Calculating The Size of a Server Room Air Conditioner

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A quick guide to show you how to work out your requirements for an air conditioning unit for your Server Room or Data Center.

In principle it’s easy to calculate the size of air conditioning unit you need for your Server Room, just add together all the sources of heat and install an air conditioning unit that can remove that much. In practice it’s rather more complicated. This guide does not go into detail of every possible heat source, but it should give you an idea of the amount of coling you might need.

Fire regulations often require that Server Rooms have levels of insulation far above that of a normal office. Providing sufficient cooling is essential to ensure reliable running of servers, routers, switches and other key equipment. Failure of the air conditioning can have serious consequences for the equipment itself and for your company. Early warning of problems and spare capacity in the cooling system are both highly desirable.

Calculating Heat Load

The amount of heat generated is known as the heat gain or heat load. Heat is measured in either British Thermal Units (BTU) or Kilowatts (KW). 1KW is equivalent to 3412BTUs.

The heat load depends on a number of factors, by taking into account those that apply in your circumstances and adding them together a reasonably accurate measure of the total heat can be calculated*.

Factors include:

  • The floor area of the room
  • The size and position of windows, and whether they have blinds or shades
  • The number of room occupants (if any)
  • The heat generated by equipment
  • The heat generated by lighting

Floor Area of Room

The amount of cooling required depends on the area of the room. To calculate the area in square metres:

Room Area BTU = Length (m) x Width (m) x 337

Window Size and Position

If, as is quite common, your Server Room has no windows, you can ignore this part of the calculation. If, however there are windows you need to take the size and orientation into account.

South Window BTU = South Facing window Length (m) x Width (m) x 870

North Window BTU = North Facing windows Length (m) x Width (m) x 165

If there are no blinds on the windows multiply the result(s) by 1.5.

Obviously if you are in the Southern Hemisphere you would swap the conversion factors as the heat on North facing windows is then greatest.

Add together all the BTUs for the windows.

Windows BTU = South Window(s) BTU + North Window(s) BTU


Purpose built Server Rooms don’t normally have people working in them, but if people do regularly work in your Server Room you will have to take that into account. The heat output is around 400 BTU per person.

Total Occupant BTU = Number of occupants x 400


Clearly most heat in a Server Room is generated by the equipment. This is trickier to calculate that you might think. The wattage on equipment is the maximum power consumption rating, the actual power consumed may be less. However it is probably safer to overestimate the wattage than underestimate it.

Add together all the wattages for Servers, Switches, Routers and multiply by 3.5.

Equipment BTU = Total wattage for all equipment x 3.5


Take the total wattage of the lighting and multiply by 4.25.

Lighting BTU = Total wattage for all lighting x 4.25

Total Cooling Required

Add all the BTUs together.

Total Heat Load = Room Area BTU + Windows BTU + Total Occupant BTU + Equipment BTU + Lighting BTU

This is the amount of cooling required so you need one or more air conditioning units to handle that amount of heat.

So what size of unit do I need?

Small air conditioning units have a cooling capacity of between 5000 and 10000 BTUs. Small units may fit in windows, venting to the outside world.

Larger units may be rated in tons of cooling. 1 ton of cooling is equivalent to 12 thousand BTUs.

Disclaimer: This calculation is intended as a rough guide only. Complete accuracy cannot be guaranteed. Before you decide on an air conditioning unit you should commission an audit from a suitably qualified air conditioning equipment specialist or installer.


say me.what i habe to do

My room is 20/15 .so what kind of ac i want to buyy
any tons view.


Dont know much about these units but i have came across a hotel heat an air unit an was asked what the routing is? how do i figure this out or is it just the routing of the power cords? Im confused and not getting specifics for routing conserning just one thing on heat an air unit?

how to arrive Equipment load & lighting load

why equipment get multipled by 3.5

why lighting multipled by 4.25

how to measurement and calculate the new setup clean room

i have room need to install air con, the dimension is 30m x 20m x 5m height, may i know how to calculate for unit air-con for full-fill inside the room 24'c


What would be the Cooling and heating required for an enclosure of alcomat sheet material which is dome shaped structure.. : with radius of 11.65m and height of 6.7m ?
it does not consist of any windows and consists of 150 persons.

how much tonns of central air conditioning is required ?

please reply .


choosing the right size airconditioner to cool my room.

how can l alter my calculation of sizing my airconditioner ?becoz by multiplyng the L(m)xW(m)of the roomx25,the outcome btu is too small to size up my plz help me!?

how to door BTU caculate


formula for count kw

i have 4m*4m room size and can you please tell me how to calculate kw

what is formula to get calculat the cooling in room by ton ex

what is formula to get calculat the cooling in room by ton exm my room is 36ft by 36 ft how many ton will use in that room

Practically for every 250

Practically for every 250 sqft, 2 ton cooling is required by calculation the total area we get 1296 and dividing it by 250 we get about 5 to 6 ton cooling

for a normal residential

for a normal residential building you need 350 sf/ton. for a commercial building 300sf to 350 sf /ton is sufficient.

Question; i need calculate

Question; i need calculate the AC unit needed to maintain a temp.of 5 degrees in a cooling room for fruits with dimentions of 13*22m.
please help me .

Ambian Temp

What about amb temp.shoud it be taken into consideration


pregunta espero que me ayuden porfa

como es la formula para transformar BTU a W

room heat calculation

we want to ac install in my room size 37 meter to 27 meter please help me

Cite BTU values?


Can you provide the source of your information? Why multiply by these values, i.e. 337 for area for example?


how to compute for a 10 tr chiller usage per area, what is the basic formula per area sir>>>?????

what r the minimum standard

what r the minimum standard power load for a five star hotel room

the minimum standard power

the minimum standard power load for a five star hotel room

4.5 kVA/room bay


how much energy does air con use to cool 1kw?

kw consumption

depending on the energy efficiency of the system and the type of system used, it takes 1 to 1.3 kw/ton for a DX refrigerated cooling system

what is the value??

greeting,may i know wat is the value for 337 at floor area of the room?? the window value 870,165,1.5 ..and why the equipment must times by 3.5??and the lighting too...tq very much^^

pool air con load

i have swimming pool are 72 sqm ,,,pool area 30 sqm ,,,2 sides and roof of the pool made of polycarbonite multiwall
what the AC capacity required in ton ?
i will install dehumidifier capacity 1500 m3/h and evaporation rate 3.6 l/h

good to see the questions

very clear picture about the heat load calculations..however thanks for web and all

need help - compressor is freezing

I am operating a test system in Dubai that have 2 trailer type rooms (8'x10') each. Room 1 has the AC mounted on one side of the room and lots of test equipemt that generate heat, room 2 is a control room with 1 3'x3' window and 4 people. Room 1 has 5 AC vents (14"x6") each, room 2 has 1 vent (14"x6"). The return from room 2 to room 1 is about (14"x6"). The thermostat is in room 2. Ambient temp is Dubai is about 100 deg F. I usually set the thermostat to 70 Deg F. After few hours of operation, the Compressor freezes over. The objective is to keep Room 1 much colder than room 2 due to heat being generated in room 1. Are the sizes and quantity of the vents sufficient? if Not please help.. also why is my compressor freezing over? The AC system is 6 tons.

Try to check the pressure on

Try to check the pressure on the system.Maybe lack of freon charge or overcharge

heat load

Dear Sir
I have total heat load around 25270W or 25KW so how I can calculate the capacity of air conditioning system in Ton or BTU .
best regards

for 25kva 25 kva=25 x

for 25kva
25 kva=25 x 0.8(power factor)
for this 5.5 tr Ac is required

Capacity in ton=25/3.517


calculate the capacity of air conditioning in ton or BTU

i think it is sample ,all you need to know and here its
1 BTU=0.293w ,so 25000w=x
so the capacity you need it in metric ton =6.5ton and in BTU=85324.
salah .sudan

regarding the water flow

Dear Sir,

Please help us for the normal ahu with the chilled water coil what shall be be the required flow rate of water. to get the cooling efficiency at the best.


Sensible Cooling LoadS

HI here
You can't simply just add the loads together and choose a unit that will satify total

Server room load or (machine load) is a sensible load and all air conditioner coils have a sensible heat ratio SRC

This can be around .6 to .7 depending on the coil size and brand.

This factor must be taken into consideration.

Yes but...

... you are only calculating the heat load for a room : Total Heat Load (in BTU) = Room Area BTU + Window BTU + Occupant BTU + Equipment BTU* + Lighting BTU

To size the A/C unit to handle this load, you are correct. When purchasing the A/C you need to account for this.

SHR = qs / qt (1)


SHR = sensible heat ratio (ratio of sensible heat load to total heat load)

qs = sensible heat (kW, Btu/hr)

qt = total heat - sensible heat and latent heat (kW, Btu/hr)

... as shown in this simplified example, it can be a lot more complex than this.

hear load

hope when we calculate the LxWx337 it should be in feet then calculation become ok but when we calculate in Mtr. then it showing very low BTU unit

it's indicated in meter

it's indicated in meter (m)...

East and west window heat load?

What is the multiply factor to use for east and west window?

Equipment loads

I am busy Designing Server room HVAC. I ask IT guy to give me the actual kW electrical load for racks. He does not understand equipment rating. what method can i use to get those load?


And this guy you are talking to works in IT?


is ther standerd convetion for room size = btu arcon need to use.


Why you didnt consider East& West windows for windows heat load calculation?

window computation

which is the correct formula in Window Computation? is it
Total Area = L x W x No. of equal size window? or....
Total Area = L x W x 165? / 170? and also where are these or how did you get this 165 and 170?

What is the Standard Heat Load Calculations?

i was researching for heat loads calculations and i end up with 2 identical measurements. but some numbers are so confusing because the values of of deriving the numbers is changing. so, maybe you can help me the standard number of calculating heat loads. like for example:

1. The Floor Area computations
what is the difference in the calculating the Floor Area in BTU
L (in ft.)x W (in ft.)x 31.25 to: L (in meter)x W (in meter)x 337?

2. Windows Size and Positions
is the calculations of North Window BTU is = Area x 164? or 165?
and the South Window is equal to Area x 868? or 870?

3. Occupants
in calculating the number of occoupants is it....
Total Occupants is equal to number of occupants multiply by 400? 500? or 600? (total occupants = no.of occupants x 400? or 500? or 600?

sir, i am so confused about this. could you pls helped me? i am looking forward to hear from you in enlightening me about the Heat Load Calculations. Thank you sir. God Bless.

how to calculate heat load of the matel base cieing

How to calculate the heat load of matel based cieling like acrelic & iron deka seat cieling , my confrence hall size is 75*41*16,pls tell me how require for this area

UPS cooling

Hi, does the about calculation include cooling the UPS?

If i have to calculate heat

If i have to calculate heat load of a cooling plate (used to cool mass that is kept on it) using water circulation as cooling medium.. what all factors do i need to consider ????

Data Center Cooling Caculation

Device Watts Qty Total Watts BTU

C6509E 6000 2 12000 40944
C4948 300 2 600 2047.2
C2951 340 2 680 2320.16
MCS 7835 780 2 1560 5322.72
MCS 7816 351 1 351 1197.612
MCS 7825 351 1 351 1197.612
C2960S-24PS-L 276 4 1104 3766.848
Cisco 2901 150 2 300 1023.6
ASA 5520 190 2 380 1296.56
CPS-MSP-1RU 300 1 300 1023.6
CIVS-MSP-4RU 900 6 5400 18424.8
D9854 37 9 333 1136.196
D9887B 200 5 1000 3412
DCM 9901 225 2 450 1535.4
Lightning Fixtures 18 8 144


TOTAL BTU 94314.848
1 TON = TO 12000 BTU/h 7.859570667

Required CRAC 8 TONs

Dear Sir, Please do let me

Dear Sir,

Please do let me know,

how do you know the 144 watt = 2448BTU

Enter power in BTU/hr:

Enter power in BTU/hr: 2448BTU/hr

Watts result: 717.43797936 W

Heat Load

Is a 150KW heat load the same as 150KW electrical load?


This depends on the type of

This depends on the type of cooling equipment you use
- For DX type: Factor is 1.0
- For Chiller Systems: Factor is 0.7

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