Controlling trvs with backup heat

mburg

A customer put an addition on there home about ten years ago and used a gas fireplace to heat it up until now. we are putting a few panel radiators in the addition now, unfortunately due to the customer not overly liking the look of the radiators we cant put enough in the space to completely heat on a design day. they are fine with this and are expecting to turn on fireplace on colder days. we are putting trvs on all three radiators. normally I would put a thermostat to allow them to shut zone off when they want and have setback when they go to work. unfortunately they do not want two thermostats on wall (one for fireplace and one for radiators) I thought about a two stage stat but I figured if I set it at say 70 with all trvs on 68 to have constant circulation than it would start fireplace thinking radiators where not keeping up. I Also thought about using a set point controller to turn pump to radiators on whenever outdoor temperature was bellow say 65 and let outdoor reset and trvs take over from there with existing stat for fireplace remaining as is, but than they loose setback on radiators. Any suggestions on how to control this with only one thermostat on the wall.