I don’t think the previous system was using space heaters though, the PTAC they had before presumably had a heat pump in it if it was generating condensation.
The temperatures we’re talking about (1000C) would be incredibly dangerous in residential applications, plus a small installation would lose too much energy to the environment due to the ratio of surface area to volume. More practical IMO is to use a daily cycle like what Harvest Thermal is doing: store energy in your water heater tank during the daytime and release it at night.
Also radiosity for offline rendering got largely replaced by sampling based techniques, first things like photon mapping and more recently by path tracing. Sampling approaches are easier to parallelize and generalize better to other types of materials.