heat exchangers

Chris Craft direct replacement heat exchanger allows use of hot water cabin heater in cooler climates.

Alas, neither cite fits the bill. One is a marine water-to-water unit, it appears; the other URL is a paper on engine heat. Neither is useful on a 2 cyl. aircooled generator.

Original VW beetle heat exchangers maybe. I don't know the details from having one, although I know some people that have, but they used exhaust heat exchangers to heat the cabin air. IIRC the only problem was when the heat exchangers became perforated and started passing exhaust into the cabin air.

Yes, any plan to capture generator waste heat should include redundant CO detectors. If going this route, the entire generator should be enclosed to capture the heat radiated from the block as well, with combustion air ducted in to the carb from outside, the exhaust routed through a few turns of oversized pipe and then outside, and fan forced cooling air over the whole mess.

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Check the marine engines. We do this all the time to keep salt water out of the engine cooling jackets.

But those are for liquid-cooled engines; this is not one.

There are industrial ones that are pricey like these:

I suppose you could also adapt a standard household gas fired water heater. One of the ones with the helical gas coil inside would probably be more efficient than the straight tube up the center type Art.

To the best of my knowledge, the VW heating system directed engine cooling air into the cabin, and very little of it at that. In 1963 they started installing a gasoline fired heater which I found totally unreliable although the latter models were somewhat improved. On the other hand, an "after market" accessory for the model "A" Ford was a cast iron shroud around the manifold ducted to a butterfly valve through the firewall into the area of the front seat passenger's knees. Gerry :-)} London, Canada

They were exhaust heat exchangers, Gerry, as Dave Billington mentioned. Living in Michigan when I had my '64 VW, I became intimately familiar with them.

They had insufficient output, especially for the windshield defroster. By the time the air got up there is was barely warm and the flow rate was feeble. The original equipment just bled a bit of cooling air from the high-pressure area under the sheet metal cooling shroud.

The cure was one or two blower-boosters that we usually bought from J.C. Whitney. You could get one for each side. They worked like a charm.

But they do cool the exhaust as well. There are water jacketed exhausts with two coaxial pipes. The exhaust runs thru the inner pipe and water circulates in the space between the two pipes.

Then there are water injected exhausts that have a sort of upside-down u-trap after the engine's exhaust manifold. Water introduced into the exhaust at the downstream side of the trap cools the gases and the plumbing enough that rubber hose can be used beyond that point.

The water jacketed system would be the most practical for reclaiming exhaust heat.

One approach is to take a (non-leaking) gas-fired hot water heater and pipe the exhaust to go up the stack of it (in place of the burner gas flow). You could do the same with an old oil-fired boiler, or with a gas instant hot water heater exchanger.

You can probably find something in the boat industry, but it might be just as fast/cheap to get one tigged up. Best if it breaks the exhaust stream up into multiple streams, and the closer it is to the headers, the better. Before/instead of the muffler, not after it, preferably.

One of those stainless steel flat plate heat exchangers would probably work fine (if a large enough one was selected) until it coked up - they are not great for cleaning.

I have not seen them for small, ie less than ~50 Hp, but exhaust to water exchangers are common for exhaust heat recovery on larger engines. One thing you might want to watch if making one, is that the water vapor in the exhaust will condense, and it will be corrosive due to sulfur content in the fuel. Hence the unit should be made of stainless or something else that won't corrode. A simple shell and tube unit would be easy to fabricate from some tubing. Be sure and have a T & P valve or relief valve in case water circulation is lost.