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

[Vance Nelson]

I have a Webasto DBW 2010 (45,000BTU) on my Grand Banks 32.  The control on 
cycling is in the amount of fluid that you have in the system.  The more 
fluid, the less it will cycle.  With my unit you need a total of about 12 
gallons of fluid.  I have two zones - one in the v-berth/head and one in the 
saloon.  This seems crazy on this small a boat, but in fact works very well. 
The saloon is all glass and the v-berth/head is all enclosed.  With guests 
aboard we close off the v-berth.  If we had only one thermostat one area 
would be very hot or cold while the other would be comfortable.

One of the deciding factors in my decision was the maintainability of the 
unit.  The burner head comes off the unit on the 2010 without disconnecting 
the plumbing.  Some of the other smaller units require the whole unit to be 
removed for servicing.

I have three air exchangers each 7,000 BTU, heated bunks, and heated 
domestic hot water.  The buffer tank is located in the engine room and the 
plumbing along with the tank tend to keep the engine warm for morning 
starts.  There is a total of 100 feet of PEX tubing used in the installation 
and it runs through the closet to provide warm shirts and jackets, and 
behind the drawers to warm your shorts.

What initially seemed overkill on a 32 foot boat has worked out very well. 
We were live aboard for a year on the Great Loop.  When we left the boat for 
three weeks, we just set the thermostats to 45 degrees and walked away.  The 
temps got as low as 16 degrees, but our furnace kept the boat from freezing.

It has been installed for just over a year, so no comment on life of the 
pumps.

----- Original Message ----- 
From: "Arild Jensen" <2elnav at netbistro.com>
To: "David&Joan" <djmarchand at cox.net>; 
<trawlers-and-trawlering at lists.samurai.com>
Sent: Monday, October 29, 2007 1:16 AM
Subject: Re: T&T: : Hydronic Heaters- which is best?


>> -----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
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