A thermostat assembly (105, 400), comprising: a first portion (205, 405) comprising: a power circuit (310, 420) configured to receive power via internal housing line voltage wiring (135, 215, 470); a power conversion circuit (305, 425) configured to convert the power received via the line voltage wiring into power at a second voltage level lower than the line voltage; a first connector; and a second portion (210, 410), comprising: a second connector configured to removably connect to the first connector and receive power from the first portion at the second voltage level; a temperature sensor configured to measure an ambient temperature of an outside environment; a communication chip configured to communicate wirelessly with a primary heat source; the thermostat assembly characterised in that the first and second portions are separated by a barrier (235, 415) located in a frame of the first portion; the barrier comprises a dielectric and thermodynamic insulator that inhibits dissipation of heat from the first portion to the second portion to reduce an effect of a temperature of the first portion on the temperature sensor; and the barrier is positioned to prevent a human user from touching any electrical components of the first portion that receive power at the line voltage when the second portion is removed from the first portion. a first portion (205, 405) comprising: a power circuit (310, 420) configured to receive power via internal housing line voltage wiring (135, 215, 470); a power conversion circuit (305, 425) configured to convert the power received via the line voltage wiring into power at a second voltage level lower than the line voltage; a first connector; and a power circuit (310, 420) configured to receive power via internal housing line voltage wiring (135, 215, 470); a power conversion circuit (305, 425) configured to convert the power received via the line voltage wiring into power at a second voltage level lower than the line voltage; a first connector; and a second portion (210, 410), comprising: a second connector configured to removably connect to the first connector and receive power from the first portion at the second voltage level; a temperature sensor configured to measure an ambient temperature of an outside environment; a communication chip configured to communicate wirelessly with a primary heat source; the thermostat assembly characterised in that the first and second portions are separated by a barrier (235, 415) located in a frame of the first portion; the barrier comprises a dielectric and thermodynamic insulator that inhibits dissipation of heat from the first portion to the second portion to reduce an effect of a temperature of the first portion on the temperature sensor; and the barrier is positioned to prevent a human user from touching any electrical components of the first portion that receive power at the line voltage when the second portion is removed from the first portion. a second connector configured to removably connect to the first connector and receive power from the first portion at the second voltage level; a temperature sensor configured to measure an ambient temperature of an outside environment; a communication chip configured to communicate wirelessly with a primary heat source; the thermostat assembly characterised in that the first and second portions are separated by a barrier (235, 415) located in a frame of the first portion; the barrier comprises a dielectric and thermodynamic insulator that inhibits dissipation of heat from the first portion to the second portion to reduce an effect of a temperature of the first portion on the temperature sensor; and the barrier is positioned to prevent a human user from touching any electrical components of the first portion that receive power at the line voltage when the second portion is removed from the first portion.