Rubber hoses off gas when heated up. Enjoy the chemicals in the water.

When I started working construction back in the 80's there were some great designs to save on energy costs.

One pretty cheap one was special windows on part of the attic facing south. That part of the attic was turned into a insulated room painted black. The heat was transferred to copper water pipes that carried the hot water to a underground rock pit heating it up. The hot rock pit had another series of pipes that heated the house at night.