Bus Heater: Series or Parallel?

[TomSoko]

I'm planning to install a "bus" heater in the main cabin of my 40' sailboat. My question to this group is whether I should plumb the heater in series or in parallel with the water heater. The use would only be occasional in fall and spring. Thoughts?

[atoll]

probably in series, but with 2 valves and a bypass hose to divert flow when not in use.

[svHyLyte]

Originally Posted by TomSoko

I'm planning to install a "bus" heater in the main cabin of my 40' sailboat. My question to this group is whether I should plumb the heater in series or in parallel with the water heater. The use would only be occasional in fall and spring. Thoughts?

While motoring during cool/cold weather, we heat the cabin on our boat with a Heater Craft "hydronic" heater shown (click on) here. The coolant discharge line from our engine to the engine heat exchanger has two T-connectors. The T-connector closest to the block discharge has one leg, with a valve, leading to the input side of the heater while the other leg leads to a second T-connector, one side of which is connected to the discharge side of the heater and the other to the input side of our heat exchanger. When cabin heating is wanted, opening the valve controlling flow to the cabin heater allows water to pass through that and then continue on to the engine heat exchanger. The cabin heater has a 3-speed fan that controls the rate of air-flow through the heat exchanger on that and, accordingly, the heating of the cabin. The arrangement works very well, even in quite cold weather. Of course, during warm weather, closing the valve on the input side stops the flow of water to the heater. Ideally, both the input and discharge lines from the cabin heater should have valves to isolate that circuit entirely but we haven't found that necessary, at least so far! (The arrangement is similar to the way a typical hot water heater is plumbed.)

FWIW...

[TomSoko]

Atoll,
Thanks for your thoughts. I did some scribbling on a sheet of paper, and I think I can put in a tee and a three-way valve instead of two on/off valves for a bypass. One way is cabin and water heat in series, or turn the valve for water heat only. I was concerned that the flow of coolant thru the bus/cabin heater would be too much during hot summer months, and having a bypass should solve that problem.

HyLyte,
I plan to plumb the cabin heater similar to yours, but using the water heater circuit, which is already in place and close to where I want to put the cabin heater. Thanks.

[Jim Cate]

FWIW, our "bus heater" is left in the loop full time (we don't have a domestic water heater). There is not much heat transfer to the cabin from the hoses (under the cabin sole) or heater heat exchanger when there is no air flow through the heater. Hasn't been a problem for us, even in the tropics.

YMMV, as always.

Jim

[oleman]

Gates.com has a good selection of water control parts on line. They primarily supply the heavy truck and equipment industry but you could possibly fine something there. They are an industrial supply operation but will ship to individuals.
Good luck with your project.

[Stu Jackson]

A story from a friend:


Tech Wiki – Catalina 34 International Association

[MartinR]

I will follow this thread with great interest. I just mounted two fan heaters in my boat, but the hoses arrived too late, so they are not connected to the Webasto, yet. For me a serial installation seems much simpler, but Webasto recommends to install all of this in parallel.

[gjordan]

I delivered a boat down the Washington/Oregon coast with this type of heater. It was WONDEFULL. I had looked at a couple for my own boat but they were too large. The smaller ones shown in the link will fit. Here goes some more money. _____Grant.

[atoll]

Originally Posted by MartinR

I will follow this thread with great interest. I just mounted two fan heaters in my boat, but the hoses arrived too late, so they are not connected to the Webasto, yet. For me a serial installation seems much simpler, but Webasto recommends to install all of this in parallel.

with multiple heater units if installed in series the first one gets really hot,the next one less hot and the third one not really hot at all!

this is why multiple heaters need to be in parallel,.
so as to get even flow and heat distribution, the pipe size,BTU's and circulation pump flow will need to be carefully calculated so the heaters at the end of the string have sufficient hot water.

[tml]

We installed a bus heater four years ago after a particularly cold trip down the ICW.
No problems at all; installed in series with the water heater.
Not clear on what problem the extra complication of parallel installation solves.
In any case per dollar terms or time to install one of the best things we have ever put on the boat.
TML

[CaptTom]

I've coveted a bus heater for years, but it's never made it to the top of the list.

Then yesterday I was looking at prices (Defender, Hamilton Marine, Amazon) and stumbled on those cheap Chinese knock-off parking heaters (similar to Espar, Eberspächer, Planar.)

Wow, those prices have come down! For about $200 you can get output comparable to a $400+ bus heater. And it works even when the engine isn't running.

It's totally changed my thought process. I have a Planar already, but it really only heats the master berth. A couple of these cheap ones (one in the forward berth, one as a spare) would be a better deal, for me.

[DeepFrz]

Originally Posted by svHyLyte

While motoring during cool/cold weather, we heat the cabin on our boat with a Heater Craft "hydronic" heater shown (click on) here. The coolant discharge line from our engine to the engine heat exchanger has two T-connectors. The T-connector closest to the block discharge has one leg, with a valve, leading to the input side of the heater while the other leg leads to a second T-connector, one side of which is connected to the discharge side of the heater and the other to the input side of our heat exchanger. When cabin heating is wanted, opening the valve controlling flow to the cabin heater allows water to pass through that and then continue on to the engine heat exchanger. The cabin heater has a 3-speed fan that controls the rate of air-flow through the heat exchanger on that and, accordingly, the heating of the cabin. The arrangement works very well, even in quite cold weather. Of course, during warm weather, closing the valve on the input side stops the flow of water to the heater. Ideally, both the input and discharge lines from the cabin heater should have valves to isolate that circuit entirely but we haven't found that necessary, at least so far! (The arrangement is similar to the way a typical hot water heater is plumbed.)

FWIW...

Good gracious, the price on that heat exchanger is egregious. Even a Webasto heat exchanger is about half that price. https://www.heatso.com/webasto-kuba-...xoCcekQAvD_BwE

[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?

[MartinR]

Originally Posted by atoll

with multiple heater units if installed in series the first one gets really hot,the next one less hot and the third one not really hot at all!

this is why multiple heaters need to be in parallel,.
so as to get even flow and heat distribution, the pipe size,BTU's and circulation pump flow will need to be carefully calculated so the heaters at the end of the string have sufficient hot water.

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.