Positive pressure ventilation loft units – Which?

Dry air takes a lot less energy to heat up though, so it’s still a benefit.

I’ve just installed one of those vent-axia Tempra things in our utility room; we dry all our washing in there when we can’t hang it outside (most of the time) and even with the window cracked open all the time it could be quite a humid place, with condensation on the windows and the side of the freezer and clothes that took a while to dry.

It’s only been in since Sunday but I hung up a whole load of towels to test it and they were dry in two days, no condensation anywhere and it’s a lot warmer than leaving the window open. Sticking your hand underneath it you can feel the incoming air is much cooler, but not as cold as outside, so it seems to do what it’s meant to.

The only down side so far is it’s louder than I thought it would be; if you’re in the kitchen next door it sounds like the fridge is on. It’s fine for what we want it for, but I could never cope with it in a bedroom, for example.

I thought about the heat-sava, it’s continuous speed adjustment sounds clever, but just couldn’t justify the huge price difference over the vent-axia.

Both of them have a very low boost rate compared to a normal extractor fan, so I’m not sure how good they would be in a bathroom; it would be dry after a while, but in the short term it could still be very steamy.

Phill why didn’t you just buy a tumble dryer? Which would be better for the clothes and getting rid of the associated water.

Air inside houses is almost always more humid than outside because people breathe cook, wash and shower. The relative humidity is kept below condensation point by heating.

An exception is hot humid days in Summer when it’s much cooler inside than out and condensation forms when hot, humid outside air meets cool inside surfaces.

To keep humidity down dry towels, bathroom mats etc. under cover outside rather than on a heated towel rail and mop up the bath, shower and sinks after use. Simmer rather than furiously boil vegetables.

To keep humidity down dry towels, bathroom mats etc. under cover outside

We just leave all the windows open during the day (even in winter).

No it doesn’t. When its warm you sweat, if its humid your sweat cant escape so you feel warmer. Lower humidty allows sweat to escape easier, so you feel cooler. Even sat doing nothing in a house at 20 degrees the same effect is happening.

But I’m not sat sweating in my house. The converse argument goes: if you’re outside in cool weather, and it rains (100% humidity), you feel colder. The water content of the air (just before rain) can extract more energy from your *hot body* than dry air.

The system wouldnt work if the air was moist, its the fact that the air in the loft is stable and dry that it works.
Solar gain and heat from the house dry the air out in the loft, and then you put that in to the house

The system can’t do anything about the humidity of the incoming air, air in the loft can’t be dried. Solar gain/heat loss can however raise its temperature, which lowers its relative humidity, which may well be ‘dryer’ than the air in the house so I’m kinda happy with that argument.

Air inside houses is almost always more humid than outside because people breathe cook, wash and shower.

Unless its raining, or foggy… Have a look at the trend from my weather station from the last 24hrs.

Even when it’s raining and foggy outside the air in the house still contains more water. The absolute humidity is always higher.

I’ve experienced the feeling colder when the air is humid. The air in ski resorts is often very cold but with low humidity, at -20°C at 2000m on a clear day a good ski jacket keeps you warm. At -18°C in freezing fog at 170m in Germany I had my ski jacket over many layers and shivered.

Phill why didn’t you just buy a tumble dryer? Which would be better for the clothes and getting rid of the associated water.

We have a tumble dryer (well, a washer/dryer) but it uses an order of magnitude more electricity per load and doesn’t help with the pile of stuff that says it can’t be tumble dried anyway.

Well, just ordered one so will install next weekend and see….

Chiefgroove / Jambo – how are you both getting on with your units?

Sitting in a box waiting for me to get time to fit it.

Does the heater circuit need wiring separately or is it powered by the main transformer?

Wired separately. The heater bit on ours is wired through a wireless thermostat so we can switch it on/off if we want to

Ah. That’ll be the White box then. Switched fused spur would be easier, no?

Where are you putting your switched fused spur though, in the loft, and climbing up each time you want to switch it? Or having an exposed cable on your wall, or chasing it in to the wall…

Wireless was just least hassle IMO, but to be fair overkill for an on/off switch, but does mean can time switch it off and on

I’ll run it on a cable for now and chase it in when we redo that part of the house.

Why do you want to control the heater seperately from the pump? I thought it had its own thermostat?

The default trigger point for the heater is 10deg.

In a long cold snap, that potentially could mean the heater would be on 24hrs a day. The cost would add up.

Least with a timed switch can set it to come on just before we get up etc.

Our house isn’t being renovated anytime soon, so wireless was a cheaper/less hassle fix than chasing out walls.

But if it’s that cold, do you want to be pumping cold air into your house? Surely you just turn the whole unit off?

We haven’t got a heater in hours and never turn the fan off. It lives in an insulated box so can draw direct outside air all the time in summer and divert to attic in winter – but so far this year still on outside air and not noticing cold.

I think the way they work stops the breeze being too noticeable. It slowly brings in cool fresh air at high level so mixes with warm air that has risen (so not as noticeable as leaky doors or an open window). The combination of high level input, mixed temperatures and positive pressure then also promotes convection currents which I believe is how they provide better ventilation through the whole of a small to medium sized house.

In our bungalow I think the majority of the outgoing air leaves through the wooden floors – so again I’m slowly shoving out the coldest air at floor level.

The other thing people forget when comparing with dehumidifiers is that it is FRESH air – not the same old exhalation and farts of an airtight house with the mositure removed 🙂

Fitted today, seem pretty straightforward so we’ll see how it goes.

Well its certainly improved things, more so downstairs than upstairs at the moment.down to 62% RH in the back bedroom this morning as opposed to 75-80% before. still 70% in the main bedroom though but seems to be slowly heading downward. resealed the loft hatch last night so will see how much difference that makes to the upstairs rooms.

just bought a new wireless thermostat for the boiler so may repurpose the old one to control the heater.

still 70% in the main bedroom though but seems to be slowly heading downward

That will always he highest as you have two people breathing out moisture for 8 hours every night….

Glad its working. We noticed the immediate drop. In all it took about a week to fully settle down. We now get between 60-65% which we are happy with.

I assume you have noticed the air feeling fresher too ?

still had some condensation on the windows over the last couple of nights but then its been sub-zero outside and the windows are crap. working out the dew-point they would only need to be ~9degree for condensation to form.

still had some condensation on the windows over the last couple of nights but then its been sub-zero outside and the windows are crap. working out the dew-point they would only need to be ~9degree for condensation to form.

Same here and we have top end double glazed sash windows….

Bedroom is worst but then that’s to be expected with two people breathing out 1l of moisture each overnight.

So a week on and with a bit of dry weather the humidity levels have dropped right off. 55% last night and windows clear.

An interesting thread which prompted me to purchase a drimaster-heat.

Fitted yesterday in under 3 hours, most of which was cutting the chipboard flooring away with a blunt blade in the fein saw 🙁 .

Naturally, as an electrician I’ve bodged the wiring temporarily until I can move all the stuff out the way and run cables properly. No heat on it yet; maybe another bodge tomorrow……

Anyway, first night which was a cold one (zero degrees) and only limited condensation on the windows. The air quality feels better but is moving the stale air from son number one’s festering pit bedroom around a bit too much for my liking.

I had limited options for locating it on the landing, with the light, loft hatch and inconvenient joist placement meaning I was around 800mm from 2 walls and just over a metre from another.

Fan speed is set to 3 and can barely be heard. Vibration is non-existent even though the unit is bolted to the floor using their mounting kit.

The landing feels cooler, but not unacceptably so. It’s hard to explain but it’s a “dry” cold that is not uncomfortable.

The instructions were a little unclear as to the best way to configure windows etc. Our house is an old stone building with wooden but double glazed windows and good fitting doors. There are no trickle vents fitted but there are two woodburners, a vent in one of the living rooms and a chimney vent in one of the upstairs bedrooms. The windows can be cracked open and locked on a night setting if required.
The downstairs walls are lime plaster. Upstairs is still cement/gypsum plaster.

After some research my view is the best way to use the system is to try and get what is in essence a windtunnel effect established. The idea being that the drimaster puts in just enough air to establish a slight pressure differential that will use the natural leakage points the house has. This means we’re not opening windows as this would require the fan having to run at a higher speed to shift sufficient air to get movement from inside to out. It also should stop any windy conditions working against the system.

We’re also reducing the moisture content it has to deal with by running the extractor fan in the kitchen when cooking, opening the bathroom window when showering (no extractor fan) and wiping the shower down with a squeegie to reduce the amount of evaporation having to take place. Washing is dried in a closed utility room with a dehimidifier running.

Our main problem is damp/mold in the corners of our bedroom. Because this is cement/plaster it is cold and there is no opportunity for condensation to travel through it and out via the lime rendered outside walls. The walls are cold and we get a lot of moisture condensing on them. The hope is that we’ll see this be reduced and maybe disappear altogether.

If we don’t see an improvement over the next couple of weeks, we’ll try having the window cracked open at night.

I think the key to success with this device is:

a) reduce the amount of work it has to do by fixing some of the basic issues that cause condensation (washing, cooking, showering etc).

b) match fan speed to property size/levels of natural air leakage.

c) ensure that the loft is well sealed so that the leakage is out the structure so recirculation doesn’t occur.

First impressions are positive but time will tell.

Rich.

Got it running on Friday night. Bloody miraculous! We’ve gone from huge amounts on condensation to barely any within 48 hours. Very happy.

Agreed.

I’ve knocked back the fan from setting 3 to 2 with no discernible difference other than its not so drafty on the landing now.

I hung mine as I could hear the fan at night when it was mounted to the rafters.

I’ve knocked back the fan from setting 3 to 2 with no discernible difference other than its not so drafty on the landing now.

I did this over the weekend too. Our upstairs is much warmer now, and no increase in Humidty or condensation.

To be honest though, at the moment air humidy is lower, these systems have to work harder in slightly warmer, damp weather.

Sounds like everyone is having good results.

One tip when cooking is to use those 2 or 3 level steamer pans. For a start it is just a single pan boiling away (rather than 2 or 3). Then by the time the steam reaches the top lid it condenses and drips back down, so only minimal steam actually gets ejected.

Also fit a proper beefy in-line bathroom extractor fan from screwfix – not those piddly things in B&Q etc.

You can go too far with bathroom extractors… I recently changed a 120m^3/hr fan for a 245m^3/hr one, but it was much noisier in an air-being-sucked-through-a-pipe kind of way so it didn’t get left on for as long after a shower so actually didn’t have as much of an effect. I’ve knocked it back to 180m^3/hr, the “slow” setting, as a compromise which seems better.

So how are people getting on?

My son now has not been in hospital since the system was installed, which is incredible. I know we can not say for certain that it is this system, but it is very coincidental.

I’ve just got back from a week away, and previously the house would have a wet dog type smell, and it felt completely fresh.

Mould is non existant.

All on a relatively low fan speed setting of 2.

Our heating bills havent changed that much, probably very slightly down, but the rooms heat up quicker. Hopefully it wont be long now before solar heating starts to take place, and warm air is drawn in to the house, further reducing heating bills.

We’re pleased with ours. Fan is on 4 but we’ve a biggish, stone house with a narrow landing.

Very little condensation on the windows even on the very cold mornings.

Without the heater we felt it slightly cold on the stairway, but it was not a damp cold like before.

Feels fresher than it did, but doesn’t rid the house of stale clothes and trainers from number 1 son’s pit of a room. However, miracles can’t be expected.

We don’t have a tumble dryer but use a dehumidifier in the utility room to dry them. This seems to require emptying much less frequently than before.

Only problem I had was wiring in the heater. The connectors in the box broke and I had to solder direct to the board.

Other than that, I would definitely recommend it.

Rich.

Sorry for the thread resurrection!!

I have been considering one of these and wanted to know how people have been getting on? We don’t have massive condensation problems (90s house) but our bedroom is north facing and we get a fair bit on the windows in the mornings. As such mould does form in these areas but we don’t get wet walls or such like.

Would one of these things be suitable or overkill?

Thanks

Would one of these things be suitable or overkill?

Our walls never got wet, just mould used to grown in the corners, and windows used to be damp in the morning. Neither things happen now.

The other thing they do if nothing else is keep the air in your house fresh without having to open windows. I think even if a future house isnt damp I would get one, just so that air circulates around.

You need to check that your loft space is the right type though.

Loft space seems OK – can see daylight etc. Think I’ll take the plunge…

Just looking into these. We recently moved into a detached Victorian house (with a modern extension), now the mornings are cooling we get a bit of condensation on the windows and a little mold in the living room. The old part of the house can feel a little damp in the air.

Is the heated PIV essential or is the regular one sufficient? Do they put out a cold draft in winter?

Ours is a 3 bed semi but with 4 floors. I was concerned that just the blower would be too cold so I bought the one with heater.

The fan on ours has speed settings 1-5. I started on 3 and it did reduce the landing temp and my sons bedroom temp by a degree or so which was very noticeable (it is a small landing) I then turned the fan down to 2 and you couldn’t notice any difference or feel a draught.

I haven’t used the heater once since getting it. However it is wired in using a cheap wireless room thermostat so that I could switch it on easily without going in the loft.

No mold anywhere in the house since we installed, and Windows very rarely get steamed up, in fact nothing like they used to

Thinking about it when I did put the heater on to see what it was like, it only made marginal difference, but last winter didn’t get that cold in Yorkshire

Ours doesn’t have a heater and I can’t see most needing the heat. The thing is that the manifold blows the cooler across the ceiling so it mixes with the warm air which has risen up there, which is then brought back down. I think they call it tempering.

Might just take a punt on a regular one.

I think our house is in the region of 1900 sqft, but only the older smaller half feels damp.

How obtrusive is the vent?

we have one in our house which was already fitted when we moved in. I had no idea what it was when we moved in so I switched it off.

cue massive condensation everywhere and a horrible damp feeling in the house. obviously the fact the house is rendered and double glazed means that it has issues breathing.

with the unit switched on the condensation disappears. I used to notice the cold air being pumped into the landing. I experimented and ended up turning the fan down to the lowest setting (barely a trickle) and this seems to work fine.

in short I would recommend anyone with condensation issues to fit one of these units.