Coolant System Heater Hose Length

[MJH]

Last year I installed a small REAL heater in the salon for the Admiral prior to going to Alaska; it does a good job of heating and she likes it. It is the hydronic type using the diesel engine freshwater coolant, similar to a car/truck heater. I had to extend the total coolant hose only about six feet. Overall, the cost was very reasonable compared to installing other type of heaters. Of course, the engine has to be running to get the heat but many legs going north often have to be motored anyway.

This installation has made me wonder on how to determine what the upper limit of the total hose length can be before negatively affecting the engine...I've given some thought to installing a second heater in another compartment.

Thanks.

~ ~ _/) ~ ~ MJH

[a64pilot]

I don’t think there is an upper limit, eventually if stupid long the resistance of the hose will greatly slow flow down and of course there is some heat lost from the hose, but the engine doesn’t care if the hose flow is completely blocked off or not, and engine won’t care if the heat is lost through the hose or the heater.

After all they are made to be put in the back of a bus, that’s pretty far from the bus engine if it’s a front engine bus.

If your concerned about heat loss through the hose, then wrap the hose with the foam insulation used on home air conditioner lines, it’s actually pretty good insulation.

A 30,000 BTU one with three fan speeds will fit under my bottom step of my companionway ladder.

But the engine won’t know if you have 100’ or 1’ of hose on it, and won’t care.

Curious though, how did you run the hose, serial connection with the water heater?

I’m thinking about installing one next year, I don’t do cold but for the second time I’m further North than I wanted to be later than I wanted.
I was thinking about hooking one up in the return line, after the water heater. It would take longer to get hot that way, but I think the water heater pretty quickly heats up to about coolant temp and of course from then on doesn’t absorb much heat.

[DougR]

Information on the maximum allowed external coolant volume is usually found in the manufacturers installation literature. Normally there isn't an absolute allowable volume increase, but there is a maximum allowable increase with the standard expansion tank capacity. So, if you exceed the maximum allowed fluid increase, you will normally have to increase the expansion tank capacity or you will constantly push coolant out of the system.

DougR

[MJH]

Curious though, how did you run the hose, serial connection with the water heater?
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I installed the new hose directly off the engine (new fitting required) to the heater and then installed about a two foot piece back to the original hose that goes back to the heater. All new hose was matched to the original specs.

I'm not concerned about heat loss from the hose as it all helps to warm the salon temperature. I'm more concerned with the potential affects upon the engine. No evidence thus far with coolant overflow in the reserve tank. I'll watch for that.

I'm getting all the heat I could want right now from the heater's three inch vent...it works very well. This unit is actually a defroster unit (high output blower) that included a selector switch with about four settings; I keep it at #1 (lowest setting) and it uses about 4-5 amps; other units had lower outputs that I thought insufficient but lower amperage.

~ ~ _/) ~ ~ MJH

[sailormed]

With the engine running I don’t think the amps consumed will be a show stopper.

[a64pilot]

I don’t have any way of knowing the volume of say 50’ of 5/8” hose, but doubt it’s more than a half gallon or so.

Our water heater outputs are identical to the automotive heater hoses, both of course extract heat from the engine, and the engine could care less.
Only way it could make a difference is if you were extracting so much heat that the engine thermostat never fully opens. Meaning that your engine never fully heats up. I doubt you could extract that much heat, but a coolant temp gauge would tell you.

Now of you have a little single cylinder engine or a small twin then of course you may could pull too much heat.
What size is your engine?

[MJH]

Originally Posted by sailormed

With the engine running I don’t think the amps consumed will be a show stopper.

No, it won't be. I was just trying to be transparent and preempt those that would criticize the install because it only produces with the engine running. Besides, I have 560W of solar that helps as well.

~ ~ _/) ~ ~ MJH

[Tillsbury]

On my boat the standard installation has a surprising amount of hose, as it runs around the engine compartment way to the back, across next to tanks and under bunks to the cylinder in the water system cabinet. I'd guess it was at least 40' there and back.

Which reminds me, it's probably getting time to think about replacing it...

[MJH]

Originally Posted by Tillsbury

On my boat the standard installation has a surprising amount of hose, as it runs around the engine compartment way to the back, across next to tanks and under bunks to the cylinder in the water system cabinet. I'd guess it was at least 40' there and back.

Which reminds me, it's probably getting time to think about replacing it...

I guess it all depends were you put the heater/blower and the distance from the engine.

~ ~ _/) ~ ~ MJH

[MJH]

The engine is a Volvo Penta D2-55B.

[NorthCoastJoe]

Without a lot of math, 5/8 heater hose holds about two fluid ounces per foot.
Volume of heater cores, fill one and measure it. You could add a expansion tank to the loop to handle the extra volume.

You could add a 12 volt booster pump to the loop. Be careful of trapping air in the lines and make sure that your engine temp stays normal.

We looked at a boat for sale that had a history of overheating. The problem was obvious to me, a rats nest of heater hose and many places to trap air in the lines. The fresh water pump on the engine could not keep up with the load.

[Dsanduril]

Went through this exercise with our D2-40. From the installation manual.

Hot water circuit
NOTE! Maximum external circuit volume:
D1-13, D1-20, D-30, D2-40 3.0 l (3.2 US qts)
D2-55, D75 1.6 l (1.7 US qts)
Larger volumes require additional expansion tank.

5/8" hose is about 16 feet/liter (forgive the mixed units). At least in theory you can't use much hose with the D2-55 as any heater core is likely to hold a liter or more. How much extra room Volvo leaves in their recommendation....

[EngNate]

Engines come from the factory with plugs installed at the aux heater inlet & outlet, and they are not removed unless a heating accessory is installed, thus the length/restriction of that hose is of no consequence as far as the engine is concerned, the circuit was blocked off when it left the factory. As far as getting heat, I've seen a 60 ft total loop work, but that was with a 200 hp engine.

[a64pilot]

Originally Posted by Dsanduril

Went through this exercise with our D2-40. From the installation manual.



5/8" hose is about 16 feet/liter (forgive the mixed units). At least in theory you can't use much hose with the D2-55 as any heater core is likely to hold a liter or more. How much extra room Volvo leaves in their recommendation....

It would appear from your link from the manual that the limits specified are only limits for the stock expansion tank, exceed that capacity and you need a bigger tank.
Or that’s how it looks to me.

On edit heater cores usually hold very little, they are essentially a few ft of 5/8” tubing with about four turns and a lot of fins to increase surface area.

I would insulate the hose myself as it’s most likely to be run in the bilge and that would be wasted heat, hard to heat a bilge with all that water cooled hull area.

[Dsanduril]

Yes, the limit is only based on overflowing the expansion tank because of the additional volume of total coolant circuit.

Only limit from the other side will be how much flow you get through the circuit and I haven't seen any numbers in that regard from Volvo. Eventually, with enough hose you just won't get the heat transfer you want (but as Nate notes this shouldn't affect the engine if using the aux. takeoffs).

One other minor item, Volvo does recommend moving (remote mounting) the expansion tank if the auxiliary users are above the expansion tank. The cap to the expansion tank is not sealed and if the users are above the tank they can drain by gravity when not in use.