Water heater heating rate.

[Hagar]

Last year I installed a complete hydronic heating system in our 42 footer. The heat source is either an Espar "boiler" or the engine coolant.

As part of the project I put in a heat exchanger and circulation pump system that has greatly reduced the time to make hot water in our 11 gallon Seaward compared to the standard u-loop inside the water heater tank. The pump circulates the domestic water from the tank through one side of a double-wall heat exchanger with the heating system fluid on the other side.

Based on some recent tests using the engine as a heat source the time to heat the 11 gallons from 60° to 130° went from 3+ hours with the u-tube only to less than 30 minutes with the heat exchanger/pump. This was with the engine running 1500 rpm in reverse at the slip.

It would be fairly simple to add this type of water-heating portion to an existing water heater. I am planning to write up a DIY project with information on how to do it. Many years ago I subscribed to Practical Sailor and recall a report they did on tests of various heaters part of which compared the heat-up rates when connected to an engine. On the PS website I see they did an update in December 2013. Specifically what I am looking for is data on the heating rates. Before I get too far ahead of myself I want to see if other makes of water heater are as slow to come up to temperature as my Seaward. Does anyone here have that article and would consider sharing an excerpt with the data? I believe it is permitted to extract portions from publications without violating copyrights (and fair play).

 

[Ron20324]

If it took 3 hours to make the water hot, you had some other problem that you should have asked this forum about. Probably not a problem with the heater (unless dirty inside). Can't you heat with shore power in the slip?

 

[justsomeguy]

This was with the engine running 1500 rpm in reverse at the slip.

Forgive me, one question. Why "reverse"?

 

[Hagar]

I used reverse for a couple of reasons. In my slip the boat is held better in reverse. Also, I wanted to simulate a situation where we might want to heat water while at anchor. Our Autostream prop has a flatter pitch in reverse than forward so the engine loads would be different at a give RPM. I have tested the "reverse at anchor" routine while on the hook and the loads seemed reasonable. Any more than about 1500 and I got a little uncomfortable. Of course that was highly subjective...

 

[justsomeguy]

I used reverse for a couple of reasons. In my slip the boat is held better in reverse. Also, I wanted to simulate a situation where we might want to heat water while at anchor. Our Autostream prop has a flatter pitch in reverse than forward so the engine loads would be different at a give RPM. I have tested the "reverse at anchor" routine while on the hook and the loads seemed reasonable. Any more than about 1500 and I got a little uncomfortable. Of course that was highly subjective...

So some load on the engine/transmission was needed?

 

[Hagar]

I would say not actually needed but it does increase the heat available. Engines are like us. The harder they work the more internal heat they generate. We sweat, engines get rid of it through the coolant and radiator or heat exchanger. This old engineer first learned this as a kid when driving Caterpillar tractors on our Eastern Washington wheat farm doing spring work. Usually a little above freezing but the wind always blows in the spring. We didn't have enclosed cabs in those days but had Side Curtains (think Lee Cloths) that kept us out of the wind and directed engine heat back toward the seat. It was fairly cozy until you stopped to eat lunch and the Cat sat there idling. Within a few minutes it got really cold. Raising the engine from idle to blow more from the radiator fan didn't help, in fact it made it worse because the engine thermostats closed and there was not much coolant circulating to the radiator so the air off the engine was cold.