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I moved from Europe to USA 4 years ago and I was wondering if it's possible to combine forced air heating with the heating that uses radiators.

My idea is to use the furnace for forced air to heat up water for radiators at the same time it heats up air for forced heat. Use it to heat up air and also function as a boiler. In that case I can increase the efficiency of the heating.

Next question is if I can use the same chimney for the furnace that uses wood with the furnace that uses gas(forced heat)? Where I'm from originally you are not allowed to use the same chimney but in USA I talked to a professional and he said that's ok but I'm not sure if I can believe him.

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You seem to be asking two different questions ("Can I heat water for radiators with my forced air furnace?", and "Can I use the same chimney for wood burning and gas appliances?"). You should consider creating two separate questions, instead of asking both in a single question. – Tester101 Jan 23 '14 at 15:32
If you heat water at the same time as the air, the air won't be as hot. You'd need more heat. Otherwise you'll end up with lukewarm air and water, instead of hot air. Nothing in life is free. – Tester101 Jan 23 '14 at 15:36
I guess there is a sensor and it will keep heating until it gets the heat which is needed. So I don't think that I would end up with not enough heat. I wonder if there is some documentation on your claim so that I can investigate more, thanks. – SamotnyPocitac Jan 23 '14 at 15:38
Physics will back my claim. A furnace produces a specific amount of heat, most of that heat is transferred into the air (which is then spread throughout the house). If some of that heat was transferred into water as well, there would be less available to go into the air. And so, the air would be less hot. Running the furnace longer might get the air and water to the proper temperature, but you have burned more fuel. – Tester101 Jan 23 '14 at 15:42
If you prefer radiant heat and want to change over, that's your personal preference. If you're simply worried about ventilation with a radiant system, you can surely add a ventilation system along side radiant heating. If your furnace is running every 5 minutes for only 5 minutes, there are other problems. – Tester101 Jan 23 '14 at 18:04

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