I'm not currently planning any changes to my home heating system. This is purely a hypothetical question born out of curiosity, as an amateur when it comes to these sorts of things. Think of it as an experiment in creativity.

The basic question: Would it be possible to install a hydronic radiant heating system, using metal pipes and no plastic parts, on top of a traditional smoke vent ondol system, like those developed in Korea?

Basically, my reasoning is that if anything should ever happen to the hydronic system - e.g. damage to the pipes, or the water heater/boiler, or the gas/electrical lines, etc - the simpler flue system might act as an emergency backup, assuming that it's absolutely essential to keep the space heated.

To be clear, I have no doubt this sort of paired system would be a disaster in practice. I'm just not sure exactly how, so I'd like to ask some experts, if anyone's interested. How would smoke and heat exposure affect inoperative metal hydronic piping? Are some metals more resistant than others? What if the piping wasn't in the flue itself, but separated by a layer of tile and/or concrete and/or brick? So many layers between the ondol and the room would surely affect heat conductivity, but by how much?

Also, a couple more minor questions that I'm curious about: 1) In all my research, I've read nothing anywhere about using brick tile for the top floor layer of a radiant heating system, only other types of tiles. Is there a reason why brick floors wouldn't work well? They store heat so comfortably. 2) How large a space do you think a traditional ondol could sufficiently heat? The only information I've found about the size of ondol systems is that furnaces could be placed on different walls of the kitchen to heat adjacent rooms, and one "great room" of a temple that housed up to thirty monks at a time was heated by an ondol. I can't figure out the square-footage to furnace size ratio.

They are interesting, but like all masonary heaters, they are sensitive to fire quality and require maintenance cleaning. The lower the fire quality, the more maintenance... Smokey fires leave unburnt gasses. These condense on cooler surfaces and form creosote. If creosote gets ignited, and has a source of air, it burns like rocket fuel. Had a chimney fire when I was a kid. Ever seen a picture of a jet taking off of an aircraft carrier at night? Long blue to yellow flame out of the tail? It was a lot like that shooting straight up into the night sky. Destroyed the chimney liner, but the heavy stone chimney casing kept it from taking the house .Now imagine that happening under your floor... It has been done for a long time, but the structure has to be built for it and attention payed to making it easy to maintain. Very close attention must be paid to keeping a very hot clean fire. I have seen a few masonary heaters built with a rocket stove for a heat source which burns very cleanly, with passages and access ports for easy cleaning.

As for piping thru that environment, it obvioulsy has to be able to withstand/survive the environment without water(stainless?). The system would also have to be non pressurized in case the flow stopped, to allow someplace for the water to go if it should get to a boiling point(probably not likley as that seems way above typical temps in a floor heat system). Also circulating cool water thru that environment will tend to cause them to condense any products of combustion that are not fully consumed by the source fire. Kind of like a cold copper pipe condensing and dripping water in a humid space... You must be able to clean the pipes easilly.

If I only had brick and mortar as a building material, this might make sense, but with so many other material sources out there, there are a whole lot better ways to extract heat energy from combustion and deliver it to a floor system IMO...
As always my .02...

Building a traditional Hanguk style ondol system only as backup for when the grid melts down seems a bit silly, expensive, and is likely to run into building code/inspections issues. It might be deemed "worth it" if you made it your primary source of heat, but not as back up.

A wood stove would serve the same function, is cheaper, and you wouldn't have to explain it to the building inspectors.