A shameless plug for me:If you are in the usa close to new jersey with free power you should buy an s-3 from me.
Seriously an s-3 is good if you have very cheap or free power.
It does 300 gh up to 500gh at around .8 watts per gh
My s-3's and many s-3's have quiet fan mods.
So the s-3 = really quiet
Cheap to buy well under 100 usd
Nice space heater will use 250 to 400 watts .
The down side is they are 300gh to 500gh depending how you clock them. Which is not a lot of hash power.
They are only good if your power is free or you absolutely know you are going to run a space heater.
Now the s-7 cost over 1650 shipped to you home.
The s-7 is loud and hard to make quiet.
The s-7 does 10x the hash about 4800gh
The s-7 burns .25 watts a gh