T&T: : Hydronic Heaters- which is best?

[Arild Jensen]

> -----Original Message-----
> From:  David

> 50 to 100K BTU/hr on a 40' boat. Wow!!! Many houses have only a 100K BTU
> furnace. You should be fine with 20K BTU/hr in anything but the dead of
> winter in New England. You don't want your system to be too big.
> A smaller  system that operates at a more significant duty cycle will keep
> your boat at a more even heat.
>
> David


REPLY
David is quite right. Many of the problems with diesel fired on board
systems stem from not being sized correctly.
too often the retailer will up sell to a bigger unit to make a bigger
profit.
Good installers who know their stuff will more often recommend the right
size. A sales clerk in a store may not even know or realize the problems
inherent in over sizing a furnace. They don't have to live with the
consequences.

Unlike home furnaces which can be fine tuned with different nozzles, most
boat furnaces cannot be adjusted that much.
Over sizing a furnace means it short cycles. More frequent start up and shut
downs means more wear and tear on the components. The firing chamber expands
and contracts each time the furnace cycles. You are more apt to get sooting
and clogging of the burner. On the flip side, an under sized furnace will
never shut down and will wear out too soon.

Something else to consider. Ask the manufacturer how many hours the
principal pump/fan motor is rated for.
It used to be Espar and Webasto furnaces had a 3000 hour rating on their
pump motor.
In a live-aboard situation this amounted to about two years of normal use.
My last new furnace lasted exactly one month past the warranty period, then
the blower bearings started to squeal.

Hopefully the new generation of Espar Hydronic heaters have ball bearing,
10,000 hr rated motors.

Another frequent cause of problems was the fluctuating DC power supply.
Automotive, truck and RV  equipment is designed to work on a nominal voltage
of 13.6V  That has been an industry standard for as long as I remember back
to the 1970's.
All too often the battery voltage varies  from a high of 14.5V to a low of
12.0 or even lower.
Unfortunately once the voltage drops below the 13.6V level things start to
malfunction or not work at optimum.

I'm not surprised to hear the new ESPAR runs at 24V. It makes sense since
this forces the installer to include a DC-Dc converter which now provides a
regulated steady supply at optimum voltage, regardless of what the battery
is doing.

Regards
Arild