Reverse Air Heat in winter

[cyfarkas]

I winter in the water in NY I visit the boat most days as I'm nearby. Wouldn't do it any other way, I consider It the northern way to a 12 month season.

This year, I did not winterize my reverse air forward till mid January. My salon (main, and aft). Is still on, and blowing heat at a surface water temp of 37. I set the electronic thermostat at 60 when I leave the boat. I shut and winterized the forward unit when I noted frost on the coils. The aft unit is more inboard plus I have a reflected 100w bulb pointed at it at its return.

Although I have auxiliary portable electric heat, nothing is as comfortable as the cruiseair unit. A Diesel furnace is not an option.

My understanding is that even dead cold water has heat. The problem is that the coils on the unit freeze and shut off (or damage) the reverse air condenser unit when the temp drops.

My question is how to stretch that. Efficiency is not my first concern (I pay a flat 'maximum' electric rate). Should I use a food warming bulb to enhance my present warming of the coils? Instead of raw water, Should I consider plumbing into my 20 gallon hot water heater which is always on? Or should I consider a hydronic toe kick heater tied to that same hot water heater?

Experiences?

 

[River Cruiser]

In my experience a de-icer pushing warmer water to the hull helps a reverse cycle in winter. I wouldn't leave it running if no one is onboard, what happens if the power goes out overnight, are you in fresh or salt?

 

[DavidM]

Newer reverse cycle cooling/heating systems have a temp sensor that shuts it down when raw water temps get down to a bit less than 40 degrees. Older ones don't but will freeze the condenser when it gets down to the mid 30s and then shut down.

A few years ago in Oriental, NC my buddy who lives aboard full time froze his condenser. That was in overnight temps of the upper teens and a skim of ice on the brackish water. After it warmed up, we used a hair dryer to thaw it out- the condenser and all of the plumbing from the thu hull in and out of it. It worked fine for the rest of the winter and hasn't frozen this winter- yet.

You are in a lot colder climate and I would expect your A/C to trip out or freeze up and stay frozen for weeks at a time. There isn't any help for it.

Yes, water has heat in it at any temp above the absolute temperature of -xxx F. But as you pull heat out of it to warm your evaporator, it drops the raw water temperature about 5 degrees. When it starts freezing up on the coil, there is nothing more to do except wait for warmer weather.

Your system might be able to tolerate colder weather with an ice eater. It will bring up warmer bottom water and keep things from freezing up.

David

 

[Alaskan Sea-Duction]

My units were working good until the river temp got to 38f. Then my units stared to freeze. I have had to shut my systems down until the river warms up. I augment my heat with electric heaters for the few weeks we have the cold weather, a little more this year.

 

[fryedaze]

A live aboard told me he puts electric heat tape on his reverse cycle to stretch the time he is able to use it in the winter.

 

[rwidman]

I had two such reverse cycle ACs fail in cold water. After the second and no warranty service on the 4 year old second on, I switched to an AC with electric resistance heat.


You probably don't want to do this, but keep in mind the possibility of ruining the unit by operating it in cold water.

 

[Insequent]

To the OP a modified hydronic system would be my suggestion. I have a Webasto hydronic system to which we added a 'pre-heat' loop. This is simply a 750W water heating element in a 1 gallon cylinder that is plumbed into the hydronic circuit. This was done when the baot was in the PNW, I don't need any heating at all these days.

In cold weather I can use shore power at the dock to stop anything freezing on board, without having to run the Webasto unit itself. The 'pre-heat' unit probably gives me 7° or so increase in temp. Thats fine for overnight and unattended boat situations, and its a very safe heating arrangement. If on board during the day you can run additional electric heating to be more comfortable.

 

[dhays]

I think in your shoes I would consider some type of portable heater. My limited understanding is that to get the heat out of the water, the coolant has to be cooled to below what the water temperature is. As David mentioned above, to get a temp differential between raw water that is close to freezing means that your coolant temps will be below freezing, causing the coils to ice up. So unless you can warm up the raw water before it enters the heat exchanger, you have a problem.
I think you are simply asking too much from a system that wasn't designed to operate in those conditions. There are ways around it as other have mentioned (I like the heat tape idea), but if the power goes out for long in very cold weather, your system could freeze up anyway.

 

[psneeld]

My last live aboard (37 foot sportfish) and this live aboard (40 ft trawler)required between 10,000 and 15,000 BTUs to be liveable in the Annapolis and NJ coastal areas.

To keep yours at 60 degrees in all but the worst conditions means 2-3 radiator type electric heaters.

That is 25-40 amps of electricity.

if you are visiting the boat regularly...you might be able to shift between heating sources to keep the boat the way you want it.

Personally, reverse cycle is forced air and the least comfortable of heating types due to cold starts and sheer airflow.

The electric radiators are silent and no forced air.

 

[ranger58sb]

My question is how to stretch that. Efficiency is not my first concern (I pay a flat 'maximum' electric rate). Should I use a food warming bulb to enhance my present warming of the coils? Instead of raw water, Should I consider plumbing into my 20 gallon hot water heater which is always on? Or should I consider a hydronic toe kick heater tied to that same hot water heater?

When some dock neighbors replaced their really old AC/reverse cycle heating unit... they also added a resistive electric heat source incorporated into the main unit's blower system. When water got too cold, they simply shut the sea-cock and switched the system to use the auxiliary heat source as primary. Said it worked fine.

All components were Cruisair, meant to coexist, etc. Presumably the auxiliary could be added to most existing system. I can find product numbers if it helps...

-Chris

 

[O C Diver]

Last year I had my trawler on Chesapeake Bay till near the end of January. The reverse cycle Webasto units worked well down to about 37 degree water temperature. The output fell off dramatically at 35 degrees and the brackish bay water froze in the condenser at around 33 degrees. Two 1500 watt electric heaters kept the boat above 50 degrees till I left to go South. All that would work well till you get a bitter cold snap and lose shore power. Not sure you could keep stuff from freezing and breaking with a 48 hour stretch of single digit temperatures and windy conditions.

Ted

 

[psneeld]

Last year I had my trawler on Chesapeake Bay till near the end of January. The reverse cycle Webasto units worked well down to about 37 degree water temperature. The output fell off dramatically at 35 degrees and the brackish bay water froze in the condenser at around 33 degrees. Two 1500 watt electric heaters kept the boat above 50 degrees till I left to go South. All that would work well till you get a bitter cold snap and lose shore power. Not sure you could keep stuff from freezing and breaking with a 48 hour stretch of single digit temperatures and windy conditions.

Ted

 

[Ski in NC]

I lived on my boat in NC all last winter while I was building my dirt house. Many nights into the 20's and brackish water down to about 40F. Rev cycle 6.5 and 12kbtu could not keep up. Portable heaters did the job, but had to turn off rev cycles to avoid going over 30amps. And it was COLD in the mornings, probably 55-60F. One night I ran gennie as it can make 40amps.

I have frozen my evaporators probably a total of ten times each. So far it has not damaged them. They do not trip, but a frozen evaporator does not load compressor that much so no harm there. But freezing in a HX can not be good for them.

One trick I learned was to defrost quick, just switch it to ac for a few minutes. That will thaw it out quick. And will freeze you in the cabin.

Rev cycle units are not the tool for the job to keep a boat livable in sub freezing temps. They will fail to make heat when they freeze up, and the freezing can damage them. If you are going to leave a boat in the water in these conditions, you need another strategy. Resistance heat will work but it takes GOBS of power to keep it warm. Not too much power needed if you are just heating to provide freeze protection, but it won't be livable.

OCDiver has the right solution. Gets cold? Go south.

 

[cyfarkas]

Thank you all. I thought I'll update: it's now March and the salon unit is working like a champ I've measured water s low as 35, bout its closer to 40 now.

One thing that helped I believe, was that I replaced the water hoses with 3/4 pex, minimal bends (and even there I used 'sweep' type 90s). I did so because I noticed some kinks around bulkheads, as well as some build-up of gunk. Flow has increased dramatically, and as I recall a techy once told me it's all about the flow.

Under another thread, I wrote about installing a small magnetic pump to cycle hot water from the water heater to the engine block( the reverse of what it normally does. ). Very happy with that, the ship has never been so toasty. In conjunction with the reverse-air, it's been a great winter. My ultimate backup, a portable butane tank powered mini patio heater remains unused.

So ok, NY getting a blizzard tomorrow. Do I sound worried?

 

[Comodave]

I used Barnacle Buster on my main engines and saw a significant drop in engine temp, 5 degrees on one engine and 10 degrees on the other. So I used it on my generator and A/C units also. While I can't tell if the A/C units are working more efficiently or not, I have to believe that they are if they are cleaner inside the heat exchangers. It might help the reverse cycle efficiency also.

 

[FF]

Folks replacing a dead water fed air cond/heat pump should think about the newer air sourced units.

These operate on Euro boats well down in under freezing temperature .Perfect for a NE liveaboard.

Finding a place for the exterior air handler might be a hassle , tho they are getting smaller.

They also can be ducted from a central location if desired.

For folks that pay electric meter their 300% to 500% better heating could easily pay for a unit in one winter.

Mitsubishi 12,000 BTU ...
ACWholesalers.com
$510.00


Mitsubishi 15,000 BTU ...
ACWholesalers.com
$609.00



Mitsubishi 17,200 BTU ...
ACWholesalers.com
$734.00



Mitsubishi 17,200 BTU ...
ACWholesalers.com


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[cyfarkas]

Couldn't agree more. The ductless split system is the way to go. As empty nesters, we installed one in the bedroom to avoid running the central Ac unit. One note though, Mitsubishi drains by gravity only out of a wide collection tub and then into a tube . We found out the hard way that if the wall unit is not perfectly level, condensate leaks. This is a problem on a rocking boat that has to be addressed before installation.

 

[DavidM]

FF:

Those apparently low prices for those Mitsubishi units are only for the indoor air handler. It also takes an outdoor compressor unit at $$$ to make them work.

David

 

[FF]

Dozens of Mfg create the Mini Split type units , my Google was only to get someone in the right area.