.

I am now leaning towards upper 6000 to lower 7000 because in the winter with the amount of electrical stuff it can pretty much heat itself.

The heat bugs me, I can't concentrate or work in high temps. and humidity at all.

Thanks for your input!


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## Elvandil (Aug 1, 2003)

There's a simple rule-of-thumb for approximate heating requirements for a room (and it should work almost as well for cooling). Take the total cubic footage (say, 12x14x10=1680) and double it for a very well-insulated room (3360 BTU), triple for normally insulated room (5040), and quadruple for a very poorly insulated room (6720 BTU). So, I'd say a standard 5000 BTU unit should be fine. I know I have used them to cool areas quite a bit larger than recommended and they have proved to be enough.

(And we are talking the northeast here for those heating estimates, so we are talking extreme conditions with days below zero. So the estimate will be high most other places and more accurate for cooling in the south.)


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## Cookiegal (Aug 27, 2003)

77 would be way too hot for me too, especially if it's humid. I keep my place at around 65 at night and 70 during the day. 

I've had an A/C unit installed through the wall for many, many years because I didn't want to have the burden of putting one in the window and taking it down all the time. I replaced it with a new unit last year and did a lot of research on the BTUs. It's 12,000 and does my entire house. The rule of thumb is it's better not to get a bigger unit than you need as the compressor will just cycle on and off too rapidly and it will not bring down the level of humidity that efficiently. I would go with the 5,000 or 6,000 at the most for that size room.


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## Elvandil (Aug 1, 2003)

It would also be nice if you found one with an inside/outside switch. Switching it to inside makes for much more efficient cooling since it takes air from the room that is already cooled and recycles it. But there are certainly times when you'd like to bring in fresh air from outside, and that is when the other setting is handy, even for just refreshing the air with the compressor off.

I've seen those only a few times so am not sure about their availability. Many manufacturers are reluctant to make them because their rating for efficiency and energy usage drops if hot air from outside is to be cooled. But it's worth mentioning for when you are shopping.


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## lexmarks567 (Aug 13, 2006)

go here and do as it says it will tell you what size unit you need

http://www.consumerreports.org/cro/...ir/air-conditioners/reports/sizing-worksheet/


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## jp1203 (Jul 21, 2005)

Elvandil said:


> There's a simple rule-of-thumb for approximate heating requirements for a room (and it should work almost as well for cooling). Take the total cubic footage (say, 12x14x10=1680) and double it for a very well-insulated room (3360 BTU), triple for normally insulated room (5040), and quadruple for a very poorly insulated room (6720 BTU). So, I'd say a standard 5000 BTU unit should be fine. I know I have used them to cool areas quite a bit larger than recommended and they have proved to be enough.
> 
> (And we are talking the northeast here for those heating estimates, so we are talking extreme conditions with days below zero. So the estimate will be high most other places and more accurate for cooling in the south.)


Now I'm beginning to think 5000 BTUs will be perfectly fine. Mine would actually be a touch less than your example, since I have 8 foot ceilings, not 10 foot ones.



Cookiegal said:


> 77 would be way too hot for me too, especially if it's humid. I keep my place at around 65 at night and 70 during the day.
> 
> I've had an A/C unit installed through the wall for many, many years because I didn't want to have the burden of putting one in the window and taking it down all the time. I replaced it with a new unit last year and did a lot of research on the BTUs. It's 12,000 and does my entire house. The rule of thumb is it's better not to get a bigger unit than you need as the compressor will just cycle on and off too rapidly and it will not bring down the level of humidity that efficiently. I would go with the 5,000 or 6,000 at the most for that size room.


Thanks for the input, Karen. With us living more "up north"...certainly you more than I, we're used to it cooler I guess. With yet another opinion, I'll probably go with the 5000 BTU, or right around there.



Elvandil said:


> It would also be nice if you found one with an inside/outside switch. Switching it to inside makes for much more efficient cooling since it takes air from the room that is already cooled and recycles it. But there are certainly times when you'd like to bring in fresh air from outside, and that is when the other setting is handy, even for just refreshing the air with the compressor off.
> 
> I've seen those only a few times so am not sure about their availability. Many manufacturers are reluctant to make them because their rating for efficiency and energy usage drops if hot air from outside is to be cooled. But it's worth mentioning for when you are shopping.


I didn't know some had that feature. I'm picturing something like the "recirculation" or Max A/C in the car. Makes sense, I'll look for one like that when I get one. I'm not too sure I've seen them around here, but if I do, I'll go for it.


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## Cookiegal (Aug 27, 2003)

JStergis said:


> Thanks for the input, Karen. With us living more "up north"...certainly you more than I, we're used to it cooler I guess. With yet another opinion, I'll probably go with the 5000 BTU, or right around there.





> I didn't know some had that feature. I'm picturing something like the "recirculation" or Max A/C in the car. Makes sense, I'll look for one like that when I get one. I'm not too sure I've seen them around here, but if I do, I'll go for it.


You're welcome. Mine is a Fedders that I purchased around this time last year and it has the inside/outside switch, which I agree is good to have. I rarely get to use it though as my neighbours are always smoking me out with their outdoor fireplaces and smudge fires. Fresh air is scarce around here and it bugs me no end.


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## jp1203 (Jul 21, 2005)

Cookiegal said:


> You're welcome. Mine is a Fedders that I purchased around this time last year and it has the inside/outside switch, which I agree is good to have. I rarely get to use it though as my neighbours are always smoking me out with their outdoor fireplaces and smudge fires. Fresh air is scarce around here and it bugs me no end.


Fresh air is pretty good here, with a house about every tenth to quarter mile.

Right now, I'm blowing in cool air after this rain with the window fan. 68 outside, 76 in here. Got hot earlier, but cooling off now.

As soon as I can, I'll be looking at a 5000ish BTU unit.

Thanks for the help everyone!


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## hewee (Oct 26, 2001)

With more then one window in the room you can always crack the other window to bring in Fresh air. But if it is a window AC the higher you can put it in the window the better because it is hotter buy the ceiling so it will suck in that hot air and blow out the cold air. I have mine in a single hung widow so it it is really low. When it gets really hot you can feel the heat coming down from the ceiling that is not insulated and it gets hot in here even with the AC on. I got the size they say is needed but I think I should of gotten one size bigger. Also I keep it on high all the time. The stat is always on 10 the highest it will go so I can not make it cool more.


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## Cookiegal (Aug 27, 2003)

Yes, they should be high up as Harry said. Mine is high up on the wall near the ceiling.


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## hewee (Oct 26, 2001)

Cookiegal said:


> Yes, they should be high up as Harry said. Mine is high up on the wall near the ceiling.


But from the winter picture you posted of your place you will not need it with all that snow around your place. 

I got a ceiling fan also and when it get really hot you can feel it bring the heat down. Got to move after 16 years because they sold this place so where ever I find a place it had better have a good Central AC that will make it cool when it's really hot. Been so long I forget what it is like to stay cool all summer long in a house that I will never leave the house in the summer.


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## jp1203 (Jul 21, 2005)

I keep saying..."Eh, I can live without it..." and thus haven't gotten one yet.

But now, after not sleeping more than an hour for days because of the heat, I'm about ready to go down and get one now. I know someone who installed one in a casement window with plywood and whatnot. He said he'd help if I wanted it. This window can't be seen from the road or the yards anyway, so I really don't care too much about how it looks.

I'm thinking 5200 BTUs will be plenty, as the rest of you mentioned. It doesn't need to freeze me out, just keep it upper 60s and not humid. I ditched the monster CRT that generated loads of heat, and put in an LCD instead, so that should help. 

Other question. We have a 100 amp electrical service (just replaced the panel and all the wiring to it because of a huge lightning strike) This room has a 15 amp breaker. It runs my Brother HL-5240, but the lights flicker very slightly (though not as much as with the old panel). According to the specs on the 5150 BTU GE unit I'm considering, it says it draws something like 530 watts. The laser printer draws 630. I wouldn't run both simultaneously, with the amount I've been printing lately I'd probably go a week without having to fire up the brother anyway. 

Will a constant 530 watt A/C plus 120 watts of lighting, two computers, and an LCD monitor be bad to run on a 15 amp breaker? I could eliminate one PC if I have to, I've been seriously considering doing that anyway, I'd like to move it to the basement instead and gain back some room.


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## paisanol69 (Sep 7, 2005)

JStergis said:


> I keep saying..."Eh, I can live without it..." and thus haven't gotten one yet.
> 
> But now, after not sleeping more than an hour for days because of the heat, I'm about ready to go down and get one now. I know someone who installed one in a casement window with plywood and whatnot. He said he'd help if I wanted it. This window can't be seen from the road or the yards anyway, so I really don't care too much about how it looks.
> 
> ...


.....at the specs on the A/C unit you are considering, you might find that the wattage rating is based on the A/C ubit requiring 240 VAC power. 530 watts sounds waaaayyyy too low, if the A/C unit is powered by 120 VAC. 

So check carefully, because you will need to run a dedicated 240 VAC electrical service line for your A/C unit, if I am correct.

Whatever you do, I hope you find a way to cool off soon!!!


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## jp1203 (Jul 21, 2005)

It is powered by 120. I checked that because The closest 240 line I have is across the house. I was looking at that GE one because the wattage seemed very low.


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## buck52 (Mar 9, 2001)

You should have no trouble with that unit on a 120v 15amp breaker... absolutely no need for a 240v curcuit

If you turn everything on at once you might wish for a 12 awg wire run and a 20 amp breaker...other than that you should have no trouble...


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## jp1203 (Jul 21, 2005)

buck52 said:


> You should have no trouble with that unit on a 120v 15amp breaker... absolutely no need for a 240v curcuit
> 
> If you turn everything on at once you might wish for a 12 awg wire run and a 20 amp breaker...other than that you should have no trouble...


Alright, thanks! That makes me feel better. All I think I'll watch for is not to fire up the laser printer at the same time, that might trip the breaker.
The panel is brand new as of a month ago and the electrician said the wiring all looks good other than the line into the panel that he replaced, so the electrical in this house is in good shape.

I didn't figure I'd need a 240 for any reason...the only A/C units that take that are 18,000 BTUs and up for the most part as far as I know, and there's no possible way I could need 18,000 BTUs for a less than 200 sq. foot room, I think 5000-6000 will do nicely based on what others have said here.


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