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Old 11-15-2019, 01:01 PM   #21
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There's a good chance you'll be fine with reverse cycle in that case. A 1500W space heater is only good for 5100 btu.
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Old 11-15-2019, 01:02 PM   #22
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No plans to leave the heater on when no one is onboard. Just need the heat for the trip down from Maryland. There are 7000, 10000 and 16000BTU ac units onboard, so maybe reverse cycle will suffice, just not sure.

That's about the equivalent of 6 space heaters and way less amp draw.
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Old 11-15-2019, 01:12 PM   #23
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Those should work just fine for you. We use ours in northern Virginia until the water gets below 40 degrees, which is usually around mid to late December. Below 40 the units will freeze up and stop heating. As others have noted, they reverse cycle heat pumps will throw a lot more heat using much less power than electric units. When the water is warm enough to run ours, the cabin stays plenty warm down into 20 degree air temps. Once we have to switch to electric, we generally are only able to heat the saloon without over taxing our electrical system. In fact, if we stay on the boat in the dead of winter we usually sleep in the saloon pull out as it is difficult to heat the entire boat with just electric. We consider diesel very year, but the really cold weather only lasts a couple of months.
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Old 11-15-2019, 04:50 PM   #24
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My reverse cycle heat quits at a water temp of about 45 degrees.
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Originally Posted by O C Diver View Post
Unless you're going to be in water colder than 35 degrees, it makes a lot more sense to run the air conditioning in reverse cycle for cabin heat. It will produce a lot more BTUs with a lot less amps.

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Old 11-15-2019, 05:01 PM   #25
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We live aboard in Maryland having spent two past winters. When even really cold (single digits overnight) we are still able to keep the boat to 72 degrees using four resistance heaters, all on separate circuits. We just need to shut one off when using the toaster, microwave, or coffemaker. None of the four cause an outlet to become warm. It costs about $5/day to run one heater for 24 hours. Fortunately, the temps are not single-digit cold very often such that we need to run all four. More often it is just two, perhaps three during the day. We sleep cold, 50 degrees in the owners' cabin warm and cozy with just a down comforter.
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Those should work just fine for you. We use ours in northern Virginia until the water gets below 40 degrees, which is usually around mid to late December. Below 40 the units will freeze up and stop heating. As others have noted, they reverse cycle heat pumps will throw a lot more heat using much less power than electric units. When the water is warm enough to run ours, the cabin stays plenty warm down into 20 degree air temps. Once we have to switch to electric, we generally are only able to heat the saloon without over taxing our electrical system. In fact, if we stay on the boat in the dead of winter we usually sleep in the saloon pull out as it is difficult to heat the entire boat with just electric. We consider diesel very year, but the really cold weather only lasts a couple of months.
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Old 11-15-2019, 05:30 PM   #26
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My reverse cycle heat quits at a water temp of about 45 degrees.
What do you mean exactly by quits? Does the system freeze up or is there a temperature sensor in the raw water line that shuts the system down?

My Webasto units worked down to around 35 degrees (with reduced BTU output). Down around 33 degrees they started to freeze up, but that is a function of insufficient raw water flow. With the new raw water pump in brackish water, I could probably get down to 32 degrees, but BTU output probably makes it unrealistic.

Ted
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Old 11-15-2019, 05:43 PM   #27
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Best money I ever spent and peace of mind was for two 450 watt Extreme Bilge Heaters. Light weight, long heavy duty plug in cords. I can winterize in 30 minutes including engine room vent blocks, gravity drain Fresh water system, and plug engine exhaust. I run rv anti-freeze thru both my ac/h units only as a over kill precaution in case electric power goes off. 😁
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Old 11-15-2019, 08:34 PM   #28
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We lived aboard Sandpiper for two winters while building our current house.

Sandpiper has no built in heat.

Our marina at the time had unmetered AC !!!!!!!!!!

I installed a second shore power inlet, split the AC panel and ran two 30 amp cords to shore. Bought 5 Caframo True North heaters and ran them at 600 watts. Installed 20 amp dedicated heater outlets with 12 ga wiring and a 20 amp breaker

Kept the boat real warm. Opened windows for temperature control.

Comes in handy now when we boat in winter and a second shore power outlet is available.
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Old 11-16-2019, 03:15 AM   #29
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By "quits" I mean that the units stop producing any useful amount of heat.
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Originally Posted by O C Diver View Post
What do you mean exactly by quits? Does the system freeze up or is there a temperature sensor in the raw water line that shuts the system down?

My Webasto units worked down to around 35 degrees (with reduced BTU output). Down around 33 degrees they started to freeze up, but that is a function of insufficient raw water flow. With the new raw water pump in brackish water, I could probably get down to 32 degrees, but BTU output probably makes it unrealistic.

Ted
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Old 11-16-2019, 07:04 AM   #30
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By "quits" I mean that the units stop producing any useful amount of heat.
That may be a function of water flow or design of the unit. My Webasto produces near full output with 40 degree water temperatures. Most reverse cycle home heat pumps and split units produce good heat at or below 40 degrees. My home geothermal will work well down to 20 degrees (antifreeze in loop) although it's never been below 45 yet.

Also there is a noticeable improvement in heating and air conditioning BTU output when I changed water pumps. The output is now about 7 gallons per minute (measured at hull discharge) for each unit (12,000 BTU).

Ted
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Old 11-16-2019, 07:39 AM   #31
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Hmm, Ted, water flow. As it is, I have always been suspect of the volume of warter flow. Since purchase five years ago it never seemed all that strong even after have acid-cleaned the innards. I will take a look at the model of pump I have. Perhaps it is underpowered. I will report back. Thank you for your insights.
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That may be a function of water flow or design of the unit. My Webasto produces near full output with 40 degree water temperatures. Most reverse cycle home heat pumps and split units produce good heat at or below 40 degrees. My home geothermal will work well down to 20 degrees (antifreeze in loop) although it's never been below 45 yet.

Also there is a noticeable improvement in heating and air conditioning BTU output when I changed water pumps. The output is now about 7 gallons per minute (measured at hull discharge) for each unit (12,000 BTU).

Ted
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Old 11-16-2019, 07:42 AM   #32
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Hmm, Ted, water flow. As it is, I have always been suspect of the volume of warter flow. Since purchase five years ago it never seemed all that strong even after have acid-cleaned the innards. I will take a look at the model of pump I have. Perhaps it is underpowered. I will report back. Thank you for your insights.
Check the hose between the hull valve and the pump. Mine fills up with sea creatures so I have to replace the hose. Cleaning it out is not good enough.
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Old 11-16-2019, 08:22 AM   #33
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Hmm, Ted, water flow. As it is, I have always been suspect of the volume of warter flow. Since purchase five years ago it never seemed all that strong even after have acid-cleaned the innards. I will take a look at the model of pump I have. Perhaps it is underpowered. I will report back. Thank you for your insights.
A relatively simple test you can do if 2 or more of your air conditioners run off the same pump, is to plug one air conditioner's line so that all the water flow goes to the other unit and then measure the heat or cooling output temperature. A simple digital HVAC thermometer (<$20) is a good way to do this. The thermometer is also a great tool for periodically checking performance and discerning early warning signs of potential problems.

Ted
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Old 11-16-2019, 09:01 AM   #34
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Just read the original post again. It was not the outlet that was getting hot, it was the plug. Could just be an undersized crap plug. Iíd cut off the end and replace with a plug rated for 15 amps. Also I would stay away from the practice of placing a 20 amp outlet on a 15 amp Circut. The 20 amp outlet is visible and sends a signal that you can insert a 20 amp load. Thatís why different loads have different plug designs. The plug tells you the wire/load capacity.
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Old 11-16-2019, 09:03 AM   #35
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Plugging a line, not simple but doable. I may do so as our mid-cabin unit (1 of 3) has never been nearly as good a performer, heating or cooling, as the other two. Plugging that line for now would hardly be a loss as we rarely run it anyway.

The pump is a Dometic. It is supplied by a 3/4 inch raw water hose. Would a one-inch hose make any difference? Since the three output hoses look to be 1/2 ID, I would not think so. Thoughts? I am going to replace the hose anyway. It is only about a 6-foot run.
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A relatively simple test you can do if 2 or more of your air conditioners run off the same pump, is to plug one air conditioner's line so that all the water flow goes to the other unit and then measure the heat or cooling output temperature. A simple digital HVAC thermometer (<$20) is a good way to do this. The thermometer is also a great tool for periodically checking performance and discerning early warning signs of potential problems.

Ted
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Old 11-16-2019, 09:09 AM   #36
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I had a lot of 3/4 inch hoses on my AT. When I changed my hull valves from plastic to bronze, I upped them to 1 inch.... on advice. Yes the 1 inch A/C hose, from the hull valve to the strainer, sill gets plugged up with critters but, not as often.
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Old 11-16-2019, 09:20 AM   #37
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Just read the original post again. It was not the outlet that was getting hot, it was the plug. Could just be an undersized crap plug. Iíd cut off the end and replace with a plug rated for 15 amps. Also I would stay away from the practice of placing a 20 amp outlet on a 15 amp Circut. The 20 amp outlet is visible and sends a signal that you can insert a 20 amp load. Thatís why different loads have different plug designs. The plug tells you the wire/load capacity.

While possible it was only the plug heating up, in my experience and my particular problem it was the cheap outlets heating up and they also heated the plug. If you didn't check the outlet, one might miss it.


If you put in a 20A outlet but keep the 15A CB protecting the circuit...it's no different than having a 30A CB protecting a 30A panel that you plug in too many appliances to and pop it. And that is VERY common.



Sure change it out eventually, but I don't see it as a safety hazard short term until you find a better 15A receptacle or rewire/CB.
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Old 11-16-2019, 12:48 PM   #38
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While possible it was only the plug heating up, in my experience and my particular problem it was the cheap outlets heating up and they also heated the plug. If you didn't check the outlet, one might miss it.


If you put in a 20A outlet but keep the 15A CB protecting the circuit...it's no different than having a 30A CB protecting a 30A panel that you plug in too many appliances to and pop it. And that is VERY common.



Sure change it out eventually, but I don't see it as a safety hazard short term until you find a better 15A receptacle or rewire/CB.


People have reported that some manufacturers use identically the same brass guts for the spec grade 20 a and the 15 a receptacle. Only the plastic cover is different. I suspect this is not true on the 59 cent recepts.
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Old 11-16-2019, 11:03 PM   #39
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The pump is a Dometic. It is supplied by a 3/4 inch raw water hose. Would a one-inch hose make any difference? Since the three output hoses look to be 1/2 ID, I would not think so. Thoughts? I am going to replace the hose anyway. It is only about a 6-foot run.
Wow!
What size is the seacock? Most of the pumps that run air conditioners are centrifugal and often magnetic drive. As such, they have modest suction capability and produce minimal output pressure. They do produce good volume. When subject to either suction restriction or output restriction, volume rapidly diminishes. With a smaller diameter and or longer supply hose the pump experiences parasitic line loss. Simply, the walls act as friction to slow the flow down. Curves also add to the restriction. I have a 12' run with some sweep curves between my supply manifold and the pump. The supply hose is 1.5" ID. Too give you some flow perspective, over a 100' run with a 2 psi pressure drop, these sizes can flow the following gallons per minute.

Size----GPM
1/2"----1.25
3/4"----3.5
1"-------8.5
1.25"---14
1.5"-----22

While the numbers are somewhat different in suction, one can clearly see that going from 3/4" to 1" should more than double the flow for the same inches of vacuum. There will only be modest improvement if the seacock is only 3/4". If you have a 1" or larger seacock, I would run that size hose and reduce it as needed at the pump.

On the discharge side I would run 3/4" from the manifold to the AC units. from the pump and the plumbing in the manifold, I would use 1" to reduce head pressure caused by parasitic line loss.

Before you embark on this project, see if you can identify the pump manufacturer and model and post it here. Most offer flow chart graphs based on head pressure and will have minimum pipe size recommendations.

Ted
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Old 11-17-2019, 08:20 AM   #40
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Used to be reverse cycle units air or water stopped when the air or water got to near freezing.

The modern mini splits solve this problem and can produce heat even at -20.

There computers know when the ice forms , they flip the coolant passages and by stealing a bit of heat from the interior can de ice the unitbrapidly.

At that point the unit reverses the valves and resumes heating.

The only complaint is the unit will go to max heat for a min or two to make up for the stolen heat , and some folks can hear rhe fan speed up.

A boat reverse cycle unit will usually quit till the water warms up , and may switch over to a wire heating element , like the one in a toaster.

With a limited electric supply a stand alone resistance heater in the cabin is usually more efficient.

The higher buck ceramic units have a nice feature , when on they will run at 500-600W at all times , only adding the 1000W heat as the thermostat demands.

The cabin temp is more constant.
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