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Old 17-11-2014, 20:10   #1
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Diesel heaters- can I use existing ducts?

Can I plumb a Webasto or Espar diesel heater to my existing Cruisair HVAC ducts? I would prefer that to running my generator overnight in cold weather.
The guys at the boat show said no, but they also didn't give a reason, and weren't very interested in discussing with me.


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Old 17-11-2014, 23:42   #2
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Re: Diesel heaters- can I use existing ducts?

A qualified yes is the answer. AC Ducting is not usually very heat resistant and will become brittle or even melt depending on how close it is to the heat source. The heat from a reverse cycle AC is no where near what you'll get from a diesel or gas heater. In addition, it's ribbing is more resistance to air flow than good heater ducting and heater ducting appears to have a better reflecting surface that should help heat loss (or cold loss) on long runs.

Having said that you can keep using your AC ducting if it is far enough from the heat and you connect the heater initially to heater ducting. I did this before converting virtually all of my system over to heater ducting and had maybe 10ft of heater duct before in connected to AC ducting. Still the AC duct eventually became brittle. The only part my system that still has AC ducting is the run from the blower to a junction box.

The good news is your boat has the space already set up for heater ducting and heater ducting makes great AC ducting. There are by the way splitters("Y" tubes) which have baffles in them so shifting from the AC to the heater can be as easy as turning a knob or lever.

Two more things to consider about diesel heaters is how you'll use them. Several brands including Webastco and Espar are designed to run at top speed and heat. Otherwise they eventually carbon up. If you are going to only be using it caccasionally it shouldn't matter. If on the other hand you are going to use it frequently at low speed you may want to check this out. This also could also have a bearing on what size unit you buy. Second check the annual cost of having these things serviced. There can be a significant difference that'll add up quickly.

Good luck.
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Old 18-11-2014, 02:21   #3
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Re: Diesel heaters- can I use existing ducts?

I wouldn't use your existing AC ducts with a diesel heater. I installed a Webasto 16,000 btu diesel heater on my 46' ketch. When you turn it on... regardless of the setting, it goes through a pre-programmed start-up sequence which includes an initial slow start-up for about 2 minutes... then it increases to full bore heat output for 10 minutes or so. (It's part of it's cleaning soot process.) The air temp coming out the heat duct is 200 degrees! When running in the high setting. Normal AC duct is not designed for that high of temp. But maybe you could take out your AC duct and replace it with the high temp heater duct and use most of the down stream path for either. It was tough, but I found space to keep my AC as is and run separate heat ducting as recommended. I found I only had to run one (90mm) duct to my saloon and one to my aft cabin for the boat to be perfectly cozy even on the coldest of Winter days. I also ran the cold air return duct to the aft cabin. I installed one of those 90 mm duct Y-valves already discussed so I could put all of settings heat either in the saloon (when I first come on the boat) or some/ all the heat flow to the aft cabin when I turn the unit way down to a low setting at night. FYI- I close off my v-birth (just storage) during the cold Winter months... saves almost half of my saloon heat loss. Put the system in 7 years ago and we love it/ no issues.


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Old 18-11-2014, 07:10   #4
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Re: Diesel heaters- can I use existing ducts?

From experience in installing an Espar in my Beneteau 400 the information is correct, the heat will melt AC Ducting. The correct duct from Espar or Wabesto is pricey however the same product is used in Hot Air Organs, you can buy from a company in Cleveland, "The Cleveland Organ Co". it is about a third cheaper.


In my case I started from the heater with 100mm and reduced it down the line to 90 and then 80 and 75 mm at the branches, The reason is to increase the pressure to make the air flow better to the far end of the runs. Another little trick I was taught was to put the Y,s in backwards to allow the air to run straight down the ducts, You want to get as much air to the far end as possible then you can reduce the flow at the outlets ( which close) and get more air at the earlier outlets, if you allow to much pressure to escape the system to early you will not get as much air flow the end of the longer runs, ours works pretty good, btw we do not have a cold air return in the boat, we have the heater mounted in a cockpit lazzerette and it just uses outside air.


I have a few parts for an espar system 40% of oem price.
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Old 18-11-2014, 07:42   #5
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Re: Diesel heaters- can I use existing ducts?

Quote:
Originally Posted by malbert73 View Post
Can I plumb a Webasto or Espar diesel heater to my existing Cruisair HVAC ducts? I would prefer that to running my generator overnight in cold weather.
The guys at the boat show said no, but they also didn't give a reason, and weren't very interested in discussing with me.


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I know it's a temptation but I don't think it's a good idea. I installed an Espar system on my last boat and am in the process of installing a Webasto system on my current boat and both boats had a preexisting air conditioning system with ducting so I was tempted just as you are. Sometimes you have to be really creative to find a way to route all those ducts but it's worth it to be able to dry the boat and make it warm.

Besides possibly melting your AC ducting, I suspect that the Espar heated air would flow backwards through the air conditioners so you wouldn't get adequate heat distribution, particularly to more distant areas. Before I start cutting holes for the ducts, I spend literally hours and days considering just how I'm going to route the diesel heater ducting, and sometimes you even have to fabricate rectangular shaped ducting if the only available location through an area demands it. I've also used aluminum ducting originally intended as dryer ducting and it worked just fine.

One word of caution while cutting holes in the bulkheads to accommodate your ducting, watch out that you don't break your thumb or wrist! My Nordic 44 had some bulkheads that were "only" 3/4 marine plywood plus a layer of fiberglass tabbing on either side and that was hard enough to drill through with a 3" or 4" hole saw, but some of the main bulkheads had more than double that thickness with a layer of fiberglass in between the two layers of plywood in addition to along both sides. To avoid burning out your drill, buy or rent a big one that you use whenever space allows, and invest in the best hole saws you can find because cheap ones will quickly get dull, slowing down the whole process and causing more heat/wear on your drill as well as more risk of it "grabbing" and the torque being transferred back to your wrist or thumb. No, I haven't broken my wrist yet but I've what I felt were several very close calls. Good luck with your install!
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Old 18-11-2014, 08:21   #6
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Re: Diesel heaters- can I use existing ducts?

Regarding not having a cold air return and just drawing air from the cockpit. I'm sure you know that lowers your resulting heat output inside the boat since you are starting with much colder outside air... seems like it would be pretty easy to cut a 100mm hole in the locker and snake a return duct pipe to draw in your (much warmer) inside air. But regardless it's really important to make sure wherever the intake air is coming from that it's not restricted in any way. Forced air diesel heaters must not have any air restrictions on either outflow or intake sides or damage and/ or protection system shutdowns will be triggered as the firebox will reach over temp condition w/o proper air flow through the system. I do like the idea, however, being able to get some (adjustable ) amount of fresh/ low humidity air into the boat. One issue with Winter stays on a boat is condensation forming when the eventual high humid air from breathing and cooking comes in contact with a very cold hull. This moisture can cause mold/ mildew issues, especially in early Spring when hull temps are more favorable to growth. I do a monthly inside hull wipe with cleaner/ weak bleach combo and in Spring I keep 120v fans running in each main area with cushions/ access doors ajar that foils behind the scenes mold and mildew development.


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Old 18-11-2014, 10:23   #7
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Re: Diesel heaters- can I use existing ducts?

No. Our Webasto has new, separate duct work.
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Old 18-11-2014, 20:18   #8
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Re: Diesel heaters- can I use existing ducts?

I am hearing about the issue with AC ductwork melting or getting brittle, and that makes sense as it is higher volume, lower temperature design. I am also hearing a concern about reverse flow through AC unit- I would make a damper valve of sorts if I were to do this.

1. If I were to replace my AC ducting with more heat resistant ducting- other than cost, would there be a drawback? Is it too big in diameter since it is higher airflow system?
2. Does anyone think I am stupid for thinking of this? I really don't want to devote more locker space to a second set of ducts, and I suppose I can run the genset to heat the boat... I imagine once I factor in the price of components and value my time, i could probably replace most parts on my generator.


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Old 19-11-2014, 04:48   #9
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Re: Diesel heaters- can I use existing ducts?

Quote:
Originally Posted by malbert73 View Post
... 1. If I were to replace my AC ducting with more heat resistant ducting- other than cost, would there be a drawback? Is it too big in diameter since it is higher airflow system?
2. Does anyone think I am stupid for thinking of this?...
No problem having oversized heating duct. It will be much quieter.
You're wise to consider all implications of a modification.
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Old 19-11-2014, 05:49   #10
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Re: Diesel heaters- can I use existing ducts?

I agree no problem with larger ducting if it indeed larger. Most of the ducting for my Webasto ACs was 3". I put on a Wallas diesel system that also used 3". I know other brands use other sizes however.


One thing to consider is where are you going to use this heat - mainly while docked or cruising? In my case, I took a Florida boat to northern Europe and spent two winters in London. I was afraid the water would get too cold for the reverse cycle AC and diesel is very expensive there (and has to be carried in.) I found an electric duct heater built for RVs (caravans) in Denmark that I hooked into the AC/heater ducting that has worked like a charm. It has a very small foot print, quieter than the AC and uses a 2" duct (again no problem going from small to larger). Here is the url: Kronings :: Kronings Heat According to Kroning it will run on 220v 60hz as well as 50hz.


One other thing about AC heat, at least on my Webasto units, the blower runs constantly whether the compressor is engaged creating heat or not. Sleeping with cold air blowing on you, even it is at room temperature, is not something I enjoyed. The Kroning only blows air when it is heating (or going through a brief cool down cycle).


Finally consider how the return air will work. On the Wallas system, I ran a return duct from the saloon to the heater. So hot air enters the sleeping cabins and then travels to the Saloon to be reheated. I am not sure if Webasto or Espar use a return air system so this may not be a consideration with their products.


BTW we still used the diesel heater a lot while cruising. Northern Europe can be cold in any month.
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Old 19-11-2014, 09:11   #11
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Re: Diesel heaters- can I use existing ducts?

Quote:
Originally Posted by malbert73 View Post
I am hearing about the issue with AC ductwork melting or getting brittle, and that makes sense as it is higher volume, lower temperature design. I am also hearing a concern about reverse flow through AC unit- I would make a damper valve of sorts if I were to do this.

1. If I were to replace my AC ducting with more heat resistant ducting- other than cost, would there be a drawback? Is it too big in diameter since it is higher airflow system?
2. Does anyone think I am stupid for thinking of this? I really don't want to devote more locker space to a second set of ducts, and I suppose I can run the genset to heat the boat... I imagine once I factor in the price of components and value my time, i could probably replace most parts on my generator.


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I think it could be done if you can find a valve that would stop the hot air from leaking out through your AC unit(s). Maybe even a manually operated shutoff would be OK since you'd normally be using either heat or AC, but not both on the same day. If you replaced the AC ducting downstream from the shutoff valve with heat resistant ducting, that should solve that problem and you wouldn't have to replace all the AC ducting, just that portion that's downstream from your shutoff valve. To avoid condensation related issues when you are using that same ducting for AC, you'd want to insulate it if it didn't come that way. Maybe you can buy heat resistant, insulated ducting? Even though the AC ducting is larger diameter than diesel heater normally is, as long as it's sealed tightly at all the joints, the airflow at the outlets will be unaffected. I use 3" wide metal tape to make sure I have no leaks at any of the intersections in the ducting. I like it because, unlike duct tape, it's easier to remove and doesn't leave such a sticky residue, plus it doesn't get brittle over time and you can squeeze it tightly around oddly shaped objects such as hose clamps so it makes a good seal.

One comfort issue is that normally, AC outlets are located high in the living space but you'd really prefer to have your heat outlets located as low as possible so your toes can enjoy the heat too.

For sailing in cold climates, a diesel heater is such a big upgrade from reverse cycle AC which requires running the genset!

Even on very cold days I turn it off at night but the first person awake in the morning can turn it back on to take the edge off without waking everyone else aboard.

If you're leaving your boat during a hot day and expect to return late at night when it will be much cooler, to avoid that damp, cool feeling when you return, if your heater is on a thermostat, you can leave it set so it will come on when the boat cools in the early evening.

Offshore you can leave it on so no matter how cold and damp it is while on watch on deck, the inside of the boat is a warm, dry haven no matter how nasty it is on deck. If you did that with a genset and reverse cycle combo, you'd use a lot more diesel and the noise of the genset would eventually get on some peoples nerves, especially if you are under sail rather than motoring. I wouldn't worry about putting hours on your genset though because they are made to run almost continuously. It's the short cycles where it doesn't get thoroughly warmed up that kills gensets prematurely. Running it all day while offshore is better for it than running it for a short time just for a quick shot of heat in the morning.

If you have a heat outlet in your shower area, you can use it as a drying hanging locker where the off watch hangs their foulies so when it's once again their turn to go back out on deck they can don warm, dry clothing instead of the same clammy feeling clothing they removed hours ago. It makes a huge difference in attitude and comfort. Also, with a heat duct in your shower area, before showering you can make it 80 degrees in that small area so there's no temptation to waste hot water just trying to get warm. 65 or 70 degree air is fine when you are dry and dressed, but when you're wet and naked, it feels COLD!


I think it's an interesting problem and if you decide to go ahead with it, would enjoy seeing a diagram of your system and what you use for ducting and shutoff valves. I don't think it would work on my boat because I have two AC units located at opposite ends of the boat but if your one set of ducting is set up so it reaches everywhere you want heat, it might work. I can appreciate your reluctance to undertake the installation of a separate set of ducting when you already have ducts, but the heat ducting is much smaller diameter and I find that I can usually locate it in a locker fastened against the top of it so most people never notice it's there and it doesn't steal hardly any usable space.
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Old 20-11-2014, 09:58   #12
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Re: Diesel heaters- can I use existing ducts?

I have had two Espar systems in two different boats, I suggest you do not use the same ducts for air and heat, as stated you want the ac outlets high and the heat low. The heat ducting warms the whole boat, it is like a long warm snake, does a great job to reduce the moisture in the boat. In the total budget the ducting is a smaller item, it is the heater, the outlets ( use the right ones, the others will melt) the y,s, the thermostat. You can get the Espar and Wabesto parts a lot cheaper from a truck dealer than a marine dealer. You just need to be sure you use double wall stainless exhaust tubing and wrap it with asbestos. Trust me on this, it gets very very warm, ( like hot as hell)
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Old 23-12-2014, 06:41   #13
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Re: Diesel heaters- can I use existing ducts?

Thanks everyone for your replies. Very helpful.

2 more questions:
1. on a 40 foot sailboat (mine is an 87 Tartan, so not as cavernous as today's 40 footers), can you get away with a single main cabin duct if you sleep with cabin doors open? I would imagine the heat would convect.

2. Webasto or Espar? Looks like espar may be less expensive? Why?
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Old 23-12-2014, 07:40   #14
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Re: Diesel heaters- can I use existing ducts?

Actually air doesn't move very well on its own (except drafts!). But some of this depends on how cold it is outside and how far away. and how warm you like it in the sleeping area. Boats only have a R value of about a cardboard box so when temps drop to high 20s- low 30s there is a lot of heat loss. The two ends of the boat have a disproportionate amount of their area's hull/ bulkhead exposed to outside temps on the other side. So while SOME of your main cabin warm air will waft into the sleeping area, it likely will not be enough to make up for the extra heat loss occurring in that area. I can easily get a 10 degree difference on our aft cabin if I shut off the duct. A 120v or 12v fan positioned to push the warm into the space will help... but as you know moving air that is only so-so temperature can actually make you feel colder.

I know it's a pain to run ducts in boat environment (got the T-shirt) but well worth having a warm and cozy boat for years to come without noise/ added issues of fans. If the duct route goes under the bunk there is an added benefit of warmed (well... less than icy cold) mattress. We also use a heated mattress pad to warm bed to 'toasty' before turning in. (It then gets turned off)

My duct route also went by the head. I added a 2" floor vent which feels very nice in the morning and it's louvers can be shut if max heat is needed elsewhere. But we usually just leave it open and seems to help maintain even heat throughout boat (46 Cal ketch). Good luck.


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Old 24-12-2014, 08:14   #15
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Re: Diesel heaters- can I use existing ducts?

I agree - move at least some hot air to the farthest areas away from the return that you can reach. Keep your return intake low so it pulls in the cooler air in the cabin/boat. Same with hot air outlets so the hot air can rise and then get sucked into the heater return when it cools.

Heating blankets and very small space heaters can help if you can't get a duct somewhere like a head. You can use a flexible closed cell foam with an aggressive adhesive to line lockers and under headliners to add some insulation. This is very easy to apply and cut. It also comes in different thickness if I remember properly.
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