The line of sight range with no obstructions is rated at 100 meters (about 325 feet), but this is based on completely wide open space, with line-of-site between the transmitter and receiver. Real-world conditions will almost inevitably reduce that ideal range. It's impossible to say how a particular set of conditions will affect things exactly without testing, since every situation is different (obstructions, radio interference, etc). Generally speaking though, the sensors will work well throughout an average-sized home, or in the same or perhaps adjacent room with them inside a refrigerator or freezer, etc. Again though, it's all very dependent up on the specifics of the installation, so testing and perhaps a bit of trial and error can be necessary.
With obstructions in place, particularly if there is also a substantial distance involved, often the signal strength and connection reliability can be very dependent upon small changes in placement. One thing to keep in mind is that water, or anything containing water (like virtually all food, living things, etc) is a very efficient absorber of Bluetooth signals. Keep this in mind when placing the equipment.
Additionally, the transmission strength can depend even on the relative orientations of the antennae, so it's worth even playing with the orientations of the sensor and/or the gateway antenna to see if you can improve things that way.
It's best to just change one thing at a time and watching for a bit to see if things improve. If the devices are communicating intermittently, that's an indication that the system is right on the edge of getting enough signal to work reliably, so any small improvements can make the difference.
Learn more here: http://www.sensorpush.com/articles/signal-range-and-sensorpush-products