Diesel Heater - Fresh air from outside or inside?

[Rosco]

These are many discussions on this question. Let's assume that the professional installs properly and no CO is leaking into the cabin as that's tragic, horrid but another topic. New appliance, pro install. This is a condensation and / or heating warmer air is more efficient question.

 

[Jerry VB]

Since the exhaust exits the boat, the combustion air must come from outside the boat via one path or another. If not, the boat would collapse in on itself due to the vacuum. ;-)

Since the combustion air must come from outside the boat, the question is reduced to whether it comes via a duct directly to the heater or whether it comes via leakage paths. I would expect ducting would be better than leakage; leakage implies uncontrolled drafts and drafts make you feel cold.

In practice it probably doesn't matter. Adding an external air supply duct after installation seems like a fairly simple matter which could be done if the drafts are objectionable.

 

[Rosco]

Thank you Jerry,
This is from my current (but sold) boat which has a Wallas stove/heater unit with similar furnace. I should have thought of the old manual as it is a diesel furnace (air exchange type unit)..

"Make-up air taken from the cabin is typically warm (because the furnace has already warmed it), moist (because of condensation and respiration) and oxygen poor (because of respiration). Makeup air taken from outside the cabin is typically cool, dry and oxygen rich. If a blend of these kinds of air can be fed into the location of the furnace, then heating, drying and oxygen replenishment to the cabin can be accomplished. If the furnace is mounted in a hanging locker or closet, that space will become a very active drying and warming space. This can be a very important addition to any boat. If the furnace is mounted in an away space like a lazarette, then warm air from the cabin should be ducted to the mounting area in order to improve furnace efficiency. All ducting to and from the cabin should be insulated if it passes through unheated areas."

So either or from the manufacturer Wallas, in this scenario. a blend is optimal. I think a drafty older boat has a natural amount of "breathing" occurring especially with the companion way hatch slightly cracked open as we typically do.

 

[Loren Beach]

Our new forced air furnace draws the air to be heated from outside, and both our installer and surveyor say that's a requirement. The air for combustion comes from a separate intake point, and I would note that there is no lack of air flow -by design- into the boat, given the ravenous appetite your engine has for air.

 

[Nick J]

A heater is on my list of items I would like to install. One part I can't figure out is how to route the duct (with a forced air system) or coolant hose (with a hydronic system) through the cabin. Can people who have already gone down this path post some pics of their install? 32,35, and 38s with the forward head would be particularly helpful. Exhaust and air intake photos too

 

[Loren Beach]

Can people who have already gone down this path post some pics of their install? 32,35, and 38s with the forward head would be particularly helpful.

Not much clue about your particular model, have I. However.... from helping others with some installs over the years and talking to pro's, I decided to keep our boat's duct scheme as simple as possible. One reason is that with the more duct work you have, the more flow/friction loss you have and the further you push the air, the more heat it loses. I know owners who said they were somewhat sorry that they spend much time and money putting in a small duct to a forward cabin or head.

Best advice, and backed up by installers, is to have a larger duct pointing into the main cabin, aimed forward away from the companionway. The moving warm air will find its way into the ends of the boat, albeit at a slower rate.

That is how we did it in our boat, altho with our aft head we did easily install a 3 foot small branch outlet for the head. That is just a lucky break for any boat with an aft head configuration.

However you do it, you will really like forced air heating.... tap an icon on a screen or push a button and you have warmth!


EDIT: I did add an engine coolant-driven small heater to our cabin, many years ago. It puts out copious amounts of heat, but of course only when the diesel is operating. The pair of 5/8" coolant hoses are indeed easier to route than an air duct. Note that all of the "hydronic" boat heaters do use a lot of power to run a separate fan for every radiator, and also have to use power to pump their heated fluid all around the boat interior. They have distinct advantages and... disadvantages.

 

[Rosco]

Our new forced air furnace draws the air to be heated from outside, and both our installer and surveyor say that's a requirement. The air for combustion comes from a separate intake point, and I would note that there is no lack of air flow -by design- into the boat, given the ravenous appetite your engine has for air.

That makes absolute sense and clarity for my brain. Thank you Loren. The drying effect is accomplished in an elegant way. Thank you so much.

 

[Rosco]

Not much clue about your particular model, have I. However.... from helping others with some installs over the years and talking to pro's, I decided to keep our boat's duct scheme as simple as possible. One reason is that with the more duct work you have, the more flow/friction loss you have and the further you push the air, the more heat it loses. I know owners who said they were somewhat sorry that they spend much time and money putting in a small duct to a forward cabin or head.

Best advice, and backed up by installers, is to have a larger duct pointing into the main cabin, aimed forward away from the companionway. The moving warm air will find its way into the ends of the boat, albeit at a slower rate.

That is how we did it in our boat, altho with our aft head we did easily install a 3 foot small branch outlet for the head. That is just a lucky break for any boat with an aft head configuration.

However you do it, you will really like forced air heating.... tap an icon on a screen or push a button and you have warmth!

A heater is on my list of items I would like to install. One part I can't figure out is how to route the duct (with a forced air system) or coolant hose (with a hydronic system) through the cabin. Can people who have already gone down this path post some pics of their install? 32,35, and 38s with the forward head would be particularly helpful. Exhaust and air intake photos too

Awesome, thank you very much. God what a great group on this site.

 

[Pete the Cat]

I have had a Wallas Diesel heater on my Tartan for 25 years and love it. It is an expensive option, but I think it is worth it as I think it is more sophisticated software (lessens maintenance) than others that are made for trucks and it comes with all the stuff to install it on a boat. Draws combustion air outside from a collar around the the exhaust tube--which keeps the exhaust tube cool. The room air is drawn from both inside the boat and from outside--as noted previously. I have no clear idea how I would route the duct work in my Ericson to get forward in the boat due to the TAFG--I might be able to mount it in the hanging locker in the aft cabin and run the ductwork under the stove and sink to the salon, but that is a guess-I am currently using a Heater Buddy, but I really do not like it---it produces a lot of moisture--the Wallas dries things out. I used it to dry out the boat even the years I spent in the tropics--getting rid of damp is a great plus of forced air heaters. Very important to insulate the ductwork (I think I got my insulation from Home Depot) of any forced air option or you will lose much of your heat in the cold unreachable places.

 

[Nick J]

Not much clue about your particular model, have I. However.... from helping others with some installs over the years and talking to pro's, I decided to keep our boat's duct scheme as simple as possible. One reason is that with the more duct work you have, the more flow/friction loss you have and the further you push the air, the more heat it loses. I know owners who said they were somewhat sorry that they spend much time and money putting in a small duct to a forward cabin or head.

Best advice, and backed up by installers, is to have a larger duct pointing into the main cabin, aimed forward away from the companionway. The moving warm air will find its way into the ends of the boat, albeit at a slower rate.

That is how we did it in our boat, altho with our aft head we did easily install a 3 foot small branch outlet for the head. That is just a lucky break for any boat with an aft head configuration.

However you do it, you will really like forced air heating.... tap an icon on a screen or push a button and you have warmth!


EDIT: I did add an engine coolant-driven small heater to our cabin, many years ago. It puts out copious amounts of heat, but of course only when the diesel is operating. The pair of 5/8" coolant hoses are indeed easier to route than an air duct. Note that all of the "hydronic" boat heaters do use a lot of power to run a separate fan for every radiator, and also have to use power to pump their heated fluid all around the boat interior. They have distinct advantages and... disadvantages.

I hadn't thought about the power draw of the hydronic heater. That could really add up with a water pump, and at least two exchanger units with fans. The route on my 35-3 is really difficult, but I could pipe the outlet of a forced air unit to the back of the quarter birth and the return above the ice box in the galley (next to the propane panel). That would be a relatively easy install. Are there any concerns with getting the heat all the way to the V birth? You and the other aft head folks are lucky when it comes to heater installs. At least the exhaust run is simple on all these boats.

Rosco, keep us updated with your install.