UGH! Window AC not cooling my room. Defective unit or undersized?

[BBQ&Love]

I have a 14x40 shop and am converting 16' of one end into a bedroom with 3/4 bath. Hate to lose the space but it's the right thing to do for now. So that leaves me with a 14x16 room with 8' walls.

I put R19 insulation in the walls even though the walls are 4 1/4" instead of 5 1/2". So I know I am not getting R19 but it's better than R13. So let's go with R15 in the three exterior walls. The 14' interior wall is only R13 because there will be a conditioned space on the other side of this. The ceiling is insulated with 2 layers of R13 plus about 8" blown in on top of that. So that's in the upper 30s or more. There is one insulated door on the interior wall with a double pane window and one 24x36 double pane window in another wall.

When I was in the business I never installed HVAC equipment without doing a full heat loss/gain. But since I was just putting in a little window unit and since it was a small, reasonably well insulated room I just went by the numbers on the AC units. A 6,500 BTU unit is supposed to cool a 250 sq.' room down quickly so I bought it. Don't want to oversize because that costs me, is less efficient, and less comfortable.

I have the unit in and it ain't cutting it. The other evening I put the temperature probe on my Milwaukee multi-meter and checked the numbers. Unit was set on 70 degrees. Outside temp was 88 degrees. Room temperature was 78 degrees.

In the middle of the day, with outside temperature being 105 degrees, the inside temp was 89 degrees.

Something seems wrong with this picture. I guess I will install my software and run a heat gain on it. But this seems pretty far off.

Am I missing something here? (Besides failure to do the calcs?)

 

[sneezer41]

air leaks

 

[aandpdan]

I think you are a bit undersized.

Punching the room size into a couple of online calculators I get results from about 7500-7900 btu/hour.

Sorry.

 

[BBQ&Love]

I think you are a bit undersized.

Punching the room size into a couple of online calculators I get results from about 7500-7900 btu/hour.

Sorry.

Irks me that I didn't do the calcs like I have "preached" for years. That's embarrassing. After all that, to get careless and rely on generalizations on my own project? Well, I guess I proved myself right.

 

[Steves32]

My garage is 420 sq ft, R19 walls, R38-R50 ceiling- all 5/8 drywalled. Has a commercial roll up door & 2 4x4 double pane windows & 24 T8 bulbs for light.
I installed a Fujitsu 22 SEER inverter 12k HP mini split (with a load calc). It's about 85 outside, inside it's 72 right now.
I almost guessed in a 24k- just because it was a garage. Glad I didn't.

 

[godrifttoday]

I go the next size over.so, if u room requires a 10000 btu I get a 12000 btu and it would be just fine

 

[6768rogues]

I have a similar setup with a 12 1/2 by 20 room and 8 by 8 bathroom in a corner of a barn. It has about half of the insulation you have. I put a 6000 BTU air conditioner through the wall and the place will cool down quickly. When it is in the 90s outside, the room will go down to 68 and the A/C will cycle on and off to hold it there. The room is very air tight, though, and I don't know how air tight your room is.
Put a thermometer in the cold air outlet and see what the discharge temperature is. That will tell you if it is actually cooling the air.

 

[BBQ&Love]

You have 16* of temp difference.

Not bad.

I could get that much or more with a good evaporative cooler.

 

[BBQ&Love]

I have a similar setup with a 12 1/2 by 20 room and 8 by 8 bathroom in a corner of a barn. It has about half of the insulation you have. I put a 6000 BTU air conditioner through the wall and the place will cool down quickly. When it is in the 90s outside, the room will go down to 68 and the A/C will cycle on and off to hold it there. The room is very air tight, though, and I don't know how air tight your room is.
Put a thermometer in the cold air outlet and see what the discharge temperature is. That will tell you if it is actually cooling the air.

47.4 degrees. But there is barely any airflow. If I urinated as weak as that air flow is I would go to the doc for a checkup.

 

[green.bubbly]

I am not an AC specialist and I would not know the first step to calculating heat load but I can tell you my experiences. At my last house, I built a 16x16 shop. 3.5 inches of fiberglass in the walls and in the ceiling, one door and two windows. I had a 6,500 btu window unit and it worked great. I live in hot and humid Louisiana.

With that said, I think you have an issue with your window unit or some other heat gain that is not being accounted for.

 

[99LeCouch]

I have a Kenmore 5200 BTU unit that does a great job cooling a room of that size. It'll hold the room at 72 just fine overnight without much cycling. I'd check your window unit.

 

[Jackfre]

My garage is 420 sq ft, R19 walls, R38-R50 ceiling- all 5/8 drywalled. Has a commercial roll up door & 2 4x4 double pane windows & 24 T8 bulbs for light.
I installed a Fujitsu 22 SEER inverter 12k HP mini split (with a load calc). It's about 85 outside, inside it's 72 right now.
I almost guessed in a 24k- just because it was a garage. Glad I didn't.

It is imteresting sizing these inverter units. With the modulation you have to consider some other things. I had a good customer call with a "large" room (no dimensions offered) in a super insulated home in ME. He put in a 24k unit. That 24 will go down to about 10.5kbtu. His problem was he told the customer that it would dehumidify the space as well as H/C. Super insulated homes can pose some unique challenges. It is now a cold wet space, whcih is no good. When he came back with the load calc he should have done first, engineering pointed out that for the dehu and best use of the "dry" mode in that type building especially, that the low end has to be considered above the high. Had he used the 12RLS, whcih will modulate down to 3.6 kbtu he would have rung the moisture out of the place. Bummer for him, but that is what he did to solve the problem. I'll be interested in how it operates thru the year. He is going to report back

 

[Falcon67]

I think you also probably have a defective unit. The 12K that was in my 20x24 shop worked "OK" but never worked like I thought it should. It could still keep the indoor temp at around 80F with the outside over 100F. But you had to leave it running all the time to do it. We later bought an 8K window unit for the back 18x18 bedroom (with only one insulated wall) and it ran rings around the 12K in terms of cold air output and fan volume. When we moved, I took the 8K and stored it and left the 12K. The 8K will be wall mounted in my 12 x 24 work area. It also has a remote LOL - now that's lazy. I think a lot of the small units are imported, so that quality "3 great, 1 *****" deal may well apply. You may just be "lucky".

 

[99LeCouch]

All the little A/C units I've seen in discount stores and big-box stores are made in China these days. The big ones might still be made somewhere in the Americas, but darned if the little window ones are.

 

[Major Ramifications]

99Le,
No window units are made in or anywhere near America anymore.

My question to the OP is this: Are you leaving the unit on all the time or not?

 

[BBQ&Love]

All the little A/C units I've seen in discount stores and big-box stores are made in China these days. The big ones might still be made somewhere in the Americas, but darned if the little window ones are.

Tried it both ways.

 

[6768rogues]

47.4 degrees. But there is barely any airflow. If I urinated as weak as that air flow is I would go to the doc for a checkup.

Sounds like some type of airflow problem. Could be a bad fan motor, squirrel cage spinning on the shaft or blocked airflow. If insufficient air is flowing over the evaporator, it will shut down the compressor to prevent an iced up coil.