Air Versus Hydronic Heater

[DeepFrz]

George, looks nice and comfortable on a cold windy day.

[jtsailjt]

Originally Posted by goboatingnow

There must be 100s of boats here with Eberspacher or Webasto air heater. All take air from inside the boat. I've actually never seen a external air intake.

Dave

The external air intakes may not be obvious. For example on my previous aft cockpit boat I installed the Espar unit in a lazarette, up against the transom, with a duct led to a vent in the side of the starboard coaming box where it couldn't be seen unless you had your face touching the cockpit seat. Even if I had not added the duct, the ambient air where the Espar heater lived was mostly dryer ambient outside air rather than recirculated air from inside the boat. For the installations you are familiar with where air is taken from inside the heated part of the boat, this type of installation misses out on one of the best benefits available to air type diesel heaters. I realize that it's not always possible to install the heater with an external air source but IMHO it's worth doing a lot of head scratching to figure out a way to do it if at all possible. I'm going through that "head scratching" phase for the installation of a heater on my center cockpit boat right now....

[jtsailjt]

Another consideration while installing an air type heater with an external supply of air is how to get that source of clean, external, dry, air without it being polluted by the exhaust. Since space on a boat is limited, it is desirable to have short exhaust and fresh air supply ducts just as long as you can somehow manage to have them separated enough to keep your heaters exhaust from being sucked into its fresh air supply. If your boat is almost always kept on a mooring or anchored so it's facing into the wind, that is easier to do than on a boat kept at a dock where the direction of the wind against the boat varies from port to starboard, from forward to aft.

[mub]

My humidity levels..

Firstly I need to qualify the boat usage.

We (4 to 6 of us ) shower on the boat and cook what we want. However I have a range hood / extractor above the cooker and 12 dorads.
She is well insulated.

I have no issues with humidity close to the heater. However in the fore head - which is about 40ft of duct work away from the heater often has condensation on the sail locker door and hatch.
If I add some additional heat there it is not a problem.

The issue we have is that the air really wants to heat the saloon and not bother getting to the end of the system.

Sent from my HTC One X using Cruisers Sailing Forum mobile app

[rw58ph]

What ever brand you install make sure there is parts and service in you area. We have the Webasto service every year as its our primary heating during the winter. I recommend you use an installer as they can help with the sizing, lay out, installation and they can sell you the boiler parts at the same price as will pay buying direct. So you sort of get their assistance/help for free. I did 80+% of the install and the install did the final 20% required for warranty. The system is size down to 0 F.

I would never install a warm air system on an existing boat. The boiler/hot water heating system is the easiest to install as only 1” holes are required for the hose, and hot water retains its heat longer than air does. We installed the Webasto in the engine room to keep the engine room and bilge warm and dry.

The Webasto draw the air from the engine room, through air vents from the out side. The interior air is drawn and heated through small heater exchanger units, similar to vehicle heaters, though out the boat. We have 7 exchange unites, 2 in the master stateroom/bath, 1 in each of the two small staterooms, 1 in the main bathroom, 1 in the galley/salon, and one in the salon. The hot water hoses are run through the cloths/storage closets so the boat is kept warm, 65+ degrees and bone dry.

If sized and installed properly there the boat should be dry and warm with no condensation.

[goboatingnow]

Originally Posted by jtsailjt

The external air intakes may not be obvious. For example on my previous aft cockpit boat I installed the Espar unit in a lazarette, up against the transom, with a duct led to a vent in the side of the starboard coaming box where it couldn't be seen unless you had your face touching the cockpit seat. Even if I had not added the duct, the ambient air where the Espar heater lived was mostly dryer ambient outside air rather than recirculated air from inside the boat. For the installations you are familiar with where air is taken from inside the heated part of the boat, this type of installation misses out on one of the best benefits available to air type diesel heaters. I realize that it's not always possible to install the heater with an external air source but IMHO it's worth doing a lot of head scratching to figure out a way to do it if at all possible. I'm going through that "head scratching" phase for the installation of a heater on my center cockpit boat right now....

They are usually mounted in the lazarette , but its still not outside air

dave

[lonesoldier0408]

From an install point, smaller hoses provide for an easier install. The ability to go over bulk heads, improve your chances of maintaining bouncy in an emergency. Heat retention of the liquid system should reduce fuel consumption. As heat rises, a low mounted system requires less effort to radiate than attempting to blow hot air down. Once out the nozzle, heat will rise immediately, floor will always be cold. We and our actions are the cause of the moisture that condenses on the cold spots. Air flow to remove condensation is the order of the day or a collection system to the bilge for disposal. More than one way to skin a cat. Heating and air conditioning principles are straight forward, "The air in the bowl can be cooled and the air trapped under a cover can be heated." Knowledge reinforced in Iraq..!

Sent from my KFTHWI using Tapatalk HD

[GeoPowers]

Many install challenges are the same for both hydronic and forced air systems, like mounting primary unit, control board, intake air/exhaust, etc. The hoses of a hydronic system are of course easier to install than air ducting. However, hydronic systems seem to me to be much more complex and difficult to install.

Challenges for installing forced air systems:
-Big duct work, which makes it harder to route to more than one location.

Challenges with hydronic systems:
- Hoses must make a loop, not one-way like air ducts.
-Heater cores/ blowers required, which take up space, need 12V wiring/fusing, air duct(s) (smaller and shorter than forced air), cutouts for vents, & vents. You want multiple heater cores/blowers throughout your boat or you give up zone heating and the great benefit (IMO) of hydronic.
- Heat exchanger for hot water system, plus additional valves/hosing for summertime isolation of the rest of the system if you want to use it as a hot water producer during times other than cold weather. Not installing means giving up another big perk of hydronic.
- Expansion tank mounting/space, at least 2.5 gallons or larger depending on the system.
- Increased 12V demand with all those heater cores/blowers cycling on/off. Often overlooked until on the hook and watching the battery monitor...

For fuel consumption, not sure about forced air since I've never had one on my boat and can't compare apples to apples. For the hydronic, the fuel consumption is based on the temperature of the coolant, not the air temp. Sometimes on milder winter days the heater will kick on to heat the coolant when the heater cores/blowers are off since the t-stat hasn't tripped yet. Probably less of a consideration the more cold it is outside!

Frank

[FlightPlan]

Mub: You need dampers in the Salon to force air forward. It is difficult to diagnose without more information, primarily the temperature control.

I have a test and balance company that does system set ups for new construction. We open all the dampers which are on all the grilles, measure the CFM at each grille, and total the CFM for all the grilles and compare it to the design specifications. We then start tapering the grilles to get the desired CFM to all the grilles as specified. Without getting into the weeds, it is not easily done in one pass.

I saying if the thermostat is tapering the output temperature before the forward head is satisfied, then you have a loosing battle.

If you are not inputting outside air in the system then you can't drive out the moisture. Also if that is the case, close the salon 75% and open the forward head 100%. That will drive up the heat forward and it will work back thru the salon to the return air fan grille.

[FlightPlan]

Originally Posted by GeoPowers

Many install challenges are the same for both hydronic and forced air systems, like mounting primary unit, control board, intake air/exhaust, etc. The hoses of a hydronic system are of course easier to install than air ducting. However, hydronic systems seem to me to be much more complex and difficult to install.

Challenges for installing forced air systems:
-Big duct work, which makes it harder to route to more than one location.

Challenges with hydronic systems:
- Hoses must make a loop, not one-way like air ducts.
-Heater cores/ blowers required, which take up space, need 12V wiring/fusing, air duct(s) (smaller and shorter than forced air), cutouts for vents, & vents. You want multiple heater cores/blowers throughout your boat or you give up zone heating and the great benefit (IMO) of hydronic.
- Heat exchanger for hot water system, plus additional valves/hosing for summertime isolation of the rest of the system if you want to use it as a hot water producer during times other than cold weather. Not installing means giving up another big perk of hydronic.
- Expansion tank mounting/space, at least 2.5 gallons or larger depending on the system.
- Increased 12V demand with all those heater cores/blowers cycling on/off. Often overlooked until on the hook and watching the battery monitor...

For fuel consumption, not sure about forced air since I've never had one on my boat and can't compare apples to apples. For the hydronic, the fuel consumption is based on the temperature of the coolant, not the air temp. Sometimes on milder winter days the heater will kick on to heat the coolant when the heater cores/blowers are off since the t-stat hasn't tripped yet. Probably less of a consideration the more cold it is outside!

Frank

I am assuming when you say coolant that you are using antifreeze, which has a different heat coefficient than water. I also assume that the temperature control is operating the liquid side of the system. Therefore, it would be prudent to lag the temperature control 4 degrees from cool to heat, and visa versa.

I have 4 packaged water source heat pumps on my boat that use sea water for the condenser side of the unit. They become inefficient for heating when the water temperature is below 45 degrees. The degeneration of efficiency in not linier in input to output of the unit. So when you are talking "hydronic" I am assuming that you are chilling and heating water to deliver to the "core" zone coils. If that water temperature is constant, then there should be a control valve to a thermostat to control the zone. I think that is an expensive and complicated system on a boat unless you run a generator full time like the big boats do.

One other point regarding the outside air discussion. Using outside air on the heat side pressurizes the vessel and forces air out of the boat thru the various leaks in vents and hatches. Recirculation systems are good for cooling, because the treated air returns to the evaporator coil, is condensed and dropped into the condensate pan and out of the boat thru the proper drain. If you guys have water in the pan, the fan will pick it up thru evaporation and put moisture back in the boat. One thing to check whether heating or cooling.

[rw58ph]

Our installations is controller by the room thermostat. The thermostat activates the boiler furnace to heat the water up to a temp. There is a temperature sensor in the coolant/water line that when the coolant/water reaches a temp of 120 degrees it allows 12 volt current to pass through to the exchange muffin fans. When the room thermostat shuts off it shuts down the boiler and the muffin fans. If the coolant/water gets up to 150 degrees another sensor will shut down the boiler only, but still allow the muffin fans to blow. Once the water/coolant has cooled down the sensor will allow the boiler to fire again until the room thermostat shuts off.

So the room thermostat turn on and off the boiler and fans. The fans do not turn on until the coolant/water gets up to temp, 120 degree, so no cold air is blown, and the coolant/water can not be over heated, 150 degrees, as the boiler will shut down. So the boiler and fans are not on/running unless there is a demand for heat from the thermostat.

As for 12 volts DC amp demand usage, the small muffin fans use less than a large air blower, and the boiler firing is about the seam weather its water and/or air. The primary reason we went with the coolant/water boiler is the heat requirement in the front main stateroom/head is about 40 ft and the air would cool down to much.

We started with a 2 zone heating system, but quickly change to one zone to heat the total boats at the same time to use the max heat available in the coolant water and reduce the number and length of times the boiler is firings. Our Webasto is the biggest model, 1010, 110,000 btu. Temps between 40 and 60 degrees we use 5 to 10 gallons per week, temps between 30 and 50 degrees we use 10 to 15, 20 to 30 degrees 15 to 20, and 0 to 20 degrees 20+ gallons. We use on average about 400 gallons per year, which also heats the hot water.

[Pau Hana]

Originally Posted by goboatingnow

There must be 100s of boats here with Eberspacher or Webasto air heater. All take air from inside the boat. I've actually never seen a external air intake.

Dave

Here in Seattle, it's very common for a heater to draw air from outside the boat to heat. The idea is to slightly pressurize the cabin, rather than recirculate the air already in the cabin.

We have a Wallas 40DT, which has 2 air inlets; the install instruction strongly recommend that 1 inlet (return air) take air from in the cabin, and the other (makeup air) take air from outside.

[GeoPowers]

Originally Posted by FlightPlan

I am assuming when you say coolant that you are using antifreeze, which has a different heat coefficient than water. I also assume that the temperature control is operating the liquid side of the system. Therefore, it would be prudent to lag the temperature control 4 degrees from cool to heat, and visa versa.

I have 4 packaged water source heat pumps on my boat that use sea water for the condenser side of the unit. They become inefficient for heating when the water temperature is below 45 degrees. The degeneration of efficiency in not linier in input to output of the unit. So when you are talking "hydronic" I am assuming that you are chilling and heating water to deliver to the "core" zone coils. If that water temperature is constant, then there should be a control valve to a thermostat to control the zone. I think that is an expensive and complicated system on a boat unless you run a generator full time like the big boats do.

One other point regarding the outside air discussion. Using outside air on the heat side pressurizes the vessel and forces air out of the boat thru the various leaks in vents and hatches. Recirculation systems are good for cooling, because the treated air returns to the evaporator coil, is condensed and dropped into the condensate pan and out of the boat thru the proper drain. If you guys have water in the pan, the fan will pick it up thru evaporation and put moisture back in the boat. One thing to check whether heating or cooling.

The diesel is combusted and heats a closed loop of coolant/antifreeze that has an expansion tank. This closed loop is circulated throughout the boat via hose to heater cores, which act as a heat exchanger and blower that converts the hot coolant/antifreeze fluid to warm air. The antifreeze is heated again by the diesel heater. Temp variances are minimized via an expansion tank. This system is separate from our air conditioner/reverse cycle heat pump.

[GeoPowers]

Originally Posted by rw58ph

Our installations is controller by the room thermostat. The thermostat activates the boiler furnace to heat the water up to a temp. There is a temperature sensor in the coolant/water line that when the coolant/water reaches a temp of 120 degrees it allows 12 volt current to pass through to the exchange muffin fans. When the room thermostat shuts off it shuts down the boiler and the muffin fans. If the coolant/water gets up to 150 degrees another sensor will shut down the boiler only, but still allow the muffin fans to blow. Once the water/coolant has cooled down the sensor will allow the boiler to fire again until the room thermostat shuts off.

So the room thermostat turn on and off the boiler and fans. The fans do not turn on until the coolant/water gets up to temp, 120 degree, so no cold air is blown, and the coolant/water can not be over heated, 150 degrees, as the boiler will shut down. So the boiler and fans are not on/running unless there is a demand for heat from the thermostat.

That's a nice set-up. In ours, the fans are controlled by a room t-stat, but it does no interface with the heater. Cold air is blown by ours until it warms up (about 10 min). Our heater runs separately so may run when the fans aren't running.

As for 12 volts DC amp demand usage, the small muffin fans use less than a large air blower, and the boiler firing is about the seam weather its water and/or air. The primary reason we went with the coolant/water boiler is the heat requirement in the front main stateroom/head is about 40 ft and the air would cool down to much.

I have 5 zones on my boat (three cabins/heads + two for the saloon). Four zones would probably wok fine, but this is what came with the boat (we're second owners). I think it would depend on how many zones you have for the DC usage, but I don't see the hydronic units being more 12V friendly unless you need more than one forced air unit for larger boats.

We started with a 2 zone heating system, but quickly change to one zone to heat the total boats at the same time to use the max heat available in the coolant water and reduce the number and length of times the boiler is firings. Our Webasto is the biggest model, 1010, 110,000 btu. Temps between 40 and 60 degrees we use 5 to 10 gallons per week, temps between 30 and 50 degrees we use 10 to 15, 20 to 30 degrees 15 to 20, and 0 to 20 degrees 20+ gallons. We use on average about 400 gallons per year, which also heats the hot water.

I'm running a Thermo90S, which I'm seriously considering upgrading to the 2010 model. I hear it is much more liveaboard friendly and requires less maintenance than mine. I'll probably talk to the Sure Marine folks about what would be needed for the conversion. We used to be berthed out of Everett, WA, and the system we have was installed by them.

Frank

[rw58ph]

My primary focus was to heat the front master state and bathroom with the minimum of diesel used. At the time we had a CAT propane catalytic heater in the salon and heat rises. So 5 of 7 exchangere where installed down in the state, bath and hallway. When the bow state room is 65 f the salon is 70+ f.

Since used an experience installer that was willing to work with me he knew exactly the design and how to keep the diesel usage to a minimum. He original had one zone but I had him change to two, salon and staterrooms, but soon agreed one zone has heat rises.

Best investment we made to the boat and one of the main reasons we been a live a board so long.