Also it should be remembered, even if the Arc Reactors don't produce heat just about anything using the power does.
So Assuming a 50GW Arc Reactor compared to a 50GW fusion reactor in a spaceship:
The fusion reactor is fusing Helium-3 with itself which, from what I understand, produces entirely charged particles. So using the Direct Conversion method it's possible to get up to 90% efficiency although real world stuff seems to have only achieved between 48% and 60%. Now the Citadel races are pretty good but not perfect so lets say they've managed 85% efficiency.
Step 1 - Energy Production - 42,500MW Useful Energy + 7,500MW Waste Heat
Now the three biggest power drains would be the Engines, Weapons and Eezo*. So lets say 90% of the captured energy goes to those three systems and for simplicity sake say it's spread equally. That gives each of those three systems a total power 12,750MW
*Covering everything from the FTL drive, to grav-plates, to kinetic barriers.
While it was hard some googling gave me a peak theoretical efficiency of a fusion torch at 80% which means the Citadel can probably manage around 70% efficiency.
Step 2 - Engine Power - 8,925MW Thrust + 29,750MW Remaining Useful Energy + 11,325 Waste Heart
Yet more googling has revealed that Coil Guns are estimated to have a theoretical peak efficiency somewhere in the range of 90%+ therefore we'll be using 85% efficiency for them.
However while the majority of the weapons power will be going to the accelerators some will also be going to the GARDIANs. I'm going to assume a 70/30 split.
While high efficiency lasers are a thing that's starting to come out IRL we know that in mass effect that's not the case. Lots of stuff tends to use Lasers with 20% efficiencies but I'm going to be kind and say that in ME they have 50% efficiency.
Step 3 - Weapons Power - 7,586.25MW Accelerators + 1,912.5 GARDIANs + 8,925MW Thrust + 17,000MW Remaining Useful Energy + 14,576.25MW Waste Heat
We don't really have anything to use as a basis for extrapolations related to Eezo so I'm going to just say it''s 90% because.
Step 4 - Eezo - 11,475MW Eezo +
7,586.25MW Accelerators + 1,912.5 GARDIANs + 8,925MW Thrust + 4,250MW Remaining Useful Energy + 15851.25MW Waste Heat
Finally the remainder of the energy gets spread out across the other miscellaneous systems which much like Eezo I'm just going to give 90% efficiency.
Step 5 - Misc - 3,825MW Misc + 11,475MW Eezo + 7,586.25MW Accelerators + 1,912.5 GARDIANs + 8,925MW Thrust + 16,276.25MW Waste Heat
Over All Efficiency = 33,723.75/50,000 = 67.44%
So a normal ship with a 50GW reactor has to deal with approximately 16,276.25MW of waste heat during combat and 13,025MW during regular operation.
Now if we just swap out the fusion reactor for an Arc Reactor and the fusion torch for a Repuslor, with their 100% efficiencies, we instead get the following:
Step 1 - Energy Production - 50,000MW Useful Energy
Assuming the additional 7,500MW are spent normally. Giving an energy break down of 15,000/15,000/15,000/5,000
Step 2 - Engine Power - 15,000MW Thrust + 35,000MW Remaining Useful Energy
Step 3 - Weapons Power - 8,925MW Accelerators + 2,250MW GARDIANs + 15,000MW Thrust + 20,000MW Remaining Useful Energy + 3,825MW Waste Heat
Step 4 - Eezo - 13,500MW Eezo +
8,925MW Accelerators + 2,250MW GARDIANs + 15,000MW Thrust + 5,000 MW Remaining Useful Energy + 5,325MW Waste Heat
Step 5 - Misc - 4,500MW Misc + 13,500MW Eezo + 8,925MW Accelerators + 2,250MW GARDIANs + 15,000MW Thrust + 5,825MW Waste Heat
Over All Efficiency = 44,175/50,000 = 88.35%
So just swapping out for an Arc Reactor and Repuslor engine means combat heat production is cut down to a
third (35.8%) of what is previously was.
That means the ship can basically fight for 179.42% longer then it's citadel counterpart. For example if the ship could original fight for 60 minutes before overheating this one could fight for 167.7 minutes.
If we look at the non-combat heat figures then it drops from 13,025MW down to 2,000MW, 15.3% of the normal ships heat production.
