Originally Posted by Dockhead
I've thinking about heating systems for my hypothetical new boat.
I sail in cold places and plan to sail in even colder places, so heat is mission-critical and even a life safety
In my opinion diesel-fired hydronic systems are functionally superior to other types of heat, but they have a big disadvantage in that the furnaces are not easily user serviceable, and they do need service from time to time.
So I thought to back up the hydronic system with a pot-type heater with coils, maybe in the pilot house. Something which would allow you to see the flames, which would be cozy.
One reason why the hydronic furnaces coke up and require service is running with light loads. It occurred to me that two birds might be killed with one stone by installing TWO of them in series, a small one and a larger one. You could run both when you need max heat -- initial warming of the boat, or really cold weather. Then shut one down and continue on the small one for maintenance heat. There would be two of them, so if one stopped working while cruising in a remote
place, you'd still have the other. No special control system would be required. Just have two control panels
and do it manually. I wish you could get a readout of what heat stage each furnace is using -- they do Low, Medium, High, and Power, and I wish to hades that I could see which at any given time.
If complexity were not object (it always is an object, so this is purely hypothetical), other things on my dream wish list:
1. Engine and generator cooling
circuits spliced in with plate-type heat exchangers.
2. Some kind of heat storage so that the engine or generator waste heat could be stored.
3. Separate kerosene (paraffin) tank to supply the heaters periodically, to burn off carbon and extend the service interval.
4. Radiators instead of fan coils wherever possible for zero power consumption
. Maybe supplemented with fan coils for when high output is needed.
I would think that this would be robust enough for remote
area polar cruising. You could carry parts, diagnostic harness, and even a complete spare furnace, if you wanted to.
You bring up a topic near and dear to my heart after living and boating
for over 30 years now...
I can offer some feedback from both living on land and boats in cold climates.
Your numbered points are spot on, and I think you will need both radiant [passive] and fan forced capability at your heat dissemination zones. [zoned, thermostatically controlled radiators and fan forced heat exchangers- based upon experience elaborated upon below.]
Also consider radiant heat under the sole where applicable- in addition to radiators and fan forced exchangers. Amazingly efficient and silent... [I installed this under the framed floors in my home in Fairbanks...]
RE: Heat storage: Install the largest, best insulated, heat exchanger capable water tank you can fit [or more than one... I believe the IsoTemp SPA line is very cost effective, but may not be large enough for your application if you had only one... Here is my blog post about ours
Also use the engine(s) as a heat sync plumbed into the hydronic loop. [more below...]
I'll briefly outline experience and expand on what I would consider doing if I were building a new boat...
First, I agree that hydronic is the way to go for fast BTUs in cold climates. [I had a Webasto hydronic (I don't recall
which model) on a Tayana 47 and loved it.]
boat came with a forced air Espar installed, and we dedicated a tank that only holds [untreated] #1 fuel
oil for it- drastically reducing maintenance requirements.
Before we go further north with our current
boat, I will add hydronic, and keep the forced air to mitigate running one or the other at low settings- the same reason you outlined with two hydronic units in series. [I have no where to install a drip heater without extensive remodel effort...]
Both offer the advantage of choosing where to run the ducts/hoses. e.g., You can heat select lockers and stowage areas; attach hydronic hose [heater hose and/or pex tubing] runs under seating/berth areas to heat the seats/mattresses, etc.
Ventilation: I am always harping on people to do as you mention and keep the ventilation open on their boat- especially in winter- for all the reasons we are already familiar with.
However, having lived on a Valiant Esprit 37 for a few winters [and many summers...] in Prince William Sound, Alaska
, [where it would reach -28C several times each winter] I can attest to the fortitude it takes to keep the ventilation going when you can't keep the boat as comfortable you would like.
[Side note: I installed a very reliable, double vented Sigmar drip stove (separate intake and exhaust
vents to prevent blow-outs from back-pressure during high wind
gusts...) Nothing like a sooted cabin and no heat during a cold windy night at anchor
How to solve the issue of fresh air exchange without loosing too much heat?
In our homes in interior
Alaska [and many other cold climates around the world] we use Heat Recovery Ventilators. [HRVs; not to be confused with ERVs used in hot climates...]
e.g., I installed a Canadian made Venmar 3000 in my home in Fairbanks and wouldn't hesitate to put on on my boat... That particular unit is not sheet metal, but rotomolded polyethylene. The only metal is the [AC] fan motor. It is very compact, lightweight, quiet, and offers HEPA air filtration. At 84% efficiency, that will keep your boat dry with lots of fresh, clean air when you are in cold Wx without dumping your heat.
An HRV makes a huge difference in quality of life in a climate where we have snow on the ground over half of each year...
This will resolve mold
and allergen issues and allow you to seal up your normal ventilation during cold Wx- preserving heat and actually improving air quality.
Ducting requirements: Run discharge ducts as high up as possible, and in as many cabins as convenient. A single
return duct is all you need, near the headliner
, and in the main living area if possible (to draw all the air discharged into the cabins to this area...)
If you did this, you could also consider a forced air heater to supplement your existing hydronic heater and cover your needs for redundant heat and balancing use of the heat plants based upon need and to keep them running on high for reduced maintenance.
RE: Hydronic plumbing
1) Do plan to plumb in any coolant loops from engines so you can pre-heat them and/or use them as heat syncs and of course, run your hydronic heating off the engine when motoring...
i.e., Why let the main engine cool down when it is a centralized radiator? Alternatively, reduce the amount of heat the engines receive, but keep them warm to reduce cold wx related maintenance and condensation.
I did this on the Tayana 47 and it was marvelous since both engines were centrally located in an island of cabinetry amidships.
2) Bleeding hydronic loops, following is an excerpt from one of my blog posts regarding heating systems on boats
: [Several of those posts will link back to discussions on this forum...]
Bleeding air from hydronic loops can be quite a chore as the top of each loop is not always conveniently accessible. [I know ours aren't...]
To make this easy, we use small, cheap, automatic air bleeders used in home boiler heating systems. Typically we install a T at the top of each hydronic core and install the air bleeder in the highest port of the T. [i.e., Where the coolant return line to the engine exits the core.] Basically, air bleeders need to be installed at a high point in each coolant loop.
I'm happy to elaborate on any of these points further if that would be helpful.
Best wishes planning your new vessel!