I wanted to share something that helped me be able to have a warmer house during the winter, in case it helps someone else. I cannot tolerate natural gas furnaces or wood burning stoves. The thing that helped me is an air source heat pump. A heat pump is similar to one of those outdoor A/C units, but it can work in reverse and provide heat in the winter as well as A/C in the summer. It is connected to our central air/heating system in the basement through pipes that transfer the heating/cooling fluid. We have a 3-ton heat pump and it is rated to produce about 35,000 BTUs at 47 degrees Fahrenheit, which is equivalent to the heating capacity of about seven 1,500 watt space heaters. The colder it gets, the less heat the heat pump produces. But even at 17 degrees Fahrenheit it will output 20,800 BTUs. We supplement the heat pump with electric space heaters in colder times.
I probably wasn't familiar with heat pumps because hardly anyone has them where I live, as heat pumps don't do as well in colder climates. But the heat pump technology has greatly improved over the years. They now have models that work quite well in colder temperatures. In such a system there is a 2-stage or variable speed compressor that works harder in colder temperatures to provide more heat. Some of the higher-end models I looked at were $13,000-16,000. The model I purchased was a more standard model that cost under $4,000, which included replacing the A/C unit with the heat pump and installing the thermostat inside the home. They hardly even had to do any work inside the home, which was good for MCS issues. And I figured since running the A/C didn’t cause MCS symptoms, the heat pump wouldn’t either, and that proved correct.
If you have electrical sensitivity you can get an extension kit and place the heat pump pretty far from the house without much of a decrease in efficiency. However, you will still have some EMF from the fan located in the heating system inside the home. And be aware that some models are wi-fi capable.
A mini-split is a smaller heat pump and some of those models can produce heat at full efficiency at temperatures below 0 degrees Fahrenheit. Those can be installed in an attic or on an exterior wall--you don't necessarily need ducting. And you can put more than one in a home. LG and Mitsubishi are among the companies that manufacture those. Mini-splits require some construction work to install—making openings in a wall or ceiling, etc.
Other options I have considered include radiant floor or baseboard hydronic systems, powered by one of the following: (1) a ground source heat pump; (2) solar heating systems such as evacuated tube collectors; (3) a boiler in an exterior building powered by natural gas or another fuel. I liked some of these ideas but they are more expensive and easier to do on new construction.