PiV system not very effective

[Custom45]

Hi
A year ago I had a piv system installed to help with condensation and high humidity at home (4 bed detached house, just me living here at the minute). However I'm still getting indoor humidity levels of around 70% and in the bedroom i get about a 1 inch band of condensation on windows.

House is heated to around 20⁰ in morning and evening and maintained at around 16⁰ during the day and overnight.

A few details..

-The loft is insulated (300mm)
-Loft humidity is quite high too, often 70-80%
-Loft eaves partly blocked, partly open. I've tried opening felt to impove ventilation and there are 2 small velux windows that I keep open by an inch. Not seen condensation on felt, but velux windows occasionally have some.
-Loft is quite cold compared to house, so I don't think much warm air is getting up there
-Internal wall insulation (50mm rockwool)
-Double glazing throughout
-Both bathrooms have inline extractor fans fitted
-Kitchen and bathroom windows have trickle vents
-Humidistat extractor in kitchen
-No clothes dried indoors on rads
-No obvious signs of water ingress/leaks
-Some exterior ground levels a bit high, but -French drain was fitted and I don't think this is a problem

I measured humidity outside today, around 55% at 5⁰. Loft was about 70% at 7⁰.

I'm wondering if the piv system is pulling the humid air from loft and pumping it into the house, keeping RH% high in house?

Any input greatly appreciated, thank you!

 

[endecotp]

Loft was about 70% at 7⁰.

I'm wondering if the piv system is pulling the humid air from loft and pumping it into the house, keeping RH% high in house?

Saturation increases from 10.3 mbar at 7 C to 17.7 mbar at 16 C and 25 mbar at 21 C
( https://www.engineeringtoolbox.com/relative-humidity-air-d_687.html )

So air with 70% relative humidity at 7 C will have 70 x 10.3 / 17.7 = 40 % RH at 16 C and 70 x 10.3 / 25 = 25 % RH at 21 C. I.e. the air from the PIV is drier than the air in the house. (The outside air is even drier though.)

I don’t know why you are suffering condensation. You seem to be doing the right things. The PIV ought to be helping. Does the air from the PIV actually reach the problem areas of the house, or do closed doors prevent that?

 

[Custom45]

The bedroom door is shut at night, but there is a gap underneath for airflow (about 5-8mm). Leaving door open would probably help, but planning on renting the property out, so can't guarantee tenants will do that.

There's a couple of old fireplaces, one in dining room, one in lounge, I'm wondering if moisture from outside is getting through those. Would RH% be noticeably higher in these areas if that was the case?

The temperature on the upstairs landing & hallway that the bedrooms come off rarely goes above 16-17⁰ (with mid 60%RH), because of the draft from the PIV.

I'm worried as currently it's only me here, but once rented the house will sleep up to 8, which is a lot of additional moisture being produced.

 

[foxhole]

Keeping the temp high does not help reduce humidity, quite the opposite.

 

[Custom45]

Keeping the temp high does not help reduce humidity, quite the opposite.

It reduces relative humidity though doesn't it? When the heating is on relative humidity levels reduce, according to the hygrometer.

Regarding the loft, I just checked, it's at 7⁰ 74%rh, condensation on velux windows again (they were open about 2 inches last night).

Roofing felt (bitumen) appeared dry. But I looked underneath felt and there is condensation on underside of tiles (so between felt and tile). I would've thought the air flow from gaps in the tiles would've prevented that?