I think you guys might be looking at this wrong.
Renew Rank 6:
- 205 Mana
- 400 Healing - over 15 sec
400 heal over 15 seconds should be 80 health per tick with no +spell power.
Base Renew: 400/205 = 1.95 Health / Mana
3/3 Imp Renew: 460/205 = 2.24 Health / Mana
3/3 IR/ 5/5MA: 460/184 = 2.50 Health / Mana
With Empowered Renew you gain an entire extra tick of healing which is an addition 20% healing.
Base Renew: 480/205 = 2.34 Health / Mana
Base Renew: 552/205 = 2.69 Health / Mana
Base Renew: 552/184 = 3.00 Health / Mana
This is Base, without any +Healing.
With 178+ Healing
Base Renew: 578/205 = 2.82 Health / Mana
3/3 Imp Renew: 638/205 = 3.11 Health / Mana
3/3 IR/ 5/5MA: 638/184 = 3.47 Health / Mana
Now add Empowered Renew:
We have (178 +Healing + 15% Bonus) + 20% (Instant Tick)
Base Renew: (605+121)/205 = 3.54 Health / Mana
3/3 Imp Renew: (665+133)/205 = 3.89 Health / Mana
3/3 IR/ 5/5MA: (665+133)/184 = 4.34 Health / Mana
So a Rank 6 Renew at 178 spellpower will hit a 4.34 Ratio of Health/Mana
If you use a Rank 3 Renew with 178 spellpower
Rank 3 Renew with Improved Renew (IR) and Mental Agility (MA) 178 spellpower + Empowered Renew.
Rank 3 Renew Maxed: (406+81)/94 = 5.18 Health / Mana.
Basically just click it after casting any other heal, it won’t stretch your 5 sec timer and you will get one of the most Mana efficient heals in the game.
For Context -
Greater Heal (Ranked 1) with 3/3 Improved Healing and 5/5 Spiritual healing and 178 spellpower:
Greater Heal - Rank 1: 982/370 = 2.65 Health / Mana
GH - 3/3IH+ 5/5 SH: 1080/315 = 3.43 Health / Mana
w/ +178 Spell Power: 1235/315 = 3.92 Health / Mana
This means Rank 6 Renew gives you .42 more Health / Mana - Or 11% more efficient vs Greater Heal when both are maxed out this phase with 178 spell power. If you calculate a 12% crit chance on greater heal it bumps it from 3.92 to 4.15 Health / Mana spent.
Keep in mind this is THE MOST EFFICIENT version of Greater Heal.
And still falls way short of Renew (RANK 3) @ 5.18 Health / Mana spent.
CONCLUSION:
Compared to any other Vanilla spells Renew is Hands Down without question the most mana efficient healing in the game.
I personally think it works great with only a single healer. Falls apart in raids due to overheal. I’ll continue to spam it, wait until my tank is 50% health and then hit them with my big heal hoping for a crit.