Bus Heater: Series or Parallel?

[Sailing Drummer]

I just ordered one from Cruising Solutions. They come in two sizes, either with or without ducts. I think the choice is 25kbtu or 40kbtu. Their prices are a little better. Shipping could offset price if you're closer to one dealer vs another.

[Stu Jackson]

Originally Posted by TomSoko

Thanks for all the replies. It looks like the general consensus is in series, especially with only two heaters (water and cabin) in the loop. Stu, thanks for the link! Right now my choice would be this one: https://shop.hamiltonmarine.com/prod...kit-22264.html
but I'm still researching. I'm wondering if 28K BTU is too much?

Hi, Tom, nice to see you here. Trust all is well with you & yours. Enjoyed my second season here in BC very much.


Size? Physically, if it can fit, bigger is better, can't hurt, just turn the fan down, get three speeds: Hi, LOW, Off. As long as the hose barbs are reasonably sized, liked 3/8 to 5/8, it should be fine.


Happy Holidays.

[Utahsailor]

We have an ITR diesel heater with two heat exchangers in main cabin and one in the forward cabin. ITR says to install in series, for some reason they were installed in parallel. The last heater in the forward cabin never worked properly: air bubbles that were very hard to eliminate, with less back pressure, the two earlier heat exchangers captured most of the flow. Two years ago I switched to series and now each heat exchanger puts out heat.

[atoll]

Originally Posted by MartinR

Sorry, I was a little unclear, of course the heaters need to be in parallel, but why they should not be connected in series with the calorifier beats me. That was my plan in any case. I looked at your installation, and the three-valve shut-off to the heater(s) is a very good idea. Minimizes losses while not using.

should be no problem in series with just the one heater,just make sure the calorifier is first in line from the engine,so it heats faster ,and first before the cabin.

water temp in the circuit will be regulated by the engine thermostat at about 90C,but the heater will also act as a radiator reducing engine temp untill the engine and calorifier reach operating temp.

putting a bleed in the far end of the system if there are long runs is also a good idea,ideally the heater needs to be below the level of the top of the heat exchanger reservoir on the engine.

if the heater or heaters need to be raised higher than the sealed engine reservoir then a pressurised header tank(as you find on most cars these days) will need to be fitted at a level higher than the heaters to fill the engine coolant loop or air will accumulate at the highest point in the system,despite there being a pump in the system.

[Stu Jackson]

Originally Posted by atoll

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1. putting a bleed in the far end of the system if there are long runs is also a good idea,ideally the heater needs to be below the level of the top of the heat exchanger reservoir on the engine.

2. if the heater or heaters need to be raised higher than the sealed engine reservoir then a pressurised header tank(as you find on most cars these days) will need to be fitted at a level higher than the heaters to fill the engine coolant loop or air will accumulate at the highest point in the system,despite there being a pump in the system.

1. Good idea. But the heater need not be below, because it is, in engineering-speak, a closed system.


2. Not necessarily. Examine the GOAL. Using the bleed would work, but you're right that any ir would not get out. Either do it manually or get what is called an automatic air vent. These are placed in the high points of building systems for closed piping systems and do just what they are called.

[Sailing Drummer]

Originally Posted by Stu Jackson

1. Good idea. But the heater need not be below, because it is, in engineering-speak, a closed system.


2. Not necessarily. Examine the GOAL. Using the bleed would work, but you're right that any ir would not get out. Either do it manually or get what is called an automatic air vent. These are placed in the high points of building systems for closed piping systems and do just what they are called.

Please explain "doing it manually". I'm installing a heater in series with my water heater. Having a really tough time getting rid of an air lock. I've tried running the engine with the cap off and adding fluid as needed. Did this about 4 times for at least 45 minutes to an hour each time. But the hose going from the engine is only hot for the first 1-2 ft. Need advice!

Larry

[Pizzazz]

An inexpensive bus heater solution could be a CPU radiator with a 120 mm computer fan. Total cost is something like $35 and the hoses are 3/8” I believe. I am not sure about the expected BTU output but that should depend on the fan.

In any case, I recommend a forced air heater instead of a bus heater.

SV Pizzazz

[atoll]

Originally Posted by Sailing Drummer

Please explain "doing it manually". I'm installing a heater in series with my water heater. Having a really tough time getting rid of an air lock. I've tried running the engine with the cap off and adding fluid as needed. Did this about 4 times for at least 45 minutes to an hour each time. But the hose going from the engine is only hot for the first 1-2 ft. Need advice!

Larry

water will not naturally flow uphill,nor will air sink to the bottom.
so a closed system even if pressurised needs to have the air in the system bled off at the highest point,and coolant added at the highest point or under pressure.
.
this can be done either manually with a valve Teed into the system at the highest point with the pump running to circulate the coolant and extra coolant added to replace any air displaced in the system through a funnel.

or by using a pressurised reservoir at the highest point.

buildings with closed system heating have mains pressure water teed into the coolant circuit to top up the coolant when nessacary

stu jackson ,though correct about automatic bleed valves in buildings misunderstands how they work and how coolant is added when air is removed from the system.

trying to fill a closed loop system at the radiator cap on the engine where pipe work and heater elements are above the level of the engine will not work.

to put it more simply, once you have filled the system at the highest point, if you were now to open the radiator cap on the engine.
coolant from above the level of the top of the engine would flow out

[atoll]

Originally Posted by Stu Jackson

1. Good idea. But the heater need not be below, because it is, in engineering-speak, a closed system.


2. Not necessarily. Examine the GOAL. Using the bleed would work, but you're right that any ir would not get out. Either do it manually or get what is called an automatic air vent. These are placed in the high points of building systems for closed piping systems and do just what they are called.

how do you add coolant to replace air that escapes with this system? if it is a closed system
,which it is not on a boat when being filled via an open radiator cap,it is a gravity system,untill the radiator cap is put back on and engine run.

[atoll]

Originally Posted by Pizzazz

An inexpensive bus heater solution could be a CPU radiator with a 120 mm computer fan. Total cost is something like $35 and the hoses are 3/8” I believe. I am not sure about the expected BTU output but that should depend on the fan.

In any case, I recommend a forced air heater instead of a bus heater.

SV Pizzazz

how is a forced air heater going to help use engine heat to heat the boat

[Pizzazz]

Originally Posted by atoll

how is a forced air heater going to help use engine heat to heat the boat

Obviously, it is a separate system (at least in the common definition of a forced air heater). Many people, especially on small boats, are aiming to use the engine for everything, heating water, making water, heating the cabin, making electricity... it sounds like a good idea but often separate systems work better. I have tried all of the above and now I am firmly in the camp where you want a balance between efficiency (using the engine for everything), reliability (separate systems) and ease of use.

For heating, I believe than once you have tried a forced air heater, you would not go back to anything else (fresh warm air, thermostat, push button operation). Hot water and electricity are easy to get off the engine. WRT a water maker, I have not made up my mind. It is super attractive to use the engine power for a high capacity water maker but it is not easy to make it work. Not clear on this one.

SV Pizzazz