Bus heaters(Red Dot)how many is to many?

[Wester Lee]

Want to add two bus heaters to my Krogen 42 one in each stateroom. Want to add them inline with the engine fed hot water heater tank. My question is will that add any problems with the cooling system. Like extra wear on the circulation water pump, or possible air locks (heaters will be lower than the engine). Thoughts?

 

[O C Diver]

https://www.trawlerforum.com/forums...ine-coolant-another-project-thread-53386.html

For lower risk on the integrity of your system, a plate heat exchanger is a good idea. Then use a separate coolant loop with its own pump. As mentioned in the thead, I have bus heaters in the forward stateroom, saloon, and pilothouse. Until the fans start cycling with the thermostats, the further into the loop heaters produce little heat. Once the boat warms up, all produce great heat.

Ted

 

[RCook]

Not sure this is still the case, but in my experience some 20+ years ago, the RedDots were very rattley noisy. Heatercraft almost silent.

 

[Benthic2]

did someone say bus heater ?

 

[Marco Flamingo]

I think the auxiliary hot water takeoff on the block for heater/hot water doesn't cause any extra wear on your water pump. The pump just does its thing and it doesn't matter where the coolant goes, as long as it circulates. It might be possible to have too much restriction in the heater/hot water circuit and it won't be super effective. That was apparently my prior owner's concern. He had a rat's nest of valves and hoses such that he could send coolant only to the hot water tank, only to the Red Dot (in the V berth), or fine tune the ratio to each. That was too much complexity and engine room space for my needs.

I changed it to a simple loop in the bilge, forward to the Red Dot and then return to the water heater and back to the block. The Red Dot first because heat was more important than hot water. A total distance is close to 40 feet. Hot water now takes over an hour of cruising and is no longer scalding when I run the Red Dot. I can live with that as a trade off for a simple system. I did add a "T" at the lowest point so that I can easily drain the coolant system.

Both the water heater and the Red Dot are lower than the coolant reservoir. I think that my auxiliary coolant returns to the reservoir, so any bubbles working their way out of the system wouldn't pass through the pump.

I don't know your boat's layout, but Red Dot type heaters basically only work underway. Are your stateroom's occupied then?

 

[Wester Lee]

Good info, thanks Marco. I was thinking of running mine from the hot water tank then to the Red Dots as my morning shower is most important after being under way for a short time then the Red Dot can knock the morning chill out of the staterooms. Richard, I will look into Heatercraft heaters for a comparison but noise won’t be much of an issue as the main engine will be running and no real occupancy in the staterooms, Thanks for the feedback.

 

[Jeff F]

I think Ted's suggestion is a good one. Rather than a big coolant loop going through two heaters and the water heater install a heat exchanger in between the motor and the hw tank, then an indepenent loop between that and the heaters with a small circulation pump. This gives maximum control and performance, and you're not circulating through the heaters unless they're on.

I like the idea of minimizing the runs and connections for engine coolant. If a heater core starts leaking it's better if it doesn't lead to a failure in the propulsion system.

 

[Lepke]

You don't need an extra circulation pump, the engine pump will do fine. I have a long boat and no problem heat reaching the far heaters.
Add shut of valves to your system so if a hose goes you can isolate the engine and keep running.

 

[O C Diver]

Lot's of good information in the link in post #2. If you haven't, read the whole thread, there's lot's of good information.

Ted

 

[mvweebles]

Lot's of good information in the link in post #2. If you haven't, read the whole thread, there's lot's of good information.

Ted

Ted - a separate heat exchanger has been described in a couple different threads recently. Do you have a link or something? I'm struggling to visualize and where to source.

Peter

 

[Jeff F]

Ted - a separate heat exchanger has been described in a couple different threads recently. Do you have a link or something? I'm struggling to visualize and where to source.

Peter

Here's an example https://altheatsupply.com/30-plate-water-to-water-heat-exchanger-pe-3x8-30.html

 

[O C Diver]

Ted - a separate heat exchanger has been described in a couple different threads recently. Do you have a link or something? I'm struggling to visualize and where to source.

Peter

This is one I'm considering:

https://www.ebay.com/itm/283774063530

Smaller units are available, but you need to be careful of back pressure relative to flow rates. The standard circulation pump in a diesel engine is capable of blocking the flow without damage to the pump. So it doesn't build up much pressure and doesn't overcome flow restrictions.

The above heat exchanger can flow 17 GPM with less than 1 PSI of back pressure. Now my engine circulation pump won't flow that kind of volume through this loop, but I don't want any flow restrictions through the heat exchanger to reduce BTU transfer. The pump on my heater circulation loop is of the same type, so it's important not to reduce its flow either.

Ted

 

[O C Diver]

Here's an example https://altheatsupply.com/30-plate-water-to-water-heat-exchanger-pe-3x8-30.html

Hi Jeff,

I appreciate the link, but that unit is only rated for 20,000 BTUs. That's less than one of my buss heaters. The one I linked in post #12 is rated for 200,000 BTUs.

Ted

 

[DavidM]

One question that hasn't been addressed above is how much heating capacity is required to supply two bus heaters and the hot water heater and how much is available from the engine cooling system. So bear with me for a bit of geekiness:

Let's start with a rule of thumb given to me by Tony Athens: marine engines turn 1/3 of their fuel burned into rotational energy, 1/3 goes out the exhaust and 1/3 is absorbed by the cooling system. So given that the Krogen 42 usually comes with the Lehman 135 hp engine and probably runs at 50 hp for moderate cruising speeds, that means another 50 hp is absorbed by the engine cooling system. Converting that to btu/hr gives approximately 130,000 btu/hr.

A small Red Dot heater produces 16,000 btu/hr so 32,000 btu/hr for both. A 6 gallon water heater, starting from a cold water temp of 60 F and heating to 140 F in 30 minutes requires 6*8.3*(140-60) = 4,000 btu or 8,000 btu/hr heating rate. BTW, this doesn't mean that there is enough heat transfer capacity to do it that fast, only how much heat is required to do it if possible.

So add them all up: 16+16+8= 40,000 btu/hr which is about 1/3 of the heat transferred to the engine's cooling system.

It shouldn't be a problem.

David

 

[O C Diver]

One question that hasn't been addressed above is how much heating capacity is required to supply two bus heaters and the hot water heater and how much is available from the engine cooling system. So bear with me for a bit of geekiness:

Let's start with a rule of thumb given to me by Tony Athens: marine engines turn 1/3 of their fuel burned into rotational energy, 1/3 goes out the exhaust and 1/3 is absorbed by the cooling system. So given that the Krogen 42 usually comes with the Lehman 135 hp engine and probably runs at 50 hp for moderate cruising speeds, that means another 50 hp is absorbed by the engine cooling system. Converting that to btu/hr gives approximately 130,000 btu/hr.

A small Red Dot heater produces 16,000 btu/hr so 32,000 btu/hr for both. A 6 gallon water heater, starting from a cold water temp of 60 F and heating to 140 F in 30 minutes requires 6*8.3*(140-60) = 4,000 btu or 8,000 btu/hr heating rate. BTW, this doesn't mean that there is enough heat transfer capacity to do it that fast, only how much heat is required to do it if possible.

So add them all up: 16+16+8= 40,000 btu/hr which is about 1/3 of the heat transferred to the engine's cooling system.

It shouldn't be a problem.

David

My numbers work as follows:

At 7 knots the engine consume 2 GPH (40 HP). 2 GPH equals 260,000 BTUs. With 1/3 available through the cooling system, that equals 86,000 BTUs available for heaters.

At 6 knots the engine consume 1.2 GPH (24 HP). 1.2 GPH equals 156,000 BTUs. With 1/3 available through the cooling system, that equals 52,000 BTUs available for heaters.

Ted

 

[Marco Flamingo]

I heat my entire house with a little heat exchanger like shown in post #11 (8x3 inch 30 plate). Only difference is my fittings are 3/4 inch. Potable water on one side and hydronic heat to a concrete slab for a 2 bedroom home. These plate heat exchangers are way more efficient size-for-size compared to the tube heat exchangers on my Lehman.

A couple things to consider. First, it is possible to be too efficient. A big exchanger can transfer a lot of heat, but your Red Dot or water heater can only use so much. Then the still warm water is returned to the heat exchanger and, because you're starting with warmer water, you don't need a big exchanger once the circuit is up and running. Also, a big efficient exchanger might be able to send out 190 degree water based on 200 degree coolant temps. I don't think my hot water tank has a temp shutoff for the engine loop and it might create a scalding situation. Same concern for other accessories. Might be too much of a good thing.

 

[rcsomany]

Bus Heater / Engine Interlock

I was surprised to find an interlock between the bus heater and the main engine in my Pacific Trawler 40. (We only have one of each.)
During a winter cruise, I was running the bus heater while underway, Once we got alongside, I was unable to shut down the main engine. While we were tracing wiring - in particular, ignition wiring - to determine the cause, I noticed that the bus heater switch was still in the "on" position. I had forgotten to turn it off but when I did so, the main engine immediately stopped.
We didn't know but we theorized that the interlock was there to prevent damage to the bus heater by running it with the engine not running.
Does that make sense and should it be taken into account in a bus heater installation?

 

[O C Diver]

I was surprised to find an interlock between the bus heater and the main engine in my Pacific Trawler 40. (We only have one of each.)
During a winter cruise, I was running the bus heater while underway, Once we got alongside, I was unable to shut down the main engine. While we were tracing wiring - in particular, ignition wiring - to determine the cause, I noticed that the bus heater switch was still in the "on" position. I had forgotten to turn it off but when I did so, the main engine immediately stopped.
We didn't know but we theorized that the interlock was there to prevent damage to the bus heater by running it with the engine not running.
Does that make sense and should it be taken into account in a bus heater installation?

Imo, that's ridiculous. If you have an engine room with a fire suppression system, will the heater prevent the engine from being shut down in the event of a fire?

Here's how they're wired on my boat. All the heater blowers and the circulating pump are wired through a relay to the house battery bank. The relay is wired as an accessory off the ignition switch of the engine. The negative wire for the relay is wired to a temperature switch in the engines coolant loop.

The blowers and pump won't come on until the engine is running and the coolant temperature exceeds 170 degrees. If the coolant drops below 160 degrees (idling the engine) the relay drops out, turning off the blowers and the pump.

Ted

 

[Bmarler]

I was surprised to find an interlock between the bus heater and the main engine in my Pacific Trawler 40. (We only have one of each.)
During a winter cruise, I was running the bus heater while underway, Once we got alongside, I was unable to shut down the main engine. While we were tracing wiring - in particular, ignition wiring - to determine the cause, I noticed that the bus heater switch was still in the "on" position. I had forgotten to turn it off but when I did so, the main engine immediately stopped.
We didn't know but we theorized that the interlock was there to prevent damage to the bus heater by running it with the engine not running.
Does that make sense and should it be taken into account in a bus heater installation?

Likely not an interlock, but a mistake. The heater is likely back feeding the engine controls.

 

[Lepke]

I have 11 marine heaters in my hydronic system and one of my Detroits at cruising speed will keep up with the cold at zero F. The marine water heaters heat the boat much faster from a cold boat than the former radiators. The radiators took about 4 hours while the water type heaters do the job in about 20 minutes. The boiler though is expensive. Installed when diesel was about 25¢. At zero F, it burns about 5-6 gallons a day. That's why I have a pellet stove with a water coil that heats the boiler.

 

[Marco Flamingo]

If you have long runs of coolant hose to the Red Dot and water heater through unconditioned space (like the engine room and/or bilge), it is possible to use "pool noodle" type of pipe insulation to cover the hose. The insulation keeps the heat for the heaters. If your hose goes through a bulkhead where noise is an issue (like emerging from the engine room), the pipe insulation tight against both sides of the bulkhead can form sort of a noise gasket covering the smaller hole used for the hose.

 

[O C Diver]

If you have long runs of coolant hose to the Red Dot and water heater through unconditioned space (like the engine room and/or bilge), it is possible to use "pool noodle" type of pipe insulation to cover the hose. The insulation keeps the heat for the heaters. If your hose goes through a bulkhead where noise is an issue (like emerging from the engine room), the pipe insulation tight against both sides of the bulkhead can form sort of a noise gasket covering the smaller hole used for the hose.

Don't know if pool noodle will fit over the hose. There is equivalent pipe insulation available at plumbing supply houses for up to 2" pipe I believe. While rubber heater hose isn't the best insulation, compared to the BTUs traveling through the hose, the loss isn't that great. I didn't insulate my 100' loop, and the system works well without it.

When going through bulkheads, I bought the next size or 2 larger heater hose that would slide over my loop hose. Then I would use a hole saw to make a hole for a press fit for the over sized hose. It worked very well as chaffing protection.

Ted