Cabin Heating with Engine Coolant (another project thread)

[O C Diver]

Follow me into the weeds for a minute.

Let me throw some numbers and calculations out to help people understand using engine coolant to heat cabin air. The heaters I installed are rated at 28,000 BTUs. Most of us can relate to it takes so many BTUs of heat or air conditioning to make our boat comfortable. For instance, my 45' boat has 3 optimized 12,000 BTU reverse cycle heat and air conditioners. While they won't heat or cool the boat quickly, they can easily maintain temperature. So, I need atleast 36,000 BTUs from my heaters. More would be better to raise the temperature more quickly. So I have 3 28,000 BTU units that aren't putting out there rated capacity. So let's look at some numbers to understand what might cause that.

A BTU (British Thermal Unit) is a measurement of of heat energy. It takes 1 BTU to raise one pound of water 1 degree Fahrenheit.

There are 8.33 pounds of water to a gallon. So it takes 8.33 BTUs to raise a gallon of water 1 degree.

When talking about heating air from engine coolant, we talk about extracting the heat from the coolant in a heater. The hotter the coolant is, the more heat that can be removed, to a point. If the engine coolant was 70 degrees and our saloon was 60 degrees, we're not going to be able to extract much heat by blowing 60 degree air over 70 degree coolant filled pipes. But if the coolant filled pipes are 170 degrees, we can get a lot of heat (maybe 10 times as much) by blowing 60 degree air over the pipes. For these types of heaters you need a substantial difference between the coolant and the air to transfer heat. For the sake of discussion, let's say heat output tapers off quickly below 120 degrees. So we want to understand how much heat can be extracted from coolant starting at 170 degrees and ending at 120 degrees. The difference is 50 degree.

Going back to there are 8.33 BTUs in a 1 degree difference in water temperature. If we have a gallon of water at 170 degrees and we extract the heat out of it over 1 hour until it reaches 120 degrees, we can say that we removed 416.5 BTUs of heat (8.33 × 50 = 416.5). So a heater using 1 GPH of water (170 degrees in, 120 degrees out) produces 416.5 BTUs of heat.

One GPH is pretty low. How about 1 GPM? Since there's 60 minutes in an hour, we could multiply the 1 GPH BTUs times 60 to to get BTUs at 1 GPM. 416.5 × 60 = 24,990 BTU. So a 1 GPM flow rate with a temperature drop of 50 degrees can generate approximately 25,000 BTUs.

These numbers look similar to my heating numbers. So if I want 3 heaters to put out 25,000 BTUs, I'll need 3 times as much coolant flow. You should be able to imagine if the starting coolant were hotter I could use less GPM. If I could draw the return temperature down further, I would need less GPM.

With 3 heaters in series, you should expect the first one to produce lots of heat with a large volume of hot coolant. The second should be about average as there is lots of flow but reduced temperature. The third one would be below average as the coolant temperature is substantially cooler.

There's more to figuring out how many heaters and how many GPH of flow you may need, but this gives you a starting point.

Ted

 

[sunchaser]

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

My plate heat exchanger is about 1/3 the size of a small shoe box. I believe it is a Bell and Gossett. One side of the exchanger takes coolant and the other side the heater coolant. The heater coolant pump looks identical to what you pictured. Flow rate of heater coolant is about 4 GPM with coolant pressure at 7psi.

The advantage of a plate heat exchanger in your case is to prevent an engine overheat due to heating system coolant loss. Your excellent setup could benefit from this safety oriented de-coupling of the two different purpose coolant streams.

 

[O C Diver]

My plate heat exchanger is about 1/3 the size of a small shoe box. I believe it is a Bell and Gossett. One side of the exchanger takes coolant and the other side the heater coolant. The heater coolant pump looks identical to what you pictured. Flow rate of heater coolant is about 4 GPM with coolant pressure at 7psi.

The advantage of a plate heat exchanger in your case is to prevent an engine overheat due to heating system coolant loss. Your excellent setup could benefit from this safety oriented de-coupling of the two different purpose coolant streams.

Ok, but if it's only pushing 2-3 GPH as you indicate below, that's not going to give me much cabin heat. Or is what you wrote below supposed to be GPM?

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.

Ted

 

[Hippocampus]

Looking mostly at keel cooled boats. Wonder if the heat exchanger could be placed in the dry stack. That’s about as true waste heat as you could get. Less stuff in the ER. A true high point for fill, bleed, reservoir and accumulator tank.
Also wonder if waste heat from the genset could be used. You are more likely to run the genset than the propulsion engine at night and it’s then heat is most important for a cruiser.

 

[sunchaser]

Ok, but if it's only pushing 2-3 GPH as you indicate below, that's not going to give me much cabin heat. Or is what you wrote below supposed to be GPM? Ted

The 2-3 GPH refers to our vessel's fuel burn off one engine. In your post #15 you stated you wanted to be efficient at a fuel burn of 2 GPH. In our vessel's case the 2-3 GPH of fuel burn provides more than enough waste BTU for heating the vessel hydronically via the plate heat exchanger.

Look up Bell and Gossett. They have quite a variety of plate heat exchangers. The install, if you had the desire, would be quite simple with all your piping/hose already in place.

 

[rslifkin]

Looking mostly at keel cooled boats. Wonder if the heat exchanger could be placed in the dry stack. That’s about as true waste heat as you could get. Less stuff in the ER. A true high point for fill, bleed, reservoir and accumulator tank.
Also wonder if waste heat from the genset could be used. You are more likely to run the genset than the propulsion engine at night and it’s then heat is most important for a cruiser.

Waste heat from the genset could definitely be used. Although in my mind, I'd rather scavenge engine heat for underway and have a fuel fired heater for overnight to avoid needing to run the generator. Otherwise, on a boat with A/C in 40-ish degree or warmer water, might as well just use the reverse cycle on the A/Cs for heat and run the generator 24/7 when away from shore power (which is a terrible solution for many reasons).

 

[O C Diver]

The 2-3 GPH refers to our vessel's fuel burn off one engine. In your post #15 you stated you wanted to be efficient at a fuel burn of 2 GPH. In our vessel's case the 2-3 GPH of fuel burn provides more than enough waste BTU for heating the vessel hydronically via the plate heat exchanger.

Look up Bell and Gossett. They have quite a variety of plate heat exchangers. The install, if you had the desire, would be quite simple with all your piping/hose already in place.

Ok, got it, fuel burn. Was having a hard time figuring out what kind of heating you could accomplish with 2 to 3 GPH of coolant flow.

What engine temperatures are you running? The B & G plate exchangers I've been looking at would have a 20 to 30 degree temperature drop between engine coolant and heater loop fluid.

Ted

 

[Pura Vida]

Thanks for sharing! Impressive!

 

[lwarden]

My Lindell 36 which we recently purchased has quite a complex hydronic system. It has a coolant loop which contains a Webasto diesel heater and a heat exchanger to the starboard engine. The delivery side has three DC powered fan heat exchangers, one for the flybridge with no thermostat on a separate switch, and two for the cabin which are linked to a single thermostat. The short loop from the engine also goes through the water heater before returning to the engine.

I need to map out the system and find all the components. I haven't found a separate circulation pump so presume it may trigger the Webasto pump when enabled for circulation. There are many valves, some manual and some powered in the system. Once I have some time I plan to map the whole thing out so I can help to troubleshoot any problems. At the moment one of the heat exchangers in the cabin is not blowing air, so that needs to be resolved. They didn't do as nice a job with the install as you did Ted, and I have no idea where the wiring for it is located, so that will be a treasure hunt.

The whole thing will be overkill when we get the boat down to San Diego, but it works pretty well up in the PNW where it currently is.

Wish my install was as clean as yours Ted....

 

[sunchaser]

Ok, got it, fuel burn. Was having a hard time figuring out what kind of heating you could accomplish with 2 to 3 GPH of coolant flow.

What engine temperatures are you running? The B & G plate exchangers I've been looking at would have a 20 to 30 degree temperature drop between engine coolant and heater loop fluid.

Ted

Engine temperatures sit between 173-175. The engine heater coolant plate is on the engine that has a Vickers hydraulic pump with a separate water to oil heat exchanger. The engine temps have never been less than that even in 40F water going slow and dodging ice in Glacier Bay.

 

[Alaskan Sea-Duction]

Awesome post and thank you for sharing Ted.


To all the would be scientist and technicians. Who cares how much heat is generated per HP. Turn the thing on and it keeps me and more importantly the Admiral with warm toes.

Looks like I have a new project....

 

[Marco Flamingo]

A couple things based on my experience. Hooking in series results in the bus heaters later in the cycle getting less heat. That can be regulated somewhat by adjustable fan speeds (if the heater has them). It can also be adjusted by connecting the heater "wrong." The owner's manual will show that the air and water travel opposite directions in order to get the most heat from the heater. If you connect the first one in series "wrong," it reduces the maximum heat output for that heater and leaves hotter water travelling to the next heater.

More important for maximizing heat output are the connectors and valves used. My system goes both to the hot water and a bus heater, therefore I needed some kind of a "T" connection. Instead, I found "Y" connections. The difference in flow rates is noticeable. Avoid any splices. Heater hose is commonly available in 50' lengths. Elbows can make things convenient, but avoid them it at all possible.

Ball valves can be the worst. Some 1/2" valves are sold with 5/8" hose barbs. Looking inside, you can see that the valve narrows down below 1/2." Big restriction. Better to buy a 3/4" or 1" valve and a hose barb that reduces to 5/8" heater hose.

Maximizing heat for me is always better because I can turn the heaters off. My hot water is separate so I can cut it out of the system for maximum hot. Or I can just have the hot water circuit open if I need hot water fast, which is rare (I can heat water on the stove).

The one thing that I don't have is valving that allows me to effectively shut off the entire system right at the engine in the event of a leak. The additional valves would reduce efficiency everyday based on the possibility of some future leak. If I lost fluid, I'd have to shut down the engine and let it cool to add fluid. Might as well fix the leak when it cools. That's my risk analysis.

 

[Lepke]

I use Heater Craft heaters from Hamilton Marine, Both the 28,000 and 40,000 models and feed them with insulated supply and return lines running most of the boat length. Instead of chained heaters in a series, I use 12v solenoid valves to break the system into 5 zones, each controlled by a thermostat that also turns on the circulation pump. Water only circulates in the zones calling for heat. Some zones have priority. I also have a temp sensor on each heater that turns on the blower when the water temp reaches 90°F, so the heaters don't blow cold air. Some areas of the boat are set to lower temps when unused.
When running the Detroit mains, both can be tied into the system. Or if the boiler is running, I can circulate hot water thru the engines before starting. Engine connections are controlled by manual valves.
Boiler is 100,000 btu and I have a Wabasto, yet to be installed, of about the same size. I haven't decided if I want to replace the boiler or have both available.
The plumbing is setup so I could add chilled water for cooling.

 

[Mako]

When running the Detroit mains, both can be tied into the system. Or if the boiler is running, I can circulate hot water thru the engines before starting. Engine connections are controlled by manual valves.

Lepke, do you isolate those two engines' feeds or is the coolant mixed? I suppose isolating them would require a flat plate heat exchanger with three loops, which I haven't seen before.

 

[rslifkin]

I'm thinking that if I add engine heat, I'd do a parallel run through a heat exchanger on each engine. So split, go to each engine (with a heat exchanger) then merge and run to the heaters. That way both engines provide heat and if one is shut down for any reason, the heat still works, just at somewhat reduced capacity.

 

[Mako]

Any particular issues with using a domestic diesel fired boiler instead of a “marine grade” unit?

 

[Datenight]

Awesome post and thank you for sharing Ted.


To all the would be scientist and technicians. Who cares how much heat is generated per HP. Turn the thing on and it keeps me and more importantly the Admiral with warm toes.

No good deed goes unpunished. Great post Ted.

Rob

 

[Lepke]

Lepke, do you isolate those two engines' feeds or is the coolant mixed? I suppose isolating them would require a flat plate heat exchanger with three loops, which I haven't seen before.

So far I've only used one engine at a time to heat the boiler. I do that in case of a leak bad enough to shut down the engine. My 671s were easy to plumb so I did them both.

I have two parallel lines, supply and return, running about the length of the boat. The boiler and each engine is plumbed in with manual valves. The engine coolant pump is enough the circulate the coolant between the engine and boiler and might be big enough to run a couple heaters if I bypassed the boiler. When a heat demand comes on, the boiler circulation pump starts and the solenoid valves to the zone open. Usually the oil burner is off. The rest of the system is blocked off with solenoid valves. When cruising I run my naturals at max continuous, so there's always enough heat from one engine. I run the same antifreeze in the engines and hydronic system, so don't see a reason for a heat exchanger.
My main hydronic lines are 1" and reduce to 3/4" where there's a solenoid and heater. The heaters are 1/2" but some zones have 2 heaters that split the 3/4" feed. Also the main supply 1" line has solenoid valves that shut off zone sections with no heat demand, so I'm not heating water that sits.
I also have a wood stove and a pellet stove with coils that are plumed in. Normally in the winter I use pellets only. In really cold weather, I also let the boiler oil burner run. Right now I'm paying about $2 for diesel. When I put in the pellet stove in it was $4. The oil burner alone in cold weather was about 5-10 gallons a day. When the boiler was installed diesel was about 25¢.
And my boiler is a house type, about 50 years old.

 

[FF]

"Any particular issues with using a domestic diesel fired boiler instead of a “marine grade” unit?"

The usual fear is vibration will cause leaks water or exhaust or parts to fall off.

Like everything sold there are quality levels ,a high quality cast boiler unit should be OK , if checked at times.

In the past the Way Wolf unit was a great piece of gear , and had mostly commercial off the shelf (COS) parts.If the weight was no hassle I would chose it for a larger boat.

Heating tubing rather than bus heaters ,or toe kick heaters would be first choice as only one water pump is required.

 

[Lepke]

My house type boiler was installed in the early 1970s. It's on its 2nd oil burner I know of. There's some light rust on the skin and I replaced a gauge. Looks like the original controls.

Boat had baseboard type radiators when I bought it. I went to forced air heaters because I wanted to be able to add chilled water cooling. A bonus was the forced air heats the boat much faster than the radiators. With a cold boat at at about 20°F the radiators would take 2-3 hours for comfort. The forced air does it in about 20-30 minutes, less if a don't heat all spaces at once.

 

[Gaylord Ballard]

That's quality work!

 

[Johnrgould]

Great project. I did something similar on my boat but I used my generator coolant for heating. Loved the article.

 

[sdowney717]

I think this will also help with engine cooling, take a load off the rest of the system.
In my area, it is mostly hot or warm most of the year, and even when cold, salon if it is sunny can warm up.

 

[Maudegun]

Existing system tie in

O C Diver,

Could I pipe from engine to my reversible chiller/heater and utilize all my existing plumbing? I have blowers throughout. Seems heated fluid is the need and I have a keel cooler that could deliver all that. Could it be that simple?

Thanks!

 

[O C Diver]

O C Diver,

Could I pipe from engine to my reversible chiller/heater and utilize all my existing plumbing? I have blowers throughout. Seems heated fluid is the need and I have a keel cooler that could deliver all that. Could it be that simple?

Thanks!

I think it's possible, but it would depend on the plumbing for your chiller / heater.

Ted

 

[mickand]

I just run a couple of ceramic heaters via the inverter when on the move.

 

[boomerang]

I just run a couple of ceramic heaters via the inverter when on the move.

If you're happy with that method of heating your boat, so be it, but that has to be the most inefficient way of heating possible!

 

[sunchaser]

I just run a couple of ceramic heaters via the inverter when on the move.

The further north you travel or when cruising in the winter, using waste heat off the engines as Ted had so ably described is the way to go. Using electric off an inverter seems a serious battery drain. Plus, in a heaving sea a portable electric heater seems a risk.

 

[HeadedToTexas]

Nice write up, Ted. Thank you. Would you please address the pros and cons of the diesel bus heater compared to the engine coolant radiators? I had been thinking along the diesel bus heater lines, but using waste heat from the engine is very attractive.

Do you run the fans on high very often? Seems like less fan may be in order, at least for me.

 

[O C Diver]

Nice write up, Ted. Thank you. Would you please address the pros and cons of the diesel bus heater compared to the engine coolant radiators? I had been thinking along the diesel bus heater lines, but using waste heat from the engine is very attractive.

Do you run the fans on high very often? Seems like less fan may be in order, at least for me.

When considering heat for the boat, in addition to what I installed, I research and considered a boiler such as a Hurricane, a diesel furnace such as a Wallas, and a diesel drip heater such as a Dickinson. Because of where I planned to cruise most, air conditioning was the first priority. With modern air conditioning comes reverse cycle heat. If you pump enough raw water through the heat exchanger (to keep it from freezing), you can get reasonable heat to 34 degree water temperature. For mine (Webasto), 37 degree water temperature produced nearly full heat. So, supplemental heat had to be balanced with the amount of use. The Heatercraft heaters I installed were pretty logical as a significant installation cost, but no real operating cost and no maintenance. This clearly made the boat comfortable while underway. I considered adding a boiler for a complete heating system, but concluded it would be used very little as a percentage of my cruising. From what I read, they seem to work well, provided you use them enough, which I wouldn't. The diesel furnace such as a Wallas, gets high reviews, but again, I wouldn't likely use it enough to keep it running properly. I suppose if I didn't install the hot water loop heating system, a Wallas would have been the logical choice. The drip style heater was briefly considered, but because of the layout of my boat, would probably taken more than one, required fans to push the air around, and taken up to much living space for the small amount of use. They also seemed to require the most operator input and lacked a thermostat for consistent room temperature control.

Ultimately, I concluded for my cruising style and projected areas, the hot water engine heat loop was best while underway, reverse cycle air conditioning heat at the dock and off the generator on non moving days, and most cold nights could be very comfortable with the electric blanket on the bed. I like a quiet boat at night, even choosing the electric blanket over reverse cycle heat at the dock. If I ended up needing more, the Wallas would be my next addition. While you might think a boiler would be the next logical choice, I like the idea of independent redundancy. So far, my coldest day was heading down the Chesapeake in January. The night before was miserable as the brackish water in the slip was around 32 degrees, preventing use of the reverse cycle heat. My systems worked well for the 6 weeks I spent on Lake Superior, so it's unlikely I will add anything else, except possibly a plate heat exchanger.

Regarding the fans, I tend to run the stateroom unit on high as it takes the most heat and I'm not down there while running the boat. The saloon unit starts on high, and is switched to low when the thermostat starts cycling. The pilothouse unit is within 2' of my helm chair, so I tolerate the noise till it feels like 70 degrees and then turn it to low. The thermostat didn't work out so well as the pilothouse is a small area. Needed to recapture the space for more helm instrumentation, so only the fan speed switch is left. Once the saloon is warmed up, enough heat comes up to keep the pilothouse very comfortable.

Ted