General: Condensation from pipes to MVHR - suggestions?

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- CommentAuthorSimon Still
- CommentTimeJan 19th 2023 edited
https://ibb.co/hym6LMF
This is our install - its' in a cupboard in our home workshop. Because that's a dusty space I didn't connect the MVHR for that room (but we open the door to outside a number of times each day and frequently open the door to the rest of the house). However, it's *possible* the room is a bit more humid than the rest of the house with two of us frequently spending the day in it. But the door to the cupboard is fairly well sealed so there shouldn't be a lot of air movement into it.

In cold weather we get some condensation on top of the machine (which runs down the side or through the case and drips onto the floor from the front right corner (which must be the lowest point). It's not a huge amount - if a pot is put under it never builds up to much and if that plastic crate is in the right place I think it collects and evaporates from there without ever overflowing, but it had got moved and there was a paint tin sitting under it....

The pipe from outside is clad in rigid insulation and the spaces it runs through are also filled with glass fire insulation (and clearly the air is still cold when it hits the MVHR cupboard).

The last stretch of flexi pipe with glass fibre insulation is clearly the worst in terms of both the level of insulation and the sealing. In fact it might not even be the pipe thats the issue - the exposed plastic nozzle it attaches to and that part of machine are effectively cold and poorly insulated.

Is this normal and unavoidable for an MVHR installed in an internal space or is there some way of improving it?
- CommentAuthorGreenPaddy
- CommentTimeJan 19th 2023
Just a thought, before discussing condensation external to the unit.

I had clients with a similar issue on the very same MVHR unit. When I investigated, the leak was actually from the condensation on the inside, not being able to drain away. There's a little spiggot type thing on the back LHS internally, onto which the drain hose is fitted. It was all gunked-up. When cleaned out with a long bottle brush, the problem disappeared. What was confusing my clients, was that I think there was carry over from the captured condensate, getting transported by the fan unit.

Maybe check that first, and report back?
- CommentAuthorSimon Still
- CommentTimeJan 19th 2023
Thanks - I gave the unit a proper clean (and washed the heat exchanger) a couple of months back but didn't think to check the condensate pipe.

However, that's definitely not my issue - this has always happened (but its been really unusually cold for some periods this winter) and the top surface of the unit had a sheet of paper that was wet so the source (maybe not the only source) is external and above.
- CommentAuthordjh
- CommentTimeJan 19th 2023
Is your workroom heated? What temperature readings to you get with an IR thermometer from the various parts (walls, MVHR top, intake duct near the MVHR, duct connection etc)? And what humidity do you see in the room? And for that matter in the cupboard? Use bits of paper stuck to the foil (e.g. paper labels) to get sensible readings.

Have you tried some tissue paper wrapped around the intake duct to make sure it's not condensation running down the outside of the pipe?

FWIW, I've never seen any condensation on or around our MVHR (but it is PH-certified).
- CommentAuthorGreenPaddy
- CommentTimeJan 20th 2023
Ok, guess no.2

The condensation is presumably the room air in contact with a cold part of the ductwork (obvious statement). This duct is presumably the intake or exhaust.

If the majority of the surface of this foil/insulated duct is not damp with surface condensation, there is likely a weak point, which may be the junction of duct and mvhr, where it's taped tightly to the plastic duct connection spigot. There may be no insulation or very squashed insulation between tape and rigid plastic. This would apply equally to intake and exhaust.

It seems quite a lot of cond for such a small area, so may be there is more at play here. Certainly, if you consider your insulated ducts have maybe 20 or 30mm of insulation, to what is essentially outside air (intake or exhaust), flowing, so bringing a considerable heat loss, I would want to have those ducts better insulated, even just from a heatloss point of view (or poorer efficiency at the HX), never mind condensation. To stop the condensation, not just insulation, but vapour tight too. Would still get cond under 200mm of wool type insulation, as the vapour passes through from the room.
- CommentAuthorSimon Still
- CommentTimeJan 20th 2023
So workroom is in the basement and we have the underfloor heating circuit turned off because it maintains a nice comfortable 19-20C through winter anyway.

I'm should look at humidity - I bought a Lidl wall clock with temp and humidity but I don't trust the readings from it but I don't have anything portable or definitive to compare it to (the Loxone analogue humidity sensors in our bathrooms were adjusted to match each other, and the levels for boosting the MVHR adjusted to be sensible for detecting shower use and not running based on ambient weather conditions except in exceptional circumstances rather than to be an absolute figure).

Will check the duct surfaces.

The remaining question is how to better insulate the visible ducting (the flexi duct is clearly the weakest point) given what you can see. What I've done seems to be standard - I've not seen anyÂ better solutions for it.
- CommentAuthorSimon Still
- CommentTimeJan 20th 2023 edited
"It seems quite a lot of cond for such a small area"

I'm not sure about that - a pint of beer on a hot day will generate an impressive amount of condensation on the outside of the glass that will pool on the table it's sat on. You really don't need much surface area if the object is cold.

I'm pretty sure this is only really occurring when external temps are in the low single figures.
- CommentAuthorMike1
- CommentTimeJan 20th 2023
Posted By: Simon StillThe remaining question is how to better insulate the visible ducting (the flexi duct is clearly the weakest point) given what you can see. What I've done seems to be standard - I've not seen anyÂ better solutions for it.
Flexible ducting isn't standard - or at least it isn't good practice. I'd replace at least the external supply and extract ducts (where the condensation risk is highest) with well-insulated rigid ducts.
- CommentAuthordjh
- CommentTimeJan 20th 2023
Posted By: Mike1
Posted By: Simon StillThe remaining question is how to better insulate the visible ducting (the flexi duct is clearly the weakest point) given what you can see. What I've done seems to be standard - I've not seen anyÂ better solutions for it.
Flexible ducting isn't standard - or at least it isn't good practice. I'd replace at least the external supply and extract ducts (where the condensation risk is highest) with well-insulated rigid ducts.
Agreed. Our system uses preformed insulated ducting (Ubbink) but yes, replacing the intake and exhaust ducts with something better is a good idea. Ideally you would establish the source of the condensation first, of course.
- CommentAuthorSimon Still
- CommentTimeJan 21st 2023
<blockquote><cite>Posted By: Mike1</cite>Flexible ducting isn't standard - or at least it isn't good practice</blockquote>

That's true, but when we self installed 8ish years ago, it seemed to be - every install I can remember seeing a pic of back then had flexi pipe for the final connections. I've seen some lovely looking installs with rigid pipe looking around now but of course they've all got loads of space around them. MVHR takes a surprising amount of space in a smaller house.

My laser thermometer had flat batteries and I'm out of 2032 cells so a more detailed look at surfaces will have to wait a few days, but I think I've found the main issue. The flexi pipe surfaces don't feel cold - but that shaped plastic nozzle it's attached to definitely does, and so does that corner of the unit (as you'd expect).

However, up above the flexi pipe, round the back, the last fixing for the rigid pipe looks like this. And that exposed rigid pipe DOES feel cold and damp. It must have been a 'will work out how to improve/solve that but other jobs are more pressing' that was immediately out of sight and mind.

I think the main issue is there and condensation then running down the sides of the pipe inside the insulation and collecting (and exiting) at the lowest point. I'm thinking this is a job for a bit of spray foam but that it will have to wait until it's warmer outside and everything is dry....
- CommentAuthordjh
- CommentTimeJan 21st 2023
What's the insulation inside the flexible ducts? If it's glass wool or similar then it'll be soaked if the condensation is running down inside. Which would be another reason to replace the ducting.
- CommentAuthorcjard
- CommentTimeJan 22nd 2023 edited
Somewhere between about 20mm of wool or, if your contractor is like the one that did my FIL's install, none because it got in the way of fitting the flexi duct over the rigid (flexi inner diameter smaller than rigid outer) so they ripped all the wool out. It's double skinned if you have faith that the inner skin is 100% puncture free then the wool will be fine

The cupboard was dripping to the extent they called a roofer insistent that there was a leak. I maintained all along that it was simply condensation puddling all over the lid of the MVHR and the floor but they couldn't believe it. Roofer found no problem.. I guess the condensation still happens, I ducked out of the diagnosis at that point

Quite an effective dehumidifier if it is condensation though!
- CommentAuthorcjard
- CommentTimeJan 22nd 2023
Flexi duct makeup (width exemplified by top right where inner foil shows)
- CommentAuthorDominic Cooney
- CommentTimeJan 23rd 2023
Posted By: Simon Stillflexi pipe for the final connections

I also think this is very common and is what we have, as supplied by BPC ventilation. I expect the final connection can be tricky to get it all lined up perfectly, especially for self-installers (I connected ours up last year). For starters, the 2 spigots are too close together to get 2 rigid insulated ducts attached next to each other (If I recall correctly) so you would have to have one out the top and one out the side, which makes the horizontal wall space required much larger than if they are all out of the top.

The flexi duct did and still does feel a bit dissatisfactory though, and you are right, MVHR can take up a lot of space in a small house, especially if it's not in the loft but in a plant/utility room.
- CommentAuthorborpin
- CommentTimeJan 24th 2023 edited
Posted By: Simon StillThat's true, but when we self installed 8ish years ago, it seemed to be - every install I can remember seeing a pic of back then had flexi pipe for the final connections.
Yes my feeling too. My install of 10 years ago has just flexi duct and I cannot remember being offered or seeing available the rigid duct you can get to day.

I recently had issues with condensation on my MVHR system when we had the -10Â°C weather.

Last year I fitted a new MVHR unit. In the process I installed an in-line coarse filter to remove some of the larger particles in the air (which works well). This is a metal box from VentilationLand. The trouble is, there was a massive amount of condenstaion on the soutside of this box when the air is cold!

Because this is a Komfovent unit, it does not need to be turned off at low temperatures as there is no risk of freezing (the type of heat exchanger) so it runs even in these low temperatures.

When I had connected the flexible duct, I had not sealed the ends, so just attached the inner sleeve to the spigot. This allowed the condensation forming on the metal box, to be absorbed by the rockwool of the flexible duct eventually saturating it.

I have now replaced the duct with solid insulated duct and covered the filter box with 10mm EPDM tape on all sides which seems to have largely solved the problem. There are still the spigots on which condensation can form, but I will replace the remaining flexi duct in the summer and seal the ends so no damp air can get between the 2 layers of the flexi duct.

Check and see if the rock wool insulation inside the flexi duct, is damp/wet. If it is, the water is draining out. If not, then it is simply the cold air making the surface of the unit cold enough to cause condensation.

In that case, you could do what I have done with the filterbox and cover it with EPDM tape.

As an aside, my Komfovent unit has a very well insulated case - presumably to prevent this. My old Helios unit, was just an uninsulated metal box.
- CommentAuthorSimon Still
- CommentTimeJan 24th 2023 edited
Thanks all - Given the restricted space I really don't think we're going to get to rigid duct but
- spray foam the exposed pipe
- replace flexi duct. and maybe add some secondary insulation

@borpin why did you replace your unit? They're expensive, and mine is showing no signs of wear (touch wood) after 7 years. I'm hoping for a lot more than a couple more years from it as any increase in efficiency is never going to pay back.

Another question-
I mentioned the room the cupboard is off is currently unventilated. It's a wood workshop (we restore furniture) and has an in and outlet currently unused. (system was designed so this room would be balanced by itself and could thus be left disconnected). Obviously it's dusty which is why it's not on, but can you get duct filters that we could put on the extract duct so that we could connect the room without wrecking the MVHR unit?

I've found some extract terminals aimed at kitchens - I guess I could just replace the grease filter with a dust filter in these and replace often https://www.paulheatrecovery.co.uk/product/vf-filtered-kitchen-extract-terminal/

(also, I didn't bother with this in my kitchen - I'm relying on a really good Berbel recirculating hood to take out grease before it reaches the MVHR extract. Which I think is working.)
- CommentAuthordjh
- CommentTimeJan 24th 2023
Posted By: borpin
Posted By: Simon StillThat's true, but when we self installed 8ish years ago, it seemed to be - every install I can remember seeing a pic of back then had flexi pipe for the final connections.
Yes my feeling too. My install of 10 years ago has just flexi duct and I cannot remember being offered or seeing available the rigid duct you can get to day.
Our install was done eight years ago and the insulated duct was definitely available then.

Last year I fitted a new MVHR unit. In the process I installed an in-line coarse filter to remove some of the larger particles in the air (which works well). This is a metal box from VentilationLand. The trouble is, there was a massive amount of condenstaion on the soutside of this box when the air is cold!

Because this is a Komfovent unit, it does not need to be turned off at low temperatures as there is no risk of freezing (the type of heat exchanger) so it runs even in these low temperatures.
Hmm, all PH-certified units have to run continuously all the time. No closing inlets or reverse defrost cycles etc. They're all also required to be properly insulated. It may be a case of you get what you pay for.
- CommentAuthordjh
- CommentTimeJan 24th 2023 edited
Posted By: Simon StillI've found some extract terminals aimed at kitchens - I guess I could just replace the grease filter with a dust filter in these and replace often https://www.paulheatrecovery.co.uk/product/vf-filtered-kitchen-extract-terminal/

(also, I didn't bother with this in my kitchen - I'm relying on a really good Berbel recirculating hood to take out grease before it reaches the MVHR extract. Which I think is working.)
We have one of those kitchen terminals. The filter is just a square piece of foam that fits in the metal case. I initially relied on the cooker hood but after a couple of years I noticed that there was dust/dirt/whatever on the inside of the right-angle bend above the normal kitchen extract terminal so I bought one of the filtered ones and a box of filters and that seems to have solved the problem nicely. The filters are very easy to wash so can be used several times. I've never found any dirt behind any of the other extract terminals.

I see that Nuaire do something called a Q-aire filtered extract valve a bit cheaper but I don't know anything about what it is or what type of filter it uses.
- CommentAuthorborpin
- CommentTimeJan 24th 2023
Posted By: Simon Still@borpin why did you replace your unit?
Because one of the fans was failing again and yes, expensive, but I was throwing good after bad.

Posted By: djhHmm, all PH-certified units have to run continuously all the time. No closing inlets or reverse defrost cycles etc. They're all also required to be properly insulated. It may be a case of you get what you pay for.
True, wasn't as much a thing 11 years ago when I did all the investigation (look back here 11 years ago). PH also wasn't really something widely available - yes the assessment was around but not much else unless you paid a very high price. In the 3 years to your 8 year point, things changed markedly. (not that I'd expect you to agree).
- CommentAuthordjh
- CommentTimeJan 24th 2023
Posted By: borpinIn the 3 years to your 8 year point, things changed markedly. (not that I'd expect you to agree).
I I don't know what was available three years before I bought, so I'll take your word for it
- CommentAuthorfabio
- CommentTimeJan 29th 2023 edited
No, this is not normal in a well-designed system.
Ideally your external intake and exhaust should be wrapped with closed-cell foam insulation. We spec one or two wraps of 25mm armaflex lagging when designing MVHR, this is around preinsulated polypropelene pipe (15mm thickness).
This both eliminates condensation risk to the outside of the pipes and minimises heat loss within the house / thermal envelope.
So, I would firstly increase / redo the insulation to these two pipes as that is likely the cause. Or better, replace with Zehnder Comfopipe and wrap it once or twice.
Second, is it possible to add an extract to your workshop? Perhaps you have a spare port on the manifold, or you could branch off before it. Removing the humidity wouldn't be a bad idea. Need a good filter though for that dust.
By the way, no real need to insulate the internal supply and extract ducts. They are carrying warm air in a warm space. Bear in mind that a highly insulated supply duct will deliver cooler air to a room than an uninsulated duct, in most cases.
- CommentAuthorSimon Still
- CommentTimeJan 30th 2023
Thanks @fabio

I really struggled to find insulated duct options when I was installing this. The rigid pipe is lagged with https://www.bes.co.uk/domus-easipipe-insulation-1-m-long-x-100-mm-dark-grey-22422/

As mentioned above, the workshop has capped off pipes for supply and extract (with the semi rigid capped off at the manifolds in the cupboard).

I think the plan now is to look into
- seeing if we can use rigid connections (although it's a tight awkward space and you can see that either the internal supply or extract needs to get over the top of the external supply somehow....)
- sprayfoam the small exposed section of rigid duct I've found.
- add additional armaflex. I'm thinking that sticking that to the 'cold' section of the MVHR, and to that final connection area would be a worthwhile. Doesn't need to look pretty.
- connect the workshop vents (with an external filter on the extract)

The location of the unit was always a compromise and the runs from outside are much longer than advised, but we're a gap in a terrace so limited external walls and didn't want to lose space to a plant room on the ground floor so it's all in the basement. I could maybe have put the mvhr so that the external connections would have been shorter, but would have lost a load of useful space getting all the semi rigid duct to the unit (whereas the routing for the external ducting now wasn't usable)

The batteries for my laser thermometer turned up and I took some readings -
External Air temp - 6C
Room 19C

Outside of the rigid insulation - 18C
Flexi - mostly 18C, some 17C but at the bottom where it's crushed on the bend and I'm pretty sure wet - 14C

the MVHR unit
14C on the exposed plastic nozzle, 15C at various points the case on the 'cold' side'
18C on the warm side

The bit of exposed plastic pipe was 10C.

I tried again when the outside temp was lower and it looks like the external air is warmed by about 4C as it runs through the heated envelope before it reaches the MVHR based on that section of bare white pipe. Nothing I can do beyond the sections of pipe that can be seen. Not idea, but still getting most of the value from the heat exchange.
- CommentAuthorborpin
- CommentTimeJan 31st 2023 edited
Posted By: Simon StillIn cold weather we get some condensation on top of the machine
Lots of focus on the pipes, but you said it was on the top of the machine. Is the rockwool insulation in the flexible duct wet at the bottom so it is wicking down onto the unit? If so, it may be difficult to dry that out, so it would need replacing.

If the rockwool type insulation is sealed at the ends, then the humid air cannot get between the 2 layers of aluminum, pass through the insulation and condense on the cold inner pipe. This was my downfall. Replace the duct, seal the ends and then do something to insulate where it connects to the metal duct.
- CommentAuthorSimon Still
- CommentTimeFeb 27th 2023 edited
So the flexible pipe I've used is clearly a poor solution, but it's going to be very difficult/awkward to use rigid pipe here.

Has anyone used 'semi rigid' metal pipe? Any reason not to?
This sort of stuff -
https://www.dustspares.co.uk/semi-rigid-uninsulated-flexible-ducting-3-metre-length.html#prod_id=5745

it holds its shape well, is smoother internally and doesn't crush like flexi-pipe so I'm thinking it would be a lot easier to use for the final connections and fairly easy to insulate well using Armaflex.

While I'm at it I'm thinking I'll add a silencer to the supply side -
Any recommendations? https://www.bpcventilation.com/ducting-accessories/acoustic-solutions
I'm assuming I'd not need to rebalance the system as any resistance it adds is before the manifold.
- CommentAuthordjh
- CommentTimeFeb 27th 2023
I haven't used any metal pipes. The insulated plastic ones I used are semi-rigid in any case. When I saw you mention metal semi-rigid and looked at the picture I thought 'an attenuator will do that job', like the Quiet-Vent Semi Flexible Silencer Range shown in your link. I do have one similar to that.

I suppose that as long as your MVHR unit is a constant volume one, there'd be no need to rebalance. It should adjust how hard it is working automatically.
- CommentAuthorSimon Still
- CommentTimeFeb 27th 2023
<blockquote><cite>Posted By: djh</cite>I haven't used any metal pipes. The insulated plastic ones I used are semi-rigid in any case. When I saw you mention metal semi-rigid and looked at the picture I thought 'an attenuator will do that job', like the Quiet-Vent Semi Flexible Silencer Range shown in your link. I do have one similar to that.

I suppose that as long as your MVHR unit is a constant volume one, there'd be no need to rebalance. It should adjust how hard it is working automatically.</blockquote>

pre Insulated semi rigid plastic? what are those?
My understanding is that you only want an attenuator on the supply from the unit to the house - not on the external supply extract or the internal extract. And they're expensive. So that doesn't really help.

how do I tell if my unit is constant volume?
- CommentAuthorborpin
- CommentTimeFeb 27th 2023
Posted By: Simon StillSo the flexible pipe I've used is clearly a poor solution, but it's going to be very difficult/awkward to use rigid pipe here.
Looking at the Photo, I think you have plenty of space to do so. 45Â°off the unit across to under the vertical and 45Â° back to vertical.
- CommentAuthordjh
- CommentTimeFeb 27th 2023
Posted By: Simon Stillpre Insulated semi rigid plastic? what are those?
The ones I have are Ubbink; I've mentioned them before. https://www.ubbink.com/int/products/ventilation/aerfoam-insulated-mass-flow-ductwork/ I think Zehnder also have some; there may be others.

My understanding is that you only want an attenuator on the supply from the unit to the house - not on the external supply extract or the internal extract. And they're expensive. So that doesn't really help.
Ah, yes usually only on the supply. I think sometimes they're needed on the extract but I don't remember when, and not on the exhaust or intake.

how do I tell if my unit is constant volume?
It'll be in the spec/manual.
- CommentAuthorSimon Still
- CommentTimeFeb 28th 2023 edited
Posted By: djh
Posted By: Simon Stillpre Insulated semi rigid plastic? what are those?
The ones I have are Ubbink; I've mentioned them before. https://www.ubbink.com/int/products/ventilation/aerfoam-insulated-mass-flow-ductwork/ I think Zehnder also have some; there may be others.

That's what confused me - the main supply extract ducting is pre-insulated but it's not flexible is it? appears rigid?

And appears to just be polystyrene - does it have a hard plastic layer within it?
- CommentAuthordjh
- CommentTimeFeb 28th 2023
It's not flexible. It's semi-rigid. It's not PS, its PE. Full details at https://www.ubbink.com/int/getmedia/8e54b253-1537-468b-a3f9-aae5d7f571f4/Ubbink-Aerfoam-EPD-Environmental-Product-Declaration.pdf

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General: Condensation from pipes to MVHR - suggestions?