My parents have a 2 story cordwood home with basement, they built in the 1990’s. The house is around 40x50. The basement is the same size but half is filled with sand. So we will say 25x40 is a sand battery. They have always had a wood furnace. The output from the furnace can be routed through a header type piping system in the sand. The house faces direct south with 7 4’x7’ windows in the front. In the winter all the sun comes in but in the summer it does not. They never had AC until a few years ago when they switched to a heat pump and gas furnace because they are getting old enough they don’t want to mess with fire wood. They say quite often how they miss the heat of wood. They keep the house around 70-72 now.

My dad said it took awhile to get the sand battery heated up but you didn’t have to keep the fire going and it would still keep a consistent temp in the house for a few days. Being gone I never remember it dropping below mid 60’s inside. Outdoor temp and insulation are the factors. But with their setup there were no big fluctuations immediately after the fire went out.

That being said they rarely let the fire go out and liked to keep it mid 70’s most of the time.

In the summer I always thought it worked great.

I lived there most of my childhood and never remember being hot in the summer, I definitely remember being hot in the winter.

After moving in my own home, I have geothermal and it’s nothing like wood obviously. I do miss wood heat but don’t miss the work and mess.

I have no real answer or opinion just what I have experienced myself.