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Old 08-09-2016, 03:08 PM   #1
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heating: reverse cycle vs electric

I need to replace my old Lunaire AC, and I'm looking at this thing:


Ocean Breeze 18000 btu self contained marine a/c
a/c draws 13.46 amp
for electric heat option draws 3.2 kw
for reverse cycle heating option, manufacturer says it is inefficient for water temp less than 40 deg
2 year warranty
$1780


When it is used for heating, I can purchase this unit with either electric heat or reverse cycle heat. I'm leaning toward electric heat for both Norfolk winters (short term) and Puget Sound winters (long term). I think my Westerbeke 4.4 kw generator would handle the load at anchor, though it would be damn noisy on my boat. What do you think about the electric vs reverse cycle heat? Would it be much cheaper to go with reverse cycle most of the time, and fire up some portable electric heaters on the days when both air and water temperature were below 40?
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Old 08-09-2016, 04:11 PM   #2
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Would it be much cheaper to go with reverse cycle most of the time, and fire up some portable electric heaters on the days when both air and water temperature were below 40?
That's a good plan. You can buy a 1,500W electric resistance heater at Wal Mart for like $10-$15. If you really plan to live aboard during the winter in cold climates there are quite a few other considerations, but you're correct that reverse cycle won't work below 40 degrees (water temp.)
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Old 08-09-2016, 04:12 PM   #3
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The electric heat looks like it is a "resistance" heat and that is going to eat up a lot of amps. The vast majority of dock power outlets you are going to run into are 30-amp and I think you will find that is just not enough to stay comfortable with resistance heating. At 3.2 KW you are looking at a 27-amp draw, no wiggle room at all on a 30-amp power circuit. Given that your option is reverse-cycle or resistance heating I would definitely opt for the reverse-cycle.

In the Pacific North West I doubt you will often see water temps as low as 40 (in the salt portion anyway). In the coldest part of the winter I normally see water temps in the 45°-50° where we moor in Poulsbo.

We removed the two reverse-cycle units that came on our boat and replaced them with a single hydronic furnace. Would be nice to have Air conditioning for those few days when it gets hot (for us anyway) and muggy. On the east coast I can see where it would be more useful.

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Old 08-09-2016, 04:26 PM   #4
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I'd go with the reverse cycle. I have lived aboard in the winter and the heat works fine 90% of the time even with water in the 40's. When unit can't handle it, I augment with a cheapo cube resistance heater. Best of both worlds.

Loading 3.2kW onto your 4.4kW gennie is not going to leave much margin.

My cabin reverse cycle heats well drawing under 1kW. Both units together, about 19k btu, draw right about 1.5kW. Much more efficient than resistance heat.
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Old 08-09-2016, 05:43 PM   #5
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I have reverse cycle heat in the PNW and it is effective year-round. The downside is that it requires shore power or the generator to operate it. Had I purchased this boat new, I would have opted for a diesel or kerosene heating system, but haven't seen the need to spend the money to add it to the reverse cycle, yet.
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Old 08-09-2016, 05:57 PM   #6
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I installed 3 units (Webasto) with reverse cycle heat during my refit. The heat worked great down to 40 degrees; ok down to 36; quit around 32 degrees mostly do to not enough water flow to keep the heat exchanger from freezing up. Water was in the mid 40s end of January last year in Norfolk.

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Old 08-09-2016, 09:05 PM   #7
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20 year liveaboard near Toronto ... Last 10 years with a Flagship Marine furnace, a/c. The air is reverse cycle and the heat side is straight electric furnace. Bullet proof ... much higher quality build than any other unit I have seen on a boat. I've never been cold in the winter but my neighbours with conventional reverse cycle units end up with little electric heaters all over their boats.
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Old 08-10-2016, 05:32 AM   #8
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IF you purchase a std house heater , be sure it has both an overheat safety and a tip over safety .

OR get one that bolts to a wall, with only an overheat safety.

15A of 120V is not a lot of heat 3-4-5 units might be needed in 20F conditions , more if it really gets cold.

A 240 50A power hose and distribution setup is needed.

Depending on the marina electric charges 25C a KW is not uncommon , electric is best for short times , not liveaboard .
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Old 08-10-2016, 06:24 AM   #9
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IF you purchase a std house heater , be sure it has both an overheat safety and a tip over safety .

OR get one that bolts to a wall, with only an overheat safety.

15A of 120V is not a lot of heat 3-4-5 units might be needed in 20F conditions , more if it really gets cold.

A 240 50A power hose and distribution setup is needed.

Depending on the marina electric charges 25C a KW is not uncommon , electric is best for short times , not liveaboard .
20yr. liveaboard, Toronto, electric heat, last two winters on one 30amp cord, never cold, well insulated boat. Flagship Marine electric furnace, anywhere from $80Cdn to $130Cdn per month (winter only) with the most expensive electricity in North America, wouldn't do it any other way.
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Old 08-10-2016, 07:07 AM   #10
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Annapolis- 2 winters -37 foot sportfish
New Jersey- 5 partial winters - 40 foot trawler


To adequately heat both in sub 35 degree days/nights... a minimum of 3 portable space heaters were necessary to keep the interior above 65 degrees. A big factor is wind. 3 space heaters draw about 39 amps, then there are the hot water heater and any cooking aplliances on top of parasitics that can add up.


Now, you can full or partially shrink wrap which really helps, and/or you can 3M clear wrap all the windows. You can also find every air leak and prevent those...but I used to get underway all year, so some of those options were off the table.


I went with a 125/250V, 50 amp service because the 30s always seem to burn up with electric heat or air conditioning. Not just my boats but I have noticed it throughout my boating experiences, especially on the professional level.


Not to say you need more or less heat...just passing along my liveaboard experience near the Chesapeake.
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Old 08-10-2016, 07:18 AM   #11
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Quote:
Originally Posted by seattleboatguy View Post

When it is used for heating, I can purchase this unit with either electric heat or reverse cycle heat. I'm leaning toward electric heat for both Norfolk winters (short term) and Puget Sound winters (long term).

What do you think about the electric vs reverse cycle heat? Would it be much cheaper to go with reverse cycle most of the time, and fire up some portable electric heaters on the days when both air and water temperature were below 40?

It's possible to install both. Some liveaboard boat neighbors did exactly that, with the Dometic Vector Turbo reverse-cycle unit AND an in-line resistance heat source coupled to use the VT blower system. The advantage there is that all the ducting, already in place, will service the whole boat.

They used reverse-cycle until outside water temps got too low, then shut their seacock and used only the resistance source. Said it worled pretty well, but they also said they had to augment with a space heater during our coldest periods (down around 15°F, IIRC).

Their boat was a 34' flybridge model, I think with only a single AC unit. Probably would have been better if they'd had two separate VT+resistance units for during the coldest snaps...

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Old 08-10-2016, 08:16 AM   #12
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One of each? Use as needed.

I like the option of heating an area (birth) if I'm on the hard and have no water to circulate of if away and not wanting to leave a sea-valve open.

It is a good question, I will be interested in your choice.

I agree with many who say elect or reverse heating is not adequate for live aboard in cold climates, diesel would be a better choice for very cold conditions.
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Old 08-10-2016, 08:20 AM   #13
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20 year liveaboard near Toronto ... Last 10 years with a Flagship Marine furnace, a/c. The air is reverse cycle and the heat side is straight electric furnace. Bullet proof ... much higher quality build than any other unit I have seen on a boat. I've never been cold in the winter but my neighbours with conventional reverse cycle units end up with little electric heaters all over their boats.
That's the brand and style I went with as well. My name brand reverse cycle unit failed at ten years and the replacement at less than five years. No warranty.

So - Electric resistance heat means the compressor, pump, etc. are not running during the heat mode, only the heating coil and fan. To my, that indicates longer life.

Yes, it's not as efficient as reverse cycle (essentially a heat pump), but since I pay a fixed rate for electricity, I don't really care.

If you're looking for heat away from the dock using the genset, current consumption could be an issue so you might want to consider the reverse cycle unit but you're going to be using the genset anyway.
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Old 08-10-2016, 01:21 PM   #14
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We have electric and diesel boiler. Electric while we are away for long periods of time, and diesel boiler when in the area. I would not have reverse cycle as all the sea cocks below water are closed when at the dock. The diesel hot water keeps the entire boat warm and dry.
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Old 08-10-2016, 05:25 PM   #15
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Reverse cycle or heat pump heat produces 2-3 times as many watts of heat output (actually heat transferred from the raw water) as resistance heat which produces 1 for 1.


When we lived in Oriental, NC a live aboard friend used reverse cycle heat and it worked for all but a week or so when the water got so cold that it would freeze in the evaporator (in heat pump mode). In Puget Sound it almost never gets that cold.


But a slick system would be reverse cycle with a heat strip so you can get the best of both worlds- efficient heat pump when the water is warm enough and resistance heat when it isn't.


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Old 08-11-2016, 06:06 AM   #16
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"$80Cdn to $130Cdn per month (winter only) with the most expensive electricity in North America"

Cost per KW?

"Yes, it's not as efficient as reverse cycle (essentially a heat pump), but since I pay a fixed rate for electricity, I don't really care."

But your marina does , "fixed rate is leaving as meters are only $30.00 or so.

"I like the option of heating an area (birth) if I'm on the hard"

Heating the bunk makes the most sense as it can be done with 120V or 12V.

Voyaging where electric is scares , a 15 min warmup with a truckers electric sheet , makes it feel like 5 fat girls just moved over for a watch stander hitting the sack.!

AS a liveaboard , coming home after dark, ,even to a 70F interior , the joy of "The Fat Girls" having warmed the bunk is a real delight!!!

Amazon.com: Twin, Heated Mattress Pad by Electrowarmth, Non ...

https://www.amazon.com/Mattress-Elec....../B001122SZQ


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Rating: 4.1 - ‎37 reviews
RoadPro RP-203EC 12V 12' Extension Cord with Cigarette Lighter Plug ... Electrowarmth bunk warmers radiate heat from below allowing you to relax into a .... The best thing to do is set the heater on high while the truck is running and then ...
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Old 08-11-2016, 08:27 AM   #17
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Quote:
Originally Posted by FF View Post
"$80Cdn to $130Cdn per month (winter only) with the most expensive electricity in North America"

Cost per KW?

"Yes, it's not as efficient as reverse cycle (essentially a heat pump), but since I pay a fixed rate for electricity, I don't really care."

But your marina does , "fixed rate is leaving as meters are only $30.00 or so.

"I like the option of heating an area (birth) if I'm on the hard"

Heating the bunk makes the most sense as it can be done with 120V or 12V.

Voyaging where electric is scares , a 15 min warmup with a truckers electric sheet , makes it feel like 5 fat girls just moved over for a watch stander hitting the sack.!

AS a liveaboard , coming home after dark, ,even to a 70F interior , the joy of "The Fat Girls" having warmed the bunk is a real delight!!!

Amazon.com: Twin, Heated Mattress Pad by Electrowarmth, Non ...

https://www.amazon.com/Mattress-Elec....../B001122SZQ

Amazon.com, Inc.

Rating: 4.1 - ‎37 reviews
RoadPro RP-203EC 12V 12' Extension Cord with Cigarette Lighter Plug ... Electrowarmth bunk warmers radiate heat from below allowing you to relax into a .... The best thing to do is set the heater on high while the truck is running and then ...
What's wrong with "fat girls"?
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Old 08-12-2016, 12:18 PM   #18
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Quote:
Originally Posted by seattleboatguy View Post
Ocean Breeze 18000 btu self contained marine a/c
a/c draws 13.46 amp
for electric heat option draws 3.2 kw
for reverse cycle heating option, manufacturer says it is inefficient for water temp less than 40 deg
2 year warranty
$1780


When it is used for heating, I can purchase this unit with either electric heat or reverse cycle heat. I'm leaning toward electric heat for both Norfolk winters (short term) and Puget Sound winters (long term). I think my Westerbeke 4.4 kw generator would handle the load at anchor, though it would be damn noisy on my boat. What do you think about the electric vs reverse cycle heat? Would it be much cheaper to go with reverse cycle most of the time, and fire up some portable electric heaters on the days when both air and water temperature were below 40?
I don't see many reverse cycle systems here in the Salish Sea. Maybe I am just not looking hard enough? If you really are going to be refitting for these winters, I would consider looking at hydronic diesel heat. The diesel is something you already have on board and is relatively cheap. The hydronic heat is great for long term use and you don't have to worry about the electrical circuits.

As others have mentioned, water temps here will only reach those 40 degree levels if you are in a shallow marina with little water exchange. Water temps in Puget Sound stay around 50 degrees year round. So the reverse cycle would stay pretty efficient here if you don't mind running the generator full time whenever you need heat at anchor.
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Old 08-13-2016, 08:04 AM   #19
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Folks in real cold areas, NYC just barely fits the class, might wish to consider a system that uses NO electric .

The most common is a Dickinson or similar diesel fired range.

When the bay is iced over , and the power goes down for 10+ days , your heated vessel will be the only liveaboard actually enjoying watching the winter storms go by.
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Old 08-14-2016, 10:22 AM   #20
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heating: reverse cycle vs electric

Everyone has an opinion on this subject. We have a webasto...3 zones and it works well. But it's expensive to install, and expensive to maintain. We had a $2,000 repair bill last year for a new heat exchanger that had rusted out. They use a lot of fuel 1 gph, are very noisy and draw ~15-20 amps DC. I know several owners who have both a hydronic setup and a diesel Dickinson heater and they swear by the latter as it sips fuel, is quiet and the heat is dry. Some even have fabricated a water heater setup. But there are trade offs: only the saloon gets heat and the Webasto keeps my Pilothouse windows free from condensation.

Personally, I wouldn't install a heatpump setup for the PNW. I'd do the hydronic thing or the Dickinson heater if I had to choose, just because of the electricity demands and I think you realistically consider upgrading your genny as well as you are on the cusp of the limits of a 4 KW genny. But..I'm not choosing.


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