first off what is the wall thermometer an old bulb type (red Liquid) or the furnace thermostat. You are 8 feet from it you are measuring air temp while it is measuring wall temperature. To get a totally accurate reading you need to physically attach the two together i.e. tape them together or something. To get a 99% accuracy you would need a laboratory grade thermometer. What is normally done is to put both sensors in a glass of water either with ice, room temp or boiling water then compare them. And different thermistors read different values at same temperature. Your temp sensors needs to be calibrated to read right. If this topic interests or concerns you study Arduino thermistor and various libraries and the different formulas to read them
Well the kit was pretty cheap and finding information about the actual discrete parts used is not something I've got great skill @. Was kind of wondering if I was being an idiot or if I'm just another chump in the crowd lol. Being new to something makes you question your intelligence alot.
I would be more inclined to trust the DS18B20 than the thermometer on the wall, and no, they don't need to be calibrated. They are not thermistors.
Here's a thread on calibrating the sensorhttp://www.avrfreaks.net/forum/calibrating-ds18b20-temperature-sensors-better-accuracy
my quick $.02 - the quality of the sensor matters - in terms of library support and usability. I spenmatht way to many hour cursing temp sensors, and getting BS readings, until I switched the sensor type I used. I'm now using an AM2302. cost a few bucks more, but worth it in that it works, and gets working quickly without a ton of funny calculations.
Well I tend to think that if 2 things read the same thing then they should read the same value.