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Old 29-10-2024, 10:36   #1
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Hydronics Heat on a 39' Catamaran

New cruiserforum member here. Thought I'd join the conversation.

** Background **

My wife and I lived aboard a Hunter 31' monohull at a marina in Florida for about 2 years (Fall 2017 thru Fall 2019). We had our first child (boy) during this time and moved back to shore when he started walking around and that boat started feeling a bit small.

Having the itch to get back on the water, we bought a Privilege 39 catamaran and lived on that for 6 months from Fall 2021 through Spring 2022. We had just had our 2nd child (girl) at that time. That boat had lots of wiring issues and I grew to feeling it wasn't safe for us to be onboard because of the electrical issues I kept finding.

Fast forward to now, and my job has brought us up to Virginia. Since then I re-wired the boat, so electrical is good now. That did take a minute.

Now we're planning to live aboard again but this time will be winter when we move aboard and we have 3 kids now. We're hoping to go cruising sooner than later, but financially it's going to be another year at lest.

** Heating Options **

When we purchased the boat it had an older air conditioner under a salon settee with electric heating element. This cooled/heated the salon and fwd 2 cabins. We used that heat during the winter in Florida we stayed aboard and it worked pretty well. However, the AC part of it gave me lots of trouble and the whole unit was quite rusty and old so I got rid of it as part of the boat re-wire.

One option is to install a new unit like it had. And I may still do that. But it does tie us to the dock (unless I install a genset as well) which I'm not wild about.

I've decided to install a hydronics system. Online I haven't found many detailed build threads so thought I would chronicle mine for posterity. Most of the info I've found (esp. YouTube) has been related to van-life, which is a bit simpler.

At first I was planning to install a couple diesel air heaters, but the ducting challenges, and more importantly the idea of open flames within our living spaces ended up making me decide against that option.

** Basic Layout **

10kw burner. Planning to use an HLN model which is like a higher end Chinese version.

4.5 gallon expansion tank.

6.6 gallon water heater.

10 gallon buffer tank.

3 thermostat zones within the cat: main salon and each hull.

The salon to receive the Kalori Silencio 2 radiator.

The hulls to receive a Kalori Evo 1 in each below the floorboard. These each have 4 outlets (55mm). Planning to run the 4 little air ducts to fwd cabin, hallway, head, and aft cabin, respectively.

Additionally, down the road I may add heat to the battery compartment in aft starboard engine room and to fwd lockers that have our water tanks (55 gallon in each hull).

Planning to use 3/4" main line that goes into a dual manifold such as this one that will allow each zone to be controlled independently.

In the salon I'm planning to have a control panel with the 3 thermostats as well as fan switches that control the blowers high/medium/low.

So that's the basic design. As components are installed I'll update progress.
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Old 31-10-2024, 14:39   #2
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Re: Hydronics Heat on a 39' Catamaran

I just re-started this thread under the "Plumbing" section as that is probably the better place for this. The moderators can remove this thread if they would like.

Sorry, I'm new!
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Old 31-10-2024, 18:06   #3
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Re: Hydronics Heat on a 39' Catamaran

Hydronic heater with air ducts?On our 55 foot cat we split the hot water output from the hydronic heater into 5 lines: one to salon and forward/aft in each hull. There’s a small heat exchanger controlled by individual thermostat in each of the 5 locations. That removes the need for bulky ducting and means you just needs room for two hoses if you want to expand the system. The system still uses a bit of electrical power to pump the coolant and for each of the heat exchanger fans.
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Old 01-11-2024, 02:26   #4
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Re: Hydronics Heat on a 39' Catamaran

Quote:
Originally Posted by fxykty View Post
Hydronic heater with air ducts?On our 55 foot cat we split the hot water output from the hydronic heater into 5 lines: one to salon and forward/aft in each hull. There’s a small heat exchanger controlled by individual thermostat in each of the 5 locations. That removes the need for bulky ducting and means you just needs room for two hoses if you want to expand the system. The system still uses a bit of electrical power to pump the coolant and for each of the heat exchanger fans.

Ours is almost identical to this except only 4 lines. Balancing the output is by simple 1/4 turn valves that can be completely shut off if not required. A fifth line with larger bore loop feeds the calorifier. We use this even in summer with the heating circuits off for hot water full tank within 15-20mins. This circuit has to be long enough to prevent the shut down due to over temperature in the return line.


The matrix heaters can be a little noisy so they are located in the ends of the hulls none on the bridge deck that relays on the residual heat rising up but stays quiet.


As far as the OP's sytem is concerned a 4.5 gal header tank seems enormous. What is a buffer tank?
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Old 01-11-2024, 03:37   #5
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Re: Hydronics Heat on a 39' Catamaran

A Buffer Tank adds volume, to a heating, or cooling system, and helps prevent boiler short cycling.
A buffer tank’s primary role, is to keep a minimum volume of water “in circuit”, when the heating load is very low. This prevents the heating pump from short cycling, and provides a bypass route, to maintain the minimum flow rate, through the heat pump, if most of the heating zones have shut down. The minimum flow rate, and the minimum volume of water, in the circuit, are necessary, to keep the heat pump operating efficiently.

The formula for sizing a hot water buffer tank is:
Buffer Tank Size, in Gallons = [Min. Cycle Time x (Min Output Min Load)] ÷ [Temperature Differential ▵T x 500]
Where:
Minimum boiler turndown output in BTU/hr
Smallest load in BTU/hr
Temperature differential in degrees F
Boiler cycle time (minimum) in minutes

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Old 01-11-2024, 03:46   #6
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Re: Hydronics Heat on a 39' Catamaran

Is there a heat exchanger in the buffer tank. Cannot see how this can be efficient and given the size would surely bypass the main heating circuits.


Here is a good description of the differences between a single and double feed to a header tank to achieve the same.


See the section
Two pipe and one pipe Header tanks


https://www.letonkinoisvarnish.co.uk...ers_intro.html
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Old 01-11-2024, 04:44   #7
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Re: Hydronics Heat on a 39' Catamaran

AFIK, Heat Exchangers are, generally, an available option, on buffer tanks.
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Old 01-11-2024, 19:45   #8
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Re: Hydronics Heat on a 39' Catamaran

Thanks all for your replies, very helpful!

I've moved the thread over here:

https://www.cruisersforum.com/forums...ml#post3946359
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