Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 08-05-2020, 06:46   #1
Registered User

Join Date: May 2013
Location: Potomac/Chesapeake
Boat: Hunter 36
Posts: 304
What is the point of having a heater if you can't use it when its cold out?

OK, this is as much a rant as a question, but I have a typical reverse cycle heating/AC system, and it won't work when the water temperature is below 40 degrees F.

So basically, what that means is, I can't use the heater when it's cold outside!! So what is the point?

Currently, the boat is in fresh water (the Potomac) Previously it was in partially salt water at a similar latitude (the Cheseapeake), and I didn't have this problem there. Does the the salinity/freezing point of the water make a difference for the operating threshold?
__________________

Rohan is offline   Reply With Quote
Old 08-05-2020, 06:50   #2
Registered User

Join Date: Apr 2011
Boat: center console
Posts: 182
Re: What is the point of having a heater if you can't use it when its cold out?

Many heaters will have an electric coil back up for this reason. It is the same with home heat pumps, there is not enough therms left at 40F.
__________________

1affiah is offline   Reply With Quote
Old 08-05-2020, 06:52   #3
Registered User

Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft Catalina 381
Posts: 557
Re: What is the point of having a heater if you can't use it when its cold out?

The minimum water temperature for reverse cycle heat will be a little lower in salt water than fresh. Probably about 3 degrees difference. A bigger seawater pump will often buy another 1 - 2 degrees, as more water flow will mean the water temperature drops less as it passes through the unit, so you can handle slightly colder input water before it starts to freeze in the coil.

In general, reverse cycle heat is good for chilly days early and especially late in the season, but it's not an ideal all-winter solution unless you're somewhere where the water just doesn't get all that cold.
rslifkin is online now   Reply With Quote
Old 08-05-2020, 11:50   #4
Commercial Member
 
CharlieJ's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: St. Petersburg, FL
Boat: Gulfstar Long Range Trawler; 53'; BearBoat
Posts: 1,035
Re: What is the point of having a heater if you can't use it when its cold out?

The engineering behind this is as the heat is removed from the raw water, its temperature naturally drops. Water increases in volume when it freezes so if the raw water temperature drops low enough so that it can freeze, it will expand. If this condition occurs, the expansion may burst the condenser tubes. Hence the restriction on injection temperature of about 40F.
__________________
Charlie Johnson
ABYC Master Technician
JTB Marine Corporation
"The Devil is in the details and so is salvation."
CharlieJ is offline   Reply With Quote
Old 08-05-2020, 11:58   #5
Registered User
 
S/V Illusion's Avatar

Join Date: Oct 2007
Location: Lakewood Ranch, FLORIDA
Boat: Alden 50, Sarasota, Florida
Posts: 2,367
Re: What is the point of having a heater if you can't use it when its cold out?

Quote:
Originally Posted by Rohan View Post
So basically, what that means is, I can't use the heater when it's cold outside!! So what is the point?

It's all about the water temperature. Here it gets into the 40s sometimes in winter (BRRRRRRR) and we need heat. Not often but that's the "point" to those of us who dont live in a snow belt. Location, location, ....
S/V Illusion is online now   Reply With Quote
Old 09-05-2020, 08:40   #6
Registered User
 
mvmojo's Avatar

Join Date: Mar 2018
Location: www.mvmojo.com
Boat: Robt Beebe Passagemaker 49-10 in steel
Posts: 259
Re: What is the point of having a heater if you can't use it when its cold out?

This is the reason I'm a fan of resistance heat vs reverse cycle. A reverse cycle system is more complex, more things to go wrong. The only advantage is that it's more efficient, i.e., it doesn't use as much electricity as a resistance type unit. But it also doesn't produce as much heat and doesn't produce any heat at all with water temps below 40F. I've got 3 a/c units on MOJO, each with resistance heat via a cal-rod. When it gets cold, we still have nice warm air coming from the ducts and a nice, warm, dry boat! Well worth the extra few bucks in electricity if you marina charges by the kw - mine doesn't.
mvmojo is offline   Reply With Quote
Old 09-05-2020, 09:50   #7
Registered User

Join Date: Jan 2020
Posts: 44
Re: What is the point of having a heater if you can't use it when its cold out?

- That issue isn't uncommon for heat pump systems including water cooled house ones.
- Likely the most effective cure is to use either an electric resistance coil in the system below 40 F. or a completely separate diesel powered heater or similar such as a Dickinson.
- Even our air - to - air heat pump system at home is ineffective below about 43 F. ambient which is why there is a propane furnace system in the mix as well.
- Heat pumps that are effective to a lot less than 40 F. ambient are available but expensive which is a reason that most people don't install them but use another heat source when it is at "BRRRRRR" temperatures.
- A similar issue happens to the cooling side of things with heat pumps when that ambient temperature is very high.
- Almost always is really "boils down" to upfront price and cost effectiveness where either people don't want to pay for really high efficiency or the projected use does not warrant the expenditure.
Cheers,
Niall.
Niall leslie is offline   Reply With Quote
Old 09-05-2020, 10:00   #8
Registered User

Join Date: Feb 2018
Location: Boat-Middle Chesapeake Bay, us-WV.
Boat: Beneteau 361, 36
Posts: 38
Re: What is the point of having a heater if you can't use it when its cold out?

Another solution is to sail south, until the winter water low temp is 50 degrees or above. No more problems with your reverse cycle Heat/AC not producing heat.

This is my chosen solution. Intend to do that this fall, and never winterize the #@%& thing again.

Cheers!
Gripfast is offline   Reply With Quote
Old 09-05-2020, 10:23   #9
Writing Full-Time Since 2014
 
thinwater's Avatar

Cruisers Forum Supporter

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 7,073
Re: What is the point of having a heater if you can't use it when its cold out?

IMHO, reverse cycle is disfunctional in climates that get actual freezing, like the northern Chesapeake area. I had AC and propane heat on my PDQ.

The way I see it, I want to be able to winterize the AC system and still have heat in any weather. Having heat you can't use in frosty weather is frankly, useless.


The other thing is power. I don't need AC in the summer when anchored. It's nice, but I really only need it in marinas, where there is no wind. But in the spring and particularly the fall, there is nothing like a warm cabin at anchor. Glorious sailing, and then a nice little cabin on the water to relax in at night. Fuel based heat takes little power and can be run quietly on the hook. Some of my favorite nights were in the fall, with my wife, the heat purring along.


Install fuel-based heat.
__________________
Gear Testing--Engineering--Sailing
https://sail-delmarva.blogspot.com/
thinwater is offline   Reply With Quote
Old 09-05-2020, 10:31   #10
Registered User
 
Bill O's Avatar

Join Date: Jul 2015
Boat: Bruce Bingham Christina 49
Posts: 1,302
Re: What is the point of having a heater if you can't use it when its cold out?

Quote:
Originally Posted by 1affiah View Post
Many heaters will have an electric coil back up for this reason.
+1 Assumed the water would be too cold to get any heat out of it, purchased one w/an oil filled coil heating element for heating when I was living aboard and working in DC A couple of those years, the Potomac froze solid and we had some major snow storms. Was glad I had the heating element and the electric bill for the winter was ~$30/mo. for a 40' sailboat, so not too bad.

Our current boat has no heat pump and we use electric oil filled radiator type heaters to heat the boat in the winter.
__________________
Bill O.
KB3YMH
https://phoenixketch.blogspot.com/
Bill O is online now   Reply With Quote
Old 09-05-2020, 10:41   #11
Registered User

Join Date: Jan 2018
Posts: 2,240
Re: What is the point of having a heater if you can't use it when its cold out?

Quote:
Originally Posted by Bill O View Post
Our current boat has no heat pump and we use electric oil filled radiator type heaters to heat the boat in the winter.


These deserve a lot more credit than they get.

What warm, lovely heat they produce that really radiates out giving you a much nicer feeling than forced hot air.

Its the next best thing to wood stove heat.
Chotu is offline   Reply With Quote
Old 09-05-2020, 15:41   #12
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 8,615
Re: What is the point of having a heater if you can't use it when its cold out?

Quote:
Originally Posted by Rohan View Post
OK, this is as much a rant as a question, but I have a typical reverse cycle heating/AC system, and it won't work when the water temperature is below 40 degrees F.

So basically, what that means is, I can't use the heater when it's cold outside!! So what is the point?

Currently, the boat is in fresh water (the Potomac) Previously it was in partially salt water at a similar latitude (the Cheseapeake), and I didn't have this problem there. Does the the salinity/freezing point of the water make a difference for the operating threshold?
A reverse cycle heat pump isn't going to work with an ambient temp. 40 or less unless it has a heat strip as backup. It is what it is.
Cadence is online now   Reply With Quote
Old 09-05-2020, 15:43   #13
Registered User

Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft Catalina 381
Posts: 557
Re: What is the point of having a heater if you can't use it when its cold out?

Quote:
Originally Posted by Cadence View Post
A reverse cycle heat pump isn't going to work with an ambient temp. 40 or less unless it has a heat strip as backup. It is what it is.
With water cooled units, it's water temp that matters. High 30s is about the limit there, but the air temp can be as cold as you want provided the water is warm enough.
rslifkin is online now   Reply With Quote
Old 09-05-2020, 15:54   #14
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 8,615
Re: What is the point of having a heater if you can't use it when its cold out?

Quote:
Originally Posted by rslifkin View Post
With water cooled units, it's water temp that matters. High 30s is about the limit there, but the air temp can be as cold as you want provided the water is warm enough.
I believe he said the water temp was 40 or below.
Cadence is online now   Reply With Quote
Old 09-05-2020, 16:07   #15
Writing Full-Time Since 2014
 
thinwater's Avatar

Cruisers Forum Supporter

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 7,073
Re: What is the point of having a heater if you can't use it when its cold out?

Quote:
Originally Posted by Rohan View Post
OK, this is as much a rant as a question, but I have a typical reverse cycle heating/AC system, and it won't work when the water temperature is below 40 degrees F.

So basically, what that means is, I can't use the heater when it's cold outside!! So what is the point?

Currently, the boat is in fresh water (the Potomac) Previously it was in partially salt water at a similar latitude (the Cheseapeake), and I didn't have this problem there. Does the the salinity/freezing point of the water make a difference for the operating threshold?

There isn't enough difference in freeze point between DC and the ~ 20% salinity of the Annapolis area to measure.


However, the Bay does stay a little warmer than the Potomac due to shear size. But only a few degrees.



Get fuel-based heat. You can use it away from the dock too. Reverse cycle is for areas that merely get cool, not freezing.
__________________

__________________
Gear Testing--Engineering--Sailing
https://sail-delmarva.blogspot.com/
thinwater is offline   Reply With Quote
Reply

Tags
heater

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What type of heat system do people use on boats when its cold? videorov Liveaboard's Forum 86 04-01-2019 15:43
Its Not How Much Someone Costs, Its What You Bring to the Table. s/v Beth Our Community 27 28-02-2012 10:50
Argh . . . Can You Judge a Boat by its Name ? watergypsy Off Topic Forum 35 13-09-2010 05:06
Point No Point Lighthouse For Sale TaoJones Atlantic & the Caribbean 10 25-11-2007 08:14

Advertise Here


All times are GMT -7. The time now is 14:41.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.