I have an older cabin which is not equipped with conventional HVAC duct. This makes it entirely hard to heat in the winter. In the study room, we’ve installed a compact, natural gas heater. This furnace is a ventless, single-period heater. Because it is ventless, it creates an oily film on the windows in the study room. I have a pair of antique French doors which each have twelve small windows. These windows are time-consuming & frustrating to clean. In the summer, I rarely need to worry about them. During the winter, they are forever cloudy & in need of a thorough scrubbing. Because the furnace is a single-period unit, it blasts heat at maximum capacity unit it achieves the temperature control setting. It then shuts down & cools itself by blowing cool air. The constant on & off cycling results in unpleasant temperature swings. The ventless furnace is also entirely temperamental & requires constant filter cleaning. At least once per week, I need to remove the two filters & meticulously scrub them. If there is any debris clogging the filters, the warning light on the unit starts blinking red, but when this happens, the furnace will no longer shutdown. It keeps running on maximum capacity, & I worry that it might overheat. Overheating could damage the furnace or even present a safety hazard. Once a year, the filter cleaning is not sufficient, & I need to take the furnace apart & scrub it with high pressure air. The pressurized air removes any buildup of dust. Unfortunately, this dust then fills my study room. I should perform this job in the summer, as a proactive strategy, when I can open the windows. Instead, I consistently wait until the furnace refuses to operate properly, in the middle of the winter.