Wet heating systems

lanerboy

lanerboy

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Hi All

After a post by Wonky on another one of my threads I thought I would start a new thread regarding wet heating systems and what people think of them, my next boat I am thinking about only has reverse cycle heating so I need to put some sort of heating system on her and was thinking about a webasto air heating system maybe 2 smaller units one for below and one for in the cockpit area.

I am also interested in peoples thoughts on a wet heating system that webasto do does anyone have this and what is the purchase / fitting cost like compared to a traditional hot air system, we used to have a wet heating system in out bessacarr caravan and it was fantastic very quiet and the heat output was great but what they like on boats

cheers shawn
 
lanerboy said:
Hi All

After a post by Wonky on another one of my threads I thought I would start a new thread regarding wet heating systems and what people think of them, my next boat I am thinking about only has reverse cycle heating so I need to put some sort of heating system on her and was thinking about a webasto air heating system maybe 2 smaller units one for below and one for in the cockpit area.

I am also interested in peoples thoughts on a wet heating system that webasto do does anyone have this and what is the purchase / fitting cost like compared to a traditional hot air system, we used to have a wet heating system in out bessacarr caravan and it was fantastic very quiet and the heat output was great but what they like on boats

cheers shawn
Click to expand...

Would have wet system over hot air any day, its a bit more difficult to retrofit so check for access first, not a huge difference in cost but certainly worth the extra if using boat all year round.
 
Years and year and years and years ago, just after I left school, I was trained as a heating engineer (National College) - degree level.
One of the subjects on our course was human comfort.
Without going into it too much (and I certainly can't remember the details), the human body is comfortable under certain different criteria.
1. Air Temperature
2. Humidity
3. Radiation - everything around you "radiates" energy.
There are probably others but I can't remember.
To answer the OP's question, the big ones are Air Temp and Radiation.

A warm air heating system has to warm up the air (obviously) and then has to warm all the items in the room/area before they can emit enough radiation to be comfortable.
This means that the air temp ends up higher than it, specifically, needs to be.
This is a high air temp - low radiation system.

Conversely
Consider a warehouse where it is too costly to heat all the air - you will often find high temperature black pipes "radiating" heat - usually from above.
Here, we have a high radiative component versus low air temp.
In this case the radiative component has to be very high to be anywhere comfortable to the human body.

So, in the good old days, we were taught that liquid filled radiators provide just the right compromise.
A radiator "radiates" just the right amount of radiation heat and also heats the air without overheating it.

So, back to the OP's point
Reverse Cycle is generally more uncomfortable for heating because it has to have a higher air temp.
Likewise, a Webasto system would also have to overheat the air to eventually heat the items in the room/area.
So the ideal system, IMO, would be a wet style radiator system similar to a conventional household radiator heating system.

In the Med, we only need a little heating during some of the winter months so I have a couple of "oil filled" radiators that we simply plug in.
One in our cabin is all we need to provide really comfortable conditions.
Most of the year, we remove them and store them in a lockup.

A very boring post - I'm afraid.
Just wait until JOHN100156 reads this
 
I am a great advocate of wet systems, with the proviso that there is sufficient space to fit enough radiators of some kind to properly load the boiler, the Webasto range of water heaters ranges from 4kw right up to 30kw so there is something to suit almost every size of boat. Generally speaking the actual unit is quite a bit cheaper than air KW for KW but the cost of rads and tube is higher than ducting so a complete install works out similar. The advantages are noise reduction, capable of heating water, and simpler to install (finding rad space apart) disadvantage is they take a little longer to warm the boat than a blown air system. Most of my full time liveaboard customers would have nothing else so that is some kind of an indicator. Like all heating systems the quality of the fit is paramount. Should you wish I have the dedicated marine install manual which covers every aspect of the system that I can send you a copy of, just drop me an email address by PM.

Edit to add that it may be possible to simply incorporate the boiler into your current A/C system, we certainly fit them with Webasto classic cool air con.
 
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I have a wet system on Little Ship and the only downside is the time to heat up the rads. Once running it's great. I also get hot water from it and can choose DH-water or C-heating or both if needed.

As David 2452 said getting enough space for rads can be a problem but you can fit heater matrix which are much smaller. You need to be aware that power can be a problem if you go down the route of matrix as they have fans to circulate the air.

From a personal point of view, I wouldn't change what I have but i will state that installation was time consuming as mine is all copper pipe work and not plastic. Towel rail in the heads and warm towels is something of a luxury ...... when it's on.

Tom.
 
fantastic system and well worth it ( especially for some winter boating in the Clyde !). Our has a matrix in every cabin with a thermostatically controlled fan behind each one with control in every cabin so you can set each to suit your requirements.Heated towel rails in the heads is another excellent benefit. Havent a clue what it costs to install as our boat came with it on but suspect it could be a few quid but def worth it in our part of the world.
downside , it does take about 8-10 minutes to get up to temp but then again it takes the same to cool down
 
I had Wesbasto wet system on a 38ft catamaran in the UK and it worked very well. As per Hurricane's post, it was much more comfortable than the warm air system on the current boat, with the fab addition for a boat that we had a towel radiator in the heads which warmed up clothes and dried out wet coats etc. Also the piping (which was plastic push fit stuff) seemed to warm up the fabric of the boat somewhat. Given a choice I would go for rads over air any time.
 
Keto in Poole are your best bet and very highly respected, not cheap but it will be done right and will qualify for the three year on board warranty, they will also be able to intigrate it into thje A/C system if suitable which will significantly reduce costs.
 
Hurricane said:
......
A very boring post - I'm afraid.
Just wait until JOHN100156 reads this
Click to expand...

Tee-hee, boring, I love this sort of thing: As you say Mike, internal environmental temperature (tei) is a function of air temperature (tai) and mean radiant surface temperature (tmr), roughly a 50/50 split. Its important for any heating system to ensure the correct system is selected for any particular purpose.

If using an air heating system, you can generally quickly heat the air in a space, it has a low thermal heat capacity so any heat introduced into it will change its temperature quickly. This air then needs to slowly raise the fabric temp, we have all experienced this, the boat air temp is high but it take a while for it to fully heat up. Now with a well deigned air system you can get very close temperature control.

If you can recirculate the air only mixing the required amount of fresh outside air, you save a lot of heating energy. Problems with 100% fresh-air systems is that when you warm air from -1C to say 30C (typical design criteria from say a heater might be to supply air at say 10C above the room temp, so say 30C - eberspacher supplies at higher temp to reduce duct size). This will expand its volume hence the air is dryer, the relative humidity of the supply air heated from -1C saturated is around 30C at 13% relative humidity....

With a reverse cycle heat pump, in heating mode, it works just the same - on/off control of a heating coil over which air is passed (refrigeration side is more interesting but is another matter - Superheat6k can do that bit, defrost/what happens when outdoor section freezes, etc) but they are the same but a far more energy efficient system (you get 3kw or more heat for 1kW electrical energy in. I am a great believer in heat pumps but there are problems when trying to achieve close temp control I will explain if asked.

Now with a radiator system, which has both a radiant and convective heat component, we get a hot surface and warm convective air currents permeate the space raising the tai and tmr. People see a rad, think arrrh thats hot, colder people sit near to it, warmer people sit away from itm they find there space so despite greater much greater temperature fluctuations in the space the incidence of complaint is generally lower!

But remember the air systems both heat and ventilate the space.

For closest control, say a close control lab or pharma project, we use an air ventilation system, mix fresh air if we can, pre-heat, heat recovery, cool, dehumidify or humidify and re-heat to get the precise supply air temperature and humidity that we need to offset the sensible and latent space loads.....we use low temperature hot water or steam and chilled water. Its quite an art if you like that sort of thing, just commissioned a close control lab for Imperial College may put up the results later, currentlt designing a pharma project fro GSK in Chittagong, Bangladesh.....
 
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Play d'eau's heating system needed re-working. We already had reverse cycle air con and heating but it had proven to be really poor at heating for many reasons. The decision was made to find a separate good heating system.

In discussion with suppliers, we chose a hot water system. Why? Two decisive reasons precluded a hot air system. First, hot air ducting in this length of boat would cool the air too much and reduce the airflow by the time it reached the end of the boat, particularly unwelcome given our master cabin was in the bows. Second, access along the boat did not allow sufficient space for large enough holes to be cut to take the diameter required for hot air ducts.

Apparently, the cut-off point for water versus hot air is some 50’.

Also, a hot air system dries air really efficiently. Why is this an issue? Dry air causes dry eyes and dry and sore throats. Hence, another tick in the box for choosing a hot water system.
 
Thanks Piers I am really interested in the wet heating system after reading all the positives on here, sorry to ask what may be a silly question but where would they fit the radiators on a 40ft sports boat and do the radiators have fans on them to circulate the air

cheers shawn
 
lanerboy said:
Thanks Piers I am really interested in the wet heating system after reading all the positives on here, sorry to ask what may be a silly question but where would they fit the radiators on a 40ft sports boat and do the radiators have fans on them to circulate the air

cheers shawn
Click to expand...

There's the rub with a wet system, you may be able to get finrads in somewhere, you may not even need them if it can be incorporated into the AC system as the air handlers will distribute the heat. There are numerous options available including fan assisted and only a survey and a searching discussion on site will properly answer what is the best solution for you, your budget and your usage pattern.
 
lanerboy said:
Thanks Piers I am really interested in the wet heating system after reading all the positives on here, sorry to ask what may be a silly question but where would they fit the radiators on a 40ft sports boat and do the radiators have fans on them to circulate the air

cheers shawn
Click to expand...

There are many ways this can be achieved. Play d'eau has one radiator in the saloon, and the rest of the areas use small fan matrices. I've already sent a copy of the report I did for the Fleming Owners' website to LJS, but if someone can tell me how to add a document to the forum, I can add the info here. It also has pics in it to explain.
 
My Sunline had a fan assisted heater matrix, and we never used it, due to the noise of the fan, it was really intrusive. You also have to be careful that the water does not freeze up when you are away from the boat. Popped the matrix our first winter.
 
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