How hot does your diesel heater blow?

Tim Good

Tim Good

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I have just rebuilt a Webasto DW80 heater which heate hot water and pumps it round the boat to individual heat exchangers which then blow hot air into each cabin on thermostats. At full whack it is rated at 7.5kw and it is on a 43ft boat.

It is now working and I have bled the system and all the individual heat exchangers. However it only blows warmish air and not piping hot. I have never had a diesel heater before so are they meant to blow hotter air that this?

Fuel consumption wise it is certainly using it at the rate indicated which is 0.92L p/h at 7.5kw. For that I'd kind of expect it to get toasty quite quickly.

Either the setup has a problem or my expectations of a diesel heater are a little high?

Thoughts?
 
How hot is the water a) leaving the heater b) reaching the matrices c) leaving the matrices d) returning to the heater.

Is the heat going anywhere else, e.g. are your heating pipes heating the hull and keeping the mullet warm, are you warming your water or diesel tanks etc, heating the engine, calorifier etc etc.
Do the matrices' fans shift enough air?

Does the heater run at full chat for hours on end, or does it throttle back once the water is warmed up?
 
northcave said:
I have just rebuilt a Webasto DW80 heater which heate hot water and pumps it round the boat to individual heat exchangers which then blow hot air into each cabin on thermostats. At full whack it is rated at 7.5kw and it is on a 43ft boat.

It is now working and I have bled the system and all the individual heat exchangers. However it only blows warmish air and not piping hot. I have never had a diesel heater before so are they meant to blow hotter air that this?

Fuel consumption wise it is certainly using it at the rate indicated which is 0.92L p/h at 7.5kw. For that I'd kind of expect it to get toasty quite quickly.

Either the setup has a problem or my expectations of a diesel heater are a little high?

Thoughts?
Click to expand...
Heating water takes some time as it's circulating in the pipes / radiators.
Hot air heaters will deliver max heat faster than a water heater.
The heat from the radiator (heat exchanger) depends on the water temp going in and the surface on the radiator.
One of the benefits of water heating is better heat distribution in the boat - not a lot of heat at on point.
Do you have enough radiators to consume 7.5 kw?
 
My eberspacher certainly blows hot air. Not so hot that you can't stand in front of the vent, but definitely hot rather than warm. That's after about six metres of duct through the bottom of the cockpit locker and then along the uninsulated hull side below the waterline.

That's an air system; I'm not familiar with water ones but it certainly doesn't sound like yours is working right. Can you get at the coils inside the blower units to feel if they're getting hot?

Pete
 
I was initially a bit disappointed with my warm air heater (a 3.5 KW Makuni), which produced warm, but not hot, air, on a 40' boat, with about 8-9m of ducting. It always ran at max power. THEN I insulated the hot air ducting and it made a significant difference - the air is considerably warmer and the heater throttles back to half power as it is now reaching the required air temperature. Are your hot water pipes insulated? Does the hot air from your heat exchangers go directly into the cabin, or are there lengths of hot air ducting?

Neil
 
Matrix are quite inefficient at the temperatures generated by heaters like yours which throttles back to 2kw when the coolant hits 68C. Do you have a coolant temperature dependant relay output from the boiler for the blower(s)? Do you have it piped in parallel or series?
 
neil1967 said:
It always ran at max power. THEN I insulated the hot air ducting and it made a significant difference - the air is considerably warmer and the heater throttles back to half power as it is now reaching the required air temperature. Are your hot water pipes insulated?
Click to expand...

Yes I think that might be the first port of call. I'm surprised this wasn't done. There is a lot of ducting through to all cabins in uninsulated pipes. I just checked under one floorboard compartment and it is toasty warm. What type of insulation did you use in the end?

David2452 said:
Do you have it piped in parallel or series?
Click to expand...

I'm not totally sure but trying to figure that out. What is best practice?
 
I have a D5W running a single matrix serving the aft cabin, heads and a calorifier in a 42 foot centre-cockpit ketch.
In normal use I leave the matrix blower off until the system, including calorifier, is up to temperature. The heat coming out of the matrix then gets the cabin warm enough but not burning.
The plumbing is car heater hose insulated with foam and foil lagging.
One day I will swap the header tank which takes up cupboard space and effectively doubles the amount of water, for a sealed system as kindly described by David 2452.
I would also like to add a radiator or two to the main saloon if I can find something compact enough. Any ideas?
At the moment I rely on a Taylors drip-feed heater in the main cabin.
 
I have a 10kw Eber hydronic system driving 3 matrix heater, 9 hot air outlets and a large calorifier on a 46ft boat.

When I bought the boat I was disappointed with the heat output from the matrix heaters, warm air but by no means hot. 10kw should be enough to make the boat tropical, even in Scotland!

The system is pipe in parallel and all the hot water pipes are insulated with standard foam insulation. But when I bought the boat there wasn't any insulation on the hot air ducting, so I spent quite lot of time insulating the ducts with foil backed "bubble wrap". Most of the time was spent taking the furniture apart to access the ducting, which was obviously installed before the furniture was fitted. I also fitted some sound insulation to quieten down the fans in the matrix heaters.

Thinsulate would probably have been better, but I had several rolls of foil coated bubble pack left over from some work on the house, so I used that. I cut it into strips and wrapped around the ducting, securing with tie wraps and foil tape.

The difference is amazing, the air is now hot, almost too hot to hold your hand in front of any length of time and the thermostats trip off at 20 deg C quite quickly.

Although bubble wrap probably isn't as effective as Thinsulate, it doesn't absorb water, which may be an advantage if I ever have a flood of some description.

Hope this helps
 
northcave said:
You mean the temp range of -50 to +110C? Would a dry heater system really exceed that?
Click to expand...

A dry system air temperature is considerably higher that of a matrix based one, if the coolant is at say 70c then that is all the air can possibly be, more likely quite a bit less, the air distribution components of a dry system should be rated at 140 degrees.
 
David2452 said:
A dry system air temperature is considerably higher that of a matrix based one, if the coolant is at say 70c then that is all the air can possibly be, more likely quite a bit less, the air distribution components of a dry system should be rated at 140 degrees.
Click to expand...

Do they tend to be equally efficient? I appreciate the water versions help distribute heat further up the boat on bigger vessels whilst dry air gives instant heat... but in terms of heat for your buck which tends to be better?
 
northcave said:
Do they tend to be equally efficient? I appreciate the water versions help distribute heat further up the boat on bigger vessels whilst dry air gives instant heat... but in terms of heat for your buck which tends to be better?
Click to expand...

Not really something I have bothered to calculate other than capital cost, I suspect the difference in fuel consumption favours a dry system comfort level for comfort level but it's not comparing apples with apples, the suitability of the system for it's owners expectations and usage pattern come much higher up the list in my view.
 
duncan99210 said:
One point about a blown air system is that it supplies fresh heated air through the boat, helping to reduce if not eliminate condensation.
Click to expand...

Exactly, installed correctly that is, most seem to be either recirculated or dragging in air from a locker in my experience, mind you that situation does seem to be improving. Actually a matrix based system can do exactly the same but will really struggle in cold weather.
 
If your pipework is 15mm, that's quite small for 7.5 Kw, with Eberspacher D5WS systems, I use 18mm and with D10W, I use 20mm hose. The smaller diameter will restrict flow and heat output. Insulating the water hose and air duct will help heat output a lot. Armaflex closed cell insulation is good stuff and it won't absorb water.
 
PBooth said:
If your pipework is 15mm, that's quite small for 7.5 Kw, with Eberspacher D5WS systems, I use 18mm and with D10W, I use 20mm hose. The smaller diameter will restrict flow and heat output. Insulating the water hose and air duct will help heat output a lot. Armaflex closed cell insulation is good stuff and it won't absorb water.
Click to expand...

Actually I hadn't noticed the pipe size being used, for ALL Webasto water heaters it should be 22mm with minimum 15mm taps to the load and piped in parallel.
 
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