wood hydro boiler/stove/H2O htr ???
 

My new living addition(approx 1,000 sq') will have high mass hydronic radiant heat for primary heat. I am researching back up/supplemental heat source for heating water with wood to supply my hydronic radiant floors. Being also a very air tight space with heat recovery fresh air, combustion devices add unwanted issues without outside intake air. Anyone aware of indoor units that have, can be converted or DIY modified to have outside fresh air intake? Outdoor boiler systems are overkill for what I need.

I believe any high efficiency wood boiler will have a dedicated air intake, and obviously exhaust.

I will look into those further and see how small of one is available. If one chooses to build a low heat/cool demand living spaces by using passive solar and super insulation and heat recovery finding heating sources for meeting that lower demand is overkill in capacity and cost. Especially if you go rural electric(off peak) for primary and really need a backup source in case of interruption. Few, but the consumer/individual, are really concerned about lower energy bills.

I know A few people who have an air inlet vent behind the wood stove so the stove can breath properly. If your house is too tight the wood stove will burn weakly
If you ran a large diameter fresh air inlet metal pipe to the front the wood stoves damper area you could feed it mostly outside air.

They must make a small wood heater with a ducted intake vent for a cottage,

Google for wood fired stoves with back boilers in the UK. They have a lot of them there and the typically 2/3 of the heat goes to the storage tank or rads and 1/3 goes into the room.

I know this is not a hydronic solution, but I have a tight house in northern NewJersey that I heat with a single wood pellet stove. It is a two story raised ranch, and the stove is on the lower level.

Your wood pellet stove should have a dedicated air inlet. I'm sure there is a fresh air kit available for it. I have a woodstove and bought the fresh air kit but still have not installed it.