First time trying to improve efficiency- any advice welcome

We are about to start an extension in wattle and daub which will be our main living area. Currently we heat our very small home with a stove (model pictured) that definitely loses a lot of heat up the chimney. I was wondering if I could use this stove with some kind of heat exchanger like in this video    to pump the extra heat into the bedroom?

Or is it better to build from scratch?

Hi Eilidh, thanks for sharing that video, I found it interesting. It was a little concerning that he appears to have reduced his flue slightly at the exchanger, but it seems to work well.
Is your bedroom beside the new living area or above? Not that it probably matters, but I'm trying to get a picture in my head of what you're arrangement might be.

Nancy Reading wrote:
Is your bedroom beside the new living area or above? Not that it probably matters, but I'm trying to get a picture in my head of what you're arrangement might be.

The bedroom is beside and will share a wall with the living room. If this setup seems feasible it would just be a hole knocked through for the flue but I was also thinking I could make the dividing wall a heat exchanger chimney so at least some of that heat will radiate into the bedroom. Something like this (not sure what it's called, all the images I can find for this kind of setup seem to be in Russian or Polish)

You need a a well insulated section of your smoke stack to raise the temperature high enough to burn the smoke.  Perhaps you can do this in the first 90 bend and horizontal run.  Not sure how long this section should be but that's important.

Welcome to the forum!

While I really do not know, I feel adding thermal mass would be more efficient:

https://permies.com/t/135449/Thermal-Mass-Wood-Stove

https://permies.com/t/72030/Affordable-add-mass-existing-woodstove

Insulating part of the stovepipe leading from the stove is not going to make it burn fully. Depending on the stove, the exhaust will only be hot enough to keep burning when the stove is burning at its highest rate, and stovepipe is not made to endure fire inside. It will quickly corrode through and create a hazard.

Pulling heat from the stovepipe without burning everything first is a recipe for disaster, as creosote will condense and build up, and eventually during a hot fire start burning and destroy your chimney and maybe your house.

Adding lots of thermal mass around but not touching the stove is the only safe way to improve performance, aside from making sure you always use dry seasoned wood and keeping the fire burning briskly rather than smoldering slowly.