Diesel Heater Outlet Size Planning - 4 x Spaces To Heat

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Hello,

I have a Mikuni model MY30AFD-2 air heater with 80 mm ID outlet. Currently it has 2 x 80 mm outlets, aft cabin and saloon. I will be rerouting, extending and increasing the number of outlets by two into: fore cabin and waterproof cupboard.

I am looking for advice on sizing of the outlets. The saloon is obviously the largest space by far, then the aft cabin, fore cabin and lastly the locker for the waterproofs. Is it worth stepping down pipe for the smaller spaces or just run 80 mm and use the open / close dampers to adjust / balance air flow in the cabin spaces. I assume that at least one outlet must never be closed so that the hot air always flows.

The heater is mounted under the aft cabin bunk so the flow is from the aft cabin, saloon, water proof locker in the forward heads, fore cabin.

Any advice appreciated.

Available dimensions of ducting from Mikuni web site here

Thanks,

BlowingOldBoots
 
I went the other way and cut down from five outlets to two. One day I might fit a second heater for the three abandoned outlets - the pipework is still in place.

The reason I did it was that five outlets were just too much. The runs of ducting were simply too long and any heat that set off for the forecabin never seemed to make it.

Have you considered fitting a second heater to go with the new ducting?

By the way, the loss of the outlet that went to the wet locker is one of the downsides of the mod I made. However I find nipping onto a pontoon for shorepower and using an oil-filled radiator and de-humidifier with the gear hanging up in the shower compartment was always the best way to dry things.
 
There is a good Eberspacher guide for ducting ( which I cant locate now!!) if you cant find for mikuni.
One suggestion could be just to run the proposed ducting along walk ways first to be sure that you have sufficient heat where you want it. If ok then install the ducting runs properly.
 
Don't forget to insulate the ducting with 3M Thinsulate or similar, it'll make a significant difference to the heat coming out of the end of the duct, it's really worth the additional cost.
And
Make sure the insulation is rated for the very high temperature the hot air will be close to the heater. I can remember the temperature rating required, but it has been discussed on this forum many times.
 
pcatterall said:
There is a good Eberspacher guide for ducting ( which I cant locate now!!) if you cant find for mikuni.
One suggestion could be just to run the proposed ducting along walk ways first to be sure that you have sufficient heat where you want it. If ok then install the ducting runs properly.
Click to expand...

Mikuni don't seem to publish the same level of advice that Eberspacher do. I guess it's reasonable to assume similar fan performance. The problem with adding too much ducting, elbows, Y-joints, etc, is that the added friction just slows the airflow.
 
pcatterall said:
There is a good Eberspacher guide for ducting ( which I cant locate now!!) if you cant find for mikuni.
One suggestion could be just to run the proposed ducting along walk ways first to be sure that you have sufficient heat where you want it. If ok then install the ducting runs properly.
Click to expand...

Thanks for the tip, a quick google and trawl through some of the sites produced the guide. It describes how the coefficients for each fitting and pipe length must not exceed a certain number when added up.

https://www.butlertechnik.com/downl...e_Installation_Guide_Airtronic_D2_D4_&_D5.pdf

Although not directly comparable, about 8 m of 80 mm ducting and the four outlets and Y pieces would easily exceed the maximum of 10. Not an option then for my 4 outlets as I doubt that it is not that much different for Mikuni.
 
Last edited by a moderator:
Thanks everyone for the advice, a second heater may be an option as the Minkuni web site does suggest that 2 units are used for my plans.
 
Insulation is far cheaper than a second heater and probably just as effective. Four inch loft insulation wrapped round and covered with plastic sheet and held with cable ties is the most cost effective method.
 
An odd theory but working on how a lot of large shops are heated with small heat sources would be to have an outlet close to the entrance to "block" the cold air so possibly either sice of the companionway (just think the blast of heat from the fans and you walk through the doors into a department store). It may not be so useful for large boats with cabins I agree, but on a modest boat with only the v-berth door open it could work?!?
 
petehb said:
Your existing unit won't drive 4 outlets efficiently unless two of them are blocked whilst the other two are being used.
Click to expand...

I was wrong about the Mikuni web site information: -

http://www.mikuniheating.com/MY30_M4.cfm

This kit is for providing heat to four areas of the boat. The air from the heater is split in 4 directions by the addition of three 'Y' branches included in the kit. The second, third and fourth outlets have open/close vents so you can control the air flow. The kit includes an exhaust silencer for exceptionally quiet operation - so you don't disturb any neighbours at night! The electronic thermostat operates the heater automatically between 3.5kw and 1.75kw output. The motor can also be run on its own to provide cool air circulation in the summer.
Click to expand...

It looks like it can supply four spaces with 10 m of 80 mm hose all the way. It could very well be limited and only work effectively in the saloon as you suggest.
 
When I was installing on Play d'eau, the engineer said the duct diameter must increase the further it has to go to decrease the drag and allow the hot air to flow more easily. Otherwise the air slows down and becomes ineffective.
 
Piers said:
When I was installing on Play d'eau, the engineer said the duct diameter must increase the further it has to go to decrease the drag and allow the hot air to flow more easily. Otherwise the air slows down and becomes ineffective.
Click to expand...

I was wondering if going up to 100mm would help. There are 80mm x 100mm reducers easily available online as is 100mm insulation, ducting, lots of options on eBay. Thanks for passing on the installers advice.
 
BlowingOldBoots said:
I was wondering if going up to 100mm would help. There are 80mm x 100mm reducers easily available online as is 100mm insulation, ducting, lots of options on eBay. Thanks for passing on the installers advice.
Click to expand...

On the other hand, you may be constrained by the size of the available gaps and spaces to run the ducting.
 
Piers said:
When I was installing on Play d'eau, the engineer said the duct diameter must increase the further it has to go to decrease the drag and allow the hot air to flow more easily. Otherwise the air slows down and becomes ineffective.
Click to expand...

Surely increasing the duct diameter will slow down the airflow?
 
pvb said:
Surely increasing the duct diameter will slow down the airflow?
Click to expand...

Exactly, so it'll come out of the vent faster. Whereas if it was more constrained in the ducting and flowed faster it'd come out of the vent slower. Simple when you think about it. :)
 
pvb said:
Any idea what's happened to Mikuni heaters? ......
Click to expand...

I don't pvb, my interest has been limited to improving what is already onboard. A lot of the ducting had been damaged and during the refit all of it was removed anyway. The unit has proven reliable, hence my reason for keeping it.
 
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