Thanks for an interesting post. You've convinced me of the...

Thanks for an interesting post. You've convinced me of the benefits of underfloor heating the way you have it. It's a shame it can't be retro fitted and you would have to install the best tubing available because a leak would be a nightmare.

Do you have a heat exchanger to keep the water under the floor seperate from the water in the tank?

Heat pumps/rev cycle A/C only heat the air and it doesn't take long for the temp. to drop when you turn it off. Similar to a car where it's almost instant when you turn it off. A wood heater seems to soak heat into the walls and floor much better and it takes hours for the temp. to drop, as long as 24 hours after it's gone out.
To place that heat straight into the slab makes perfect sense.
Did you insulate under the slab to stop the heat bleeding into the ground?

I agree with the size of wood being used, it makes a big difference to the quality of the burn. You need to top it up more often but once an hour isn't a problem and it gets you off your backside which is good.

The venturi cowl is widely available for less than $100.
The top is open and they might spin the line that rain never falls straight down so you don't get much water going in. Of course that's nonsense or a rain gauge wouldn't work but when the fire's going it's not an issue and at other times the flue is always well ventilated with it's natural up draught of dry air from the house. My sister has one and they didn't use the wood heater this winter but it's still dry inside. Since I mentioned it they leave the damper open to help the flow, just in case.
I worried about it at first but with almost 900mm so far this year and no hint of water i've stopped worrying.

I've got the middle version. All SS apart from the base plate which is galvanised.