November 15, 2015

Using heat from the engine [hydronic heater cores]

We occasionally participate in various boating forums. [See our Some Forums We Read sidebar for links...]

Some of those topics may be relevant here, so once in a while we will repost on our blog for reference.

The following may be one of those cases. To accommodate our non-boating blog readers, sometimes we add some {additional information and links} to the original forum post, below. 

There are also additional references listed at the end of some of these forum posts with related information. 

Link to original forum post [11-Nov-2015]

Re: Adding a heater to boat

Originally Posted by TurboTim View Post
Does anyone know where one can purchase some kind of heater that runs off engine coolant to heat my boat so I can start boating earlier in the year and later in the year?
Hi Tim,

Not knowing anything about the type, size, use, or current/desired cruising grounds for your vessel, I'm providing this feedback in the blind, so it may not apply to your circumstances.

We love the stainless steel Dickinson Radex heater in our pilothouse. [It uses computer pancake fans, so it is quiet- even though our engine isn't...]

In addition, since we have central forced air diesel heat [Espar] we use at anchor or when cool weather sailing, I am preparing to piggyback a hydronic core into the same forced air ductwork to pipe heat throughout our sailboat when we are motoring. [We enjoy winter outings...] This would be supplemental to the previously mentioned Dickinson Radex unit already installed in our pilothouse.

If you are interested in a central hydronic core running using waste heat from your engine(s), I have found that the REAL brand appears to be first rate. [Not that other brands aren't just as good, if not better, but I scrutinized some hydronic core products at the Seattle boat show earlier this year and the REAL brand looked to be superior. However, I haven't purchased anything yet so I cannot provide first hand information about using REAL products... But that is the brand I will be going with.]

I know Sure Marine Service carries the REAL brand and just about every other heating component one might need. [But I haven't done business with them yet...]

I'll close by sharing a couple of thoughts with you regarding the install of hydronic heating loops:

1) Ball valves in coolant loops: We tapped into our engine auxiliary coolant inlet and outlet [same used for your water heater heat exchanger] and installed short bodied ball valves at the engine and to each hydronic loop so we could shut off these coolant loops for maintenance, leaks, or when a hot heater core in the main salon is undesirable...

2) Proper fluid flow: Plumb the hose containing coolant from the engine into the lowest pipe of each hydronic core. [i.e., Coolant flow should be bottom-up in each core- to purge air; just like when changing the lube in an outboard engine lower unit.]

2.1) Longer runs may require the insertion of an additional coolant pump [12 VDC or to spec.] in the hose circuit to ensure adequate coolant flow throughout the system.
3) Bleeding air from hydronic loops can be quite a chore as the top of each loop is not always conveniently accessible. [I know ours aren't...]

To make this easy, we use small, float style [vs. Schrader valve; e.g., Watts brand] automatic air bleeders used in home boiler heating systems. [Cheap at ~US$10-15/each] 
Typically we install a T at the top of each hydronic core and install a ball valve [to isolate the bleeder when not needed, and for maintenance...] then the the air bleeder in the highest port of the T. [i.e., Where the coolant return line to the engine exits the core.] Basically, air bleeders need to be installed at a high point in each coolant loop.
We installed air bleeders on our water and bus heaters. They eliminate manual bleeding- even when first commissioning a hydronic system...

In case this is useful.



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Follow-up post [11-Nov-2015]

Re: Adding a heater to boat

Re: Adding a heater to boat


I have existing diesel forced air ducting in our new to us boat (but no forced air system currently), would be very interested in hearing more details about how you plan to piggyback into the whole ducting system... I would consider doing that instead of installing a Red Dot heater if it seemed manageable for the semi (semi-semi?) skilled.

Originally Posted by wrwakefield View Post
In addition, since we have central forced air diesel heat [Espar] we use at anchor or when cool weather sailing, I am preparing to piggyback a hydronic core into the same forced air ductwork to pipe heat throughout our sailboat when we are motoring.
Wow, these are three super useful suggestions for this... printing this one out now... thanks!

Originally Posted by wrwakefield View Post
1) Ball valves in coolant loops:
2) Proper fluid flow:
3) we use small, cheap, automatic air bleeders used in home boiler heating systems.
Thanks, Bass.

I'm glad some of it was useful for you.

RE: Having both diesel and hydronic heat sources sharing the same forced-air ductwork, there are a lot of variables, but that doesn't mean it has to be complicated.

For example, my Espar is mounted in my engine room [which is underneath my pilothouse.] The Espar has one main duct that branches outside of the engine room to feed 5 outlets positioned throughout the boat.

It is important to note that the Espar return air is ducted outside the engine room in an adjacent cabin [not outdoors... direct marine air wreaks havoc on these heaters...] This means odors from the engine room aren't being distributed throughout the vessel when that unit is running...

I will do the same with whichever hydronic unit I install.

As far as tying into the existing forced air duct, my first try will be simple: I will just insert a Y [not a 90° T...] in the heat duct near the Espar. [One with a diverter flap; e.g., A purpose made unit like this one for heating systems- similar in concept to those you can buy for diverting your clothes dryer vent into the house...] I plan to run a control cable to it for convenient access, and add switching that heat source flap to the check list for turning on the heaters.

I haven't done all of the engineering yet, but some considerations include:

1) BTUs available from engine waste heat [i.e., You can only tap so much heat from a particular engine without causing it to run at lower that desired temperatures. This can be somewhat mitigated by using the individual coolant loop ball valves I mentioned in my previous post as flow controls...]

2) Airflow capacity of existing ductwork: e.g., My Espar D5 pushes 137 CFM air on high. The hydronic cores I'm looking at push almost twice that much. [e.g., I reference a unit, below, that pushes 206 CFM.]

Will that be too much air flow for the existing duct network? [e.g. excessive duct noise, heat loss, etc.] If so, I plan to mitigate by running a couple of new ducts from the new hydronic core to areas adjoining the engine room [e.g., galley, workroom, and pilothouse] thus reducing airflow into main duct system. That would not be difficult in my boat, but does start to dilute the concept of sharing duct work and subsequent shorter installation time and cost...

Multiple ducts could easily be accomplished [in my set-up] with a unit like this one...

I hope this all makes sense. I'm just sharing my initial thinking before I have delved into the minutia... My approach may require adjustments once I get to that stage...


SV Denali Rose

Short on opinions; focused on research, facts & experience [yours and ours...]


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