They say it can't be done, but it is done routinely in Europe. For proof, here is German gasifier boiler claiming 90 percent efficiency and 70 percent output to water http://www.he-energy.de/Downloads/HEE_Walltherm_engl.pdf and designed for the living room. Yes, it is expensive, and doubly so priced in Euros. But here is the British made Stratford SEB-20 which is 73 percent efficient and delivers 60 percent of its output to water. www.eco-boiler.com I have one in my garage at this moment; I bought it on www.ebay.co.uk and got delivered this month for $2,300, all in, thanks to the depressed British pound. So why does this site say in an article about domestic hot water: "A woodstove cannot produce the volumes of water needed to heat your home through a baseboard or radiator system." And why does woodheat.org say "The first thing that needs to be said is that a wood stove is not the right device for heating water for in-floor radiant. You would never get enough heat off a wood stove to make a dent in radiant heating needs." What they mean to say is that you wouldn't take your U.S.-built horse and buggy out onto the Interstate. They are mum on efficacy of aiming a Mercedes or Land Rover at the divided highway. (To be fair, Europeans have enjoyed 30 years of coherent energy policy. The U.S. stove industry has been whipped from pillar to post.) Why does indoor matter? Given adequate storage, an indoor boiler can deliver btus at far greater efficiency than OWBs, to say nothing of the charm of flames dancing in your living room. The average attentive homeowner can tailor relatively short, hot, nightly burns with far greater effect than an OWB cycling in and out of idle mode. The question of handling wood outside vs. inside comes down to how much wood we're talking about. If the German Walltherm burns a third as much wood as an OWB, would you be reluctant to cart it into the house? Trouble is, the U.S. industry wants you to think there is no choice. Here is the Hearth Patio and Barbecue Association, the trade group for stove retailers on the subject of EPA certifications: "In the U.S., it is illegal to buy a new wood stove unless it has been EPA-certified." And the EPA on the same subject: "In some states and jurisdictions, it is illegal to offer for sale, purchase, operate or sell a house containing a wood stove not certified by the EPA Wood Heater Program." Obviously you want to check, and reach for the salt shaker if someone says "trust me, I sell stoves."