Homeowner Advice

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PIVs Explained

6th January 2023

If you are fed up with damp or find yourself fighting a losing battle with mould, installing Positive Input Ventilation could be the solution that you so badly need. In this series, we take a look at what PIV is, how it works, and whether it could be right for your home.

The first Positive Input Ventilation system was developed in the early ‘70s to address ventilation problems for existing properties. The fact that they are easy to install with limited disruption made them a convenient way to tackle condensation, mould and damp.

But what exactly is Positive Input Ventilation?

Positive Input Ventilation provides a continuous source of fresh, filtered air into the house which then forces stale air out. A PIV consists of a unit, which is installed in the loft of a house and which links to a distribution diffuser in the ceiling of the room below. The slight positive pressure that the PIV supplies continuously means that the air throughout the property is constantly moved and diluted, which results in better indoor air quality.

Is PIV the same as an extractor fan?

An extractor fan that you might find in a bathroom is great at removing humid air and reducing condensation caused by using hot water and appliances. However, an extractor fan doesn’t influence how that air is replaced. A PIV controls the airflow IN to a property, filtering air from outside and circulating it inside the house, to replace the humid air.

Can PIV help with allergies?

Positive Input Ventilation doesn’t just help with preventing condensation, it can reduce allergies too. Because it filters the air that is circulated, it can reduce the concentration of allergens, such as pollen, within the home.

Is a PIV as good as an MVHR system?

MVHR, or Mechanical Ventilation with Heat Recovery, is effective in preventing damp issues and improving ventilation and air quality in a home. However it requires ducting, which can’t easily be installed in an existing property. Unlike MVHR, PIV is easy to retrofit in almost any property.

Is PIV cost effective?

A PIV system costs around £700-£1,000, including installation. As always, there are a range of models available and there are higher budget ones which offer better performance – and vice versa. Once a PIV is installed, it costs a few pence a day to run; a relatively small amount in comparison to the improvement in air quality and reduction in damp and mould.

At Trust A Trader, we understand that fighting damp can seem like a constantly losing battle. Installing a PIV system could be the solution that you have been looking for all along. Next week, we will take a look at the process of installing a PIV system, as well as its pros and cons.

Follow us on Facebook or Twitter for more information, or get in touch with a builder or handyman to find out more about getting a PIV system installed.

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Find clear, practical answers to common homeowner advice questions, helping homeowners understand everyday issues, know what checks they can carry out safely, and when it is best to contact a qualified professional.

What home repairs should I never attempt myself?

Gas work - full stop. Any work on gas appliances must be done by a Gas Safe registered engineer by law. Structural changes like removing walls, altering roof timbers, or touching anything load-bearing need professional assessment and often Building Regulations sign-off. Electrical work involving the consumer unit or new circuits must meet Part P. And if your property was built before 2000, be aware asbestos may be present - it can only be handled by a licensed specialist.
Which home improvements add the most value to a property?

Improvements that add usable space or modernise the rooms buyers scrutinise most tend to deliver the strongest returns. Loft conversions consistently top the list - adding a bedroom and bathroom can add more value than the work costs in many areas. Kitchen and bathroom updates are next. Open-plan ground-floor extensions connecting to a kitchen-diner have become one of the most sought-after layouts in UK family homes. And energy improvements - insulation, a new boiler, solar panels - are increasingly influencing buyer decisions as running costs become a bigger part of the conversation.
Should I renovate my home or move house?

There's no universal right answer - it depends on your situation. Moving gets you what you want without living through a building site, but stamp duty, estate agent fees, and moving costs can easily add up to tens of thousands of pounds. Renovating lets you stay put and invest in your own property, but comes with disruption and unexpected costs. The most useful comparison: get a clear view of what your home could realistically be worth after the work, and what a move would actually cost end to end. A local estate agent and a builder's quote can give you those two numbers.
What does a home survey actually cover and do I need one when buying?

A survey is an independent assessment of a property's condition carried out by a qualified surveyor - separate from the mortgage valuation, which only tells the lender what the property is worth, not what's wrong with it. A HomeBuyer Report flags visible defects and anything that needs further investigation. A Full Building Survey goes deeper and is worth the extra cost on older, larger, or unusual properties. Given that a house is likely the biggest purchase you'll ever make, skipping the survey to save a few hundred pounds is a false economy - a single missed issue can cost far more to put right.
What should I do before starting any major home improvement project?

Get your paperwork in order before anyone picks up a tool. Check whether you need planning permission or Building Regulations approval. Find out whether a Party Wall Agreement applies. Confirm your home insurance covers you during the works. Get at least three written quotes and make sure the scope of work is clearly agreed in writing with whoever you hire. And have a contingency budget - on almost any renovation, something unexpected comes up. The projects that go smoothly are usually the ones that were properly planned before they started.
What is the difference between freehold and leasehold and why does it matter for home improvements?

If you own the freehold, you own the property and the land it sits on outright - you can generally do what you like subject to planning rules. If you own a leasehold property (common with flats), you own the right to live there for the remaining lease term, but the freeholder owns the building. This matters for home improvements because many leases require you to get the freeholder's written permission before making alterations - sometimes even internal ones. Always check your lease before starting any work, as doing alterations without the required consent can cause problems when you come to sell.

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