Switching to Flo Gas from Bord Gais.

I use c13000 Kwh each year. Is that considered heavy usage?

It's half what I use, but it's meaningless as we don't know how big your house is and how many people are living in it.

the only way to figure it out is to put the figures into a calculator:

Flogas are charging me 3.7c per unit (ex VAT), there's also carbon tax of 0.37c and standing charge of €80
so for 13000 units your annual cost would be about €690 inc VAT.

For Electric Ireland do the same calculation on their rates and subtract whatever cashback they're giving you.
 
Am Flogas customer since 2007 after changing c/h system from oil to gas - handy for instant supply and no more waiting at home for oil delivery. Still receiving paper bills - no bother for me as this came useful for verifying our home address whenever requested. Also it provides an excellent annual reminder to lookup switching websites.