Originally Posted by
tjspiel
The loads of a residential heating system (enclosed, insulated space) do not come anywhere near what you are proposing. The operation (energy) costs of such a system would be very high in this climate. The maintenance costs of something that large would be astronomical. Installation isn't cheap either.
Doesn't necessarily have to be. Sewers tend to be quite warm. That warmth can be xfered to bicycle paths either by running the sewers directly underneath where possible or using passive heat pipe (plug for a local 3M product) to pipe it up. Not sure how costly any of this would be (the fun of being an arm-chair planner).