Trickle vents and retrofit

[TakeshiKovacs]

Our property has older double glazed units with no ventilation/trickle vents in situ. The main frame material is aluminium.

 

The rest of the house has no explicit ventilation, except for a continuous extraction fan in the bathroom (providing trickle extraction and boosting when either humidistat or light switch triggers it).

 

In the colder months we do get a fair bit of condensation on the  bedroom windows each morning. Mindful that we need a combination of passive/active measures to combat this but as a first step, can those frames be retrofitted with trickle vents of some kind and has anybody actually done this?

[marshian]

Just fit a Positive Input Ventilation (PIV) unit - that’ll solve 99% of your condensation issues

[Mike]

Most likely your aluminum windows were build without a thermal break. That means that there's pretty much nothing you can do to prevent condensation forming, short of leaving the heating on overnight or replacing the windows.

[Nickfromwales]

6 hours ago, marshian said:

Just fit a PIV unit - that’ll solve 99% of your condensation issues

Not without trickle vents?

[Nickfromwales]

6 hours ago, TakeshiKovacs said:

Our property has older double glazed units with no ventilation/trickle vents in situ. The main frame material is aluminium.

 

The rest of the house has no explicit ventilation, except for a continuous extraction fan in the bathroom (providing trickle extraction and boosting when either humidistat or light switch triggers it).

 

In the colder months we do get a fair bit of condensation on the  bedroom windows each morning. Mindful that we need a combination of passive/active measures to combat this but as a first step, can those frames be retrofitted with trickle vents of some kind and has anybody actually done this?

Buy a trickle vent and see if it physically fits at the head of the window. If so, it's just a matter of drilling a series of 10mm holes along the length of the vent, and two more holes for fixing screws.

 

If you are budget shy for new doors and windows, you could maybe install some 4mm neoprene insulation 'tape' both inside and out on the frames, then dress over these with white PVC D section 'makeup' trim, if you're happy to have a DIY improvement at least. Not much more you can do as aluminium (when old style frames which are shockingly bad for bridging cold) is horrid stuff; realistically you need to change the windows / doors etc, as you prob already know.

[marshian]

1 hour ago, Nickfromwales said:

Not without trickle vents?

I disagree

 

You don't need trickle vents if you have leaky property - air finds it's own path - past windows - past ceiling roses - anywhere that's not sealed

 

Build Hub "Built it tight - ventilate it right" 100% agree but I'll put £20 on the fact that the OP has a leaky property from an air tightness perspective and a PIV unit will resolve his condensation issues

 

Experience is what you get when you don't want it

[Nickfromwales]

12 minutes ago, marshian said:

I disagree

 

You don't need trickle vents if you have leaky property - air finds it's own path - past windows - past ceiling roses - anywhere that's not sealed

 

Build Hub "Built it tight - ventilate it right" 100% agree but I'll put £20 on the fact that the OP has a leaky property from an air tightness perspective and a PIV unit will resolve his condensation issues

 

Experience is what you get when you don't want it

Agreed, but won't the PIV be in the attic blowing down into the open landing? Or are you suggesting blowing air from atmosphere into the bedrooms?

 

If the former, the input air will seek out the path of least resistance, eg you can't guarantee it'll solve the bedroom issues.

 

I have 4 kids, so am defo up for taking the £20 prize money on offer.

[marshian]

33 minutes ago, Nickfromwales said:

Agreed, but won't the PIV be in the attic blowing down into the open landing? Or are you suggesting blowing air from atmosphere into the bedrooms?

 

If the former, the input air will seek out the path of least resistance, eg you can't guarantee it'll solve the bedroom issues.

 

I have 4 kids, so am defo up for taking the £20 prize money on offer.

 

Unless there is a open window the air will take all paths open to it it doesn't need to be much of a leak to cause a dramatic reduction in humidity and as a result condensation

 

 

[Gone West]

12 hours ago, Nickfromwales said:

Not without trickle vents?

I'm gradually replacing all the windows, without trickle vents, in my old bungalow, and was going to install a PIV unit, and decentralised Mechanical Extract Ventilation (dMEV)) in the bathrooms and kitchen. Is there any reason that is a bad idea.

[JohnMo]

27 minutes ago, Gone West said:

I'm gradually replacing all the windows, without trickle vents, in my old bungalow, and was going to install a PIV unit, and dMEV in the bathrooms and kitchen. Is there any reason that is a bad idea.

 

Air takes the easy route - so PIV, will just feed the dMEV, no ventilation in to dry rooms. Not a good idea. Either pick PIV or dMEV not both. 

 

Doing away with trickle vents is a bad idea - have trickle vents just install a self regulator that adjusted for humidity then you get the right venting the right place. You plan is is well ventilated hallway and wet rooms. But no ventilation, in dry rooms.

[Onoff]

13 hours ago, Nickfromwales said:

Buy a trickle vent and see if it physically fits at the head of the window. If so, it's just a matter of drilling a series of 10mm holes along the length of the vent, and two more holes for fixing screws.

 

I've long been under the clearly mistaken impression such vents had to fit over a slot in the window head. There was me considering fitting them and how I'd set a router up to achieve it accurately without taking the window out! A line of holes, much easier!

 

Doesn't a positive ventilation unit push "heat" out through the trickle vents though thus your bills go up?

Edited October 4 by Onoff

[Redbeard]

1 hour ago, JohnMo said:

 

Air takes the easy route - so PIV, will just feed the dMEV, no ventilation in to dry rooms. Not a good idea. Either pick PIV or dMEV not both. 

 

+1. I prefer dMEV but some prefer PIV. It is a personal choice. Swot up on the alleged advantages and disadvantages before you commit, and form your judgement based on te best info you can get.

[Gone West]

3 hours ago, JohnMo said:

Air takes the easy route - so PIV, will just feed the dMEV, no ventilation in to dry rooms. Not a good idea. Either pick PIV or dMEV not both. 

So if I ducted the PIV to the dry rooms then the dMEV would then suck it out.

[Redbeard]

5 minutes ago, Gone West said:

So if I ducted the PIV to the dry rooms then the dMEV would then suck it out.

 

Yes, it probably would - an interesting thought to those who don't want to use trickle vents. More expensive, though, and one more 'moving part' (another - PIV - fan). (And come to think of it, surely one of the 'advantages' suggested for PIV is that you can just sit it in the loft, blow down onto the landing and then it finds the gaps on the gr floor? If you need to duct to dry rooms you may be getting as 'complicated' (in the eye of some 'beholders') as MVHR).

[JohnMo]

6 minutes ago, Gone West said:

So if I ducted the PIV to the dry rooms then the dMEV would then suck it out.

Are you not making work to prove a point? Either have window or wall trickle vents - with humidity control - Job done.

 

But no trickle vents in wet rooms.

And with internal door undercuts to allow air to flow as required.

[Nickfromwales]

8 minutes ago, Gone West said:

So if I ducted the PIV to the dry rooms then the dMEV would then suck it out.

Wouldn’t that mean huge infiltration during winter? The problem is, the time you need the ‘benefit’ is the most detrimental time to use such a system.

 

Retrofit of MVHR has got to be on the table at this point? 

[Mike]

3 hours ago, Gone West said:

was going to install a PIV unit, and decentralised Mechanical Extract Ventilation (dMEV)) in the bathrooms and kitchen. Is there any reason that is a bad idea.

PIV is a bad idea as it pushes internal moisture-laden air through gaps in the building fabric where it can to condense out and cause problems (except in old buildings where the gaps are so big that it flows out freely, or if the trickle vents are guaranteed permanently open in perpetuity). And when it's cold outside it's often not comfortable to be drawing in cold air. Central extract (MEV) would be preferable and is much used here in France. MVHR would be the gold-standard.

 

dMEV is OK if all units are installed on the same wall, otherwise it tends to create an air tunnel from one side of the building to the other, which can be problematic when windy.

[Gone West]

@Redbeard, @JohnMo, @Nickfromwales, @Mike Many thanks for the comments, plenty to think about there. Sorry to the OP for derailling his thread.

[Nickfromwales]

30 minutes ago, Gone West said:

@Redbeard, @JohnMo, @Nickfromwales, @Mike Many thanks for the comments, plenty to think about there. Sorry to the OP for derailling his thread.

All quite relevant, to get a practical solution   

 

“Continue….”.  

[Nickfromwales]

12 hours ago, Gone West said:

Is there any reason that is a bad idea.

No heat recovery, and a lot of cold air infiltration over the winter.

[Gone West]

11 hours ago, Nickfromwales said:

No heat recovery, and a lot of cold air infiltration over the winter.

I've done the very low energy usage, new build, fifteen years ago, this is an 1840s/1970s, single storey, stone build. I learned a lot from the new build and the works I am doing, are to make it primarily comfortable. If I fitted PIV, it would have a simple electric post heater. This would be used for maybe three months of the year and would only be lifting the input air temperature to around 24C. The levels of infiltration would be much the same as in my new build.

[craig]

On 03/10/2025 at 20:59, Nickfromwales said:

if it physically fits at the head of the window. If so, it's just a matter of drilling a series of 10mm holes along the length of the vent, and two more holes for fixing screws.

What Nick said.

[Nickfromwales]

1 hour ago, Gone West said:

I've done the very low energy usage, new build, fifteen years ago, this is an 1840s/1970s, single storey, stone build. I learned a lot from the new build and the works I am doing, are to make it primarily comfortable. If I fitted PIV, it would have a simple electric post heater. This would be used for maybe three months of the year and would only be lifting the input air temperature to around 24C. The levels of infiltration would be much the same as in my new build.

These can be used for sure, just the electric bill to take into consideration as a part of the space heating costs.

[Iceverge]

There's no magic with dMev Vs PIV. 

 

Both are just a method of moving a continuous stream of air through the house. 

 

I used to leave the hob extractor on when I went out in an old damp rental cottage we had to dry the place out. It's just a fan moving air after all. 

 

In both cases you'll still get condensation if you have trapped pockets of air like behind curtains etc. 

 

 

@TakeshiKovacs as an experiment try leaving a bedroom door open to the hallway, curtains open and the bathroom/kitchen extractor fan on constantly for a night. If you can manage the light and noise.

 

It'll solve the condensation I bet. You could also crack the window open a few mm and leave an air gap to allow some air flow through the bedroom to the extractor.

 

Keep us posted.

 

 

 

 

 

 

[Gone West]

4 hours ago, Nickfromwales said:

These can be used for sure, just the electric bill to take into consideration as a part of the space heating costs.

Run off the battery system, charged by PVs and off peak cheap electricity.