Air con for heat in winter?

[Mauruuru]

Reverse cycle heat pump is very efficient You get more energy-both heating and cooling-than you put in electrically.
Think of a Heat pump as an energy Accumulator in this case you take energy out of the 48 degree water and put it into your boat. In cooling mode you take it out of the boat and put it into the water.
An electric strip heater gives you one unit of heat per unit of electrical input , high efficiency gas maybe 80 percent of fuel becomes heat , diesel stove who knows maybe 50-60percent but none of those three options give you cooling in summer or dehumidification!
If you already have it, use it if its not big enough supplement it as needed

[Lodesman]

Originally Posted by CamWrenRoo

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!

With a single unit, I think you are realistically only heating/cooling the forward or aft part of the boat, depending on how you install it. It will work until the water temp hits 39-40F - then the water will freeze in the outlet and the pump will stop working. Been there, done that. I would suggest install it to ensure your sleeping area is comfortable and perhaps put a wood stove in the salon. I'm not a fan of leaving fires burning while sleeping - you should install CO detectors, but beware you may get false alarms on really cold days.
You will have a lot of condensation issues regardless of how you heat - check under your mattress(es)/cushions - and expect your bilge to fill.

[Mauruuru]

The suggestion to use a fresh water tank is nonsense unless you are interested in creating a block of ice. The whole point of a heat pump in heating mode is to take heat out of the water and put it into the air in your boat. If you use a fixed container of water you will eventually remove enough latent heat that the tank will freeze into a solid block of ice....there is no perpetual motion machine allowed by the laws of thermo dynamics. The reason a heat pump works is because you are extracting an infintesimal amount of energy in the source (sea water or atmosphere) compared to the area you are heating and vice versa in cooling mode! The benefit of a heat pump is one unit of electrical input gets you two or three units of energy out everything else is at or below unity. The other advantage is you get dehumidification of the internal air and no flame or smoke stack.......

[Mauruuru]

the only possible way that this could work is if the refrigeration unit is expelling heat into the water tank while the heat pump is extracting it and sooner or later the heat will be gone and the tank will freeze---unless of course there is another source of heat putting energy back into the tank as fast as the heat pump extracts it.

[David Mathis]

My boat launched late March in upstate New York with the Hudson River water at 40 degrees and the air 50s during the day and 30s at night. This is common for us so here is our experience with reverse cycle ac, heat pumps, with cold water and cold air temps.
The system doesn’t get much heat from water below 45. Below 40, expect the water in the system to freeze and become inoperable until you attack it with a hair dryer. The boat is in fresh water so icing is more of a problem than in salt water. With the water at 50 or above, keeping the boat warm is less of a problem. When the water gets to 55-60, the system blows hot air rather than warm and keeping the boat warm isn’t an issue. Be aware that the system adds heat to the air as it passes through the core and only adds a few degrees to it. So, if the air inside of the boat is 40, the first pass through might raise it to 45 or 50 but then it mixes with the cooler air and may only raise the inside temp a few degrees over the first hour or two. Now the air, which is up to 45 goes through again and the inside temp is up another few degrees. The point is that for the first few hours, you may need a portable electric heater to get the temp up to where it can be maintained by the heat pump. After the inside of the boat is comfortable, the heat pump can maintain it with 45-50 degree water. If the water is below 45 and the air cold, you may have to add an electric heater to stay comfortable.

[rslifkin]

There's no way a refrigeration unit would put anywhere near enough heat into the water tank to keep up with the heat removed by a heat pump. Plumbing a heat/AC unit to the water tank is just downright stupid, end of story. If you don't want it plumbed to use raw water, then you need an air cooled unit (and associated ventilation for it).

[doog]

just have to add that the dickinson solid fuel heater is a thin metal can with a very short useful life and marginal function, and their diesel heater is a bit of a fire hazard. Tricky to light and nearly burned a neighbors boat and killed his partner in a horrible accident. A good stove is available in tiny models like the Cubic or others with a tile or brick liner for real use, not the Dickinson. (Ive built several stoves and stove builders of ice shack stoves even of titanium will state, not for extended or continual use..Metal burns up) And nothing better than reverse cycle heat pump but 12K btu is pretty low. All depends on the efficiency and installation and the temps you are dealing with.

The cheap Chinese diesel heaters are being sold by rv people and many love them..A few hundred bucks and they burn clean and are very reliable with a few glitches at times..

[timb7734]

I never had good heating from heat pumps, also never felt the heat pump removed moisture from the air. I successfully used electric heaters with no extension cords while leaving the heat pump fan on to circulate the air. One of my boats has resistance heat in the a/c unit, Flagship Marine is the manufacturer. I also have an espar diesel heater for backup or on the hook. Nights on the Canadian border get pretty cool even in summer.

[Lost Horizons]

Originally Posted by CamWrenRoo

So, for those of you in a similar climate, do you think that it will generate decent heat?

Yes, it will. However, it will be loud. Significantly louder than diesel heaters and electric forced air portable heaters. I am not comfortable running the heat pump continuously on my boat for that reason.

[merrydolphin]

Yes, that unit should work well dockside. If your heat pump were air cooled it wouldn’t work under those conditions. I worked HVAC and installed a 12k btu unit in my Tartan 37 a while back. It worked fine both summers and winter in northern North Carolina. It will be plenty for your boat. Even without you could run the unit with a honda 2000 or similar generator off the dock. And with a soft start kit it would be even better. And as said you can always supplement with small space heater while ashore.