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Old 10-11-2019, 10:08   #16
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Re: Who’s pumped for a heat pump—-> this guy!

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Originally Posted by Sailmonkey View Post
This is the real problem, imho, with large air conditioners on small boats. You may be able to maintain your set point during the heat of the day, but at night the short cycling of the compressor means that you’re living in a cool rainforest.
Sorry, I’m not super well versed on these systems.

My understanding is it will BOTH heat and cool, and by just kicking on once and a while it will knock the humidity down to spec.




Also side note I’d like to have one duct go into the engine room to zap moisture in there, if possible.
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Old 10-11-2019, 11:50   #17
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Re: Who’s pumped for a heat pump—-> this guy!

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Sorry, I’m not super well versed on these systems.



My understanding is it will BOTH heat and cool, and by just kicking on once and a while it will knock the humidity down to spec.









Also side note I’d like to have one duct go into the engine room to zap moisture in there, if possible.


You really don’t want a duct into the engine space. The addition of air in there will force engine smell put into the living spaces.

Regarding the humidity, an air conditioner unit needs to run for a period of time to pull the moisture out of the air. Here comes the balancing act, a unit that has enough reserve cooling capacity to cool a typically in insulated space during the heat of day will have excess capacity when the sun sets. This means that the compressor will run for a short period of time to accomplish its cooling task, but hasn’t run long enough condense meaningful moisture from the air. When this occurs you end up with a cold clammy environment.

An AC unit with a reversing valve will heat and cool, but that’s got nothing to do with the humidity levels.

I’m only bringing all of this up, as I’ve seen fat too often a massive AC unit installed on a small boat. It’s great during the day when the sun is beating down, the companionway is opened and closed, etc....but at night the boat is uncomfortable, even though it’s at the correct temperature.
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Old 10-11-2019, 14:03   #18
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Re: Who’s pumped for a heat pump—-> this guy!

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Originally Posted by Sailmonkey View Post
You really don’t want a duct into the engine space. The addition of air in there will force engine smell put into the living spaces.

Regarding the humidity, an air conditioner unit needs to run for a period of time to pull the moisture out of the air. Here comes the balancing act, a unit that has enough reserve cooling capacity to cool a typically in insulated space during the heat of day will have excess capacity when the sun sets. This means that the compressor will run for a short period of time to accomplish its cooling task, but hasn’t run long enough condense meaningful moisture from the air. When this occurs you end up with a cold clammy environment.

An AC unit with a reversing valve will heat and cool, but that’s got nothing to do with the humidity levels.

I’m only bringing all of this up, as I’ve seen fat too often a massive AC unit installed on a small boat. It’s great during the day when the sun is beating down, the companionway is opened and closed, etc....but at night the boat is uncomfortable, even though it’s at the correct temperature.


Got it, now if I’m only going to be in FL for the winter for the most part and up in New England for the summer, how would that factor in? 6k btu?

Also what’s the best bet for keeping the engine bay dry? Just a little dehumidifier back there?
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Old 10-11-2019, 14:56   #19
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Re: Who’s pumped for a heat pump—-> this guy!

New England in Summer isn’t close to 110 surely. So yes smaller, how small? Depends on your comfort level but I’d bet 6K is plenty, the water temp being lower makes a lot of difference too.
If your concerned about the engine, just leave an access panel off, but mine stays dry anyway, I assume because it’s not a sealed compt so there is an air exchange.
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Old 10-11-2019, 15:07   #20
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Re: Who’s pumped for a heat pump—-> this guy!

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New England in Summer isn’t close to 110 surely. So yes smaller, how small? Depends on your comfort level but I’d bet 6K is plenty, the water temp being lower makes a lot of difference too.
If your concerned about the engine, just leave an access panel off, but mine stays dry anyway, I assume because it’s not a sealed compt so there is an air exchange.
That makes sense!

It’s more right before and after the summer in FL, also just cutting moisture down to <50%

Engine area is important because it’s a large dead space that I’m using for storage of some stuff that I don’t want to be rainforested and I’ll also probably be mounting the Rpi OpenCPN pieces back in there
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Old 10-11-2019, 15:10   #21
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Re: Who’s pumped for a heat pump—-> this guy!

You’d be better off with a light bulb to keep that area warm rather than ducting AC into there
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Old 10-11-2019, 17:10   #22
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Re: Who’s pumped for a heat pump—-> this guy!

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You’d be better off with a light bulb to keep that area warm rather than ducting AC into there

Like one 60w bulb would keep that area <50%?
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Old 10-11-2019, 17:33   #23
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Who’s pumped for a heat pump—-&gt; this guy!

To be honest nothing gets “rain forested” when using air conditioning, a great many people have no air conditioning at all up North and don’t have any issues.
An air conditioner is a dehumidifier, only difference is an AC ducts the heat produced outside, and a dehumidifier mixes the hot with the cold so you actually get a slight heating effect.
Your issues with condensation will be when it’s cold and your heating, and only the areas that are heated will have condensation issues.
Best way to combat that I have found is by having a port light or some kind of vent open, yes that wastes heat, but you have to let the moisture out, you breathe moisture out and if you cook with propane apparently burning propane releases quite a bit of water vapor.
Best to move South before that happens.

For some odd reason my 6K Webasto is weak in heat mode, but OK in AC mode, my 16K Webasto is like a furnace though, I don’t know why the difference, and perhaps it’s just mine too.
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Old 10-11-2019, 21:08   #24
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Re: Who’s pumped for a heat pump—-> this guy!

Just something to be aware of when using a heat pump for heating: the units don’t generally work if the water temp is below 42 F in my experience. The systems will freeze up after 5 min. Give some thought to a propane or diesel heater for heating. They are quieter and simpler...
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Old 10-11-2019, 21:17   #25
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Re: Who’s pumped for a heat pump—-> this guy!

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Just something to be aware of when using a heat pump for heating: the units don’t generally work if the water temp is below 42 F in my experience. The systems will freeze up after 5 min. Give some thought to a propane or diesel heater for heating. They are quieter and simpler...
The cutter already has a force 10 propane heater, but it takes a good amount of cold to bother me, I’m a t shirt to like 40f kinda guy.
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Old 10-11-2019, 21:27   #26
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Re: Who’s pumped for a heat pump—-&gt; this guy!

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Got it, now if I’m only going to be in FL for the winter for the most part and up in New England for the summer, how would that factor in? 6k btu?

Also what’s the best bet for keeping the engine bay dry? Just a little dehumidifier back there?

Summer in New England? You don't need any AC at all for that regime. No need at all for AC in New England in the summer (only 1.9 days per year in Falmouth over 90F), and you might need just a little heat in the winter in Florida, better provided with a little diesel heater (or a little electric heater at the dock).



You don't need any dehumidifier for the engine bay -- running the engine will instantly dehumidify it. If you're concerned about the engine bay freezing, just use a little 75 watt tube heater.


I just saved you about $3000, so you owe me a beer.


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Old 10-11-2019, 21:40   #27
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Re: Who’s pumped for a heat pump—-&gt; this guy!

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Summer in New England? You don't need any AC at all for that regime. No need at all for AC in New England in the summer (only 1.9 days per year in Falmouth over 90F), and you might need just a little heat in the winter in Florida, better provided with a little diesel heater (or a little electric heater at the dock).



You don't need any dehumidifier for the engine bay -- running the engine will instantly dehumidify it. If you're concerned about the engine bay freezing, just use a little 75 watt tube heater.


I just saved you about $3000, so you owe me a beer.


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FL is like mid 80s and humid as a armpit right now? Plus I’ll be keeping some higher end firearms in the engine room.
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Old 11-11-2019, 11:09   #28
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Re: Who’s pumped for a heat pump—-> this guy!

You could put a small exhaust fan in the engine room that will pull some of the boats conditioned air through it. Again, more demand put on the heating/cooling unit but ain't nothin' free. If you could make the exhaust fan speed adjustable then you can tune in the balance of conditioning the engine room with a minimum amount of energy.
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Old 11-11-2019, 11:27   #29
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Re: Who’s pumped for a heat pump—-> this guy!

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You could put a small exhaust fan in the engine room that will pull some of the boats conditioned air through it. Again, more demand put on the heating/cooling unit but ain't nothin' free. If you could make the exhaust fan speed adjustable then you can tune in the balance of conditioning the engine room with a minimum amount of energy.


This is a really good idea, a small computer fan creating a small negative pressure will work quite well.
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Old 15-11-2019, 18:36   #30
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Re: Who’s pumped for a heat pump—-> this guy!

I installed the 16-17k btu CruiseAire (with an “e”) system early this summer in my 34 foot cruiser. The ACpart was capsule of freezing you. It has adjustable humidity setting too. Now it is winter here in Minnesota on the river. It provided heat on the reverse cycle that would toast you plus it has adjustable humidity too.
Then others told me it would not work below 40 deg f water temp. Well a serious hospital visit of 6 days in the ICU prevented me from finishing my winter heater install.im still not quite done with it and water temp is now 34 deg f. And it still puts out 80-85 deg heat. Enough to keep me warm down to 10 deg f outside with wind. I cheat some hear by directing a milkhouse electric heater into the cold air intake. I’m not sure exactly what this does but testing shows it remarkably effective. Both in heat output and ability to do it in excessively cold intake water temp. I had to go to a propane heater backup but mr heater units are very efficient and produce no noticeable CO. There is a good test of thi on YouTube. And I checked it the same way. It would not be the cheapest way to heat all winter unless you used a shore based tank like others do. But it works for me.
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