OK, just to clairify
The Wallas units will burn diesel fuel. This can be either #2 (most common), or #1 (cold weather formula). Kerosene burns just like #1 diesel.
My experience is that if you burn #2 diesel in an espar unit it will soot up, requiring disassembly and cleaning once or twice a season.
The Wallas units are extremely quiet. This is due to the type of combustion chamber they use, and the reduced air velocity that is utilized both in the combustion process and the heated air system. The combustion process on the wallas is a "pot" system that looks more like the burner on a stove when lit.
The Espar units use a "gun type" of combustion process. Think of it as a high velocity air stream that a mist of fuel is injected into. Thats why the espar units sound like a jet engine. The espar units also utilize a higher speed air velocity in the heated air system. This air velocity is what you hear.
BTW, the webasto and espar units operate identically.
Another source of noise which is particular to hydronic systems is the heat exchanger fans. The fan on a heat exchanger is basically a computer style fan, and since the fans are located right on the heat exchanger and the heat exchangers are located near where you need the heat, you hear these fans.
Another consideration is cycle time. A typical heating system as you know cycles on and off as heat is called for by the thermostat. This cycling on and off can cause the heater to soot up. It also uses up battery power since the ignitor on all of the heating systems is a resistor type. Each cycling of the furnace is something you can hear. This cycle time issue is not so much of a problem in very cold weather as it is in marginal weather.
Even if you turn your hydronic system to "on" all the time it will cycle on and off. Thats because the water temp reaches the max temp, and the furnace tries to reduce the output in steps but is generally not able to reduce output enough so the unit shuts down, only to restart a few minutes later.
Generally furnace salesmen will try to sell you too large of a system. Thats safe for them because larger always works, and they explain away the short cycling as part of furnace life.
What I liked about the Wallas is that the new units will infinitly modulate the output from very low power to high power based on the thermostat. That, along with sizing the units properly for my actual conditions resulted in a system that once started rarely turns off due to high temp.
On our 4788, which is by any measure a "big" 47' pilothouse boat we have three area heating needs being the pilothouse, the salon, and the cabins. The low design temp is 20F with normal temps being in the 40's andf 50's.
Using that as a guide I selected a Wallas 30DT for the cabins, a second 30DT for the salon, and a 22DT for the pilothouse with defrost capability. This gives me three separate heat control zones, which is just right for the boat.
and... The wallas units are almost silent. You cannot hear them unless you listen VERY carefully.
