instead of asking for a temperature I would use some easy obtainable physiological parameters, as IS THERE A SWEATING RESPONSE OVER THE SKIN (NO), ARE THE ARTERIOVENOUS ANASTOMOSES OPEN, (That is are the temperatures of the distal part of the fingers high(YES)) this might be an answer to your question. and  this is an easy way of determining whether a person is in an optimal thermal state , which I believe is a prerogative for comfort, and thus also for the room temperature.

See my paper: Physiological reactions to wet -cold. Av8at, space, environ Med. 46(!):33-36,1975, and

 Themal responses to w«ole body. cooling in air with special reference to AVA in fingers, Clin.Physiol.funct,imaging (2012)32 pp 463-469.

It's around 22 °C - 24°C, please before, read the papers of research about this interesting theme, it's very usefull in neonatal premature (human) enviroment incubador.

I would recommend giving this paper a read in order to delve deeper into the integrative physiology behind the Thermo-neutral set point in humans. 

Article System properties, feedback control and effector coordinatio...

Hi:

I think the comfortable room temp. ranged from 22 C to 26 C.

Great regards

28 degree C is the most appropriate temperature people feel comfortable. Try it