Hydronic System Design

[sailingharry]

I'm pretty sure you were an engineer in a prior life. Must have been.


I think you are right on the size for Hydronic. After I wrote that I started looking around, and can't seem to find smaller one. Maybe I was recollecting air types.


I think (but I'm really not sure) that the uninsulated pipes will actually dry out the bilge. They add zero water, and they raise the temperature. So that should lower the relative humidity. At least, that's my working hypothesis.


Agreed on the challenges of loading the boiler. I'm putting in a 10KW (HLN, delivered for under $400). So far, I'm planning a 5.5KW in the main cabin, and 3.5KW in the forepeak (both from t7design.co.uk, around $150USD each). I'm hoping to waste another 1KW in the piping. Also, like you, I'll run it first (in series) through a plate heat exchanger for the domestic water. I'll put in a 3 Gallon in line surge tank (AMC Expansion Tank 3 Gal - AMC Cliffv's Marine Service), and so I'm hoping to give it at least occasional full load. So far, I'm torn on the head -- I don't want to drop $200 in additional kit there, as well as space and installation time -- but it would be nice to heat it some. I'm actually thinking about the computer cooling unit mentioned earlier.


You did the math on the copper tubing. And I'm the one that supposedly is a degreed engineer. LOL.


I've about decided on a parallel install (after the DHW heater), but with only 2 heaters, it's no big deal. T7design has a nice in line manual flow regulating valve for under $20, that looks useful for balancing (if balancing is even required?).


What will be your fuel source? It seems most vendors want you to have a dedicated dip stick into the fuel tank -- probably to guarantee zero conflicts with troublesome existing installs. I have Racor 500's feeding the engine with a vacuum gauge, and those filters are massively oversized for any marine engine. I'm thinking very strongly about teeing into the line after the filter. Makes for clean fuel, and a simple install. I might add a valve on the fuel line, just in case of some crazy chance of a heater fuel leak killing the main engine.


Also, have you thought about venting the heaters? They will be a high spot in the water piping, and will have to have some sort of air vent to get the air out. I'm struggling with this one. A tee with a drain cock at each heater, probably.


Oh, I'm also leaning strongly toward a piping system of a mix between PEX for the main line, and rubber for the side runs (or maybe even PEX for part of the side runs). I think PEX is going to flow easier, and also will have less chance of kinking or squishing. I'm leaning toward at least 3/4", and maybe even 1", for the mains to reduce head losses. PEX is also cheaper.

[expozen]

Originally Posted by sailingharry

Agreed on the challenges of loading the boiler. I'm putting in a 10KW (HLN, delivered for under $400). So far, I'm planning a 5.5KW in the main cabin, and 3.5KW in the forepeak (both from t7design.co.uk, around $150USD each).

I believe your cabin heaters need twice the BTU output you're thinking. That 5.5Kw gives no information about what flow rate and coolant temp is required to meet its BTU output. I gave up on considering those Kalori heaters just because they offer no detailed specs (I don't trust that and wont buy them because of it). That 5.5Kw will most likely only deliver 14,000 BTU (best case scenario) instead of its rated 18,750 BTU. Here's a similar fan coil with more details:

https://www.suremarineservice.com/He...s/RL6400W.html

Originally Posted by sailingharry

What will be your fuel source?

I haven't actually decided on this yet. I could go either way.

Originally Posted by sailingharry

Also, have you thought about venting the heaters?

The cabin heaters I'm considering all come with air bleed valves. If your heater is at the highest point you'll want a bleed valve there too.

Originally Posted by sailingharry

Oh, I'm also leaning strongly toward a piping system of a mix between PEX

I believe that all PEX is the way to go. But I know a lot of connections may only come fit for hose, and you may not always have a PEX option.

[john61ct]

Originally Posted by sailingharry

the uninsulated pipes will actually dry out the bilge. They add zero water, and they raise the temperature

they will speed up evaporation of any water in the bilge

increasing the humidity above, until the bilge is dry

if the bilge never get dry, due to incoming flows / drips

then you're permanently running a humidifier down there in cold weather.

Not saying whether this is good or bad, depends on too many variables.

But if the bilge does get dried out faster, and it's all dry heat from then on, that would be great IMO

[Dockhead]

Originally Posted by sailingharry

Agreed on the challenges of loading the boiler. I'm putting in a 10KW (HLN, delivered for under $400). So far, I'm planning a 5.5KW in the main cabin, and 3.5KW in the forepeak (both from t7design.co.uk, around $150USD each). I'm hoping to waste another 1KW in the piping. Also, like you, I'll run it first (in series) through a plate heat exchanger for the domestic water. I'll put in a 3 Gallon in line surge tank (AMC Expansion Tank 3 Gal - AMC Cliffv's Marine Service), and so I'm hoping to give it at least occasional full load. So far, I'm torn on the head -- I don't want to drop $200 in additional kit there, as well as space and installation time -- but it would be nice to heat it some. I'm actually thinking about the computer cooling unit mentioned earlier.

Correctly sizing all the elements of the system is pretty important. I would for sure consult an actual designer for this. Whoever sells you the gear might be able to steer you to someone.


What is "HLN"? Do you mean you are installing a 10kW furnace? That sounds oversized for a 33 foot boat unless you are going to be in the Arctic. My 54' boat (probably 5x the interior volume of a 33' boat) was originally built with a 10kW furnace. If the furnace is oversized, then I think you yourself noted that it would short cycle, and this is not good for it.



As to heating the heads -- speaking from experience, there will be more occasions when you will want heat in the heads, than when you want heat elsewhere. I would prioritize this -- you do not want to "heat it some"; you want to "heat it properly". Heat in the heads dries it out and makes showering a lot more comfortable. My boat does not have separate fan coils for the heads, but ducted air from the aft cabin fan coil, and forecabin fan coil, respectively.

Originally Posted by sailingharry

What will be your fuel source? It seems most vendors want you to have a dedicated dip stick into the fuel tank -- probably to guarantee zero conflicts with troublesome existing installs. I have Racor 500's feeding the engine with a vacuum gauge, and those filters are massively oversized for any marine engine. I'm thinking very strongly about teeing into the line after the filter. Makes for clean fuel, and a simple install. I might add a valve on the fuel line, just in case of some crazy chance of a heater fuel leak killing the main engine.

You really don't want to compromise the integrity of the main engine fuel system and add potential failure points. There are other reasons not to do this as well. By all means, go with the separate pickup tube, and make the pickup point high enough that you can't run the fuel tank empty with the heater.

Originally Posted by sailingharry

Also, have you thought about venting the heaters? They will be a high spot in the water piping, and will have to have some sort of air vent to get the air out. I'm struggling with this one. A tee with a drain cock at each heater, probably.

You should consult a real designer on this. FWIW, the various systems I have seen do not have vents at the fan coils. The furnace is mounted with a significant height above the rest of the system and apparently it is all self-venting.



[/QUOTE]Oh, I'm also leaning strongly toward a piping system of a mix between PEX for the main line, and rubber for the side runs (or maybe even PEX for part of the side runs). I think PEX is going to flow easier, and also will have less chance of kinking or squishing. I'm leaning toward at least 3/4", and maybe even 1", for the mains to reduce head losses. PEX is also cheaper.[/QUOTE]


FWIW, PEX is what is usually used over here. My boat was built with all PEX piping for the heating system as part of the original build in 2001. PEX is made for this and works very well. 18 years on, my system is flawless and leak-free.


As to insulating in the bilge or not -- I would consult a real designer. In theory it sounds like a good idea to dry out the bilges, but you may lose a lot of heat there. All the professionally installed systems I've seen over here have insulated piping in the bilges.


The key piece of advice I would give you is not to try to design this yourself. You're a pro engineer yourself -- surely you understand the value of having a real professional with real experience, helping you with something like this. if you make a hash out of the design, all the equipment you end up buying may turn out to be wrong, and you may have to rip it out and start all over.

[evm1024]

I've got a system that was originally installed by SMS. Here is a link to their heating catalog. Do give them a call for information even if you do not buy from them.

https://www.suremarineservice.com/si...ng_Catalog.pdf

One thing to install if you have not thought about is is a y valve to make a summer loop. The winter loop runs hot water to your heat exchangers and when switched to summer mode the heat exchanger portion is bypassed.

Thus in summer mode your burner only runs hot water through the water heater. I have an Everhot which gives "unlimited" hot water when the burner is running and plenty of hot water for some time after the burner is shut down.

Also, do include the mixing valve to get consistent hot water that will not burn you. (see page 44 in the catalog)

SMS has produced very detailed reference design drawings ithe past that are well worth looking at. I've got a DBW-2010 by the way.

Also, do plan where to run your water tubing (3/4" PEX works fine) and place your heat exchangers. Much harder to move later.

Also, also, don't place your burner exhaust where it will melt your sheets.

Also, also, also, the AC hot water circulation pumps are "better', more reliable and so on. I use a small (400 watt inverter) run off the the master heat breaker for mine. It works fine and I'm not dependent on the main inverter to run the system. A single breaker powers the whole setup.

[evm1024]

I was out on the boat today and was working on the AC wiring so the main inverter and shore power was off and disconnected. I was running the heater off battery. You can see the temp rise and the decline. The break in the data was due to the internet uplink being down with the AC off. I was comfey at about 78 at the peak.

[sailingharry]

Originally Posted by Dockhead

Correctly sizing all the elements of the system is pretty important. I would for sure consult an actual designer for this. Whoever sells you the gear might be able to steer you to someone.


What is "HLN"? Do you mean you are installing a 10kW furnace? That sounds oversized for a 33 foot boat unless you are going to be in the Arctic. My 54' boat (probably 5x the interior volume of a 33' boat) was originally built with a 10kW furnace. If the furnace is oversized, then I think you yourself noted that it would short cycle, and this is not good for it.


I spent some time chatting with SureMarineServices -- great folks with a lot of knowledge. For my 43' boat (the OP has the 33'), for summer cruising in the Canadian Maritimes, he strongly recommended a 13KW unit. I agree with you, even 10KW is probably overkill. I hope I'm right by ignoring one of the best in the industry (at least here in the US). The problem is the next size down (in Hydronic) is 5KW (the Webasto TSL17), which seems maybe too small (I heated my Sabre34 with a 1.5KW propane heater -- Force 10 bulkhead unit -- and it may not have been quite enough)



As to heating the heads -- speaking from experience, there will be more occasions when you will want heat in the heads, than when you want heat elsewhere. I would prioritize this -- you do not want to "heat it some"; you want to "heat it properly". Heat in the heads dries it out and makes showering a lot more comfortable. My boat does not have separate fan coils for the heads, but ducted air from the aft cabin fan coil, and forecabin fan coil, respectively.


On our boat the head is a small space, directly opening to the main cabin which should be well heated. We already routinely keep the door propped open. And, so, yes, I'm giving a lot of thought to heating it -- but also, I think that 1KW is probably more than it needs, so it's a small adder. The challenge is that there is nothing installed nearby that I can tap off of. On that subject, though - in the very tip of the boat, just forward of the pullman main cabin, is a space originally built as the master head (but long since turned into storage). We see this space holding wet gear (the spinnaker, foulies, etc). In this space, we will divert a tap off the heater for the pullman cabin -- just a 2" duct -- specifically because of the dampness issues you raise.



You really don't want to compromise the integrity of the main engine fuel system and add potential failure points. There are other reasons not to do this as well. By all means, go with the separate pickup tube, and make the pickup point high enough that you can't run the fuel tank empty with the heater.


I do have a second pickup already. The boat was built with a small DC generator, not sure why it was removed. The pickup is still there. Not worried about how deep it goes -- I have two tanks. I'm more worried about a second line, second filter, etc. But I do hear the concern about the main engine.


You should consult a real designer on this. FWIW, the various systems I have seen do not have vents at the fan coils. The furnace is mounted with a significant height above the rest of the system and apparently it is all self-venting.


Where I live, "real designers" are very scarce, with limited installation experience and even less dealing with the results of their installation. We are a warm weather sailing area. You do mention the vents -- the units at SureMarineServices all come with bleed vents.


FWIW, PEX is what is usually used over here. My boat was built with all PEX piping for the heating system as part of the original build in 2001. PEX is made for this and works very well. 18 years on, my system is flawless and leak-free.


My only concern about PEX is that it is quite stiff and hard to push around. I'm thinking the last 2-3 feet in rubber would reduce mechanical loads on the air handler, and make installation easier. All PEX might be easier during original build.

Harry

[Dockhead]

Originally Posted by sailingharry

I spent some time chatting with SureMarineServices -- great folks with a lot of knowledge. For my 43' boat (the OP has the 33'), for summer cruising in the Canadian Maritimes, he strongly recommended a 13KW unit. I agree with you, even 10KW is probably overkill. I hope I'm right by ignoring one of the best in the industry (at least here in the US). The problem is the next size down (in Hydronic) is 5KW (the Webasto TSL17), which seems maybe too small (I heated my Sabre34 with a 1.5KW propane heater -- Force 10 bulkhead unit -- and it may not have been quite enough)

For SUMMER in Canadian maritimes, 43' boat, 13kW? That sounds ludicrous to me. I can tell you that 10kW is enough in a 54' boat in the Arctic -- with water full of ice and air below freezing and a lot of ventilation. From experience. The three large fan coils on my boat can't use 10kW of heat once the interior is somewhat heated even in Arctic conditions. When using electric heat, I keep my boat quite reasonably warm with about 3.8kW of electric fan heaters, even when it's below freezing outside. I don't know which 43' boat you have, but an average 43' boat would have probably, half the interior volume of my boat, and therefore half the heating demand, so my guess would be that 5kW would be enough. But I guess you'll have to make your own best guess, if you're not able to have actual calculations done. You might also make some experiments using electric fan heaters in real life conditions.



HOWEVER, note well that my boat has a fully cored hull and fully insulated interior with no part of the hull exposed to the interior. Possibly none of the figures I've given is relevant if your boat is less well insulated than that. Query however whether just heating more is the right solution to poor insulation.



Sizing correctly is important -- too small, and you won't get warm enough and/or damage the heater by running it on Boost all the time. Too large, and you will soot it up by short cycling it, requiring frequent expensive and PITA maitenance. I would not do this on a wet finger guess.


If I may throw something out, right out of left field -- you might consider installing TWO furnaces, both 5kw (or one 10kw and the other 5kW). In really cold weather, run both of them (or the larger one). In milder weather, only one of them. That would give you redundancy which you may desperately want (these things are not totally reliable) someday, and furthermore allow you to match the furnace with the load. At the cost of complexity. But this setup has some big advantages; I will have something like this in my next boat (set up specifically for the Arctic).

Originally Posted by sailingharry

On our boat the head is a small space, directly opening to the main cabin which should be well heated. We already routinely keep the door propped open. And, so, yes, I'm giving a lot of thought to heating it -- but also, I think that 1KW is probably more than it needs, so it's a small adder. The challenge is that there is nothing installed nearby that I can tap off of. On that subject, though - in the very tip of the boat, just forward of the pullman main cabin, is a space originally built as the master head (but long since turned into storage). We see this space holding wet gear (the spinnaker, foulies, etc). In this space, we will divert a tap off the heater for the pullman cabin -- just a 2" duct -- specifically because of the dampness issues you raise.

Good plan. My boat was built with a heat vent in a dedicated wet locker, and a drain at the bottom. This is a real blessing when cruising in cold and wet conditions. Crew coming off watch puts foulies in there and they are nice and toasty and dry by the next watch.



What is ghastly in cold weather on a boat is cold and WET. I don't actually find that I require the interior of my boat to be at 20C all the time, so long as it's dry inside. So I find that the key to comfort is keeping even heating on everywhere, even if it's not that much heating, and lots of ventilation. And don't burn propane inside in cold wet weather.



Concerning the heads -- your problem is different from mine -- my two heads compartments are large, with large separate shower stalls, and not connected to the main cabin. I like to superheat my own heads prior to bathing in cold weather, so if the cabin is at 15C or whatever, I will run the generator and put 2kW of electric fan heating in there for half an hour before my shower until the room is 25C or 30C. This is pure luxury and besides feeling really good -- coming out of a nice hot shower into warm, dry, fresh air -- it allows me to dry out the space quickly after I've bathed. The alternative is for that humidity to permeate the boat after every shower, which is really icky in cold, wet weather. This is such a problem at these latitudes that I know plenty of sailors who go for days without bathing, just to avoid this, something totally unacceptable for me (YMMV!). In my dream boat, the heads compartments would have heated floors and lots and lots of space heating and ventilation.



YMMV, but you may find that in weather warm enough that you don't really want to heat the whole boat up, you may still want to heat the heads if only to dry it out, so I think your plan of putting a separate small fan coil in there is a good one. I don't think 1kW is too much, even if the space is small. It is really pleasant to shower in a really warm room, in cold wet weather, and you just turn it down or shut it off when you don't need it. If you only need the cabin to be 15C or at most 20C, then you will not mind at all if the heads can be heated to 25C or even 30C, which doesn't feel that hot when you are dripping wet.


Last thing to consider is how do you dry out your towels? In cold, wet weather you can't hang them on the lifelines. I have a dryer, which is a Godsend for this case, but if you don't have a dryer, then you might think about a heated towel rail, plumbed into the hydronic system.

Originally Posted by sailingharry

I do have a second pickup already. The boat was built with a small DC generator, not sure why it was removed. The pickup is still there. Not worried about how deep it goes -- I have two tanks. I'm more worried about a second line, second filter, etc. But I do hear the concern about the main engine.

Great; use it. You don't ever want t-junctions in fuel pipes sipplying diesel engines. Second line and filter is nothing to pay for doing it right.

[GILow]

Or a 5kW hydronic heater with one or two 2kW forced air type heaters.

Cheap redundancy.

[IAmGroot]

Hey folks, thanks for the great thread. My wife and I plan to move aboard a catamaran in the upper Chesapeake next year and I had definitely planned on hydronic heating. The heat from reverse cycle AC in our last boat was definitely problematic as it would freeze-up as the water got colder.

That said, AC is a must for the Admiral and I have looked at systems for hydronic heating and AC. Has anyone done that step and how did it work out?

From my research, it appears you need to upsize the fan coils in order to make it effective.

Thx!

[sailingharry]

I played around with that idea. I really thought that combining the systems would save money and space. I came to the conclusion that it was just was a bridge too far. I was thinking that unless you used a central cooling plant, you would use normal Marine AC units and then mount a coil unit adjacent to the cooling coil. You can get fin coil generic units fairly cheap.