Thermal demagnetization furnaces are routine facilities that underpin countless paleomagnetic studies by allowing the progressive removal of naturally acquired magnetic remanence or the imparting of well controlled laboratory magnetization. The ideal thermal demagnetizer should maintain “zero” magnetic field during thermal treatments. However, magnetic field noise, including residual magnetic fields of material used to construct the furnace and induced fields caused by the heating current in the furnace are always present. As technology advances allowing the measurement of ever weaker magnetic remanences, it is essential that high-performance demagnetization furnaces are developed to reduce these sources of magnetic field noise. By combining efficient demagnetization of shielding and a new structure of heating wire, we have developed a new demagnetization furnace with low magnetic field noise. Repeated progressive thermal demagnetization experiments using specimens that were previously completely thermally demagnetized above their Curie temperature were carried out to explore the effects of fields within various types of furnace during demagnetization. These experiments confirm that magnetic field noise in various furnaces can have an observable and detrimental impact on demagnetization behavior and that this is reduced with our new design. The new heating element design and procedure for reducing magnetic field noises represent a significant improvement in the design of thermal demagnetizers and allows for extremely weak specimens to be successfully measured.