I am dubious about drain water heat recovery for residential purposes unless the DVW is specifically engineered so that other cold water sources like toilets and sinks bypass the exchanger. Also, the distance from the source to the exchanger will greatly reduce its effectiveness. IOW the cost of the equipment, additional piping and installation will be much higher than its payback. We do use the technology for large commercial applications though. Particularly hotels and hospitals where the laundry generates quite a bit of recoverable heat.