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# Calculating BTU requirement with heat sources

## Calculating BTU requirement with heat sources

#1
04-11-15, 06:38 PM
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Join Date: Mar 2013
Location: United Kingdom
Posts: 12
Calculating BTU requirement with heat sources

I have an apartment that is around 34 metres squared for the main hallway, bathroom and living room. However, I am unsure whether I should take into account the bedroom as well. I can leave the bedroom door closed during the summer, but then can't I expect at least some, or quite a bit of heat to escape from the room through the door? The air conditioner would then be working harder for that if it does.

The second thing is the building I live in has a heating system that uses oil and is always hot. This means the service cupboard in my apartment gets very warm as there is always heat radiating from the main hot water / heating unit - and I can't turn that off. The maintenance guys have told me it is a very warm building because it was not built with ventilation for the pipework.

So how can I calculate how much extra BTU I will need for these sources of heat? The hallway, bathroom, and front room are about 34 meters squared. If I include the bedroom it goes to 47 meters.

By the way I will need to get a portable air conditioner. I already have a 9,000btu which is ideal for the bedroom size, but struggles anywhere else.

#2
04-11-15, 06:55 PM
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Join Date: Dec 2010
Location: Galivants Ferry SC USA
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Rough rule in normal non drafty home is 25 btu per square foot

#3
04-12-15, 12:51 PM
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Join Date: Mar 2013
Location: United Kingdom
Posts: 12
Hmmm, that couldn't be right for a portable air conditioner. I know the wall mounted or split ones can be more efficient, but with the method of calculation you gave me I should be able to cool the open plan living room / kitchen of my apartment with less than 7,000btu. With a portable air conditioner even 9,000btu seems leave part of the room a bit warmer than the rest.

I guess the issue is how many more BTUs do you need when you have a portable air conditioner?

I still don't know how I can account for the heat sources of this apartment in the calculations.

#4
04-12-15, 01:10 PM
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Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 15,984
sry I was thinking you wanted heat loss calculation...

There are free calculators to use online...

Free Air Conditioning Calculator

An HVAC pro should be better to answer your question.. Stand by...

#5
04-12-15, 04:02 PM
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Join Date: Mar 2013
Location: United Kingdom
Posts: 12
Yes, I tried some online calculators, but then they might be calculating for wall mounted which are more efficient. That particular one you linked to varies a lot depending on the insulation type. I do have good insulation but am really none the wiser. I guess these calculators don't account for people trying to cool particular rooms or area of the places they live in.

#6
04-12-15, 05:21 PM
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Join Date: Aug 2009
Location: USA
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If the 9,000 btu works well for your bedroom and not so well for larger rooms, then you know you need something larger than 9,000 btu. What is the area of your bedroom? What are the available sizes above 9,000 btu?

#7
04-12-15, 07:24 PM
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Join Date: Mar 2013
Location: United Kingdom
Posts: 12
OK, from reading elsewhere online I think it might be best to get at least a 14,000 btu and then run the 9,000 btu in the bedroom if needed which might cool down the rest of the apartment. The online calculators vary, but I just done one for my living room / kitchen which stated I need 12,000btu for that alone with two electrical units (pc and fridge).

The optons were 14,000btu or 16,000btu for not much more money. I was concerned that getting the 16 might be too big but it probably wouldn't be. Running two units instead of one seems to be the best idea.

#8
04-13-15, 07:35 AM
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Join Date: Dec 2005
Location: VA
Posts: 5,491
Efficiency has nothing to do with size when your talking about cooling