Window Unit to cool 325 sq ft

acehApril 19, 2011

Need a window unit to cool 325 sq ft? 8,000 BTU rated for 350 sq ft should do it...or should I step up to 10,000 BTU rated for 500 sq ft?

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neohioheatpump

8,000 btu should be plenty for 325 sq. feet.

    Bookmark   April 20, 2011 at 7:42AM
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hendricus

You don't say where you are, that makes a lot of difference. In Michigan I would go with smaller, 4500 to 5000 btu.

    Bookmark   April 20, 2011 at 7:45AM
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aceh

I'm in New Orleans but house is insulated.

    Bookmark   April 20, 2011 at 12:38PM
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ionized_gw

In NOLA, insulation probably is not as important as air infiltration. I suggest that you get a model that has a "dehumidify" feature that runs the blower on low and shuts off the fan when it cycles rather than continuous fan. Otherwise, you will have high humidity. A heat pump model will likely cut your heating costs as well.

Other considerations that affect your choice are window and outside wall exposure. Which side of the building is the room on, Lake side, river side? Oh, sorry, North, South, East or West? South and West will call for the most AC. Another thing, is this an upstairs room or ground level with a second floor?

There are web sites that might allow you to do some useful calculations. Too big is bad in the humid Gulf South climate. You can end up with a cool, clammy room especially at night.

    Bookmark   April 20, 2011 at 6:51PM
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aceh

I'm in a single story house where the A/C will be on the "river side" (south side). I need to cool 2 rooms each measuring 12.9 x 12.6 separated by an open arch. I also have ceiling fans in both rooms. I don't need the rooms to be cold just liveable.

    Bookmark   April 20, 2011 at 8:03PM
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ionized_gw

Google with terms like "window air conditioner", "capacity" and "calculation". You will get hits on sites like this:

http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/air-conditioners/sizing-worksheet/

Compare results from a couple of them. Are you quoting square foot figures on the side of the AC box or for some generic place in the US? If so, you will underestimate capacity for hot/humid NOLA.

I reiterate, the ability to turn off the fan when the unit stops cooling in its cycle is important. It can be called many things. Sometimes there is an "energy saver" mode that cycles the blower every few minutes when the compressor is not running (no cool called for by the t-stat). This is almost as good as completely stopping the blower. Both types allow the water to drip off of the coils while the blower is stopped. When the blower runs continuously, the water just re-evaporates into the room and makes it feel very sticky.

A setting called "dry" might also be found that runs the unit in a very slow fan setting with no thermostat input. That is nice too. Both will hold your humidity low. Unless your place is very well sealed, you will get high humidity and be very uncomfortable (not to mention getting lots of fungus growing all over) when the unit is cycling. That would be on not so hot days and at night. Sizing too big will give you humidity trouble so keep it close to what you need without oversizing. Two smaller units (preferably not the same size) might work better than one if you can swing it. You choose one on cooler to average days, and at night. Turn on two when it gets really hot or when you walk in the door.

A fan on the floor blowing air at the box can really increase their efficiency.

    Bookmark   April 21, 2011 at 7:09PM
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aceh

Thanks ionized. The unit I have in mind has a dehumidfy function and when the compressor stops so does the fan after a few seconds.

    Bookmark   April 21, 2011 at 7:39PM
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aceh

I purchased the 8000 BTU window unit (cools up to 350 sq fet) to cool 325 sq ft. It is doing rather long runtimes before shutting off. So far the weather here in New Orleans is rather "mild" compared to the opressive summer heat and humidity that's just ahead for us.

Is it better to do long run times than shorter run times about 20 minutes between on/off cycles? While I still have a chance to exchange the unit, I'm beginning to think maybe a 10,000 BTU unit would be better for the heat and humidity that's ahead in New Orleans. What made me NOT get the bigger unit was the warning that too large a unit would cause even more humidity which I certainly don't need. Unit is placed on the sunny side of the house where it will get the sun from about 12 Noon until sundown.

P.S. Before purchasing the unit I took and online evaluation (I forgot the website), which included the sq feet to be cooled, height of ceilings, number of windows and size of windows, where the unit will be placed, number of people in the area to be cooled etc. It was a very indept evaluation and it pointed be towards the 8000 BTU unit.

    Bookmark   April 28, 2011 at 10:33AM
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ionized_gw

Too big will have worse humidity control for sure. I disagree about the temps in NOLA this month. We have been running 5-7 degrees above the normal seasonal average highs and 10 F higher than average lows. IIRC, that has been for the last two or three weeks. Check some weather sites for yourself to confirm it. The best system is one that runs continuously on the hottest day of the year and you are at the high end of your comfort zone. If you shave it too close you obviously are uncomfortable for a few hours for a few days.

It seems like you have big Southwest exposure. Ask yourself, is the current unit running continuously in the late afternoon? If you have 20 minutes between runs in the hot part of the day now, you are probably going to be O.K. That is a SOTP evaluation. It sounds like the web site you used did a good job if in addition to what you mentioned it asked about insulation and geographic location.

OTOH, if you have a quality unit with different fan speeds, the fan can be made to shut off between cycles and it has a "dry" mode. You can probably get by with a little extra capacity. That will get the temp down faster too when you switch it on after being out. Does it have a timer?

    Bookmark   April 28, 2011 at 2:23PM
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aceh

ionized,

I just got the unit late tuesday evening. Wednesday was rather mild and a cool front came through that night dropping temps down to the mid 60's in the morning with low humidity. Not the ideal conditions to fully test the unit.

It's 2:45 PM Thursday and the temperature is 74 degrees with 44% humidity rather low for New Orleans thus the weather is actually very nice and mild.

The unit I purchased is a Frigidaire FRA086AT7 8,000 BTU Mini Compact Window Air Conditioner.

    Bookmark   April 28, 2011 at 3:49PM
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aceh

I decided to return the 8,000 BTU unit and will get the 10,000 BTU unit which is rated to cool up to 500 sq ft. I need to cool 325 sq ft but I'm also considering the New Orleans hot, extremely humid summers.

I was able to run the unit Saturday and it took 2 hrs and 56 minutes for it to reach a set temperature of 72 degrees with a room temperature of 80 degrees and outside temperature of 88 - 90 degrees (which is not nearly as hot and humid as it will get later on).

Thanks to all who replied to this thread. I really appreciate your input.

    Bookmark   May 2, 2011 at 2:17PM
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ionized_gw

Given your test results, it was probably a good move. How does the humidity go at partial load at night?

We've been having near record temps for April. Over the weekend, I was wondering if I should have waited until July to start painting the outdoor trim. It might be cooler!

    Bookmark   May 2, 2011 at 7:19PM
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aceh

ionized,

There didn't seem to be a problem with the humidity in the house at night. The 8,000 BTU unit had a Dehumidification of (Pints/Hour): 1.7 while the 10,000 BTU unit is 3 Pints/Hour.

    Bookmark   May 2, 2011 at 9:47PM
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ionized_gw

That is a big difference relative to the cooling capacity difference. I don''t know if there is any standard for the dehumidification capacity.

    Bookmark   May 3, 2011 at 2:42PM
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aceh

I'm glad I got the 10K BTU unit. According to the latest weather forecast here in New Orleans, we are experiencing record or near record highs for this time of year (mid to upper 90's) and the 10K BTU unit seems like it's working a little overtime to keep up. Then again it just may be working exactly as it should considering the temperature. I've been getting run times of 30 to 45 minutes with off times lasting about 20 to 30 minutes.

    Bookmark   June 1, 2011 at 5:16PM
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aceh

Local weather report just came on the news and we have record high temps...98 degrees with a "feels like" temp of 104 in New Orleans.

    Bookmark   June 1, 2011 at 5:20PM
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weedmeister

Sounds like you have a near-%50 on/off cycle. This is fine.

    Bookmark   June 1, 2011 at 7:28PM
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aceh

weedmeister,

I'm sure that 50/50 ratio will change as it gets hotter. Here in "Nawlins", we haven't even begun the super hot and super humid weather yet.
:-(

    Bookmark   June 1, 2011 at 7:50PM
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ionized_gw

I dunno, I am working on painting exterior trim now. Sometimes wonder if I should wait until July. It might be cooler :-( We have a lot more days near record highs than near the average highs for this time of year.

    Bookmark   June 1, 2011 at 8:28PM
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aceh

The 10K BTU unit is rated @ 925 amps of power consumption. I know this is when the unit is on high. Would it use this amount of power when the compressor is on and the fan speed is on med or low?

P.S. The unit also has an "auto fan" feature where the fan speed automatically adjust to the needs of the room.

    Bookmark   June 2, 2011 at 9:18AM
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weedmeister

Do you mean 9.25? For sure you do not have 925 amps available at the outlet.

    Bookmark   June 2, 2011 at 2:49PM
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aceh

Sorry 'bout that. I meant to say 925 watts (according to the specs).

    Bookmark   June 2, 2011 at 6:44PM
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