Reverse Cycle Cooling/Heating in Great Lakes Waters

[Durangutan]

I apologize if the question is inappropriately placed or has been asked and answered. We have the opportunity to equip a new boat with a generator and HVAC. We’ve been spending vacations sailing on Lake Michigan anywhere from mid May to October on a boat with no environmental and have gotten by with fans and a small space heater when on shore power. We intend to regularly use the new boat in more remote locations for longer trips on the Georgian Bay, North Channel and Lake Superior. Since we haven’t been there, we simply don’t know what to expect or whether the limitations of reverse cycle may be problematic in some of the cooler waters up there. I realize an option is to supplement heat with a diesel fired hydronic or forced air system or some other augmentation if necessary but I’d like to avoid these if it’s something we’d rarely need. I’d much appreciate any insight from anyone with experience cruising these waters during the typical boating season with reverse cycle cooling & heating. Thank you!

[rslifkin]

On Lake Ontario we've yet to have an issue with insufficient heat from the reverse cycle units. But at least here, unless you're wintering in the water, it's rare to have the boat in the water with surface temps below about 40* F (just about the minimum for many reverse cycle units in fresh water). My biggest issue with reverse cycle for heat is that it's basically worthless away from the dock, as it requires constant generator usage (with the resulting noise and fuel consumption).

[toddster8]

You can download the manual for the unit you're considering and check the specifications.

My Webasto unit specifies water temperatures between 40°F (minimum for heating) and 90°F (maximum for cooling.) I did run it for a few days this winter when the water temperature was 36-38, and it warmed the cabin to around 55-60 - not enough for comfort, but enough to keep systems from freezing. The pumps and fans make quite a lot of noise.

In contrast, the small oil-filled radiator that I usually use at the dock is cheap, quiet, and simple. But it doesn't cool.

I would never have considered installing a heat pump, except the offer was a deal too good to pass up. I think I got it for $300.

[redneckrob]

I'm in mostly fresh water in the Chesapeake and my reverse cycle works until just before a skim of ice starts forming on the top of the water which is right around 32 degrees F. I assume the intake water is probably around 35 at that point under the hull. The heater puts out plenty of heat until then, the problem is that the cold side of the heat pump is below freezing and the raw water freezes in the heat exchanger pipes.

[GordMay]

Lake Superior's surface water temperature varies from about 40°F [June] to 65°F [Aug].
May be slightly warmer in anchorages.

[David Mathis]

Most of my boating is in cool northern waters. We launch late March and haul late October so the early and late season sees cold water. We have two reverse cycle units which are trouble free. When the water gets below 40, the performance is poor and if the temp gets near freezing, the water will freeze in the coils when heat is removed. In cold weather, we have two small plug in electric heaters. When the water temp is about 50, they put out enough heat to have the inside of the boat at 70. As to the ac feature, a couple years ago we had a 102 degree day. The inside of the boat was 68.
After having the comfort for a season, you won’t go back to fans and diesel heaters.

[captstu]

I'm currently sailing a Travel Trailer, after 50 years of boating, until I can find the right Rossborough, this will do fine.

I suggest you look at a a Gree (or similar) mini-split. I replaced a Dometic cooling unit with a reverse cycle Dometic for the following:

1. It makes nearly no noise - at normal settings, it is only 22 db - my wife is hearing impaired and the older unit was so noise . . .

2. It draws onl 500 Watts cooling and 510 Watts heating - easily supported by the smallest generator - I use a Honda 2k on "ECO" setting and at full power on cooling, the generator just slightly rises above idle.

3. A mini-split (most brands) don't cycle in the usual way. My unit just varies the output from a just detectable breeze to a fairly strong air current - but the output louver is so large, even at full power there is really no draft.

4. It keeps the air conditioned space at a constant temperature. The reference thermometer near the unit doesn't vary at all from the hottest summer day in South Florida (where we live) to the low thirties when I visit my kids in Texas.

5. And, finally, it is air cooled so there is no water corrosion and won't clog with floating debris that market the end of my previous Mermaid.

The unit works far better than advertised. $750 installed, $2500 installed including the installation of wiring and brackets for the generator I already owned.

You can read more about the install (if your are not already bored) at:


Winnie Gets a Quiet Air Conditioner - Shearwater IV

[Cpt Mark]

I had a rev cycle pump. I'm assuming you have a gen set on board or are planning to be in a marina when you want to use it.

I live on the Columbia river and at water temp 40 degrees I was on the edge of the the pipes freezing. It happens almost instantly, i watched it once. So I needed heat in the winterrtime. Bought a chinese diesel heater. Cheapest one on Ebay figuring they all come from the same factory and tossed out all the clamps and such as none of it was marine rated. Finally I put in the supplied fuel tank instead of using the Tee connector to my engine and that solved all of my problems I'd had. Works perfectly. Cost about $115 USD for the heater and another $ 350 for through hulls, exhaust stuff. Couldn't be happier. On low it keeps me plenty warm.

[aisleorwindow]

I'm in the same situation as the OP. Has anyone ever tried a portable A/C unit and just run the exhaust out one of the portholes? Would just use it for sleeping at the dock - and only a couple times a year.

[rslifkin]

Originally Posted by aisleorwindow

I'm in the same situation as the OP. Has anyone ever tried a portable A/C unit and just run the exhaust out one of the portholes? Would just use it for sleeping at the dock - and only a couple times a year.

I've seen it done successfully. Biggest limitations are securing the thing from moving around when underway and the amount of space it consumes.

[Boatwright]

We cruise the northern lakes from May until October and use our Webasto diesel forced air unit to take the chill off. It has been completely reliable and safe.

Big positives:

It does require a 30 amp circuit but only needs the big juice when it first ignites the burner. After that the blower draws about 100 watts and then only when the unit is running. The standby draw is negligible.

It produces a bunch of heat. In the winter when the boat is on the hard, I regularly use the heater on below freezing winter days to comfortably do projects in my shirtsleeves inside the cabin.

Webasto maintains a parts and service center conveniently located near Flint, Michigan.

[boatpoker]

Our system is a Flagship Marine system. The AC is your usual water cooled but the heat side is straight electric furnace. Perfect for living aboard as we do on Lake Ontario. Built is the US with non-proprietary parts and extremely reliable for almost 30yrs. Far better built than any of the well known reverse cycle "marine" units and with terrific customer service out of Florida.

[Durangutan]

Many thanks to all who’ve responded. It was pretty narrow minded of me to think that the Great Lakes are unique when I posed the question. I forget that when the yards and sheds there are full slumbering boats, folks elsewhere are experiencing a variety of conditions in chilly waters placing similar demands on their systems. Not everyone is in the Caribbean or the Sea of Cortez. Plenty of good information here and we’ve a little time yet before we have to make a final decision.

[Tetepare]

Originally Posted by aisleorwindow

I'm in the same situation as the OP. Has anyone ever tried a portable A/C unit and just run the exhaust out one of the portholes? Would just use it for sleeping at the dock - and only a couple times a year.

OP is more concerned about heat, while it sounds like you're asking about cooling.


Yes, we've used one of those apartment A/C with a ducted exhaust. I built a frame for the port that secures the terminal end while keeping out mosquitos and rain. The unit is probably 80cm H x 20 x25. On the previous boat it tucked right under the V berth while not in use; not sure where it's going on this one yet.

All the boats I know designed for cold weather use diesel heating, so while I know what reverse cycle is, I have no experience with it. We stay in into November, and I've gone on deck in snow, which is awfully cold. It's the dampness below decks that stinks, more than the cold. Cheapos like me induce just enough heat to drop the humidity level, then grin and bear it.