Doesn't appear that the H170 chipset supports SLI, from what I've read:
"H170 drops some of this support. HSIO sees a reduction to 20 lanes from 26, limiting interface availability slightly. H170 also dips down to “just” 8 USB3.0 ports against Z170's 10USB3.0 ports, though both support 14 total USB ports. PCI-e lane allocation on the chipset is dropped from 20 lanes to 16 on H170, and the PCI-e configuration is limited to 1 x16 on a stock H170 board.
This means that H170 will be generally incapable of supporting multi-GPU solutions. Note that the CPU itself hosts its own PCI-e lanes that can allow for multiple PCI-e slots on board, but these will be meant more for expansion cards than multiple graphics cards."
Found on this article from GamersNexus' website
Also the question is what GPU's do you want to SLI in the first place?
Also I would always recommend getting a single GPU solution, if your wanting some more GPU power for games. It costs less (if you were to buy 2 GPU's, initially) and it also keeps things cooler and is less power hungry too.
So if it was up to me, I would upgrade to a more powerful single GPU solution.