Tumble dryer ducting

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BarryB45

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Hi
I have to install a vented tumble dryer about 3 meters from the external wall where the vent is located The ducting has to run behind kitchen cabinets and so there is restricted space . Is it ok to use the flat rectangular ducting as opposed to the circular type? Will this cause any issues in terms of performance or safety?

Thanks in advance
 
Have you no space above or below the units?
 
I recently had something vaguely similar at home.

My Siemens (conventionially vented) tumble dryer started producing cold air instead of hot (it turned ot to be the overheat trip button had popped out for the first time in 14 years).

This prompted me to wonder about a replacement - i.e. vented versus condenser versus heat pump.

There are now comparatively few vented models available - no Siemens and only one Bosch model. The vast majority are condensers and heat pumps.

I did speak to my regular (and much trusted) domestic appliance engineer. We spoke about vented v condenser and I told him that I'd checked and a new Bosch vented dryer has the rear outlet in a slightly different position compared to mine and would need either a repositioned hole in the wall (almost impossible to do due to physical limitations), or use of a piece of flexible duct with a fairly sharp offset to get it to match up with the existing hole in the wall.

He cautioned against the offset saying that ideally the vent ducting tube needs to come straight out from the dryer with no sharp bends as dust/fluff could/would build up in the bend plus the flexi duct might start to collapse a bit and cause a restriction and that any such restriction would increase the dust/fluff build up and cause back pressure and reduce efficiency and, eventually, if there was a significant dust/fluff build up, could become a fire hazard (he said he's seen many, many such instances over the years).

I would be slightly concerned about rectangular ducting if I thought there was a significantly reduced flow compared to round.

I spotted this comparison but can't vouch for its accuracy

Round ducting free area100mm round kitchen ducting - 7855mm
Rectangular ducting free area -110mm x 54mm - 5424mm

What would concern me most would be if there had to be a right angle round to rectangular adaptor close to the outlet of the dryer and the air flow was sufficiently restricted there by the adaptor to cause a build up of dust/fluff within it.

I do know that when I checked the inside of my existing ducting (a mix of straight, smooth, plastic 4" tube and a short length of aluminium flexi duct) there was quite a build up of dust/fluff and I 'm thinking that this build up is what caused the overheat button to trip. - I've reset the button and it's been fine for a couple of weeks now.
 
I have often wondered what is the effect of the circular [conventional] corrugated ducting drag co-efficient on air flow is compared to the rectangular smooth internal surfaces?

Ken.
 
Mr.B said:
We spoke about vented v condenser and I told him that I'd checked and a new Bosch vented dryer has the rear outlet in a slightly different position compared to mine
Click to expand...

Are you sure the Bosch doesn't have an optional side or rear outlet?
 
JohnD said:
Are you sure the Bosch doesn't have an optional side or rear outlet?
Click to expand...

Yes, it has a side outlet (which is no good in my own circumstance) and it has a rear (which is sited a couple of inches from where my current Siemens outlet is.
Fingers crossed, it's still working OK after having re-set the trip button.
I just wonder if the build up of fluff on the inside surface of the ducting increased the air resistance to such a degree where it was enought to rewstrict the flow and cause the element to get hot enough to trip? It had a new OEM element two years ago - so the original element lasted 12 years - which aint bad!
 
I positioned mine so I use the side outlet, that means I do not have to line up the back positions. the big hose will flop under adjacent units if necessary.

If you ever want to clean the convoluted hose, I found taking it off and sloshing it in the sink washed the fluff out. if you have room you could stand on a stepladder and use a hosepipe. Or just fit a new one.

I like vented.

Almost nothing inside to go wrong.
 
^^^ All the above noted.

The aforementione engineer, on the other hand, seemed to lean towards condenser: I wouldn't be cynical enough to suggest it's coz it's more likely to keep him in work than a conventionially vented.

I've read that vented is no more expensive to run (cost of electricity) than a condenser.

I also read that some condensers can, in a small, windowless room - maybe like a utility room - produce condensation in the room - enough to dampen walls and surfaces on occasion. The engineer did concede that some makes can do that (he suggested Hotpoint as opposed Bosch, Siemens and Miele etc), but I've read various makes can do it).

Not only that, they apparently seem to take longer to dry clothes but I don't speak from personal experience. Plus, if you don't plumb it in to an adjacent sink, you have to keep emptying the container. It seems that heat pump dryers definitely take much longer to dry.

I guess the main advantage is you don't need the vent tube/hose.

So, I'll hope the present one keeps going, a new, genuine Siemens, heating element is £100 plus fitting which wouldn't be economically viable, given that the motor could ne next (especially on a machine of that age).
 
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My wife never cleans the fluff off that filter at the front, I keep telling her that she'll have to pull it out and find that reset button on the back herself!
IMG_20200711_152854531.jpg
 
^^^ But you will both know that tumble dryers catch fire. Quite often. Sometimes resulting in a major house fire. And that it's often due to not having cleaned the filter(s).
 
Ours is a combined Hotpoint washer drier, quite old now, it uses cold water to chill and condense. The heater duct I found collects a tremendous amount of fluff around the element, so I banned us of it to dry. Instead and much cheaper to run, I around hanging lines, a fan and a dehumidifier in the utility.
 
Mr.B said:
^^^ But you will both know that tumble dryers catch fire. Quite often. Sometimes resulting in a major house fire. And that it's often due to not having cleaned the filter(s).
Click to expand...

I think your assuming that my wife is a man! She's a woman, doesn't have a clue about fire causing appliances like we do - she probably thinks that fridge at Grenfell had a really hot curry in it. Despite me telling her that there isn't a little man living in the dishwasher who jumps out and washes everything she fails to understand why a closed garlic press rammed with the remnants of 3 cloves of garlic (or a tuppaware box with the lid still on) doesn't come out clean.
 
Well tell her, then, that the bloke who wrote the post on the plumbing section of DIYNOT about tumble dryers catching fire used to get paid to turn out at all hours of the day and night to put them out when they caught fire ... and tell her it wasn't a pretty sight. Sometimes the whole kitchen went up - sometimes worse still.

Although it has to be said it wasn't just tumble dryers - all sorts of domestic appliance catch fire.
 
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