PIV – Positive Input Ventilation
Piv unit? If you’re thinking what the hell is that? Don’t worry you’re not alone, and that was exactly what I thought 10 years ago when I spotted my first piv unit in a customer’s loft. This small funny looking little machine was dangling from the rafters and connected to the ceiling below via a ventilation tube, wired to the mains via a small thin gauge wire, and so quiet I thought it was broken.
To see which version I think is best and what is costs click here or read on…
How to fit Piv
The video above shows you how to fit a piv unit yourself, very little DIY skills are required but a qualified electrician may be required for connection to the mains, particularly for ‘heat’ version.
When I asked the customers about the strange looking device they then went on to describe how this little machine had transformed their lives, and won them the battle with very bad condensation in every room of the house after all else had failed. (thanks to builder error when the bungalows were built)
I’ve always liked to learn new things, and after they had told me the basics of how it worked, I did my own research. Since then they have proved to be a very successful recommendation at curing condensation and mould problems in tenanted properties that I have surveyed for landlords and estate agents. Especially where dehumidifiers are not always effective.
PIV – A typical domestic p.i.v. unit placed in a loft space. Equipped with a very efficient fan, it filters clean air into your home using on-board controllers, some also have the option to pre-heat air.
Just for the record I’m not trying to sell you a PIV unit, I don’t really care if you buy one or not, but over the years I’ve been converted to some of the benefits of PIV systems which I list below. But before you rush out and buy one please read the article fully, including the FAQ section at the bottom, so you are fully aware of the positives and negatives.
- Stop condensation – A rapid cure for window condensation on glass and around window frames, on walls, in bathrooms, in fact all around the home.
- A whole house solution – One small domestic unit will normally be effective on the entire house all the way up to a five bedroom detached.
- Silent running – Quiet or inaudible depending on the speed setting.
- Removing odours – Musty smells or mouldy damp smells you may have are removed permanently within days.
- Filtered air – Air quality is often overlooked, but it also supplies fresh clean air into your property that has passed through inbuilt filtration to remove pollen, dust, dust mites, pollution and all other manner of nasties.
- Cheap to run – Units draw from 1.5 -15 watts to run depending on the setting, so if left on 24 hours a day 7 days a week for a whole year somewhere between £2 to £10 a YEAR.
- Tamper proof – Very important if you’re a landlord. Students and tenants often stop using dehumidifiers through forgetfulness, laziness, breakages or a fear of increased energy bills.
PIV Unit – What is Piv and how does Piv work?
Like most things that work well the principle is very simple, It’s basically a small economical fan with a number of speed settings to adapt to properties of differing sizes, levels of occupancy and the severity of the problem. This fan then blows air from your loft space very gently through a small vent placed somewhere in the ceiling of your home, usually in a landing or above the stairs.
How PIV works – The very gentle blowing of clean filtered air is inaudible on the low settings but is just enough to raise the air pressure in the house, thus forcing out the old stale and damp air through gaps and vents wherever they should be in your home.
Because heat rises, this often ends up useless at ceiling height, and eventually in your loft as wasted energy, but with a PIV unit in your loft space this can be re-captured and recycled. Couple this with any sun rays on your roof’s surface during winter (solar gain) and it will warm all the air in the loft to a temperature warmer than that of the outside. This fresh air is then filtered and blown back into your home where it mixes with the rising heat to distribute and mix the heated air inside your home more effectively.
I don’t have access to a loft space can I still have a PIV system ?
Yes you can. There’s a fantastic little unit called the Nuaire Flatmaster or the Flatmaster 2000 which has an optional heating element. These units are ideal for situations where you don’t have access to a loft space because of a loft conversion, or because you live in a flat or apartment. You will probably find these PIV units are a little more expensive in the heated variant, but I always recommend buying the model with optional heat because it’s just that. If you buy the model with heat you can enable or disable it, if you buy the unheated version you don’t have that luxury at a later stage. Both versions of heated and unheated can usually be found on Amazon if you want to look at Flatmaster PIV costs .
PIV for Flats – This diagram gives two possible install scenarios for property’s without loft access such as flats, conservatory’s, apartments etc.
Whilst these may be easy to install by a competent DIY’er, please remember that neat holes will have to be cut through the walls to run the air ducting seen in the diagram above, and the ‘heat’ version may need to be wired in by a qualified electrician.
I have damp and condensation since I insulated my house
Yep, I’ve seen lots of this. Thanks to the rising fuel costs and increased insulation schemes, the knock-on effect has been a big rise in problems of condensation. Making a home warmer often means stopping or hindering the essential process of a house ‘breathing’ or natural air movement. If you have recently had your loft, or walls insulated and started to notice damp and mould that you didn’t have before, this probably applies to you.
Damp patches, condensation and mould – This is often seen on council funded or subsidised wall insulation schemes of older type properties. Unfortunately often there is no thought given to the after effects of moisture build up when applying modern insulation standards to older construction techniques.
Count the wall vents in the picture above, I get to 7 on two visible faces alone, it seems counter productive to the insulation process to me, spend thousands of pounds on thick wall insulation and rendering, then cut holes in it to fit air vents like the 1920’s again. This is where P.I.V. systems really come in, and are rapidly becoming more and more popular as insulation schemes expand.
Which PIV unit is best
There are quite a few very good PIV units on the market for domestic installation purposes and for landlord use. I suggest the new ECO Nuaire Drimaster series just because it’s relatively cheap and easy to fit, it also comes with or without heat in case you want that function. This version also has a wireless external heat and fan speed controller, DIY fitting or non specialised fitters can also fit these easily, an electrician may be needed for final connection to the mains though. You may also want to check out other models supplied by Nuaire, although some require specialised installers.
Does PIV help Hay fever or Asthma
Luckily I do not suffer from hayfever or asthma, but during my research I found figures that suggest that during a council pilot scheme some asthma sufferers reported up to an 50% – 80% reduction in attacks possibly caused by a reduction in damp that can help dust mites breed. Also mentioned was a tangible 50% reduction in hay fever symptoms thanks to the reduction of spores, pollen and other irritants such as particulates from car fumes which can irritate the lungs.
Air quality is something I’m starting to think is important as I get older and wiser, and for that reason alone I have now fitted my own PIV system at home just to breath fresh filtered air. Living close to the city, and near busy main roads as I do, car fumes and particles associated with diesels is something I think we could all do with breathing less of.
My house is double glazed and sealed, will stale air still be pushed out? – Yes all but the new air tight and pressure tested eco builds leak air from many places, under floors, through vents, up chimneys, under doors, around seals, trickle vents in windows, trust me it’s a big list.
Is piv noisy – On all but the high speed settings I would say it’s virtually inaudible.
Is piv draughty – Yes and no, it works by blowing air from your loft at a very gentle pace through a grill. On the lowest setting you will have to place your hand as close as possible to detect it, and on the highest it’s like someone blowing on your hand. Balance this against the many benefits, and the fact that draughts will no longer blow into you property because your house will have a positive pressure blowing out instead. I personally don’t consider it a problem, amazingly the lowest speed works quite well in my 3 bedroom semi.
Is the air cold – Again yes and no. The air will be colder than the inside of your house, but the inside of your loft will be slightly warmer than the outside thanks to solar gain and heat rising through your ceilings. There are heated PIV units available to buy that thermostatically pre-heat the air to a setting of your choice up to 20 degrees C ( 68F), but you can debate whether its economical to do so given the small impact of cool air at low speeds and the cost of powering the heating element inside the piv. I wouldn’t install a PIV unit in my bedroom or directly above me in a lounge though, and on very cold days ( < 5C ) it can blow cool on speed one and two, and cold on the higher speeds if you were to set the unit to run at a higher speed.
Common mistakes – Too often with PIV units the speed setting is set too high initially, unfortunately some councils and landlords fall into this trap. Much better to spend a little time getting the speed as slow as possible to be effective, that way tenants don’t tape over the blowing air that could be cold in winter if set too high with no pre-heat. Better to do a little tinkering at setup to get maximum benefit with minimum blow.
Will a piv unit pump hot air in during the summer – No, the onboard sensors can switch the unit off on very hot days, once the temperature drops such as in the evenings, it kicks in again to continue air filtration.
Is piv expensive to buy or run – A PIV system costs from about £300 and should last roughly 10 years running 24 hours a day, as I’ve had customers report this to me. Running costs are extremely low at about £2 per year or thereabout’s. That’s cheap!
Do I have to operate the unit – Usually once fitted and set at the push button controller during install, it completely runs itself. A separate remote heat recovery sensor is available for those who want more control over the unit, but the vast majority don’t bother, me neither.
What is the piv filter life and filter cost – Filters last for 5 years in normal operating conditions, they can also be vacuumed periodically or if you get them dirty by accident. Purchase cost is about £30 for a brand new set.
Do I have to switch it on and off – No, once installed it monitors and runs itself to optimise energy and air quality.
Can I have an bathroom extractor fan with Piv – Yes, as long at the fan isn’t constantly on as this will remove the air and stop the pressure part of the process.
Can I DIY fit a Piv unit myself – As long as you can cut a hole in your ceiling and know how to put a screw in yes, in fact I show you how to do this in a video. Make sure when you connect to the mains however this is done by a qualified electrician for insurance and safety purposes. There is usually a cable provided where a plug can be simply attached but obviously you would need a power socket available, which most people would not have in a loft space. If you’re not the handyman type buy a PIV unit and get an electrician to fit one for you, send him a link to my video if he’s never installed one before.
Which is best Dehumidifier V PIV – For private individuals who are just interested in lowering humidity and removing condensation a good dehumidifier may be the choice for you, they are portable and effective when used properly ( see my best dehumidifier link below ). The downside to even the best dehumidifier can be power consumption costs if you compare it to PIV, as piv is just so cheap to run. Another problem with some dehumidifiers is noise during night time. For the landlord however a PIV unit will do it’s job and will not be switched off, stolen or broken by the tenants.
If as a side issue however you are interested in air quality as well as lowering humidity and getting rid of condensation like me, then PIV is a serious contender.
- Cure condensation – Try the free stuff first
- Best dehumidifier – Simple PIV alternative, what to buy, how to use and where
- How to clean black mould – Clean mold and mildew
- Roof ventilation – Adding roof ventilation
- Roofing tools – Some of the tools I use day to day