Hey maker people! It's clear now that I'm never going to get around to prototyping this idea for a cheap heat recovery unit. If it works, you can ventilate your building without spending more on heating.
Idea for a ventilation fan with a *cheap* heat exchanger made from kitchen foil, foam rubber, wood, and lots of glue

@brunopostle that's pretty cool, the problem with that type of things is how to keep it clean and avoid condensation. I guess one could make a version that simply unrolls?
Sounds like something to propose to the Open Source Ecology people

@duncan_lithgow Unrolling it would probably destroy it, but yes it definitely needs some way to collect condensate

@brunopostle actually just mounting it on it's end with an airtight water-absorbing "bottom" should do the trick (sealing it might be tricky). Maybe a piece of softwood with a milled groove? The wood would also be a great way to keep an eye on potential bacteria problems - they would populate the wood first.

@duncan_lithgow I was thinking a drain tube that fed into a water trap, so maintaining air tightness.
In a heated building situation all the condensation would be in the air outlet, so mould probably isn't an issue for fresh air brought-in. It could all go wrong in an air conditioned building with warm humid air outside.

@brunopostle what about a trickle airflow through a bank of old car radiators?

@duncan_lithgow that could work, though I'm not sure they have the same internal and external area, so it might require two sets of radiators with water circulating between them

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