After checking what was causing the lag I've noticed that the smeltery causes 6 chunk updates, but when I add the Fuel Input Machine the chunk updates rise to 20+ and causes a lot of lag
Edit: Also the Fuel Input Machine drop nothing when broken (not even itself )
Another Edit: I'm using the latest version of the mod.

I can confirm this to be happening aswell; getting a fps drops of 60-80.

I had fixed the bugs. Thanks for your report!
9f562a8

Sorry for the typo