Cabin Heating with Engine Coolant (another project thread)

[O C Diver]

I've threatened several times to post this in totality, and am finally getting around to it. During my 2014 - 2015 refit I added a heating loop that runs off the engine's coolant system for heat while underway. So here are the details. Before I start, I should explain that I have CDO (Obsessive Compulsive Disorder [ in alphabetical order as it should be]). A less obsessive person could replicate this with much less effort.

The object was to circulating engine coolant through radiators through out the boat to heat it while underway. The idea is the same as most cars being heated off waste engine heat. For my boat, radiators in the saloon, pilothouse and master stateroom were chosen. In each location I installed a Heatercraft 28,000 BTU heater.

https://heatercraft.com/collections...s/500-grill-face-series?variant=2074878050335

This is the one in my forward stateroom.


They offer different size options, ducting accessories, and voltages. The ducting models would allow you to heat more than one room or mount them as windshield defrosters.

https://heatercraft.com/collections/all-marine-heaters

If you plan to install one of these, it's important to remember the blowers push a lot of air. The small louvered door to the left is an adequate air supply.


Coolant passes continuously through the heater. What heats the room is a 260 CFM blower pushing air over the radiator coil in the heater. The unit comes with a 3 speed blower switch. In addition to being able to regulate heater output, I wanted to be able to regulate room temperature. The blowers draw as much as 9 amps, so a normal HVAC thermostat won't work. What I installed are electric base board heat thermostats which are able to handle far more amps and have bimetal temperature sensors so that boat movement doesn't effect them.

Hear are the controls for my stateroom heater. The thermostat for temperature control and the blower speed switch with off position.


Plumbing the Heaters:
First you need to find where to take coolant from your engine and where to return it to the engine. My John Deere dealer told me there was a 1/2" female pipe fitting at the back of the cylinder head for such applications. Should the system develop a leak, I wanted to be able to block tthe loop with 2 quarter turn valves. So this is coolant out of the cylinder head with a valve.


Here is the coolant return feeding directly into the water pump.


My boat has a domestic water heater with a heat exchanger to make hot water with engine heat. So the coolant loop first goes to the water heater. On my system I installed a 3 way valve on the discharge from the water heater heat exchanger. The valve allows me to direct flow on to the cabin heaters or return it to the engine during the summer when I don't need cabin heat. In this picture the valve is directing flow back to the engine. The hose going up feeds the loop pump.


The loop pump may or may not be necessary depending on the size of the loop. The first system I built was on my charter boat, had one heater, and the loop length was under 15'. There was plenty of flow from the engine pump.

This system has 3 heater coils and over 100' of loop. So, I decided to add a pump. The pump is a sealed magnetic drive designed for hot water. While coolant will flow around the loop without this pump, it's fairly slow. Understand that BTU output from the heater is directly tied to BTUs in the coolant. Within reason, the more coolant you have flowing through the coil, the more BTUs you can push into the room.


So basically we have three heaters with controls throughout the boat. There's a water heater with a heat exchanger and 3 way valve. Finally, the loop pump to speed up the water flow. Now it's time to over engineer the system.

The Land of CDO
This is a picture of my thermostats (there are 2) housing. Just to the left of the dipstick is a silver tag. It's attached to a solid brass temperature switch. It senses loop temperature in the engine regardless of whether the thermostats are open. At 175 degrees it closes; at 165 degrees it opens. If going very slow or idling, I didn't want the system to pull the engine temperature way down.


Follow me at your own risk
So the system needs some excessive complication (mostly to satisfy my CDO). It is powered by a circuit on the main breaker panel. Each Blower has it's own fuse as does the pump. Each blower thermostat is a double pole switch, one for blower and one for the pump. Any thermostat can activate its blower and turn the pump on, but if none are calling for heat, the pump remains off. The negative lead of the pump and relay are controlled by the temperature switch on the engine, so that a sub 165 degree engine temperature turns off the pump and opens the relay powering the 3 heater blower circuits.

Got all that?

In the picture, the 4 fuses to the left are for the blowers and pump. Below is a 3 pole relay and some creative wiring.


Additional Information and Evaluation:
Because one of the heaters is in the pilothouse, about 6' above the engine, and there is 100' of loop hose, I added a reservoir that holds a quart and can handle loop pressure. Since it's the highest point, it makes filling the loop easy and provides a place to catch air bubbles in the system. I don't know if the pumps could have overcome the head pressure otherwise.

The system works extremely well. On a 22 degree night I headed down Chesapeake Bay in late January of 2016. With the boat around freezing, the pilothouse was in the 70s with in a half hour. The saloon took probably a couple of hours, lots of objects and walls to warm up. The staterooms took most of the day to warm up. The stateroom heater is the last in the loop with the lowest coolant temperature and has some walls in contact with the ocean. Another heater in the second stateroom would probably make all the difference once the saloon and pilothouse units started cycling off and on.

When cruising, I burn 2 GPH. So all that heat is coming from a very low fuel burn. The engine produces enough heat to keep it above 170 degrees, but it's unlikely that the thermostats are opening. My plan was to increase speed and fuel burn if there wasn't enough BTUs. That hasn't been necessary so far.

Ted

 

[Comodave]

Nicely done.

 

[GregBrannon]

This is great, Ted. Thank you very much!

Greg.

 

[DavidM]

I am impressed that you can get as much as 90,000 btu/hr out of the engine. I suspect the hot circulating pump helps.

Now you can OCD it more if you want. Set up a hydronic boiler and use a plate and frame heat exchanger to isolate the engine from the hot water circulating loop. This will heat your boat whether the engine is running or not.

You have already done half or more of the work, why not go all the way.

But you must have some heating system now that doesn't rely on the engine, right? Or maybe not. When we lived in Punta Gorda we never ran the heater in the winter, only the A/C.

David

 

[Gabe n Em]

Ok ok, but can you run it in reverse as an engine block heater?


I'm kidding, that's an awesome installation. Thanks for writing it up for us!

 

[ScottC]

Very innovative. Very impressive!

 

[boomerang]

That is indeed a very nice installation you've done! Just as nice is the explanation of the components , their layout and what they do. It was nice that you took the time so that folks would see how it's done. Professionally done!

I installed a single 16k BTU coolant-fired heater in our boat a few years ago but didn't plumb a coolant circulation pump. At idle or anything below 900-1000 rpm, the heater output is nil to limited. In addition to the low BTU output, the blower draws several amps so @ idle in the evening with running lights, electronics and several interior lights burning (most of the lights are LED but the port & starboard lights are still incandescent-my bad), the stock 65A alternator struggles to maintain a charge in the 300A house bank. I would have to assume that you no doubt have an upgraded charging system & house bank so the blowers might not be a problem but it amazes me that your single engine can come close to maintaining at idle it's coolant temperature with 3 units plumbed into the circuit, much less 1!

 

[O C Diver]

I am impressed that you can get as much as 90,000 btu/hr out of the engine. I suspect the hot circulating pump helps.

Now you can OCD it more if you want. Set up a hydronic boiler and use a plate and frame heat exchanger to isolate the engine from the hot water circulating loop. This will heat your boat whether the engine is running or not.

You have already done half or more of the work, why not go all the way.

But you must have some heating system now that doesn't rely on the engine, right? Or maybe not. When we lived in Punta Gorda we never ran the heater in the winter, only the A/C.

David

I'm probably not getting as high as 90,000 BTUs. With the heaters running, the engine temperature is in the 170s. I'm sure the unit is rated based on 190s coolant temperature. Initially the water heater is stealing some BTUs. Then each heater is seeing a progressively lower coolant temperature (less BTU output). There is also some amount of heat lost in the 100' of loop hose. I tend to run the pilothouse blower on the lowest setting as it gets a little noisy on the highest setting. While the settings aren't proportional, there is likely further reduction in heat output. As a comparison, the one on my 35' charter boat was tied to a 10 GPH fuel burning diesel with a 180s degree engine temperature. It would heat up the forward cabin area in no time. Getting in front of the blower on high became uncomfortable very quickly.

I had given the hydronic boiler some consideration when planning this out, but felt I'd almost never use it. Most of my cruising is in more moderate temperatures. If I end up leaving Maryland late to go South, I'll spend a few nights if necessary in marinas with the reverse cycle air conditioning plugged into shore power. With the high capacity water pump, it works well without freezing up, down to about 37 degree water temperature. Most of the cooler nights, I'm fine with my electric blanket running through the inverter. I like a quiet boat at night.

When I leave Maryland late next month for Florida, I'm sure I'll be using the system, maybe as far south as Georgia. It's very nice to have climate control like in a car, without having to run the generator and reverse cycle air conditioning. Essentially free heat for the cost of running the blowers and the pump!

Ted

 

[O C Diver]

That is indeed a very nice installation you've done! Just as nice is the explanation of the components , their layout and what they do. It was nice that you took the time so that folks would see how it's done. Professionally done!

I installed a single 16k BTU coolant-fired heater in our boat a few years ago but didn't plumb a coolant circulation pump. At idle or anything below 900-1000 rpm, the heater output is nil to limited. In addition to the low BTU output, the blower draws several amps so @ idle in the evening with running lights, electronics and several interior lights burning (most of the lights are LED but the port & starboard lights are still incandescent-my bad), the stock 65A alternator struggles to maintain a charge in the 300A house bank. I would have to assume that you no doubt have an upgraded charging system & house bank so the blowers might not be a problem but it amazes me that your single engine can come close to maintaining at idle it's coolant temperature with 3 units plumbed into the circuit, much less 1!

Thank you for the kind words.

I added a second alternator to the engine with a 3 stage Balmar regulator. At 220 amps, it keeps up very nicely with the house loads and maintaining the house battery bank. I have output at idle, maybe 150 amps at 900 RPM and full output by 1,200 RPM. Here are some pictures from the second alternator installation, originally with a different regulator:

https://www.trawlerforum.com/forums/members/1458-albums983.html

As mentioned in another response, I probably have far less than the rated capacity of the the units. Diesel fuel has a BTU rating around 137,000 per gallon. With an average engine efficiency of around 45%, there's lots of BTUs left to scavenge.

Ted

 

[DavidM]

Just for the sake of discussion, lets assume you are using 100 hp when cruising. Ratio down the following numbers if this isn't right.

A diesel engine uses 1/3 of the fuel energy for propulsion, 1/3 goes out in the exhaust and 1/3 leaves in the cooling system and radiant losses to the engine room. So you have roughly 33 hp available for heating.

33 hp is about 84,000 btu/hr, so you are using almost all of the available heat if the nominal capacity of your heaters is met, which you note that it isn't. Between the lower coolant temp (which gets lower for each successive unit in series) and lower blower settings I bet your maximum capability is half.

You might check your raw water temp after it comes out of the heat exchanger with an IR gun. I bet it is near sea water temp when your heaters are all going full blast as most of the heat is going to the heaters and none is left to be extracted by the main heat exchanger.

I wonder if this is good for the engine?

David

 

[sunchaser]

Ted
Nice work. A few thoughts-

On our vessel we have a fairly standard hydronic heater setup. It also has the ability to heat the entire vessel via a small plate heat exchanger off a valved short coolant loop from one engine. This way the engine's coolant system is decoupled from the hydronic coolant flow.

Given the hydronic heat exchangers propensity for developing internal leaks or at fittings, this decoupling adds a safety factor in eliminating engine over heat potential. This type of heat exchanger could easily be installed on your heating loop.

You didn't mention aqua stats. Are you using them to shut down heater fans in warm areas while fans activated by thermostats in cool areas call for heat?

 

[rslifkin]

I've been thinking of doing something similar, although I haven't yet, as I question how much use I'd get from it without also having a fuel fired heat source in the hydronic loop.

But with 2 gas engines that make tons of waste heat, I'm sure I could source enough heat to keep the boat toasty (and probably me at the helm if I have the canvas up) with ice on the decks.

 

[O C Diver]

Just for the sake of discussion, lets assume you are using 100 hp when cruising. Ratio down the following numbers if this isn't right.

A diesel engine uses 1/3 of the fuel energy for propulsion, 1/3 goes out in the exhaust and 1/3 leaves in the cooling system and radiant losses to the engine room. So you have roughly 33 hp available for heating.

33 hp is about 84,000 btu/hr, so you are using almost all of the available heat if the nominal capacity of your heaters is met, which you note that it isn't. Between the lower coolant temp (which gets lower for each successive unit in series) and lower blower settings I bet your maximum capability is half.

You might check your raw water temp after it comes out of the heat exchanger with an IR gun. I bet it is near sea water temp when your heaters are all going full blast as most of the heat is going to the heaters and none is left to be extracted by the main heat exchanger.

I wonder if this is good for the engine?

David

I think you're numbers are off a bit.

Every 20 HP generated by a modern diesel engine requires about 1 gallon of fuel. A 100 HP producing engine would burn about 5 gallons of diesel at 137,000 BTUs per gallon, or about 681,000 BTUs. Assuming a third is available for heat, that would be about 227,000 BTUs.

Yes, I assume with the thermostats are almost completely closed, and the heat exchanger is extracting almost no heat from the engine coolant. Really doubt think this is a problem as the engine temperature is still maintained in the 170s and the heater loop is acting in the same way as a keel cooler. Besides, it's a rare occasion when I find myself cruising in sub freezing air temperatures. At 32 degrees and above, the cabin heaters are all cycling on and off, and the engine thermostats are partially open depending on cabin heat demands. Really doubt this is much different than my Dodge pickup with the Cummins diesel burning 2.5 GPH in 10 degree air temperature in Erie Pennsylvania in February with the heater running full blast. In reality both the boat and truck engines are probably just starting to open their thermostats to account for the constant normal engine temperature.

Ted

 

[garbler]

Now this is what I call one interesting and informative post. You did a lot of research here and the finished job looks like a factory stock installation, actually better than most. On the subject of engine driven heaters the coastal lobster boats in Maine use what they call ‘ buss heaters ‘ that are tapped into the engine coolant system. Now coastal day-lobster boats have 3/4 wheel houses with no rear bulkhead so they are cold and these little heaters are just for your feet. But as they say if your feet are cold ————-.

I might also add that years ago Volvo had a bunch of water heater installation problems resulting in air locked cooling systems and over heating. Unlike your John Deere they were vague if not negligent about installation and hook up directions. Nice to see JD addresses this and I’m sure most engine makes do these days. Anyway great post.

 

[DavidM]

You are right. I used an internet conversion site to do the conversion of hp to btu, but I bet it was thinking about boiler hp which is a different kettle of fish. When I convert hp to kw/hr to btu/hr using conversion factors I know are right, I get your number.

David

 

[O C Diver]

Ted
Nice work. A few thoughts-

On our vessel we have a fairly standard hydronic heater setup. It also has the ability to heat the entire vessel via a small plate heat exchanger off a valved short coolant loop from one engine. This way the engine's coolant system is decoupled from the hydronic coolant flow.

Given the hydronic heat exchangers propensity for developing internal leaks or at fittings, this decoupling adds a safety factor in eliminating engine over heat potential. This type of heat exchanger could easily be installed on your heating loop.

You didn't mention aqua stats. Are you using them to shut down heater fans in warm areas while fans activated by thermostats in cool areas call for heat?

I had considered a heat exchanger to transfer heat to a cooling loop. Wasn't sure how much loss of BTU transfer would be by adding the exchanger. At 2 GPH fuel burn, I needed to be as efficient as possible with heat extraction from the engine. I was concerned about leaks, so used a premium hot water rated hose with a higher pressure rating. There are no splices in the loop, and I believe all connections are double hose clamped. The system I setup on my charter boat has been running for 15+ years with zero leaks. The system on my trawler runs at 10 PSI as regulated by the expansion tank radiator cap. I imagine your hydronic system has a higher operating pressure.

Ok, you got me, I had to look up what an aqua stat is. In a very out of character solution, I use a much more low tech priority management system. When pulling the anchor in the morning, I start the engine and turn on the heat system. Because of the heat switch I mounted on the engine, the system won't function until the engine comes up to operating temperature. I leave the saloon blower off until the pilothouse is warm as the saloon heater is before the pilothouse heater in the loop. Once the pilothouse is warm, I'll turn on the saloon blower as the reduced coolant temperature doesn't impact the pilothouse heating. The stateroom heater is last in the loop and gets the leftover BTUs till the other heaters start cycling. My heating priorities are pilothouse first, then saloon, and staterooms and heads last.

Ted

 

[wkearney99]

Several thoughts come to mind. One being dissimilar metals and potential corrosion. Be certain you're not using the wrong metals for fittings.

Second, vibration. We lost the coolant loop from one of our C12's (alarm sounded and we shut down, so nothing got wrecked) due to the valve not being supported. It had an elbow off the engine, to a quarter-turn valve and then to hose. The hose wasn't properly supported and left enough wiggle for the fitting to eventually break.

Third, de-couple coolant from the circulating system, as others have pointed out. You don't want a leak in the heating loop taking out the engine.

 

[Nomad Willy]

We have one on the Willard but almost never use it ... too noisy. It overpowers the engine.

So we just run the Wabasto.

 

[O C Diver]

Now this is what I call one interesting and informative post. You did a lot of research here and the finished job looks like a factory stock installation, actually better than most. On the subject of engine driven heaters the coastal lobster boats in Maine use what they call ‘ buss heaters ‘ that are tapped into the engine coolant system. Now coastal day-lobster boats have 3/4 wheel houses with no rear bulkhead so they are cold and these little heaters are just for your feet. But as they say if your feet are cold ————-.

I might also add that years ago Volvo had a bunch of water heater installation problems resulting in air locked cooling systems and over heating. Unlike your John Deere they were vague if not negligent about installation and hook up directions. Nice to see JD addresses this and I’m sure most engine makes do these days. Anyway great post.

Funny you mention lobster boats in Maine. One of the companies I buy from is Hamilton Marine in Maine. They're a large dealer for Heatercraft and gave me the best price on the units I bought. I would imagine that a lot of their sales go to lobster boat installations.

Ted

 

[O C Diver]

Several thoughts come to mind. One being dissimilar metals and potential corrosion. Be certain you're not using the wrong metals for fittings.

Second, vibration. We lost the coolant loop from one of our C12's (alarm sounded and we shut down, so nothing got wrecked) due to the valve not being supported. It had an elbow off the engine, to a quarter-turn valve and then to hose. The hose wasn't properly supported and left enough wiggle for the fitting to eventually break.

Third, de-couple coolant from the circulating system, as others have pointed out. You don't want a leak in the heating loop taking out the engine.

All plumbing fittings are stainless steel or brass thick walled with a 1,000 PSI pressure rating. Coolant is ethanol glycol based, so no corrosion issues.

The coolant out hose has a support clamp within inches of the valve. The return hose hangs down to eliminate leverage and is supported below the engine stringers.

While the decoupled coolant system has merit, a properly designed and installed system is quite reliable as demonstrated by the tens of thousands of recreational boats with engine heated water heaters built in the last 50 years. Doubt 5% of them have decoupled systems. Then there the lobster boats, Chesapeake bay oyster boats, and thousands of commercial small fishing boats with buss heaters and probably no decoupling.

Ted

 

[Northern Spy]

I had a bus heater with a simple thermostat for years on the boat, but when I swapped over to the Volvo, I disconnected it.

Volvo has very specific requirements, which was issued as a service bulletin for each engine series after the issues. Can be found on the internet with some diligenct searching.

The main concern is where to tap off of the block and the expansion tank size and static head location (elevation). Mine taps off the hose to the turbo! Yikes!

I have a small plate heat exchanger I purchased years ago to remedy the problem and keep the engine loop low volume. Plate heat exchangers are very efficient (~90%) when sized correctly for shear flow.

I would also like to use my diesel stove to heat the the loop as well, so keeping the heating loops and heater loop separate makes sense.

You have a nice install, but would caution others that one could induce cooling issues to the engine if not done properly.

There may be a fairly high system head created depending on hose/pipe diameter, valve types (use full bore) and heater K value.

That said it ain't rocket science, and as long as you have a high point vent, it will probably work fine.

You've inspired me to get my system installed. [emoji846] Thanks for sharing.

 

[sunchaser]

Ted
If you had any interest in installing a plate exchanger you'd likely not over cool your engine. Our plate heat exchanger setup performs flawlessly at 2-3 GPH.

 

[RCook]

We have one on the Willard but almost never use it ... too noisy. It overpowers the engine.

So we just run the Wabasto.

Hi Eric,

Could it be yours is a Red Dot ("bus heater")? They are indeed noisy. The Heatercraft units in my Nordic Tug and previous 26-footer are almost silent.

 

[Nomad Willy]

Richard I don’t know what it is brand wise.
Just don’t use it.
I one way I do use it. I use it as a high point when filling my engine w coolant. I fill it real slow and get no bubbles.

I could want to switch over as we burn kerosene now brought aboard in small plastic jugs. 2 gal? So having a good bus heater would cut down on the kero consumption. Save the kero for night.

 

[Seevee]

Great post, Ted!


Wish I did this prior to my loop trip a few years ago. Froze my arse off... never realized how cold that trip was, but still great. Just used the heat pump, but had to run the genny a lot for that.


So, I'm now looking into heat. (Also shopping boats, so probably in my next boat).


Have had boats before that took heat from the engine block and worked great. But, there's a thought to use a hydronic heater to run when the engine is not running, anchoring out, night, preheat, etc.


However, your engineering looks great. A few questions:


So, as I understand, the line off the engine runs to the water heater first, and after that, runs to the pilot house, then the saloon, then the stateroom, correct? Does not "Y" to the different heaters at all, excepting after the water heater to take the cabin heaters out of the loop when not needed.



And just one return line from the stateroom.


And when you bought the unit from Heatercraft, it included the heater, hose and everything you needed for that heater? (Not including your add ons, pump, thermostat).


Seems like a very simple and very cleaver system, and virtually free heat.


Thx again for a great write up!

 

[timb]

thanks for the write up .

my boat had a hydronic heating system (120v diesel ) with baseboard radiators and three forced air .I think the 400 model would fit where the ugly grill from the forced ail unit in the settee is .that is where all passengers would likely be and it's not that long of a run from where the new water heater is going .

I'll probably follow your setup minus the pump with only one unit. I need to do some research as to if it will upset the cooling of the American diesel. has a flow control in the fitting where the water heater was connected.

is anyone following this post pulling heat from a A/D or lehman ?

 

[O C Diver]

Ted
If you had any interest in installing a plate exchanger you'd likely not over cool your engine. Our plate heat exchanger setup performs flawlessly at 2-3 GPH.

I'm really not worried about over cooling the engine. At cruise the freshwater pump is circulating at 30+ GPM. The thermostat are a bypass style. When they're closed, there is full flow around the engine coolant loop. As they open, flow is diverted from the bypass loop through the heat exchanger. My heating loop has an approximate 4 to 5 GPM flow rate. So that room temperature or better 5 GPM gets mixed with 25 GPM going into the water pump. With 170+ degree engine temperatures, I really don't think I have a problem.

While I have nothing against plate heat exchangers, I need 5 GPM not 2 to 3 GPH from both liquids and they're both at 10 PSI or less.

Ted

 

[O C Diver]

Great post, Ted!


Wish I did this prior to my loop trip a few years ago. Froze my arse off... never realized how cold that trip was, but still great. Just used the heat pump, but had to run the genny a lot for that.


So, I'm now looking into heat. (Also shopping boats, so probably in my next boat).


Have had boats before that took heat from the engine block and worked great. But, there's a thought to use a hydronic heater to run when the engine is not running, anchoring out, night, preheat, etc.


However, your engineering looks great. A few questions:


So, as I understand, the line off the engine runs to the water heater first, and after that, runs to the pilot house, then the saloon, then the stateroom, correct? Does not "Y" to the different heaters at all, excepting after the water heater to take the cabin heaters out of the loop when not needed.



And just one return line from the stateroom.


And when you bought the unit from Heatercraft, it included the heater, hose and everything you needed for that heater? (Not including your add ons, pump, thermostat).


Seems like a very simple and very cleaver system, and virtually free heat.


Thx again for a great write up!

So the loop comes off the engine, through the water heater, then the saloon heater, the pilothouse heater, the stateroom heater, and back to the engine. One loop with a bypass after the water heater back to the engine.

All the cabin heaters are in series with the stateroom return going to the engine.

I bought the heaters without anything else but the blower speed switch. Everything else I sourced individually, didn't want cheap hose, etc.

Ted

 

[O C Diver]

I had a bus heater with a simple thermostat for years on the boat, but when I swapped over to the Volvo, I disconnected it.

Volvo has very specific requirements, which was issued as a service bulletin for each engine series after the issues. Can be found on the internet with some diligenct searching.

The main concern is where to tap off of the block and the expansion tank size and static head location (elevation). Mine taps off the hose to the turbo! Yikes!

I have a small plate heat exchanger I purchased years ago to remedy the problem and keep the engine loop low volume. Plate heat exchangers are very efficient (~90%) when sized correctly for shear flow.

I would also like to use my diesel stove to heat the the loop as well, so keeping the heating loops and heater loop separate makes sense.

You have a nice install, but would caution others that one could induce cooling issues to the engine if not done properly.

There may be a fairly high system head created depending on hose/pipe diameter, valve types (use full bore) and heater K value.

That said it ain't rocket science, and as long as you have a high point vent, it will probably work fine.

You've inspired me to get my system installed. [emoji846] Thanks for sharing.

Do you have a link to your plate heat exchanger? Everything I've seen shows low flow rates or higher pressures. If you're only feeding one heater, maybe a low flow rate works. With my system, 4 to 5 GPM makes the last heater only modest until the other 2 start cycling.

Ted

 

[Jeff F]

Ted, this is gold for me. Your comment from a week or so ago got me thinking about it, and the details and discussion here make it all clear.

I'll be largely mimicking what you've done on my boat in the next couple of months.

Thanks.