Hydronic System Design

[expozen]

I'd like hot water and heat on my boat while away from the dock, so I've decided to install a hydronic system. I'm planning on an Espar S3 D4 that runs to an Isotemp (4.2 gal) calorifier then to some fan coils and/or a ventilated convector. The cabin heaters are to be piped in parallel to each other, but in series to the calorifier. All the piping will be insulated except for the return runs of the cabin heaters which will be run down the center of the boat under the floor. This will be a pressurized system using an expansion tank with an air separator & vent instead of a header tank. There will be no heat exchange interface to the engine at this time.

Why
People have asked why I would put in a hydronic system in? Because it seems like a solid system and I like nice things. Because I want to. Because I don’t have propane. Because I like hot water and I like heat. If you’re wondering why, I’d ask you to please offer me reasons why I shouldn’t.

The Boat
Ranger 33. It’s not a real big boat. It’s all one space except for the head. The interior is constructed with a fiberglass liner (there’s probably a name for this type of construction but I don’t know what it is). The floor that you stand on is the liner, and there’s a ~4” gap between the floor and the hull. The bilge is above/inside the keel and is about 3’6 deep below the floor (it always has water in it). The insides of the hull are carpeted. The underfloor/bilge space is pretty sealed off from the cabin (there are no vents that join the spaces). The locker spaces are also sealed off from the cabin and the underfloor space. I’ve never had any issues with condensation in the boat. Maybe it just doesn’t get cold enough where I am? Maybe it’s because the locker/underfloor spaces are sealed off from the cabin which may create a buffer between the cold surface of the hull and the warm inside of the cabin? Everything I’ve read says that there should be ventilation between these spaces to prevent condensation. But it seems to be working. I’m unsure what effects heating the underfloor space (even indirectly) may have on the potential formation of condensation.

Hydronic Heater
The Espar S3 D4 has an output range of 4,436 BTU to 14,672 BTU. Upon initial start it will heat on high until coolant temp is 167 F deg then adjust BTU output to maintain that temp. If required BTU output is below 4,436 the heater will shut off once the coolant has reached a temp of 185 F deg.

System Volume
Because the piping to the cabin heaters will have shut-off valves, I’ve divided some the system design into two parts: hot water and cabin heating. The hot water configuration ignores the coolant that is contained within piping to the cabin heaters. And the cabin heating configuration ignores the fresh water within the calorifier (it assumes that the fresh water is already hot).

Hot Water
Coolant hot water piping volume: ~33’ of ¾” PEX * 0.01843 gal/ft = 0.61 gal
Expansion tank volume: 1 gal
Calorifier fresh water volume: 4.2 gal
Total system volume: 5.81 gal

Cabin Heating
Coolant hot water piping volume: ~33’ of ¾” PEX * 0.01843 gal/ft = 0.61 gal
Coolant cabin heat piping volume: ~60’ of ½” PEX * 0.0092 gal/ft = 0.552 gal
Expansion tank volume: 1 gal
Total system volume: 2.16 gal

Minimum cycle runtime
The minimum runtime is calculated from the Hot Water configuration with the assumption that there is no continuous heat extraction during the cycle. The fresh water in the calorifier is assumed to already be 90 F deg.
System weight: 5.81 gal * 8.34 lbs = 48.46 lbs
High cycle BTU: 48.46 lbs * 77 F deg = 3,731 BTU
High cycle runtime: (3,731 BTU / 14,672 BTU) * 60 min = 15.3 min
Low Cycle BTU: 48.46 lbs * 18 F deg = 872 BTU
Low cycle runtime: (872 BTU / 4,436 BTU) * 60 min = 11.8 min
Total cycle runtime: 15.3 min + 11.8 min = 27.1 min

I could not find a recommended minimum runtime for the Espar S3 series. But the recommended minimum runtime for the Espar Hydronic II series was listed as 15 min (I assume that’s 15 min at high output).

Cabin Heating cycle runtime
The cycle runtime for the cabin heating configuration would be based upon continuous heat extraction, which is determined by the BTU output of the selected fan coils and convectors. The chosen fan coil is rated at 5,800 BTU and the convector is rated at 13,649 BTU. So with a single fan coil on, the heater would run at it’s low output setting undefinedly. I’m unsure if minimum runtime should be considered every time the heater is switched on, or if it’s only a concern when the heater turns on from a cold state.

Cabin Heaters
This is the part of the system that I’m feeling the most unsure about. Not because of questions about hydronics, but because of questions about boats. There’s really two main options that I’ve been trying to decide on:

Fan Coil Option
Installing (probably 3) fan coils throughout the boat. One located in the Galley, one near the V-beth, and one probably in the head (if I can figure out where to fit it). The fan coils would be installed in newly cut holes in the fiberglass liner and would pull air from the locker/underfloor spaces and blow it into the cabin. I believe that some additional vents (return air) may need to be added so that the fan coils wouldn’t be trying to pull air from a sealed space. The fan coils would be installed behind 7-1/2” x 9-1/8” (6-1/2” X 8-1/2” cutout) teak louvered vents.

Pros

- More even heat distribution

Cons

- Cutting holes into the fiberglass liner. I don’t know if the liner is a structural component.
- Joining the locker/underfloor spaces with the cabin. I’m not sure what effects that could have on the potential formation of condensation. Also, the cabin never smells bad like a bilge or a locker, and I’m hesitant to blow bilge/locker air into the cabin. Maybe I just need to clean the bilge and lockers more often?
- Takes away some locker space. Not much tough.

Ventilated Convector Option
Installing (1) ventilated convector on the main starboard bulkhead.

Pros

- No holes cut in the liner.
- Keeps the locker/underfloor spaces sealed off from the cabin.
- Simpler

Cons

- Less even heat distribution.
- It’s not the finest looking piece of plastic to display on the bulkhead. At least the fan coils can be hidden behind some leak vents.

I’m no engineer, so if anything here looks AFU please let me know.

Data Sheets

Espar Hydronic S3 D4
https://www.eberspacher.com/fileadmi...uk_leaflet.pdf

Peak Sierra Antifreeze
https://peakauto.com/wp-content/uplo...sheet_2017.pdf

Amtrol Extrol EX-15 (2 gal) Expansion Tank
https://www.amtrol.com/wp-content/up...ttal_06_19.pdf

Amtrol Air Separator & Vent
https://www.amtrol.com/wp-content/up...ttal_06_19.pdf

Zurn Non-Barrier PEX Tubing
https://www.zurn.com/media-library/w...sheets/q_p-pdf

Isotemp (4.2 gal) Square Water Heater-Calorifier
https://www.indelwebastomarine.com/f...eaters-eng.pdf

Kalori Silencio 1 Fan Heater
https://kalori.com/pdf-t/?id=22306&lang=us

Kalori Baïkal 3 Ventilated Convector
https://kalori.com/pdf-t/?id=22343&lang=us

[Pizzazz]

Well thought out design. Do you have a total cost estimate? My only concern would be that it could be too complicated and costly given the target boat. But it would work great once complete.

The other consideration is that it may cycle the diesel heater quite often which is. It really desirable.

[Dockhead]

You would normally use one of the forced air Espar/Webasto/Planar heaters on a boat that size, but hydronic certainly distributes heat better and is a superior way to make hot water, so sounds like you've got a decent plan.

A system such as what you've designed has quite a bit of thermal inertia (one of the many advantages of hydronic) so cycling is not a big deal. The furnace has several power settings which the control unit will select automatically to match the output to your heat use. The thing to be careful about is using too little heat so that the furnace idles for long periods -- this will coke it up. In marginal situations where I need just a little heat from my hydronic system, I run the system full blast for a couple of hours then shut it down.

The disadvantage of these systems is that they require maintenance and they do break down. They are not all that hard to repair if you study the manuals, but it is one more system on the boat which needs regular attention.


As an alternative, you could consider a pot type heater (Dickinson, Sig, etc.) on a bulkhead with a coil for water heating. This is a much simpler device with much less maintenance, but has a couple of disadvantages, principle among which are (1) heat distribution; and (2) you need to cut a hole in the deck for the chimney. Nevertheless, for a boat that size, this could be a better choice. You do say that the boat is "all one space"; that's a strong use case for this type of heater where you don't need to distribute heat into different compartments which is the main strong point of hydronic.


Something like this:


http://dickinsonmarine.com/product/n...diesel-heater/


Vastly easier and cheaper to install than hydronic.


In any case, bravo to you for not having propane and for not considering it for this purpose. It's really hard to make a propane heater ABYC compliant on a boat that size and is fundamentally dangerous for this use on a boat, not to mention the pain of humping all that gas to the boat, especially when you're off the beaten track somewhere.

[Paul L]

You can save room by using a ITR Hurricane Zephyr hydronic diesel system. These include on-demand hot water, so you don't need the calorifer tank. This saves a lot of space, plus you end up with hot water in minutes.

[VanIslandGuy]

We built a similar system with our boat. It goes through two fan coil units, then the hotwater heater with a summer time loop to redirect fluid back to the Espar at this point. If the loop is open it flows forward to two more coil heaters and back all the way to the espar unit. All hoses are insulated except one small three foot run under the galley floor where I wanted the heat to radiate off to heat the floor there. All fan coil heaters push air out two separate vents per unit meaning eight outlets, and our hot water tank get heat.

I would give a big plus vote to multi speed fan coil heaters. Ours can individually run in low or high, or be turned off. They work well to draw air out of the bilges, below bunks etc, and as such dries the entire boat out much better than a radiator style heater. We normally run the fans in high to get the boat up to temperature, then just leave the fans on low the rest of the time when simply maintaining temperature. The little ducts can be pointed in any direction and with a little tinkering you should eliminate any cold spots in the boat.

Just be sure to wire your fans in parallel so that they can run all individually at different settings, (the Espar won't feed electricity to the fans until the fluid temperature is high enough to blow heat, the manual spec'd wiring the fans in series. We simply had the Espar fan power-out lead go to feed a separate bus bar, and then ran wires for each fan to that bus bar.)

The only other recommendation I have is to be sure to tape the open ends of the coolant hoses off completely to prevent any gunk from getting in them when you are feeding them through the boat during the installation. We also used a sharpie and marked an arrow for in/out to be sure there were zero issues when finally getting everything hooked up. Finally don't skimp on getting a good muffler and some insulating foam. Ours is pretty quiet but I've heard some units that are really loud.

Drawing air out of the bilges with the fan style, and the ability to control them individually low/high/off really made the choice easy for us. If you are ultra sensitive about noise, then the fans might annoy compared to the radiator only style. On low I don't notice them at all, on high they are audible but normally its only on high for 30 minutes or so until the boat heats up, then low is more than adequate to maintain temps.

[expozen]

Originally Posted by Pizzazz

Do you have a total cost estimate? My only concern would be that it could be too complicated and costly given the target boat.

I'd estimate about $2,700 (not including the calorifier, it's already in the boat). Too costly for the target boat? The value of the boat is less about money and more about enjoyment.

Originally Posted by Pizzazz

The other consideration is that it may cycle the diesel heater quite often which is. It really desirable.

I'm curious how you've come to that conclusion.

Originally Posted by Dockhead

The thing to be careful about is using too little heat so that the furnace idles for long periods -- this will coke it up.

I've tried to find more specific information about this but only find generalizations. What is 'idle'? What is a 'long period'? Is there some threshold (as expressed as % of BTU output) in which in the heater stops to 'coke up'? Or is it a gradient (lower % BTU = more coke, high % BTU = less coke)?

Originally Posted by Dockhead

As an alternative, you could consider a pot type heater (Dickinson, Sig, etc.) on a bulkhead with a coil for water heating.

I considered this option but don't like the idea of cutting a 3" hole in the deck, and fitting the min 4' of chimney just doesn't fit well for the boat (or me).

Originally Posted by Paul L

You can save room by using a ITR Hurricane Zephyr hydronic diesel system.

I don't have a place to fit something like this. The Zephyr is rated at 33,000 BTU (more than twice what the Espar D4 is rated). I hear they're quality heaters though.

Originally Posted by VanIslandGuy

We built a similar system with our boat. It goes through two fan coil units, then the hotwater heater with a summer time loop to redirect fluid back to the Espar at this point. If the loop is open it flows forward to two more coil heaters and back all the way to the espar unit. All hoses are insulated except one small three foot run under the galley floor where I wanted the heat to radiate off to heat the floor there. All fan coil heaters push air out two separate vents per unit meaning eight outlets, and our hot water tank get heat.

Sounds like a nice setup. What is the BTU rating of your Espar? And what is the BTU rating of your fan coil units? And what size piping/hose did you install?

I'm leaning toward installing the (3) fan coil units. Installing a single bulkhead mounted convector feels like it negates some of the benefits of hydronics (such as even heat distribution). I believe that the fan coils I was originally considering are undersized. I found it difficult to size them because the manufacture has zero design information on their website.

I found some nice fan coils from Sure Marine Service. So I'm thinking of installing one 6200 in the galley, one 6200 at the v-berth, and one 6000 in the head. From their design information that totals to about 16,000 BTU output (~110% of max Espar S3 D4 output).

REAL Heat 6000W 5,300 Btu Marine Hydronic Fan Heater
https://www.suremarineservice.com/He...s/RL6000W.html

REAL Heat 6200W 10,250 Btu Marine Hydronic Fan Heater
https://www.suremarineservice.com/He...s/RL6200W.html

[Paul L]

Originally Posted by expozen

....
I don't have a place to fit something like this. The Zephyr is rated at 33,000 BTU (more than twice what the Espar D4 is rated). I hear they're quality heaters though.



.......

I installed mine in the space created by taking out the calorifier.

[VanIslandGuy]

Hi Expozen. To be honest I can't remember the specific BTU's of each, I'll have to find some paper receipts to find out.

We worked with one of the best installers on Canada's west coast when designing the system. We measured the entire volume of the hull to make the determination of what to buy with him before starting any work. I hired him for a two hour consult prior to buying anything. He told us it is better to be slightly undersized than way oversized when dealing with these systems as they work better when run hard, otherwise things can carbon up quickly in the burner. Our two fan unit has one duct to the head, and one duct to our forward cabin and manages fine. Four ducts in the main salon and two for the aft cabin.

Temperatures down to 5'C it heats the boat past 21'C in around 30-40 minutes. When its snowing out, (rare here but it happens), it can take up to an hour as the walls, compression post, etc all get cold soaked and it takes time to not only heat the air, but remove the cold soaking effect. Once at temperature though, usually I can leave the fans on low just to maintain a comfortable cabin. To heat the hotwater tank in the summer from tapwater cold, if I use the summer time loop, takes around 20(warm)-30(hot) minutes. Typically on the hook in the summer I spark it up when I wake up, by the time coffee is finished, you can have a hot shower.

If we ever move to a bigger boat, I would go with hydronic again, but likely get a Hurricane system, as they replace the hot water tank at the same time, and can use either an electric element or diesel to heat the coolant. This means that when in a marina your hydronic system can run electrically which is an awesome feature that espar doesn't offer.

[expozen]

Originally Posted by Paul L

I installed mine in the space created by taking out the calorifier.

I just mean the the space where my calorifier is, is smaller then the Hurricane Zephyr. And there's really no other space on the boat that it could go.

Originally Posted by VanIslandGuy

We worked with one of the best installers on Canada's west coast when designing the system. We measured the entire volume of the hull to make the determination of what to buy with him before starting any work. I hired him for a two hour consult prior to buying anything.

I am planning on eventually finding someone for a consultation. But I'd like to have a firm understanding of how something works before getting to that juncture.

Originally Posted by VanIslandGuy

If we ever move to a bigger boat, I would go with hydronic again, but likely get a Hurricane system, as they replace the hot water tank at the same time, and can use either an electric element or diesel to heat the coolant. This means that when in a marina your hydronic system can run electrically which is an awesome feature that espar doesn't offer.

It seems that you could still heat the boat with electric even with the Espar (that's what I'm planning on). You just need to wire it so that it's possible to operate the circulation pump independently of the heater. The calorifier then heats the coolant as it's circulated through it. The new Espar's actually have a 'Residual Heat' mode that will control the circulation pump and fan coils without running the heater. But since the heating element in my calorifier is 1200W (4,095 BTU) it may only be enough heat maintain the temp of an already warm boat.

[Dockhead]

Originally Posted by expozen

. . . It seems that you could still heat the boat with electric even with the Espar (that's what I'm planning on). You just need to wire it so that it's possible to operate the circulation pump independently of the heater. The calorifier then heats the coolant as it's circulated through it. The new Espar's actually have a 'Residual Heat' mode that will control the circulation pump and fan coils without running the heater. But since the heating element in my calorifier is 1200W (4,095 BTU) it may only be enough heat maintain the temp of an already warm boat.

Yes, you can, and you can also use engine waste heat via a plate-type heat exchanger.



Downside is the noise of the fan coils. I prefer using portable electric heaters because of this issue.

[john61ct]

Using electricity to produce the actual heat obviously (to me) is only viable on shore power.

Even with ICE power readily available, once off grid you're better off burning the fuel directly.

And once you're talking about alternative sources and stored power, just ignition / controls / hydronic circulation & fans are already pretty darn significant loads, more so than a big freezer and making water put together.

[sailingharry]

Wow. You sure you're not an engineer? I'm a mechanical engineer, and, well, you've done your homework!


I'm looking at a very similar installation on my Saga 43, and so I've done a lot of the same thinking. A few thoughts.


* In your climate, you may want to consider the very smallest hydronic unit you can install. This will improve run times, and I don't think you'll ever actually need more than the small units can give. As a point of reference, a "cube heater" (typical plug in heater) is 1500W, which is 5000BTU/hr. If you can keep your boat comfy with a single electric heater, then you might find a 5000 BTU/hr hydronic would be a good fit (while saving space and money!).
* You counted the water in the expansion tank. This is a frustration for me in my design. I'd like a 2-4 gallon tank in the circuit just to add thermal inertia, but all the ones I can find are like this one. It is not actually "in the circuit" and is only a dead end off a side street. It won't get hot, and it won't cool down. It just doesn't count. I'm thinking of making something, perhaps a 4 foot long piece of 4" pipe with a fitting on each end (making nearly 3 gallons).

* You (and others) are planning on insulating the piping. I'm thinking not. To me, the insulation adds layers that can get wet, musty, dirty, etc (it is in the bilge, right?). Additionally, I would think that wasting heat to the bilge isn't a bad thing. It is heat inside the skin of the boat, and a warm floor will radiate into the entire boat. Or am I missing something? Yes, you will get a bit of heat loss through the hull into the water, but at least my boat is balsa core throughout (not my preference, but it is how it is). The balsa core is pretty good insulation.
* Not sure in a 33 foot boat that you need more than 2 outlets. Even in 43', finding places to put outlets is a challenge! LOL.
* It might be possible to heat the head with nothing more than a loop of copper pipe. 1/2" pipe, 4' long, with a u-turn and back? Not sure, but maybe? You could even polish it to a nice shine on those cold and dreary nights aboard....

* Blown heaters come with two types of blowers. The centrifugal blowers (big round box) move a lot of air -- but use a lot of power. Axial blowers (computer fans) don't move as much air -- but use a LOT less power.
* A vendor that hasn't been mentioned is https://www.t7design.co.uk/, they are responsive to emails and look to have some pretty nice gear. n Only on the fan coil side, not the boiler end of things. I think this unit is really slick, and two or maybe 3 would do the trick for you: https://www.t7design.co.uk/products/...eater-12v.html
* Why did you decide on parallel heaters? I hear both discussed, and to me parallel makes the most sense -- but is the least used.
* I'm torn on fuel. Tap off the clean side of the Racor engine filters? Run a separate line (and filter) to the main tank? Put in a dedicated tank close to the heater? Run it on diesel (cheap and easy) or kerosene (cleaner burning)? The dedicated tank allows you to easily run one kerosone tank after every 4 or 5 diesel tanks.



Keep up the good work!


Harry

[Pizzazz]

A couple of further thoughts. In terms of heating units, consider those water cooled solutions for CPUs. You can get a nice aluminum radiator with a matching variable speed 120mm fan for $30. I am not sure what the BTU output will be, it would depend on the fan. But you could build a nice, quiet system out of 4-5 of those. Not to mention that you can get these special fan speed control units with temperature sensors (all very cheap and reliable because it comes from the PC world) that can allow central control of the entire boat heating environment.

[sailingharry]

Originally Posted by Pizzazz

A couple of further thoughts. In terms of heating units, consider those water cooled solutions for CPUs. You can get a nice aluminum radiator with a matching variable speed 120mm fan for $30. I am not sure what the BTU output will be, it would depend on the fan. But you could build a nice, quiet system out of 4-5 of those. Not to mention that you can get these special fan speed control units with temperature sensors (all very cheap and reliable because it comes from the PC world) that can allow central control of the entire boat heating environment.

That's brilliant! I think that the heat output will be pretty paltry. But, at the price (and size!), it could make a really useful piece of the system where it makes sense. The head jumps out as a real possibility. This guy:
https://www.ebay.com/itm/For-CPU-Hea...s/141456522981
coupled with a nice plastic grill from Home Depot (we are talking about the head here!), could fit in a really tight spot and give those few BTUs that a head would need.
Might also work well in a hanging area where you put wet gear, that warm flowing air would help dry things out.

[expozen]

Originally Posted by sailingharry

If you can keep your boat comfy with a single electric heater, then you might find a 5000 BTU/hr hydronic would be a good fit (while saving space and money!).

I haven't seen any hydronic heaters that small. The Espar D4 is about the smallest rated I've found. I found some recommendations for sizing the system by cubic feet of air volume x 12, which on my boat is about 11,000 BTU. Lower than the Espar D4 by 3,672 BTU.

Originally Posted by sailingharry

* You counted the water in the expansion tank....It is not actually "in the circuit" and is only a dead end off a side street.

The Amtrol tanks have an insert that is installed into the connected fitting that mixes the coolant as it passes the tank (I have essentially the same tank on my fresh water system). So I do believe that it will absorb heat.

Originally Posted by sailingharry

* You (and others) are planning on insulating the piping. I'm thinking not. To me, the insulation adds layers that can get wet, musty, dirty, etc (it is in the bilge, right?). Additionally, I would think that wasting heat to the bilge isn't a bad thing. It is heat inside the skin of the boat, and a warm floor will radiate into the entire boat.

I feel really confused about the potential side effects of heating/overheating the underfloor/bilge spaces. Could adding too much heat to the space increase the likelihood of condensation? If not, then I'd be okay without insulation on the cabin heat portion of loop (supply + return).

Originally Posted by sailingharry

* Not sure in a 33 foot boat that you need more than 2 outlets.

The outlets are more sized to the BTU rating of the heater. I believe that it's important to have a combined fan coil BTU rating that is at least as high as the BTU rating of the heater to prevent short cycling.

Originally Posted by sailingharry

* It might be possible to heat the head with nothing more than a loop of copper pipe. 1/2" pipe, 4' long, with a u-turn and back?

I had the same idea. But 1" copper only looses about ~79 BTU per foot @ 99 F (delta of coolant to air temp). I calc'd the head to require ~864 BTU, which means I would need to install about 10' of 1" copper pipe (which would be quite the towel warmer). The head may not need that amount of BTU, but I believe the ability to have ample heat in the head will make it easier to use less shower water (when it's cold, shower water is overused because it feels good to be warm).

Originally Posted by sailingharry

* Blown heaters come with two types of blowers. The centrifugal blowers (big round box) move a lot of air -- but use a lot of power. Axial blowers (computer fans) don't move as much air -- but use a LOT less power.

I'm only going for axial fans.

Originally Posted by sailingharry

* Why did you decide on parallel heaters? I hear both discussed, and to me parallel makes the most sense -- but is the least used.

Piping the fan coils in parallel keeps the temperature of the coolant at the fan coils symmetrical. It also lowers the overall friction loss of the circulation loop. Since these circulation pumps are centrifugal, lowering the friction loss increases the flow. Which is good because hydronic heaters have a minimum required flow rate. But it also adds more piping (which could be good or bad). Parallel also adds complexity because it requires you to consider hydraulic balance (at least some type balancing valves may need to be installed). I'm actually thinking of doing a combination of parallel/series. One loop to the fan coil in the galley, and one loop to the fan coil at the v-berth that continues to the head. Then install a globe valve in the galley return, for balancing (this loop is the shorter). You can also use monoflo tee fittings instead of valves for balancing (which I might do, I haven't decided yet). I'm not actually sure how important this is on a small system, and piping series is simpler.