PIV Systems / Heat Recovery Units

We have good / new UPVC windows, new / well insulated walls.
The lintels in the most affected rooms are concrete...

We do not hang wet washing around the house.
Trickle vents in all windows are always open.

Both bathrooms have new / good extractors.

linconhawk said:

We have good / new UPVC windows, new / well insulated walls.
The lintels in the most affected rooms are concrete...

We do not hang wet washing around the house.
Trickle vents in all windows are always open.

Both bathrooms have new / good extractors.

Click to expand...

What do you consider to be well insulated walls? Lot's of people have 50mm of cavity blown insulation, maybe even poorly installed 100mm.

The current outside conditions could give you 'relatively' high internal humidities with ventillation, then night comes and your poorly insulated walls are 'relatively' cold.

The answer is always the same, lower humidity or increase wall surface temperatures.

Positive air pressure systems help to reduce humidity because they are constant and imo excessive, trickle vents and such just don't cut it when you have poor levels of insulation.

Heat recovery systems are even better, and have generated complaints of uncomftably dry air, but they are expensive to run if its not a passive house.

^woody^ said:

That couldn't be more wrong.

Click to expand...

So you are saying that condensation will form on warm surfaces with dry air?

Ok..........if you say so....

Our cavity's are 100mm.
Filled with new insulation, dont know exactly what Make / sort....
The yellow 'baps' that new builds have...
Thanks

Well if you have condensation you have too high humidity or to low insulation (cold surfaces), 'simples' as the meerkat says.

I would not be at all suprised if its haphazardly insulated if its a UK build.

Reasonable ventillation at this time of year, coupled with low heating, will not drive down humidity and not warm the walls.

Excessive ventillation is a fix, or find and fix the flaws in the insulation envelope.

No way out of it that will not cost you money, either long term higher energy bills (more ventillation and heating) or up front in better insulation.

All the walls are insulated well / correctly.
Built the bungalow myself....

I don't mind spending money. I just want to know what to spend my money on !

I don't know what else to do / try....

All the walls are insulated well / correctly.
Built the bungalow myself....

I don't mind spending money. I just want to know what to spend my money on !

I don't know what else to do / try....

Get yourself an laser/infared surface temperature reader, condensation needs cold surfaces.

At 70% RH surfaces need to be about 14°C for condensation. This is a bit of a high humidity, but if you have trickle ventillation and intermittent heating not unreasonable to expect during autum/spring (or mildly cold humid weather). If it is new build and of decent construction, then it is not unreasonable to expect wall surface temps of +16°C if the air temp is 20°C, but some areas of poor insulation may be colder than that.

Can you ensure that the insulation is not wet for any reason, that will significantly affect it's performance.#

Can you eliminate interstitial condensation as a cause https://en.wikipedia.org/wiki/Interstitial_condensation

At 20°C air temperature, the following approximate humidity / surface condensation figures apply

60% RH needs 12°C for condensation
50% RH 9°C
40% RH 6°C

You can see lowering humidity significantly effects how cold surfaces need to be.

With low heating and more air changes (like the PIV system) you won't get near 40% RH, maybe 60% RH. Again, not unreasonable to expect well insulated surfaces to be only a few degree's lower than the internal air temp.

Mechanical heat extraction needs a well insulated AND AIRTIGHT house to work effectivly, the kind of house with 200mm of insulation minimun, so it is not really the solution for you.

Thanks for your help...

Thinking of getting the PIV Drimaster 2000..

Is this going to help...

Thanks for your help...

Thinking of getting the PIV Drimaster 2000..

Is this going to help...

Lots of marketing speak, but basically heat recovery 'sucks' the heat from outgoing air, and adds it to incoming air (unless it has its own heating element it can't put more in than it takes out, that is nonsense).

Do they work?

Yes, but they should only be fitted in very well insulated airtight buildings for them to be economical.

I had a huge mould issue in bedrooms - its a 1820s stone build house so non insulated walls. Fitted a nuair unit and it helped out with the mould brilliantly. I wouldn't say it cured it but it made the situation a million times better. My resolution has been somewhat two fold, I added an extension to the house and also in the older part with stone walls as they have been renovated 50mm of insulation has been added to inside walls and then plasterboard. Not a cheap fix but it has worked.

the PIV has now been switched off with no adverse affects.