Greetings.
I have an idea im not sure if it would work.
Say i attached 3 RF modules onto arduino mega.
I then send command to turn on fan to 3 different receiver modules attached onto Uno respectively.
Would this work? 
Every transmitter-receiver combination and every transceiver is capable to transmit data to more than one receiver. I think you only need one transmitter.
In theory yes, it's possible.
But why use 3?
You could also do it with just 1 RF transmitter?
However, u need to provide more specifics as to how you want to control the fans to get any meaningful input.
You only need a single "transmitting" module. I have a single "master" 2.4GHz transceiver communicating with several "slave" transceivers in model trains.
Each slave is given a different ID number when it is programmed.
The master sends a message for each slave in turn with the ID of the slave in the message. All the slaves hear all the messages.
When a slave receives a message with its ID it knows to do something.
...R
thanks for the replies guys.
I assumed that 1 transmitter works for 1 receiver.
i just bought 433 modules. Robin mentioned 2.4ghz. I'm guessing his modules covers wider range?
holymarder:
i just bought 433 modules. Robin mentioned 2.4ghz. I'm guessing his modules covers wider range?
Not necessarily. Range depends on transmitter power and the antenna used.
I don't have experience of 433MHz modules but I suspect you can use them as I described for the 2.4GHz modules.
...R
Hi,
Check out;
https://arduino-info.wikispaces.com/Nrf24L01-2.4GHz-HowTo
You can use them as a pair or a network, in your case a master and 3 slaves, and they are a Tx/Rx unit.
Gargle for more info..
Tom.... 
holymarder:
thanks for the replies guys.I assumed that 1 transmitter works for 1 receiver.
i just bought 433 modules. Robin mentioned 2.4ghz. I'm guessing his modules covers wider range?
Assuming you've bought simple ASK/OOK 433 MHz modules, you can use a single transmitter and multiple receivers. They are not channelized, so it would be pointless to use multiple transmitters at a single node. The contents of the message transmitted will be received by all receivers and interpreted by the Arduino associated with each receiver. Thus your transmit protocol must identify the specific node which is to act on a particular command. The protocol might be a cyclical sequence like "Turn on fan 1", "Turn off fan 2", "Run fan 3 at half speed", and repeat . . . The Arduino at fan 1 would see the first message and turn on its fan. When it sees messages intended for other nodes, it does nothing with them.
The simple 433 MHz receivers will tend to pick up noise and present garbage on their data pin if nothing is being transmitted so you need to have some recognizable message structure transmitted to distinguish between a real message and random noise picked up by the receiver.