Today I installed the first Aquahot heat exchanger. I installed this one in the bathroom. The unit sits in the space where the water pump is located and comes out into the bathroom on the floor below the closet door. I don't have the circulating pump hooked up yet, but just for a test I ran the hot water out the bathroom faucet for about 30 seconds or so and connected the fans on the unit to a battery. Just in that short time, the heater was putting out quite a bit of heat and was very quite (almost not noticeable).
Now waiting on the circulating pump.