Thank you for your reply.
The electricity is not free, but it's included in the rental price of my appartment. I do know it's forbidden to run servers but that's because of fair use of the network (internet is also included in rentalprice).
There is only 1 meter for X amount of apartments so what I, or any other tennant, use more than the average is always considered to be coming from a pool of X unidentified apartments. Two S5's running 24/7, or two sp20's ftm, will not be noticed. Also: I (pre)paid to use a certain amount of electricity and as long as I stay under max usage, noone cares.
If you choose AntMiner S5 or SP20 make sure that you understand these things:
1. How difficulty will impact your operations. You can find number of Mining calculators which can help you. For example:
http://www.coinwarz.com/calculators/bitcoin-mining-calculator2. Since you believe your eletricity charge is included of rental price - do you know what is a maximum usage? Do you know how much will these boxes consume per 24hours?
3. Both boxes are great of perfomance, but they are noisy and producing lot of heat. You need to run it on place where you have connection to Internet (using ethernet cable)
I like your approach, just be prepared and understand your business. Good luck