Which type of heat exchanger would be best for my use?

Hi there! I'm new to this forum, but damn, what a great amount of detailed information we can find here!

So, I am renovating an old house in Slovakia, I am about to be done with the electricity, and I am working on the plumbing designs, especially the heating part.
Winters are cold here, and I don't have access to gas lines.. so my central heating system will be mainly fed with a mass heater, solar thermal panels in the future, and complemented with the cheapest electric heater I will find 2nd hand.

My first thought was to bury a copper pipe inside the mass of a rocket stove, to act as a heat exchanger for the heat-transfer liquid sent to my domestic heaters... but then, I found a video from a guy, who added an extra conduit and a fan, from the top of the mass heater's body to drive hot air released by the oil drum into corrugated pipes, to warm the air inside the rest of the house (a geodesic dome in his case, here's the video: ).

That would be feasible for me too, and air-to-air heat exchanger seems simple and more efficient to me than using a heat exchanger to warm up the water, to warm up the radiators in the rooms...? I am no expert on these questions, so I thought you guys might have better insights! What is your opinion on this technique? What seems the most efficient, knowing that my house is small (single story, 75m2 house... so there souldn't be a lot of heat loss when carrying neither air nor heat-transfer liquid to the different rooms)?

I'm looking forward to your replies!
Cheers

Welcome to Permies!
You mentioned a few different heating methods, radiators(hot water), solar thermal, RMH, and electric as a backup.
I sense that you might be trying to integrate all (most) of them into one (hydronic?) system? (the electric being the exception, though it might not need to be?)
75m2 is about 800sq.ft. for the non-converts here in the U.S.

Solar thermal with a loop circulating in the RMH bench could be good for spring and fall, for charging the bench during the daytime and not needing to burn a fire.
I'm not sure if in colder weather, this would work as well? The bench would be warmer by fire (maybe?) than the solar could make it? meaning the solar wouldn't be an addition?

Possibly, if a hydronic loop began HOT in the mass, then to WARM at radiators, then COOL return water could go through solar to get a WARM boost before returning to the mass again? This gets complicated on the control side, to open and close the solar thermal "zone" when it is/isn't producing... and doesn't always line up neatly...(clear and sunny versus bad weather or nighttime)

One idea for connecting solar thermal to a mass, is a radiant floor system in concrete (could be earthen floor too). Another would be some sort of storage tank, which could also be integrated with a domestic hot water system.

Hey, thanks for the answer =)

Yes, you are right, I'm looking into an integrated central heating system, that would combine thermal solar, Rocket mass heater with a heat exchanger coil, and a cheap electric backup heater for when I'm on holidays for example, to prevent freezing.
My initial thought was indeed to have this system working for hot water heating through radiators, and sanitary hot water (boiler) for showers, kitchen tap etc.

Here is the diagram of my system, as I thought of initially:


So the hot water loop is first pushed by the pump into the 3-way valve, which depending on the needs will redirect the flow to the boiler, the radiators or both. the water cools off (as it warms the sanitary water or the radiators) before going to the RMH, the solar panels and the electric heater to heat up, then back again to the pump for another loop. Bypass loops allows me to cut parts of the circuit (for example to drain and prevent water to go in the solar panels in winter when it might freeze, or to prevent hot water from the solar panels from heating the RMH's mass on hot summer days). I didn't show this idea with anyone yet, so I hope it's not ridiculous, but it seems feasible to me, and I hope it would greatly reduce my electrical bill...

Now my question is mainly regarding that air-to-air heat exchanger in that video, and whether it wouldn't be smarter (in terms of energy efficiency) to directly heat up the air in the rooms with the RMH through a ventilation system, instead of heating water to be sent to the radiators. Obviously the limitation of this system would be that I can't really heat up the sanitary hot water with a air-to-air system, but for the space heating, I wonder which would be the best..?

So, in Rob's video, he has integrated his RMH with an earth tube system. He is taking excess hot air in his dome greenhouse, and cooling it (storing it) in the floor of the greenhouse via earth tubes. The earth tube system is balancing/shifting the heat day/night, and to some extent seasonally. The mass in his RMH is the floor., and he's sharing the tube system as a way of distributing the heat.

In your case, I'm not sure if it's necessary? Considering the size of your house (I'm guessing it is a compact, square-ish shape?) and you (already have?) are planning a hydronic system... It seems like an extra layer, a second heating system...duct work/vents between rooms.

Nice diagram of your system!!