Trying to install ecobee3 with only 3 wires? No Y wire?

So, I bought the ecobee3 to replace a really antiquated thermostart.

It looks like I only have 3 wires: G, W and R.

At first, I thought I was only missing the C wire which would be taken cared by the PEK adapter.

I only have heating through the thermostat. I am planning to add Central Air in a couple of years.

Will my ecobee3 work with only 3 wires for Heating Only? or do I need to hire someone to run a new cable?

I am not a handy person at all.

Thanks

submitted by /u/hombre_lobo
[link] [comments]