Tapping the cooling system for a heater

Has anyone done this off a Cummins 6BTA? Simple?

Yes, it's very simple and does quite a good job. I teed off the exhaust manifold and returned to the water pump inlet.

Ted

What you want is often called a bus heater. Heatercraft, among others makes the exchanger/blower unit. You use the same engine taps that supply coolant to your boat's hot water heater, if installed. You typically plumb the water heater first and then the coolant flow goes to the bus heater and then back to the engine.


There are some hydraulic tricks about elevation and venting that need to be observed.


You also need to know that heat will stop fairly soon after you shut the engine down.


David

If your boat has a diesel heat system, you can use the engine heat loop and a heat exchanger to heat/run the heating system while underway. But it would only matter if you have an existing heating system.

We run the Wabasto underway. Much much quieter than the bus heater fan in the salon. When the Wabasto is running while underway I only realize it's on when I step outside to the aft cockpit.

"You use the same engine taps that supply coolant to your boat's hot water heater, if installed. You typically plumb the water heater first and then the coolant flow goes to the bus heater and then back to the engine."

Too many domestic HW heaters attempt to regulate the HW temperature by using a thermostat that blocks the coolant flow.

The heater in series will have almost no water flow after the HW is warm

You can remove this thermostat , or use a parallel setup for HW and boat heat .

Either way an ANTI SCALD valve in the fresh water system is advised , esp if kids or old folks are aboard.

Interesting. I haven't encountered a thermostat controlling coolant flow to a domestic HW tank, but would remove it too if I did encounter one.

And I very much encourage a mixing valve as well. 180F water will burn you very quickly, and that's your hot water's temp when heated from the engine. I have also encountered fresh water plumbing devices that are only rated to 150F or some other value well below 180F. Running those devices so far out of spec is asking for failures. Whale quick connect fittings are a good example. They are only rated to 150F which is normally more than enough, except when the water is heated to engine temp....

Arcticspud said:

Has anyone done this off a Cummins 6BTA? Simple?

Click to expand...

There are two simple taps on the starboard side of the engine. The supply is on top the return is lower behind the alternator and just forward of the oil filter. Which must be removed to access the fitting.

manyboats said:

We run the Wabasto underway. Much much quieter than the bus heater fan in the salon. When the Wabasto is running while underway I only realize it's on when I step outside to the aft cockpit.

Click to expand...

My buddy's Red Dot bus heater was quite noisy. Our Heatercraft is so quiet we can barely hear it, and does a great job keeping our cabin warm and dry.

Pgitug said:

There are two simple taps on the starboard side of the engine. The supply is on top the return is lower behind the alternator and just forward of the oil filter. Which must be removed to access the fitting. View attachment 49538View attachment 49539

Click to expand...

Do you know the size and type of fittings that were used?

They are nothing special. Normal NPT thread. But you will have to look on your engine to see if they are 1/2" or 3/4". Mine are 3/4".

"And I very much encourage a mixing valve as well"

If a mixing valve runs out of cold water it will pass Hot water that can scald.

An anti-scalding valve will shut the Hot off in the same condition.

Your choice....same instal time.

I'm not 100% up on the nomenclature, but when I bought a "tempering valve" years ago for my house, it just passed a set amount of cold water, regardless of the relative temperature of hot and cold:


I ended up ripping it out and replacing it with a "thermostatic mixing valve":


I think the latter is what FF is referring to.

The tempering valve can only statically adjust the amount of cold water by turning the dial on the top. And even that didn't offer enough range for the wide swings of both the incoming cold water (seasonal) and the domestic hot water (from the boiler.)

I suspect it's the same in a boat, so I put in a proper termostatic mixing valve.

In my case, it wasn't so much about scalding - most people are smart enough not to hold their hands under steaming hot water that long - but to get a more even temperature and extend the time between having to power the water heater.

RCook said:

My buddy's Red Dot bus heater was quite noisy. Our Heatercraft is so quiet we can barely hear it, and does a great job keeping our cabin warm and dry.

Click to expand...

Also what makes a difference is fan speed and distance/turns to vent if any ducting is used. Usually remoted diesel heaters are quiet compared to surface mounted bus heaters.

Apples to apples as they say....

Not sure why I would need a mixing valve as this is for a heater, not the water heater. I do have a Wabasto heater, just trying to cut down on the use of fuel and harness some of the heat off one of the engines.

I have 3 Heatercraft units with a small pump to push the coolant around the 100'+ of hose that makes up the heating loop in my 45' boat. Dose a nice job down to around 32 degrees while the engine is burning 2 GPH. When I get some time, I will do a thread on my engine coolant heat system.

Ted

Interesting...my run from the engine to heater will be less than 10' so i shouldn't need a pump. I don't have one on the other side with the water heater.

One problem you may run into is that the heater system may cool the engine system more than normal. The thermostat bypass is designed to keep the coolant at a minimum temp and still circulate coolant to avoid hotspots, and with cold water into the heat xchanger it may be at the minimum. Add in another cooling source, at idle, and your engine may be running very cold. Newer electronic engines especially dont deal well with this.

Great points. As with everything, there is always a trade off. I suppose you just have to be aware of how you are operating the engines and switch to the Wabasto heater if operating conditions warrant.

Install petcocks at the engine where you connect so you can shut it off if you need to or if you don't need the heat.

kulas44 said:

One problem you may run into is that the heater system may cool the engine system more than normal. The thermostat bypass is designed to keep the coolant at a minimum temp and still circulate coolant to avoid hotspots, and with cold water into the heat xchanger it may be at the minimum. Add in another cooling source, at idle, and your engine may be running very cold. Newer electronic engines especially don't deal well with this.

Click to expand...

This is true, though in practice it doesn't seem to be much of an issue. The only time I have seen a noticeable engine temp drop was this past summer in Alaska. Water temps were in the 40's, air temp was in the low 40's, heat was running throughout the whole boat (and keeping up without any issue), and we were idling for a long time while picking though ice. Other than being in the arctic, I think these were about the worst case conditions. Our normal idle temp is 160F, and as I recall it dropped a couple of degrees below that, but only a couple. With any RPM above idle, it came right back up. My assumption has always been that the size of the diversion ports are small enough to prevent over cooling of the engine.

bglad said:

Install petcocks at the engine where you connect so you can shut it off if you need to or if you don't need the heat.

Click to expand...

Great idea. I need to do this on the other engine that provides heating for the water heater.

twistedtree said:

This is true, though in practice it doesn't seem to be much of an issue. The only time I have seen a noticeable engine temp drop was this past summer in Alaska. Water temps were in the 40's, air temp was in the low 40's, heat was running throughout the whole boat (and keeping up without any issue), and we were idling for a long time while picking though ice. Other than being in the arctic, I think these were about the worst case conditions. Our normal idle temp is 160F, and as I recall it dropped a couple of degrees below that, but only a couple. With any RPM above idle, it came right back up. My assumption has always been that the size of the diversion ports are small enough to prevent over cooling of the engine.

Click to expand...

I would agree with this. Cars and trucks idle for hours (I5) in the Puget Sound and the operating temps do not vary but a few degrees.

An ideling car or truck will see return water that is barely cooled enough to keep the engine from overheating.

Usually about 20deg F lower than when pumped to the radiator.

A keel cooler (without a by pass thermostat) can return coolant close to the surface water temperature.

160 F -180F out 50F return , no problem with a bypass thermostat . in the coolant , big problem if only relying on the engines stock internal unit.

djmarchand said:

What you want is often called a bus heater. Heatercraft, among others makes the exchanger/blower unit. You use the same engine taps that supply coolant to your boat's hot water heater, if installed. You typically plumb the water heater first and then the coolant flow goes to the bus heater and then back to the engine.


There are some hydraulic tricks about elevation and venting that need to be observed.


You also need to know that heat will stop fairly soon after you shut the engine down.


David

Click to expand...

That's what I did and my only question was, why did I take so long to do it.
Heatercraft about $280
great deal and works so well.

I would think that if you had the heater in the same loop as the water heater, and assuming it (water heater) is also a.c. powered, with the gen running it would help keep the coolant temp up. Just an observation, no practical experience as I havent boated anywhere that I needed cabin heat.

"You also need to know that heat will stop fairly soon after you shut the engine down."

In both our bus conversion and on LUCY we have a small circ pump in the box heater circuit.

For mild weather a 3,000 lb hot diesel will give enough heat to make it comfortable for a few hiurs after engine shutdown.

It does cost batt amps as the heater fan even at slow is a hog , but is nice and quiet .

Trouble with trying to use the hot water heater as a source for a bus heater...there is a double transfer loss (engine to water heater and then water to air at the bus heater, plus piping losses).


The water heater element is typically only 1500 watts (about the same as a space heater) but you lose at the transfer from piping to airflow thru the bus heater. So after the initial hot water is used up...you are trying to heat with a 1500 watt element inefficiently.


You would be better off with space heaters loading up the genset or piping a setup where the genset provided coolant heat transfer to the bus heater circuit or just a separate bus heater.


Unless you get fancy like FF suggests and keep engine coolant circulating after the engine is shut down.

"Trouble with trying to use the hot water heater as a source for a bus heater."

We use the 3000lb iron mass of the 6-71 as the heat source , not the puny 10G in a hot water box.

Nothing fancy , just a tiny 12V centrifugal pump.

FF, please advise the (circulating) pump details that you are using...and is it in the engine water circuit while the engine is running ? or valved off ?
and last question....does it push the water in the same direction as the engine pump (when the engine is running). thanks in advance for the info