Mechanical Ventilation with Heat Recovery (MVHR)

Even if you live in the country surrounded by fresh air, what temperature is the air from Autumn to Spring and how much moisture is in it? Anything over 70% humidity can cause damp and mould rather than prevent it. Without MVHR whatever’s outside is coming inside, because every other type of ventilation sucks it in through vents in your windows, or at least it should do. If you close those vents to stop cold draughts, or your bathroom fans run intermittently, you have no ventilation, and your house stops breathing. If you don’t close the vents and your bathroom fans run properly, every two hours you’ll be swapping a house full of warm air for a house full of cold air, which accounts for around a third of your heating bill. Traditional ventilation doesn’t filter air and doesn’t recover energy. MVHR can filter almost anything and recovers over 90% of the heat you will otherwise lose.

Some people say MVHR is pointless in a property that isn’t airtight. What they should say is that you won’t get over 90% heat recovery because some of the recovered heat will lost through the gaps and cracks in the building fabric. You might only get 75% heat recovery, but that’s still 75% more than any other type of ventilation and you’ll still get the filtration benefits. With MVHR to ventilate without wasting heat, you have a green light to make the rest of the property airtight, which in turn makes it more comfortable and efficient. That may not happen overnight, but at least it can happen. It must happen if your property is to become sustainable long term, because wasting energy has more than just a financial cost. MVHR is the first step on the road to low energy living. There’s a reason it’s mandatory under Passivhaus guidelines and best practice for the energy savings Trust.

Any MVHR system will provide ventilation and air quality like you’ve never experienced before, but cheap units normally only do that for five years whereas quality units should last over twenty. Even if you got ten years, the cost of replacing a cheap unit and paying someone to reinstall it will make it dearer than a quality unit longer term.

Quality units run almost silently without humming like a moped, they filter traffic pollution and pollen rather than just leaves and insects, they’re more hygienic because they have wipeable surfaces instead of perishable plastics, and you can adjust them from your sofa on your smartphone without crawling around on the floor of your plant room. Quality units also have options like supplementary heating or comfort cooling.

All properties are designed ‘to work’ with a given amount of air movement, forever. So, ventilation is a permanent feature and not a temporary measure. We suggest you look for other ways to economise without compromising on air quality. If you’re a developer working to regulations for the minimum cost, bear in mind ventilation problems are deemed serious defects by the NHBC, meaning you could be liable for expensive repairs if the system you install doesn’t last ten years. In our experience cheap units are a false economy.

Branch ducting is cheaper because the materials are cheaper and there’s less of it. Problem is, it suffers from high static pressure, or air resistance, which makes it noisy and puts additional load on the fan motors, which in turn can become noisy and more expensive to run. Even a small increase in running cost adds up when it’s running 24x7 forever. Radial ducting has around half the static pressure, so everything runs more efficiently.

Branch ducting is also full of sharp 90-degree bends, which create turbulence, add noise and mean the system can’t easily be cleaned in five years when it’s lined with dust and grime. Radial ducting has smooth, sweeping bends that can be cleaned. Quality radial ducting has an anti-bacterial, anti-static lining to prevent dust build up and is made from virgin plastic without contamination risks.

Finally, branch ducting connects one room to another, which allows crosstalk sound to travel from one room to room another too. Radial ducting connects to a manifold that feeds each room separately to prevent crosstalk. Cheap manifolds will distribute the air, but quality manifolds are acoustically lined to further attenuate unwanted sounds. Let’s just say radial ducting is better than branch, and anyone who disagrees hasn’t had one then replaced it for another like we have, but what about the rest of the system? Using the correct insulated ducting to connect the manifolds to the MVHR and the MVHR to atmosphere is arguably more important

Flexi duct is a popular option but is now outlawed by the NHBC for health and durability reasons. It looks ok to the untrained eye and is certainly cheap, but how much will it cost to replace when it eventually fails? PVC and steel ducting wrapped with lagging satisfies the regulations, but it doesn’t stop condensation build-up when cold air travels through a pipe inside a warm space. Condensation normally collects on top of the MVHR instead of inside it, then runs down the back and eventually through your ceiling. High grade Expanded Polyethylene (EPE) ductwork is the only product that eliminates condensation risk, even though a single bend costs the same as 5M of flexi.

Installing two 45-degree EPE bends instead of one 90-degree bend adds even more cost, but it improves the laminar air flow which makes the whole thing run quietly and more efficiently, so long term it’s another £20 well spent. Cutting corners to cheapen a system and win business is easy, but in our experience when you buy cheap you buy twice.

Ask yourself how much time and investment someone would put into a free design, pre-sales, just to close a deal. Certainly not enough to employ a qualified architect to study the drawings, speak to other architects and builders involved with the project, work out the optimal position for plant, somewhere you can live with long term, solve problems with pinch points, ducting in cold voids, fire protection barriers or acoustics from nearby roads. Will a free designer ask about prevailing wind direction or colour coordinate your roof or wall terminals, or will they just sketch some red and blue lines on a drawing, so you think you’ve got a workable design? An initial design can take minutes on AutoCAD, but a final design normally involves multiple design revisions, a site survey and some value engineering. When was the last time something free was something worth having?

In our experience your MVHR system designer needs to provide technical support throughout the project, from concept, through the build and after people move in. Ultimately the ‘free’ designer just wants one thing, to sell materials. What happens to those materials after they land on your driveway is someone else’s problem. Normally an installer who will struggle on and cost more in head scratching than you’d have paid a professional designer. If you’re still not convinced, try a free designer and come back to us with your next project.

In a word, accountability. If you buy a cheap kit online and pay your plumber or electrician to install it, what happens when something goes wrong? Your installer blames the supplier, your supplier blames the installer, the manufacturer blames them both and nobody guarantees anything. Meanwhile you’re stuck with dripping water, annoying noises, potentially no ventilation and no recourse from anyone. Because Pro-fit design, supply, install and ultimately set up your MVHR, there’s nobody else we can blame. Provided it’s been serviced, if something goes wrong, we’ll make sure it gets put right.

Pro-fit offers a comprehensive 5-year parts and labour guarantee because we know you’re unlikely to need it. Nobody has so far. It’ll be designed correctly, specified correctly, installed correctly and set up correctly. Even if we’re not around in five years our work is covered under the NICEIC’s platinum guarantee, meaning they’ll cover the cost of any remedial work if needed. That said, if we aren’t around in five years it’s bad news for everyone, because we’re the guys the manufacturers call when there’s a problem nobody can fix. For peace of mind and accountability let us design, supply and fit.

A typical service* carried out by one of Pro-Fit’s competent service engineers involves: • Replacing the filters • Cleaning the air valves (where accessible) • Removing and cleaning the heat exchanger • Cleaning inside the unit • Checking and cleaning the fan impellers • Checking the system for satisfactory operation • Re-balancing the system (optional – an additional charge will apply) •Visual inspection of external grilles (Subject to safe access closer inspection is possible but an additional charge may apply) *Please note: our standard servicing charge does not cover the cost of surveys or remedial works. If you are having operational issues with your system please provide us with full details and we will be pleased to quote accordingly