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Old 28-03-2020, 08:22   #1
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Air con for heat in winter?

Hi folks,
Our new boat came with a brand new 12000 btu heat pump type air con, ready to install
We're trying to figure out whether or not the reverse cycle heat will be adequate to heat our boat in the winter.
The boat is a 30 foot, not insulated. The heat pump draws 8.6 amps according to the manufacturer. We will be on 30 amp shore power for the winter. Boat will be in Portsmouth VA. According to noaa, the sea water temp is between 48.5 to 51 degrees during February, the coldest month for water temp. Air temp averages 36 low in January.
So, for those of you in a similar climate, do you think that it will generate decent heat? How about humidity control? We are thinking about installing a tiny wood stove to increase heat and help dry it out. Is that overkill? Ideas about average heating cost to run a heat pump in the winter? We will be paying 12 cents per kwh.
I'd like to avoid liquid/gas heaters if possible, but we're open to those options as well. My husband does not want to shrink wrap the boat.
Thanks!
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Old 28-03-2020, 08:38   #2
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Re: Air con for heat in winter?

Quote:
Originally Posted by CamWrenRoo View Post
Hi folks,
Our new boat came with a brand new 12000 btu heat pump type air con, ready to install
We're trying to figure out whether or not the reverse cycle heat will be adequate to heat our boat in the winter.
The boat is a 30 foot, not insulated. The heat pump draws 8.6 amps according to the manufacturer. We will be on 30 amp shore power for the winter. Boat will be in Portsmouth VA. According to noaa, the sea water temp is between 48.5 to 51 degrees during February, the coldest month for water temp. Air temp averages 36 low in January.
So, for those of you in a similar climate, do you think that it will generate decent heat? How about humidity control? We are thinking about installing a tiny wood stove to increase heat and help dry it out. Is that overkill?
I'd like to avoid liquid/gas heaters if possible, but we're open to those options as well. My husband does not want to shrink wrap the boat.
Thanks!

We had reverse cycle heat on the last boat, and where we were, it was great. However note well that it needs a lot of power, so won't work at anchor unless you are running a generator!


The efficiency is directly related to the water temperature, and an environment where water is warmer than air during the coldest time is ideal. System should work very well with 48 degree water (what is that, +10C?). Whether it's big enough for your boat no one can answer for you -- you will need to try it and see for yourself.


At the dock with shore power, you can supplement with electric fan heaters. At the dock I heat my boat almost excusively with electric fan heaters and in a much colder climate than yours. Off the dock I have a 12kW Eberspacher hydronic diesel fired system running 3 fan coils.


For heat off the dock, in such a small boat you should be able to get away with a cheap diesel fired air based system like Webasto, Eber, or Planar.



Or if you like, a wood stove or better diesel fired marine stove like a Dickenson, but will you find room for it in a boat that size? I would go with the Webasto myself. For the dock you won't need any of this -- reverse cycle plus if necessary, in a pinch, fan heaters, will do you fine.
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Old 28-03-2020, 08:44   #3
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Re: Air con for heat in winter?

Cool! We're thinking about the dickension solid fuel heater. The boat actually had a propane heater, similar size, on the bulk head, so there's room. Dockhead, where do you keep your boat? Thanks!
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Old 28-03-2020, 10:00   #4
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Re: Air con for heat in winter?

Quote:
Originally Posted by CamWrenRoo View Post
Cool! We're thinking about the dickension solid fuel heater. The boat actually had a propane heater, similar size, on the bulk head, so there's room. Dockhead, where do you keep your boat? Thanks!

Between 50N and 71N. This winter in Denmark.


Toss the propane heater with extreme prejudice. The Dickenson stoves are great, and you'll find that a diesel fired one will be approximately 10x less hassle to run than solid fuel (because of storage and handling of fuel and ashes). But either one of these will be extremely reliable, less service and complexity than a bus-type heater, much better owner serviceability. But much harder to install because of the chimney, and with certain other drawbacks. But if you already have a chimney because of the previous propane heater, then this will be much less of an issue.
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Old 28-03-2020, 10:37   #5
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Re: Air con for heat in winter?

Good suggestions by Dockhead.
For me, the cut off was about 45F, then IMO it just blew cold air. Everyone will be different. In the last boat, had the 16K btu reverse cycle for the AC w/an added oil filled coil for a heater in the same unit (shut down the reverse cycle portion during the winters in Wash. DC). The heater was very efficient and kept the 40' boat nice and warm.

If all these are at the dock purposes, will say I like the oil filled electric radiators type heater that puts out quiet and consistent heat. For "quick" heat, then an electric heater w/a fan is useful.
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Old 29-03-2020, 08:55   #6
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Re: Air con for heat in winter?

Heat pumps remove moisture during air conditioning mode by letting the moisture condense on the cooling coil.

In winter, it can't do that but heat pumps recycle indoor air. So warming the air, lowers the humidity. That's why indoor air gets too dry in winter.

"Conditioning only indoor air prevents new moisture from being brought in by outdoor air. A heat pump can maintain a constant indoor humidity level that prevents condensation. This function is especially helpful in the winter time when warm and humid indoor air comes in contact with a cold surface like a window."

"https://www.a1finchum.com/can-a-heat-pump-lower-the-humiditylevelinsidea-home"
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Old 29-03-2020, 09:27   #7
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Re: Air con for heat in winter?

Our 30' boat is near Atlanta GA and kept in the water all year. A/C is 16,000 BTU rated at 25A 110V. Water needs to be between 91 & 41 degrees to work. (Cool/Heat) It is ducted to the vBerth, hanging locker, and 2 in the main saloon. The more extreme the temp, the longer it takes to get to temp but once there can hold it. (5 degrees/hour) Air temp here ranges from cold in the low 30s to highs in the high 90s.

You do need to be conscious of resistance to the air flow. Our ducts are 4", but in one place I had to drill an ellipse (Several holes with a 2" hole saw) 8"x2" to keep the volume the same. (3.14 x 2 x 2 = 3.14 x 4 x 1) Don't crush the duct, you can cut away the insulation to pass through a 4" hole in the bulkhead, but volume is critical.
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Old 29-03-2020, 09:53   #8
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Re: Air con for heat in winter?

Our cat is cored above the waterline so technically has a small bit of insulation but not a lot. We have spent several winters on our boat in NC with water temperatures down to about 35f. We found that one 16k btu unit was enough to keep the bridge deck nice and warm in temperatures down to about 20f. Our units say they need 41 as well but our experience does not bear that out. When the water temp is that cold it may take a day or two to get the temp up to the 70s on the bridge deck. Once it up there it seems to be able to hold it. We have some large windows on the bridge deck and where we docked we were facing east and kept the blinds on the south side open and the north side closed during the day for a little solar gain. I think the highest electric bill we ever had was about $75 and we were paying $.25 per kw/hr. Portsmouth gets a tidal flush with relatively warm ocean water so the water temp probably never gets as low as it did in the creeks adjoining the Neuse river in NC. We woke up one morning and there was a thin sheet of ice across the entire quarter mile wide creek and heater was still working (Water intake is 2ft below the waterline). I think that you will probably find that your unit will be enough. I forgot to mention that most of our exterior walls have the classic "mouse fur" which keeps down any condensation. Our only real condensation problem is on the aluminum hatch frame directly above our heads in the bunk and on the frames of the windows and ports.
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Old 29-03-2020, 10:10   #9
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Re: Air con for heat in winter?

Quote:
Originally Posted by CamWrenRoo View Post
Hi folks,
Our new boat came with a brand new 12000 btu heat pump type air con, ready to install
We're trying to figure out whether or not the reverse cycle heat will be adequate to heat our boat in the winter.
The boat is a 30 foot, not insulated. The heat pump draws 8.6 amps according to the manufacturer. We will be on 30 amp shore power for the winter. Boat will be in Portsmouth VA. According to noaa, the sea water temp is between 48.5 to 51 degrees during February, the coldest month for water temp. Air temp averages 36 low in January.
So, for those of you in a similar climate, do you think that it will generate decent heat? How about humidity control? We are thinking about installing a tiny wood stove to increase heat and help dry it out. Is that overkill? Ideas about average heating cost to run a heat pump in the winter? We will be paying 12 cents per kwh.
I'd like to avoid liquid/gas heaters if possible, but we're open to those options as well. My husband does not want to shrink wrap the boat.
Thanks!
I think you would be fine. I may have missed something is it a water or air unit. If air without heat tapes get a small ceramic heater for the cold nights.
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Old 29-03-2020, 10:24   #10
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Re: Air con for heat in winter?

My opinion is that there will be a lot of opinions!

We have a 54 foot boat and it has 4 reverse air systems. When it gets cold, simply, they donít get the boat warm enough to be comfortable. In spring, they are more efficient.

In winter we are dock bound unless, we want to run the genny around the clock. Even on the dock, we have had to learn the limits of amp draw from those small and portable electric heaters; many trips outside to reset the breaker on the dock. Even so, we are often quite chilly with four running at the same time, which require extra extension cords hooked to a different breaker.

So, my opinion, if enough clothing and blankets are not sufficient (theyíre not) and the goal is to stay warm, the diesel heater is the way to go. Research, dock talk and these blogs support that the right sized system for your boat will keep the inside toasty.
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Old 29-03-2020, 10:28   #11
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Re: Air con for heat in winter?

What is not clear is whether you are living on the boat or not. Since shrink wrap is mentioned, I must assume you are not on the boat. If you are, however, the heat pump will be fine. IT will make your boat cozy. If you are not aboard, I would not leave a heat pump on as you will have to have an open and unattended seacock. I have a morbid fear of seacocks or hoses failing, and your heat pump will have one either an inch or inch and a quarter in diameter, and a failure anywhere along the line will not take long to sink the boat.

Having said that, I keep my boat in Kilmarnock, VA, about 40 miles north. Several boats in the marina do leave their heat pumps on all winter. Have not seen any sink. I have a Fairclough cover for my boat, and for humidity I just leave tons of damp-rid in various locations and check it once a month.
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Old 29-03-2020, 10:29   #12
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Re: Air con for heat in winter?

You should double check the current draw numbers. Reverse cycle units use more power in heat mode than in cool mode. Also, donít forget the power needed to run the water pump.

We have a 16k BTU reverse cycle unit. It heats our 42 foot boat quite well. Takes a while to warm up from a cold start but if we are staying aboard it works good enough. We supplement with a small electric space heater in the sleeping berth and turn down the reverse cycle thermostat at night.

We get by using 14A at 120V. Water temp is in the low to mid 40ís F.
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Old 29-03-2020, 10:42   #13
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Re: Air con for heat in winter?

Thank you so much to everyone who replied! I think we'll try the heat pump, and if it does not cut it, we'll use some plug in space heaters. If we're still cold, we'll use either a wood or diesel Dickinson heater. Thank you!
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Old 29-03-2020, 11:05   #14
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Re: Air con for heat in winter?

Interesting answers. I have a 16KW rev cycle heat pump and live on the Columbia river. My Cat is 35' long and 15' wide and the 16K heats the entire boat just fine drawing 10 amps 120vac including the water pump.

I cannot however, use it in the dead of winter. Water temps go down to below 41 at which point I have icing conditions in the unit. Ice as is no water pumps through at all. Very frustrating. Friend had identical boat on Lake Washington in Seattle and uses his year round no problem.

My manual says specifically do not use below 37 degrees water temp. I've found 40 is my lower limit.

But in answer to your question, a 30' boat with 12K should be more than enough to keep you very warm.
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Old 29-03-2020, 17:04   #15
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Re: Air con for heat in winter?

We lived In Annapolis for 5 years...experienced winter temps as low as 5 degrees. What worked best for us and the other live a boards was applying clear shrink wrap. Creates a green house effect. Wasn’t uncommon, when the temps were in the 30’s, to open the hatches. We used only two electric, oil filled heaters, on a 44’ monohull. Key is to use at least a 12 gauge exterior, professional grade extension cord run direct to the dock pedestal.
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