thermoneutrality

from The Century Dictionary.

• noun Neutrality as regards change of temperature; specifically, the property exhibited by salt solutions (see below) in consequence of which they may be mixed without producing appreciable change of temperature.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) Neutrality as regards heat effects.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun biology The state of being neutral with regard to heat effects; the state of being thermoneutral
• noun biology The heat-neutral temperature for a given animal: the temperature at which it does not need to regulate its body temperature