Anyone have experience of PIV (Positive Input Ventilation)

Despite good (in the sense of powerful) extractors in the kitchen plus bathroom we still have steamed up windows on a cool morning. There is no damp as such in the building. A friend fitted PIV 18 months ago and has found it very good in reducing condensation overall. Have any 'members' thoughts on it. The system I am thinking of is sold by

https://www.beamcentralsystems.com/Beam-Product-Brochure.pdf

Jim

No experience so far, but have looked at the Vent-Axia range https://www.vent-axia.com/positive-input-ventilation

A friend who is a heating engineer thinks they are a good idea, and has been urging me to bite the bullet. As yet undecided,

Rob

Really need plumbing into each room as if done to just a landing or hall as suggested on the vent axia site when bedroom or bathroom doors are closed circulation is not good.

Client of mine had a system fitted to a flat they rent out and it was OK if all doors open but still got damp when they were closed. I went in and fitted intumescent vent panels into the doors which helped a lot. Then had a change of tenants who switched it off to save on bills and damp came back! also look at cost of replacement filters

Edited By JasonB on 11/01/2023 16:45:30

When I lived in The Netherlands about 30 years ago, my house had a form of PIV installed with heat recovery. Built on reclaimed polders, something was needed to counter humidity levels in the building. It also of course saved on heating bills. If I were building a house today I'd definitely install/specify such a system. Even if confined to the upper storey, where installation in the loft would be relatively easy, it would still have a beneficial effect.

A 'passive house' build requires forced ventilation to meet building regs because they are so airtight however that is not the problem here.

The problem is that you are pulling lots of damp air into the house and when it the house cools it will condense out. What you need to do is close the kitchen door and provide an air input or open a window when the fan is operating. In the rest of the house each human will be breathing out and sweating moisture but much of that condenses on the walls, passes through the plaster and brick and goes out of the cavity wall which is why you must have unblocked air bricks in the outer leaf.
Don't be sucked into the modern factory/school/public building sales pitch of ten of whatever changes of air per hour. A typical living room contains all the oxygen needed for a person for half a day. Ventilate to a sensible level on damp days and maybe more if you have a party of sweaty bodies breathing out moist air.

Rather than a PIV system we went for a Vent-Axia MVHR system. It was relatively easy to install as we live in a bungalow so everything went up in the loft. We have the extraction side of the system running in the bathrooms, toilet and kitchen while all the other rooms are on the input side except the hallway. We don't have any condensation problems, but there again we didn't really have a big problem beforehand.

Our main reasons for installing the system was that it allowed to change all our windows so that none of them open. Better for insulation and security. It also allowed us to filter the incoming air.

Graham

Why do you say you are pulling lots of damp air into the house. This is not necessarily so.
A simple example. If the outside temperature is say 5 degrees and the relative humidity is 80 percent the air will contain approximately 4.7 grams per cubic meter of water. If you warm this cubic meter of air to 20 degrees its relative humidity will be around 17 percent. If this is mixing with say a 55 percent RH inside the house the net result is a lower RH and a dryer atmosphere.

Google dew point calculator and punch in some numbers to see what the absolute vapour content of cold air at 80 percent against warm air at 80 percent.

regards Martin

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I can't imagine living anywhere with no opening windows. Summer would be unbearable for me.

Martin.

Having no opening windows could be a fire risk - you might need to escape via a window.. Hopefully you have some of those special hammers that shatter glass.

I believe UK building regulations require at least one openable window per room but thoat would only be checked on a new build or on sale if the surveyor was a job.sworth.

On days when the RH is low you won't see the problem (next morning). It is when like today the temperature is 14C and humidity 98% that the house cooling down to 6C overnight will result in that moisture looking for a window to condense on.

Well if outside is 14 and inside 6 then it's unlikely to condense out on the inside surface of the windows which will not be that cold a surface. It is usually when the lower outside temp cools the windows that the warm moist air inside condenses on the cold surface

The OP only mentions having extractors in the kitchen & bathroom which will only do something when they are running so unless you have them going for a long time after use (hours in the bathroom) they are not going to do anything for the rest of the time. You need some means for the moist air to escape be that trickle vents, opening a window, etc. Even with PIV you want a way to let the moist air get pushed out by the less moist new air. If the house is all sealed up and draft proofed the PIV will be pumping against a resistance and won't shift the air it should.

We have doors. Our bungalow meets all the latest fire regulations.

They only require an openable window (and it must be of a minimum size and height from the floor) if the room does not open onto a hallway that leads directly to an external exit - ours do, so no need to have opening windows.

We are in the process of remodelling our house and have had our plans reviewed by our architect and local building control.

Opening windows aren't necessary with MVHR as fresh filtered air is pumped into each bedroom and living room 24hrs a day with a maximum flow rate of 500 cubic meters per hour. We run ours at just 34% to get a reasonable flow of air.

Why would I want to open a window and let cold air into the house when I can preheat it using a heat exchanger? In summer the unit automatically bypasses the heat exchanger to cool the house.

Outside doors in every room? (Sorry, being flippant). I recently helped someone with drawings for a two story extension for an older house. The building regs are quite clear on escape routes in the event of fire, opening windows are a large part of this. I believe new regs have just been introduced.

Kitchen: exits in to two different hallways at each end each with external doors.

Living Room: tri-fold doors to outside

Master Bedroom: french windows to outside

Guest Rooms x 2: exit directly into main hallway with external door.

Fire Safety Approved Document B including amendments up to 2022

2.1 See Diagram 2.1a. All habitable rooms (excluding kitchens) should have either of the following.
a. An opening directly onto a hall leading to a final exit.
b. An emergency escape window or door, as described in paragraph 2.10.

Yes single story are a bit simpler as you don't have to factor in the stairs being blocked by fire.

Although the UK seems to favour water/radiator heating systems, a ducted hot air heating system could provide efficient ventilation and heating if coupled to an air sourced heat pump. It is far easier for a heat pump to heat air to 25 C than water to the 50 C needed for radiator system. Also by using a system of ducting and shutters the same system could provide cooling in the summer. The heat pump could also act as a dehumidifier to reduce condensation issues in the winter as well as the summer. During the colder periods of the winter a supplementary heat source may be needed and if this was by using a gas "boiler" then the heat pump could be used to provide even higher efficiencies than current "condensing" boilers. Unfortunately this would be a complex system and not easily retro-fitted to many properties but new builds might benefit if developers didn't add the normal 3x markup.

Ducted hot air systems are common in the States probably because their houses have large basements able to house the necessary kit. Where hot air systems were installed in the UK these have often been blocked off and conventional radiator systems installed because the systems used expensive electric heat source for cheapness.

CS

Many thanks to all who kindly replied. Much appreciated.

Jim

Unless it’s combined with a heat exchanger doesn’t it affect your fuel bills in cold weather?