Finally -- Bus Heater Install!

[Dockhead]

I scrubbed my lithium battery install, and still feeling bad about it. But I pushed forward something I've been thinking about for a long time -- the bus heater plumbed into my calorifier loop. I ordered the heater today but would love to hear what the CF brain trust thinks about the system design.


It looks kind of like this:





The existing loop uses 1/2" heater hose. So here are the design issues:


1. Parallel, not series. Right? The feed to the heater is just downstream of the pump for maximum pressure. Do I need a balancing valve on the main line to the calorifier? The heater I ordered (https://www.t7design.co.uk/3-8kw-sta...eater-24v.html) has a water valve in it so I can reduce the flow through the heater.



2. Air removal. The pump should help with this, right? Do I need valves at the top of the loops?




I will be grateful for any comments! This will live under my companionway stairs, and will blast heat out whenever I'm motoring in cold wet weather. Especially delightful when the cockpit enclosure is up and the companionway hatch is open!

[kmacdonald]

Is the pump the circ pump on the motor or a separate electric pump? If the cooling water inlet and outlet are plumbed correctly on the engine you won't need a separate pump. If the heat exchanger fill is above the buss heater and water heater you won't need vents. If it's not above the heaters you will need a header tank that is above the heaters. 1/2" hose is fine. Yes, plumb the heaters in parallel so you can turn off the buss heater and still have hot water. No additional line loss due to the buss heater being added in parallel. It actually reduces the line losses if in parallel. They put out a lot of heat.

[kmacdonald]

Filling antifreeze SLOWLY reduces the chance of air locks. Watch engine temp carefully when testing.

[Lepke]

Depending on the engine, the coolant pump alone should give enough circulation. I'd put in some valves to isolate the engine in case of a leak. In a small system the circulation should push any air through the system. You don't have air problems with a car heater.

[wsmurdoch]

We have a bus heater. We installed it five or six years ago for our travels under power in the ICW from North Carolina to Florida in January/February. It heats the boat during the day with the companionway open driving out the moisture, and after anchoring (engine off) for the night the boat remains tolerably warm while cooking supper, then, it is quick to bed. (There is a 12V bunk heater there.) Mornings, we are just tough but bake biscuits (US), tarts, cinnamon rolls, waffles, pancakes, etc to heat up the boat. The bus heater is without equal for drying wet/damp clothing.

The heater is a Heater Craft 500. https://heatercraft.com/products/500...=2074878050335 It has a three speed fan for temperature control. My hoses are 5/8". The engine is a Yanmar 3HM35F. The water heater and bus heater are in series; bus heater first. A single 3-way valve bypasses the bus heater in warm weather. When the bus heater is in operation, the hot water is not its usual scalding hot, but it is ok. When refilling the coolant, bumping the engine to 3500 rpm immediately blows the air out of the lines.

We have yet to idle the engine at anchor to heat the boat, but we could.

We have thought about reversing the order of the water heater and bus heater, but have not. We have thought about adding an electric pump to the loop to extract the last of the heat from the engine after it is shut down, but have not.

Bill

[a64pilot]

I would put it in series, the way you have it sketched there would be little or no water flow, water will take the path of least resistance and that most likely to keep going and bypass the heater completely.
So take one of your heater hoses and Plumb the heater into it, not both.
You have a separate pump? No need the engine pump will make the water flow.

You sure about 1/2” hose? Thats unusual 5/8” is standard heater hose, least for cars and I believe boats too.

[Pauls]

I agree with the comments above about connecting them both in series. You can control the cabin heat output by controlling airflow thru the bus heater. No airflow = no heat, and airflow is easy to control.

[kmacdonald]

Originally Posted by Pauls

I agree with the comments above about connecting them both in series. You can control the cabin heat output by controlling airflow thru the bus heater. No airflow = no heat, and airflow is easy to control.

No airflow less heat, not no heat. It also restricts the flow more than parallel. It's a fallacy to assume all the flow will be thru the least restrictive path. It will be inversely proportional the restriction. One will get more flow than the other but both will get plenty. When a river forks, not all the water flows down one fork. Either water heater or air heater can be isolated and the other used if necessary with parallel. In series you don't have that option. The thermostat bypass on my new Kubota is a 3/8" hose. I hooked up my water heater to that, with 1/2" hose, and it works great. I will add a buss heater in parallel at some point.

[jimbunyard]

I'd plumb it as drawn, but since water to water heat transfer is less energy efficient than water to air, I'd either size the supply hoses accordingly, or, more likely, put a valve in each to regulate the flow through each appliance.

[a64pilot]

Both heater hoses have identical pressure, but there is water flow in a loop.
By tieing into both as drawn please explain how the water will flow?

The only way to make it work as drawn is to have valves on both the bus heater lines and water heater lines, then you could select which one gets water flow and therefore heat.

[a64pilot]

Originally Posted by jimbunyard

I'd plumb it as drawn, but since water to water heat transfer is less energy efficient than water to air, I'd either size the supply hoses accordingly, or, more likely, put a valve in each to regulate the flow through each appliance.

The difference in temp and whether the heater fan in on will determine who gets the most heat. The water heater will of course soak up a lot of heat as long as there is a big difference in temp between the coolant and the water in the heater, but as they get closer in temp, the less heat that the heater water will absorb, when they are equal there will be very little heat flow.

The heater will use a lot of heat when the fan is on high, because of course the coil will be being cooled by airflow, turn the fan off and the coil will pretty quickly reach the coolants temp and there will be very little heat flow.
Depending on which you want more is how you operate the heater, if it’s plumbed in series and the heater gets the water first and you want the water to heat first, turn off the fan, if you want he interior warmed, turn on the fan. You can control the heaters absorption / use of heat, you can’t the water heater.
If you plumb it so that the water heater gets the water first you don’t really have an option, it’s going to get the majority of the heat until the water is heated

[kmacdonald]

Dont run 4 lines like you have drawn it. Run a supply line from the engine to the heater of your choice ( see pilot64 post about that). T off that line to the other heater. Run one return line to either heater and T off it to go to other heater and then back to engine. Use valves to isolate if you desire or keep it simple and just replumb if necessary. You would still want a cutoff valve to the air heater to turn it off completely in the summer. One valve on either the inlet or outlet would accomplish that. To isolate a heater would require a valve in the inlet and outlet.

That's parallel, just like wiring a house. Change hose for wire and valve for switch.

[Dockhead]

Originally Posted by a64pilot

Both heater hoses have identical pressure, but there is water flow in a loop.
By tieing into both as drawn please explain how the water will flow?

The only way to make it work as drawn is to have valves on both the bus heater lines and water heater lines, then you could select which one gets water flow and therefore heat.

Well, house hydronic systems are often set up with radiators connected parallel rather than series. They work on pressure difference -- the loop through the bus heater is shorter so should flow fine so long as there's not too much internal resistance. I would worry more about the calorifier with longer hose runs so less pressure differential -- having the heater in parallel will reduce the flow for sure. But it's not really important what kind of flow there is to the calorifier as long as it is SOME -- 32 liters of water will heat up fast with 80C coolant going through it, then won't take any more heat out.


If I do it in series, then if I shut it off (the heater has a valve in it) then the calorifier won't get any flow. We don't get much hot weather up here, but it does happen, and I would hate to have that thing heated up when I'm trying to get heat OUT of the cabin. Otherwise I would need to set up a bypass which would add complication.


Unless there is some other good reason not to do it parallel?

[Dockhead]

Another question -- about the air. The current system flows unreliably, and I presume because I can't get the air out of the high point.


I think the circ pump should solve this, and just blast the air out of that, no? I know I could put bleed valves in those high spots, but I don't want to chop the hose more than necessary. The spot is difficult to reach, so not keen on it from that point of view, either.

[jimbunyard]

Originally Posted by a64pilot

Both heater hoses have identical pressure, but there is water flow in a loop.
By tieing into both as drawn please explain how the water will flow?

The only way to make it work as drawn is to have valves on both the bus heater lines and water heater lines, then you could select which one gets water flow and therefore heat.

Don't get me to lyin'...

Even if we knew the internal construction of both heaters, the number, size and length of hoses and dimensions of all the fittings, predicting "how the water will flow" in even a simple system like this is a hydrodynamical nightmare, and will be more of a guess than a prediction.

'As drawn' is more of an agreement to the basic layout.

If it were me, in the interest of simplicity and anticipation of future 'issues', I'd update the as drawn diagram to include a larger supply line to the tee branching out to the two heaters, a valve on both supply lines to isolate both or either in the event of problems or for troubleshooting, and as a method of regulating flow to each (as you say the heat required for the calorifer is a variable).

I'd also use a larger return line after the tee where the returns from the heaters meet, and a valve in that line to be able to completely isolate the heater's circuits from the engine, if necessary.

Though it doesn't seem so, this is all in the interest of 'keeping it simple'...