1A should give enough power to that build, if the game allows it to be fitted.
If having enough credits for that, that is.
Even 2C would be great improvement on the heat front, with negligible cost in jump range.
For Wombat's benefit, the full story looks like this assuming a 1A cannot be fitted.
The lower the efficiency number, the less heat is produced by the power plant which helps make fuel scooping a bit easier.
2E efficiency 1.0 weight 2.5T cost 1980 (comes with ship)
2D efficiency 0.75 weight 1T cost 5930
2C efficiency 0.5 weight 1.3T cost 17,800
2B efficiency 0.45 weight 2T cost 53,410
2A efficiency 0.4 weight 1.3T cost 160,210 (outside current budget)
So out of that list I agree 2C is also good choice as the weight penalty won't make much difference to jump range, the price is still low and efficiency is another step better than the 2D.
The 2B is hitting jump range a bit for hardly any efficiency improvement - B rated modules are typically close in performance to A rated modules but are always heavier.
Power output also increases as you go towards A, but any of the above produce enough power for this build.
When it comes to better exploration ships later when you have plenty of credits, look for the lightest weight A rated power plant you can fit and get the power output you need.
My Phantom runs on a 3A power plant with grade 1 low emissions plus thermal spread - efficiency 0.27.
It's installed ...... 
