I said it is a competitor, the 390 competes with the 970 and the 390X competes with the GTX 980. The R9 390 draws in 255W of power under gaming load, and the GTX 970 draws in 164W under gaming load. In terms of heat, yes, the 390 has more heat produced because heat is directly proportional to electricity. However, when they design graphics cards the OEMs (such as MSI, EVGA, Asus), they design the cooling systems to cool that amount of electricity. They are not going to release a card that has insufficient cooling - it just won't happen. Hotter cards may have better cooling systems remember, too.
For electricity, if you game 3 hours a day and have an electricity price of 20 cents per kilowatt hour (about average in the U.S.) you will save $24.96 yearly with the 970 over the 390. Chances are you won't game that long, and your electric bill could surely be cheaper than that. That was also calculated with a power supply at 80% efficiency, so higher efficiency also decreases that money saved.
You can find the full specifications of AMD vs Nvidia power consumption and money savings here: http://www.tomshardware.com/forum/id-2833574/electric-bill-amd-nvidia-mathematics-calculated.html