Robert Ray

I remember playing pool in Medicine Bow, the bar was so cramped the pool cues were cut off so you could get around the table. Long time ago, interested in hearing about your progress.

I'd give another thumbs up for the Cabela's 80L dehydrator. I still have my old Harvest MAid as back up but use the Cabela's for my dehydrating.

I have the Greenworks 20672. It's worked surprisingly well I had previouisly purchased the Greenworks battery powered lawn mower and was very impressed with it. My main use was to clear ladder fuel off of the pine trees on my property and have had no issues.

What's the town? Sounds like maybe Fort Laramie but I'd like to know. I'm thinking about going back to Wyoming from Oregon.

You might want to look at "constructed wetlands" https://www.researchgate.net/publication/256525012_Cold-climate_constructed_wetlands I've seen a system used in Pagosas Springs and it gets a bit frosty there.

Getting mauled by the new puppy on the floor and smelling puppy breath.

I think we are talking two entirely different things when we say boiler and heat exchanger.
A system where the feed resevoir is above the heated tubing and a valve introduces water is what initiated my voice of concern.
When talking scavenged heat from a flue I just don't see where we could stretch to the idea of heating a house but a coffee maker creative and doable. With the desire for instant heat small diameter tubing would be faster and far superiror than trying to create a thermosiphon with 1/2 inch tubing. A feed resevoir with an open loop to the recieving vessel would be safe and  easy to fabricate.
An open pan as has been described seems to me to be cumbersome if the desired end result is a cup of heated water. Why not a kettle on top of the stove?
Running  the tubing inside the flue presents another set of concerns, flue cleaning, acidic residue on the stainless or copper might be better served if monel tubing was used but then why make it so complicated. You have this free heat available outside the flue.
There is a reason that boilers are in the basement.

If we are still talking instant here.  Small diameter coil of soft copper bends easily without having to be annealed. Batch heating is no where near instantaneous. Physics has some crazy constants. Heat rises, volume matters, not only when we're talking heat exchange but changes from liquid to a gas state. My Toyotomi on demand water heater not only heats domestic water but also has a closed loop radiant floor heat system. If it's been offline (radiant heat portion)  as it is in the warmer months it takes a bit of time to get back online it is not instant heat like a conventional forced air heater or wood.  When working with hot water always think relief valve, better to know where it is going to pop-off than have an unintended failure in a surprise location.

When water turns to steam there is a 1700 to 1 change in volume and that is at 100c. There is a lot of horsepower in steam. So a milliliter of water will expand to 1.7 liters. so for a visual here you have talked 1/2 tube basically a roll of dimes so in a volume of 1 roll of dimes water to instant steam would change that roll of dimes to 1700 rolls of dimes, so from 3.5 inches roughly to 5950 inches of dimes in volume.  Now that wouldn't happen depending on ambient water temp volume introduced and actual temp of the tubing and ability to maintain heat.. Opening an overhead vessel with a valve to tubing heated to 250c will be initially pretty exciting there will be a cool down with the introduction of the water so depending on the tube diameter you might be making a horizontal aeolipile. Steam can be a volatile force.

At some point your resevoir plug of water above the steam coil is going to be overrun. That will depend on the length of coil and friction/weight associated with the volume of steam/water in the coil versus resevoir water weight.  Be careful Graham.