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Hydronic Heating System

 

 

Congratulations on purchasing a hydronic heating system from River Marine. Prepare yourself for an adventure as you contemplate the installation. This guide is designed to help make the installation a little bit more manageable and enjoyable. This is a guide only, and all the rules are not written in stone. Some applications require that the rules have to be modified slightly. If you do find yourself in a situation where the rules must be stretched, give us a call at River Marine, and we will try and present the pitfalls and options to you.

Getting Started

Before we get started, we must walk through some preliminary planning. A bit of extra time in the planning stage can result in the savings of many many hours of extra labor. Take the time to read this guideline in it’s entirety before proceeding with any work. This is not a good time to break open the rum.

Skills Required

There is no magic required to successfully and professionally install your system. Basic electrical skills, plumbing skills, and woodworking skills will all get their workout during the installation. If you are short of any of the above, enlisting the help of the family pet or a friend may be enough to supplement your skills to the point where the project may be completed without mishap. If the family pet or friend are not available, then it is possible to bring in professional trades to finish the aspects which you do not feel comfortable.

Tools Required

A standard home handyman selection of tools is usually enough to complete the job. The minimum requirements would be: Measuring Tape

Selection of Scewdrivers Reversible Drill (cordless or other)

Selection of Wrenches

Caulking Gun

Selection of Pliers

Sharp Chisels

Selection of wood bits

Proper Electrical Crimping Tool

Notepad and Pencils

Masking Tape

There are a few specialty tools that will make the job a bit easier, such as an angle drive ½ inch drill and a selection of hole saws. These tools may be rented from River Marine for a nominal fee usually $2.00 or $3.00 per day. Please call in advance to schedule your use of these tools.


(Click on pic to see full size plan)

Basic Concepts
In a hydronic heating system, there are three major components: the furnace, the distribution system, and the control system. The furnace burns diesel fuel, heats a mixture of water and antifreeze, the circulation pump pushes the water through industrial heater hose around the boat. Water to air heat exchangers with small low current fans are installed in the distribution hoses wherever we want to deliver heat to the boat. The water/antifreeze solution returns to the furnace, is reheated, and the cycle runs continuously until the control system is satisfied, and the system shuts down until the control system again calls for heat.

Furnace Location/Installation
Deciding on the location of the heater does not depend on location within the distribution system. Typically, the water only loses about 7-10 degrees F as it passes from one end of the system to the other. A heater placed at one end of the system will produce almost identical amount of heat as another heater at the other end of the system. Usually the critical element regarding the installation of the furnace is the routing of the exhaust. Each furnace has a limited maximum length of the exhaust flue. This will vary from heater model to heater model. Consult your owner’s manual, or contact River Marine for specific values for your heater. Ideally, we would like to keep the exhaust run as short as possible. The flue and the insulation on the flue are quite expensive, so budget concerns should get some leverage on this decision.

Thru Hull Location
The exhaust gasses generally exit the boat via a double wall stainless steel thru hull fitting. The location of the thru hull fitting is the first critical decision. Ideally it should exhaust in the aft quarter of the boat. It must be located above the water line of the boat. Consider the boat underway in severe conditions, and try to find a location that is always above the water. We do not ever want to find sea water creeping back up the exhaust flue, and back into the combustion chamber. Salt water in the combustion chamber is not a warranty issue. Under swim grid installations is not a good idea, as water will find its way up the exhaust when the boat is hit with a following sea. Once we have settled on a waterproof location, there are couple of other points of view to be considered. Exiting from the side of the hull can also create problems. The gasses exiting the thru hull are in the vicinity of 700-800 degrees F. Fenders and raingear which inadvertently get hung in front of hot exhausts tend to melt, and burn. So do docks and other boats rafted up to you on that side of the boat. Igniting clothing, fenders, piles, docks, and boats is considered to be very bad form in many marine circles, so if you want to maintain your social status, keep these factors in mind when you locate your thru hull.

Furnace Location
Ideally, the furnace will be mounted above the thru hull. Any water which did find its way into the flue from a passing wave, or over zealous washing person would then naturally flow back out. There are many installations where the heater cannot be located high enough above the thru hull to guarantee that we will not see water intrusion. In these applications we take a somewhat different tack. We can locate the thru hull low, and bring the exhaust flue up inside the boat forming a gooseneck, and then drop back down to the heater. Any water finding it’s way into the exhaust flue must pass over the top of the gooseneck before it can even begin thinking about finding it’s way back to the heater. This does solve the water problem, but it does create another small problem. When the exhaust gasses leave the heater, they are very hot. As they pass down the flue, much heat is lost to flue, and the gasses cool. As they cool, some of the gasses condense, and form a thin film of liquid on the inside of the flue. As it is uphill to the gooseneck, there is no place for the liquid to escape the flue. They will collect in any low spot in the flue, and will cause premature failure of the flue. In these applications, we would suggest the installation of a condensate drain in the exhaust. Essentially it is a collector box made of heavy guage stainless which provides a small copper drain to drain into the bilge or collector box.

Now that we have settled on the location of the exhaust, lets take a look at the heater itself. It should be located in a reasonably dry position, away from any direct or indirect salt spray. Once the heater is installed, it should provide years of trouble free operation. Somewhere down the road, the heater will require service. As most service technicians work by the hour, the more difficult it is to remove parts of the heater, and reinstall them, the more costly will be the repair bill. Reasonable clearance on all sides with reasonable access to the heater will make the installation easier, and any future service easier. The heater itself does not get above 180 degrees F, so there is no need to be excessive with clearances. It must be mounted in upright position, and securely fastened to the boat. I hate to think of the damage that a run away heater could inflict in a nasty seaway. If it is to be mounted on a shelf, make sure the shelf is securely mounted to the boat. If you are bolting the heater to a bulkhead, you may want to install grommets between the heater and the bulkhead to provide some acoustic isolation from the rest of the boat. The heater does generate some noise during operation, and the better we isolate or insulate the boat form the heater acoustically, the quieter will be the operation. We have had several customers build plywood boxes around the heaters, and install soundproof insulation to the boxes. They claim the heaters can approach the level of "very quiet".

Exhaust Insulation
The exhaust does get quite hot, so reasonable care must be taken with respect to clearances. There are several different types of thermal insulation available for the exhaust flue. Unprotected, it is a danger to anything within 6 inches, and anything which inadvertently touches it. When passing the flue through utility areas of the boat, were gear will never be stowed against or fall against the flue, minimal insulation would be one layer of rated insulation. As added protection double or triple layers may be added. One quick note on flue insulations: although rated insulation looks and feels like fiberglass sock, it is rated to much higher temperatures. Fiberglass socks and blankets begin to break down around the 600 F point. They will discolour severly and emanate some rather foul smells. There is a very real danger of fiberglass sock or blankets actually catching fire. Ensure that all exhaust insulation is rated for at least 1000 F . In locations where the flue may be in close proximity to flammables, there are high temperature blankets available to protect adjacent surfaces. Particular care must be taken where a flue passes through a bulkhead or shelf. Make sure the flue is secured. Violent motion in a seaway may cause the flue to slowly move closer to flammables than originally intended. Make sure the insulation is secured to the flue. Again, vibration and vessel movement may change the integrity of the insulation blanket. Periodically check the integrity of both the insulation and the flue. Replace any questionable components immediately.

Exhaust Material
There are 3 different types of exhaust flue available. The least expensive is the spiral wrap stainless steel flue manufactured in North America. It is fairly flexible, but cannot be bent around a corner with a radius any smaller than about 8 inches. It is also not vapor proof. This means that flue gasses can escape into the boat interior. This is very dangerous, as carbon monoxide is a by product of combustion. We do not want to leak any of these gases into the boat if we can avoid them. There is generally also a smell of diesel left in the boat from this type of exhaust. It would only be satisfactory to use this type of exhaust in locations where the heater and complete exhaust system is in a compartment or locker completely separate and sealed from the living quarters of the boat, and vented separately. The most common type of exhaust is the spiral wrap exhaust from Germany, which has had the adjoining spirals crimped together to prevent any leakage of exhaust. This exhaust flue is quite a bit more expensive, but does have the safety factor we are looking for. It is also very flexible, accepting radiuses down to about 3 inches. The last option is a rigid exhaust made from tubing and fittings. Joints and splices are either welded or clamped. This is perhaps the best exhaust, but the fittings are difficult to find and welding in place is a rather expensive option.

Safety Concerns

Carbon monoxide is a by product of the combustion of all fossil fuels. It is the same weight as air, so it does not tend to rise and exit the boat through the vents. It is odorless and colorless, so it is impossible to detect without specific monitoring equipment. It is also very deadly, so if waking up dead is not on your list of things to do, pay particular attention to these warnings. At a minimum, inspect your exhaust system annually and if there is any doubt at to the integrity of a component, replace it. Any leakage in the exhaust system should be rectified immediately.

 

Distribution System

Overview
The heat is distributed around the boat in ¾ inch heater hose. The simplest system is a single loop starting at the furnace, going to one heater, and on to the next, and the next until you have worked your way around the boat, forming one large loop. On larger boats, a manifold is installed, and separate loops service separate areas of the boat. As we mentioned earlier, there is very little difference in performance of a component of the system relative to where it is in the system.

Radiators
The wall mount radiator is the least expensive method of delivering heat to the boat, and does not use any electricity. The down side is that it does consume valuable wall space and floor space in the boat. We have seen fin and tube radiators built right into the woodwork, and it has worked fine. But it is an incredible amount of work. The other down side of radiators is the fact that it is very difficult to balance the heat in the boat without adding a balancing valve at each radiator.

Valves
There is a danger in having valves anywhere in hydronic system. If a valve is installed in a system, and it is inadvertently closed, it shuts off the flow of water in the distribution system. If the water is not flowing in the system, it is also not flowing through the heat exchanger in the furnace. If it is not moving through the furnace, there is a very significant possibility that when the furnace turns on that the water in the heat exchanger can boil before the safety limit cuts the flame out. If the water in the heat exchanger boils, we now have to deal with steam. This causes immense pressure on the system, and may result in exploding hoses or pipes causing severe personal injury if you are in the vicinity of the rupture. So if you haven’t guessed it by now, we are not very ardent believers in any sort of control valves in the distribution system.

Blowers
Most systems use small water to air heat exchangers equipped with a small low draw fan (blowers) to heat the various rooms. They are quite small and compact, and do not interfere with floor space. They come in a variety of configurations. Consult with River Marine for the right blower for your application. Each blower is about 7000 BTU. This interprets into slightly more heat than a 1500 watt electric heater. If you can comfortably heat a room with one 1500 watt electric heater, one blower should be able to maintain comfortable temperatures in that room. An average stateroom will require one blower. The salon area, if it has lots of window, will probably require 1 ½ or 2 blowers, and if it is very large, it may require more. Heads should receive at least ½ a blower. The more warm dry air we can circulate through the head, the less moisture and the less odor will be present in the boat. Once you have chosen the right blower for the room, and the preferred location in that room, you must ensure that you will be able to route the hose and the wiring to that blower.

Hose
The hot water is distributed around the boat in a ¾ inch industrial heater hose. There are many different grades of hose, and the Voice of experience tells us that this is not the place to cut corners with a special deal you found somewhere. Good quality hose does not kink around sharp bends, and seals tightly with one hose clamp on fittings without applying excessive pressure on the clamp. Excessive pressure on hose clamps will cut the hose, and lead to exasperating problems down the road. Make sure the clamp is sitting square on the hose before tightening. When routing the hose, one should try to avoid a lot of "ups and downs". Ideally, the hose should drop down between the heaters, and rise up to the heater where we have a purge point to allow air to be purged out of the system. When the installation dictates that we do have an up and a down, install a purge point at the peak of the rise if you are having trouble purging the system. When feeding the hose through the bilges and lockers of the boat, tape the end of the hose to prevent any foreign matter from entering the hose. Debris caught up in the system can cause premature failure of the pump (non warranty). Secure the hose with DJ clamps or wire ties to prevent movement and undue chafe and wear of the hose. When the hose passes through bulkheads, make sure the hole is large enough that it will not wear away at the covering. Chafe protection should be added wherever wear could be a problem.

Copper Pipe
Copper pipe may be used in areas where you want to drop a little more heat than you would with hose, such as hanging lockers, linen lockers, and wet lockers. Do not use copper pipe in lieu of the hose for the distribution system. The fittings used with copper pipe create too much resistance to the flow of water for the low power pumps that we are using.

Expansion Tank
When water is heated, it will expand in volume, and as we cannot compress a liquid, huge pressures will develop, the system will leak, and there is a good chance that the first mate may not talk to you for weeks. To accomodate this problem we install an expansion tank in a closed system, such as these, to provide a pocket of air which will compress when the water expands. The expansion tank should be the highest point in the system. It should be mounted so that when water is added to the system, it will flow by gravity to the circulation pump. This would generally dictate that the expansion tank is the last piece of equipment on the intake side of the pump. You should provide some easy access to the top of the expansion tank. You must occasionally check the water level in the system, and if you can peer down the filler spout of the tank easily, you will be more likely to check the level. When filling the system, make sure the tank is only about 1/3 full of liquid. The remaining volume should be left as an air pocket. Remember to never remove a hot radiator cap.

Hot Water Tank
Most boats are equipped with a hot water tank which has a 110 volt electric element, and a heat exchanger inside the tank for heating the domestic hot water with the coolant from the engine. How we integrate the hot water tank into the hydronic system requires some careful thought. We can leave the hot water tank alone, and just continue to heat the domestic hot water off the engine. This is fine when the boat is tied to the dock, or under way a lot, but if you are at anchor for a couple of days, you do not have any hot water.

The second easiest method is to tie the engine cooling together with the hydronic system, and we seem to have the best of both worlds. The problem with this solution is we have now introduced the engine cooling to our heating system, and the possibility of leaks and expensive damage to the engine are increased significantly.

The next choice is to install a system of valves to include or exclude the hot water tank to the engine system or the hydronic system. The problem here is that two years down the road, you may forget which valve does what, and at some time you may inadvertently close the wrong valve, with possible disastrous results. Warranty on the furnace does not cover overheating of the heat exchanger in the furnace caused by external water flow problems. This method of dealing with the hot water tank does not rate very high on our scale of options. Each heater has factory specifications as to what the minimum volume of water required in the system. If you do install a "summer loop", make sure that there is still more water in the system than the minimum requirements stated in the owner’s manual.

The next method of heating the hot water tank would be to leave the engine completely out of the heating of the hot water tank. This means does mean that the furnace must run in order to develop hot water, even in summer. This is not necessarily a negative point. It is very good practice to let the furnace run even in summer months. The maintenance on a heater which runs only a couple of times a year is far higher than the maintenance on a heater which runs regularly..

The last option on domestic hot water heating is to install a water to water heat exchanger between the hydronic system and the engine. This method does provide good separation between the two systems to prevent the loss of coolant from the one system from affecting the other system. It also provides engine preheat when the heating system is running. This type of system must have an electronic zone control so that the circulation pump in the hydronic system is activated when the engine running. We have often heard the argument that this method poses a problem because the water in the hydronic system must circulate throughout the boat, thus generating excess heat in the boat specifically in summer time. Though it is true that there is a bit of heat generated in other sections of the boat, this is not necessarily a problem. The hoses are generally routed under the floor, and in lockers. If you check these area during your summer cruising season, you will find that there is significant condensation against the hull. The small amount of heat generated by the hose tends to help keep these areas dry. The blowers themselves radiate very little heat unless the fan is on, and what little heat they do generate is well appreciated in terms of keeping the boat lockers dry.

Control System
Each system should be installed with a master on/off switch. This switch shuts the entire system off and on. It should be located in a convenient location for the operator, and clearly marked and identified.

The control system is the brains of the hydronic heating system. It is the control system which tells the furnace to turn on, and it tells the system which part of the boat to deliver the heat. The most basic control system consists of a simple thermostat which controls the furnace. When the thermostat calls for heat, the furnace starts, the circulation pump starts, and the blowers start. All components run until enough heat is delivered to satisfy the thermostat, at which point the system shuts down until the thermostat again calls for heat.

The next level of sophistication involves the installation of a zone control. With a zone control, we can add any number of thermostats and aquastats to the system, and when one of these devices calls for heat , we deliver heat only to the area of the boat where the thermostat or aquastat is located. For detailed instructions regarding the installation of the zone control, please read and follow the instructions which come with the zone control.

Warm Air Only Aquastat
Normally, the blowers begin to blow as soon as the thermostat calls for heat. Generally, this means the blower is blowing cold air until the water in the system warms up. This can last for several minutes. This can be somewhat of an annoyance if the blower is blowing the air directly on your feet or legs. A warm air only aquastat delays the fan until the water temperature has reached approximately 100 degrees, so that when the fan does begin to blow, it is blowing warm air. The aquastat must be clamped to a metal surface somewhere in the system. The expansion tank is generally a good place. When installing the aquastat, insert some heat conducting grease between the aquastat and the metal surface. Make sure the clamping mechanism does not short across the contacts of the aquastat. Consult the installation manual with the zone control for details regarding the wiring of the warm air only aquastat.

Hot Water Aquastat
If your system has a zone control, we can install an aquastat in the hot water tank. This unit can turn the furnace on independent of the room thermostats, and circulate the water in the hydronic system until the water is hot in the domestic hot water tank, and then shut the furnace off again. The aquastat is adjustable, so you can dial the water temperature which you require up or down as you wish. The zone control box has a disable switch which will disable the hot water aquastat when not required. To install the hot water aquastat, you have to remove the upper shroud from your hot water tank. Then remove the insulation. The aquastat is coated with heat conducting grease, and placed on the top of the hot water tank. The wires must be attached to it at this time, and led out through the electrical connector at the existing control panel of the hot water tank. The insulation is then placed back in position on the tank, and then the shroud must be replaced. Consult the installation manual with the zone control for details regarding the wiring of the hot water aquastat.

Wiring Details
Each furnace has wiring details slightly different from each other. Consult the owner’s manual form your furnace for details regarding the wiring, and if you have any questions, consult River Marine.

Commissioning the System
Now that all the blowers are installed, the hose is all clamped and secured, the wiring is complete, we can think about commissioning the system. The antifreeze solution in the system serves several purposes. The primary function is to prevent freezing in cold weather. The secondary function is to inhibit internal corrosion of the components in the system. Most automotive antifreezes satisfy this requirement. Do not use non toxic RV antifreeze in the system, as there are no corrosion inhibitors present, and this will result in non warranty premature failure of components.

There are two choices as to how we purge the system. The first way is to simply hot wire the pump so that it will begin to circulate the water. The other way is to disable the burner in the furnace, and activate the system. Some furnaces come direct from the factory with the burner disabled. Consult your owner’s manual for the furnace. After you have disabled the burner, you must turn the system on with the master switch, and then turn a thermostat on to provide a call for heat to activate the pump, Premix your antifreeze with water before adding it to the system.

Do not try to blow water through the system with a garden hose, and then add antifreeze afterwards. This method has two inherent problems. It is very difficult to judge water/antifreeze concentration with this method without spilling copious amounts of antifreeze into the bilge or environment. Although this is a very effective method for blowing air out of the system, it does not provide any indication of a purging problem in a system. If you installed the system without a lot of ups and downs, the system should self purge itself. If a system is difficult to purge, it will show up on the initial purge. It is much easier to install additional purge points during the installation, than when the owner is 200 miles up the coast, and experiencing problems. When a garden hose is used for purging, the installer is never aware that there is a problem in the first place.

Slowly add the antifreeze at the expansion tank until it is full. If you have followed our instructions, gravity will make the solution flow to the pump. When the tank is full, you may now turn on the pump, and begin to circulate the water. Continue to add water/antifreeze to the expansion tank as the pump pumps it through the system. When you can no longer add any water to the system, go to each purge point in the system, and let any air out. Continue around the boat checking each purge point. Check to see that there is always water in the expansion tank. You can peer down the expansion tank, and if the water is moving freely in the system, you will be able to see the water movement in the tank. Once you are convinced that the water is circulating, shut the pump down and re-enable the burner.

Test Fire

We are now ready for the test fire. Take one last look at all aspects of the system, and make sure that all hoses, exhaust fittings, and wiring is complete. Make sure the master switch (if so equipped) is in the "ON" position, and make sure there is a thermostat calling for heat, the furnace should cycle on. It may not ignite the first time around, as it may take a couple of starts before the fuel has been drawn up to the combustion chamber. If the furnace cycles off after a few minutes, simply shut off the master switch, and turn it back on. This resets the controls within the furnace, and it will now try to light again. This procedure may have to be repeated several times, depending how far the fuel supply is from the furnace. If after several tries, the furnace does not start, check the trouble shooting procedures in owner’s manual.

After the furnace starts, check to see that the hoses are getting warm. Check the exhaust system for leaks. There will be considerable fumes and a bit of smoke burnt off the exhaust flue during the first couple of hours of operation. This is entirely normal, as the metal in the pipe does have a thin film of oil on it from the manufacturing process. Check for excessive heat around all the exhaust components. If you installed a fan delay aquastat, check to see whether the fans started or not. Walk around the system, and check all hose connections for drips or leaks. If you overfilled the expansion tank, you may get some dripping out the overfill. Collect any excess antifreeze and dispose of in a safe manner. While you are waiting for the boat to warm up, go back over the system, and check all the wiring and hose. Add any final hangers or holders that you may have missed. Check all your electrical connections to ensure they are not in any danger of getting tangled up in gear, or short circuiting.

After the boat comes up to temperature, check that the system shuts down when the thermostat is satisfied. Check to ensure that the appropriate fans are being controlled by each thermostat. Check that each thermostat actually does control the furnace.

So now that everything is done, the boat is warm, you are allowed to pour yourself a rum and start dreaming of winter cruise destinations. If nobody willing to give you a pat on the back for a job well done, then give yourself one and pour yourself another rum!

© copyright 2006 River Marine Supplies and Distributors 1023 Clark Drive, Vancouver, B.C. Canada V5L 3K1