PIV or DIY approach...?

[berty3000]

Hi all,

1961 bungalow. Cavity wall insulation done in 2009 (that yellow bobbly stuff), attic insulation c.250mm, upvc double glazing (some from the 90s). A wall vent in one room blows in a draft from outside near ground level, trickle vents in two other rooms, and vents above sliding patio door in another. All vents open.

I have the heating programmed to come on three times a day for two hours each time, 7am to 9am, 12.30-14.30, 17.45-19.45.

RH is generally 58-60%, temperatures generally 18C-19.5C. Except if I have woodburner on then that room gets hotter with some effect on adjoining rooms.

I know all about good habits, like not drying clothes indoors, using bathroom and kitchen properly. No known leaks anywhere. I run a dehumidifier a few times a week for an hour or so.

I am getting condensation along the bottom inch or so of my bedroom window in the mornings even with trickle vent open. And there is some at the bottom of the massive, sliding metal door in the lounge - this thing is at least 30 years old and just seems to be a cold spot at the bottom. I have the vents open at the top. Otherwise, no obvious damp issues.

However, I would like to get RH to more like 50% average and am at the limits of what I can achieve.

Two options:

A) install a PIV. What should the cost be including installation? Loft or wall mounted better?

B) DIY option. Install a few more trickle vents, buy an extra dehumidifier, and have the two dehumidifiers running at both ends of the house for maybe an hour over night and an hour in the day using timed plugs to automate the process.

Both options presumably ventilate the house with clean air and reduce humidity. Option B more hassle.

Thoughts?

 

[phatboy]

PIV is usually well reviewed. The units are £200 - £500, as some have a heater in them to keep the incoming air a bit warmer.

Installation is quick, if you opt to jut let it use air thats come into the loft. Just need a power supply close by.

Budget half a day reasonably for an electrician to sort it for you, or a couple of hours if there is a good power supply close by with a socket.

 

[berty3000]

PIV is usually well reviewed. The units are £200 - £500, as some have a heater in them to keep the incoming air a bit warmer.

Installation is quick, if you opt to jut let it use air thats come into the loft. Just need a power supply close by.

Budget half a day reasonably for an electrician to sort it for you, or a couple of hours if there is a good power supply close by with a socket.

So whether this works or not will depend on the attic having the same cool dry air as outside the house presumably? Otherwise, could be pushing damp air into the house? So attic would need to be well ventilated...

 

[Johnytuono]

High RH outside air would be far lower when it enters into your house after it has been heated...

 

[danlightbulb]

I have a similar problem. 1930s solid wall house. Just cant seem to get humidity down. We're constantly in the 70% humidity range even with the heating on.

There's no obvious cause. A couple of gutters drip slightly in heavy rain, but nothing significant. There are airbricks and trickle vents all over the house. There's no mould growth or damp on the walls. We open the windows regularly, we also have a dehumidifier.

Like the OP how can I start tracing where this high humidity is coming from? I also want to target 50% in all conditions.

If I install a PIV system my concern is that it just pulls in more moist air from outside.

The humidity we're currently seeing must be coming from somewhere?

 

[Johnytuono]

Sounds exactly like our house, 70 plus %RH, but hardly any mould, heating on and windows opened regularly, 6” kitchen fan and in line bathroom fan. Obviously we get the odd mould spots on the bathroom and kitchen where it’s siliconed but certainly nothing extravagant. I’m hoping the PIV regular air flow will drop it 10% or so. We have tried different hygrometers so we know the reading is correct. We definitely have no leaks on gutters etc

 

[Johnytuono]

Forgot to add, we have no condensation overnight or during the day on any windows apart from when cooking and showering but we keep the fans on until it’s cleared

 

[danlightbulb]

When its colder outside we get condensation forming on the bedroom windows in the morning when we wake up (in our bedroom, plus in the other bedroom we don't use, it happens there too, so its not only the breathing that is causing it). These are fairly modern double glazed windows with trickle vents on the windows themselves and a vent through the brick in both rooms as well.

I don't know how to stop this happening because I don't know what is causing it in the first place. It doesn't make any sense.

 

[Johnytuono]

Have you tried closing the trickle vents for a night or 2 and see if it’s any better/ worse? It’s possible that the vents are cooling the glass surface too much especially with having wall vents too

 

[pcaouolte]

I doubt that a PIV will drop the relative humidity to 50%. We have one and today I am seeing RH readings of between 61% and 71% across various rooms, we don't have any mould since it was installed but do occasionally still get some condensation on bedroom windows on very cold nights.

 

[John Smith Esq.]

It is necessary to have a well ventilated loft. Soffit vents and what have you will help. A PIV should then help the attic stay dry as it will pull air through. The movement of air, especially fresh air, is key - it is true ventilation. You then need sufficient ventilation within the home below the attic so that the air being pushed through it by the PIV can move through and out. So trickle vents for instance, gaps below internal doors (10mm), then ensuring the PIV is on a suitable setting. In these circumstances, PIV should work and make a difference. A DIY approach might involve using fans in the home with sufficient ventilation to the outside to get that air movement through and in/out (any air moving out will be replaced by air moving in - which is usually drier, even if it is raining). Whether this would work would depend on the number and placement of fans, plus ventilation. But movement of air is KEY. You can have lots of vents but we have very still days outside. Ultimately, don't be too down beat by not having perfect RH levels. We do live in a damp climate and lots of us live in old homes built before modern building regulations - might not have cavities or DPMs, might be located in low lying damp areas. If you are avoiding mold and musty smells you're doing ok. That said, great to get another 10% off if you can. Drier rooms feel warmer and getting fresh air in, no matter how cold outside, crucial to good health. I am also thinking about getting a PIV, but have wondered about the cheaper fans option!

 

[Harry Bloomfield]

I doubt that a PIV will drop the relative humidity to 50%. We have one and today I am seeing RH readings of between 61% and 71% across various rooms, we don't have any mould since it was installed but do occasionally still get some condensation on bedroom windows on very cold nights.

Absolutely no mould, or damp issues here. We have DG, CWI, heating set for 14C overnight, 18C daytime. Despite 8C outdoors, the heating never ever fires overnight, the house rarely falls to 17C. We have no vents, all blocked up long ago - just kitchen extract, and bathroom extract. Humidity indoors, varies between 55, venturing sometimes to almost 70. At the moment it shows 60%, 62% outdoors. Internal doors, are normally left wide.

Drying washing in the main house is banned, only permitted in the utility, on lines, where there is a fan and a dehumidifier.

Condensation, a slight misting, on the bottom of the windows is quite normal. We also sometimes see some on the outside too. I would be concerned, if there was water running down a window.

 

[danlightbulb]

necessary to have a well ventilated loft

How do you tell if loft is ventilated enough?

On my 30s house there are no dedicated soffit vents and it's been felted. But presumably it won't be air tight, there will be gaps in places I imagine and there are old cables and pipes through in places.