I have some old L3+ laying around.
I've been thinking about making a custom box for them, out of wood. Making them look like a nice piece of furniture.
Terrible idea, or awesome present? (Fully aware they sell things like this, but I like making stuff.)
It depends what kind of price you have to pay for the electrical costs in your place.
The idea for using that L3+ for heating and maybe earn some small amount with it at the same time is good.
But be sure that the amount from what you will be earn from the L3+ is not or will be not big.
You should be calculate the price between what will be the Miner and what will be the heaters take on the electrical costs and if the Miner enough for heating.
As i said the idea is good but if its profitable you have to calculate all together.