using warm water to increase dough temperature

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im currently mixing alot of dough in cold environment (16C/61F) which results in my bulk ferment going to slowly (im in a rented kitchen so have time concerns) and my shaped doughs being cool to touch. The result is a denser crumb than i have had previously...i have been using warmer water in the mix but think i may need to go warmer does anyone have a calculation i could use to work out water temperature to bring dough up to early 20sC/70sF? 

Im afraid of going to warm and killing off yeast and making dough too extensible....

anyone any advice....

basically im looking for ways to counteract temperature drop and make good sourdough loaves over an 8 hour period

thanks