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Heat recovery ventilation?

(26 Posts)
EarSlaps Tue 21-Oct-14 13:09:20

We have big problems with condensation in our bathroom. We do have an extractor fan and run it (door and window shut) whilst showering, bathing etc. I then try and have the windows open as long as possible after to clear the steam etc, but as we have no top window bits and they are over a flat roof I need to shut them when we go out. Due to the low roof on our house, the fan is a good foot or so below the level of the ceiling, so the damp air seems to stick around and our ceiling paint gets really mouldy and is peeling off.

I was looking at replacement, better fans, and I came across Mechanical Heat Recovery Ventilation. Vent Axia seem to make ones that can go on the wall for one room only and take out the damp air and bring in fresh air, warming it with a heat exchanger. Has anyone got one of these and are they any good? Can they shift enough air to de-mist after two or more hot showers? Are there any other equivalents that could work? I think the fan is Zone 1, so would need to be rated for that.

Alternatively, could some sort of loft mounted one work? Would it be possible to have one that vented the hallway and the bathroom to add ventilation for all over the house? What sort of costs would we be looking for that?

PigletJohn Tue 21-Oct-14 14:43:42

I have used one. In a kitchen or bathroom it is less suitable than a simple extractor, because it does not create suction that prevents water vapour (and odours) diffusing round the house.

Assuming that your extractor fan is effective, you should leave it running, with the door and window closed, during and after your shower, until it has cleared the water vapour. If it is effective and you turn it on before the taps, it will prevent the steam building up so much, so the walls and window will not be so wet.

EarSlaps Tue 21-Oct-14 21:45:18

Well our fan is clearly rubbish then. We turn it on before the shower and you can run it for a good hour or mor after ((door and windows shut) and it is still muggy and steamy. Open the windows for a few minutes and it clears. That's just not great now it's getting colder as it makes the room really cold.

PausingFlatly Tue 21-Oct-14 21:55:27

It's true that HRVs don't create negative pressure to prevent steamy or smelly air drifting out through the open doorway.

On the other hand, if you're running a normal fan with the door and window closed, the fan may not be very efficient because it can't get much replacement air in through the cracks.

With what you describe, I think the HRV might work a treat. The inlet is basically replacing the open window, in a secure manner and with the added bonus of heat recover.

PigletJohn Tue 21-Oct-14 21:56:21

yes, it probably is.

The average cheap Builder's Fan is very weedy. Sometimes the duct or vent is clogged with cobwebs and thick dust, sometimes the duct (especially if flexible) falls off or fills with water.

Mine is effective, I clean the dust out of it occasionally, keep the duct clear, and swap it for a new one if it gets slow or noisy.

The best bathroom extractors I know are the inline ducted ones. They are a bit big and unsightly, and are usually fitted above the ceiling, with the duct running to the eaves, or through a cable wall, or (rarely) though a roof vent. As well as being three times as powerful, they are much quieter.

PigletJohn Tue 21-Oct-14 21:58:51

replacement air:

Bathroom fans suck it in from the rest of the house, through the gap under the door. Since water vapour is lighter than air, it stratifies, with the steam rising to the extractor, and the dry air filling the room from below. If the door is open, this stratification does not occur so well, and the incoming air mixes with the steam.

PausingFlatly Tue 21-Oct-14 22:05:28

Depends on the gap under the door.. Big gap works well. Tiny gap, not so much. Obviously.

I was recently in a house where they'd just replaced a drafty bathroom window. Now as you close the bathroom door, you can hear the fan go up in pitch as it struggles to drag replacement air in.

That one's also a candidate for HRV, now I come to think of it. It's that or shaving more off the door.

EarSlaps Tue 21-Oct-14 22:06:05

We have a good gap under the door so I think it's a fan problem. All the energy seems to go on making a noise.

Any recommendations for what to get? It's only a small room but we like our showers.

PigletJohn Tue 21-Oct-14 22:08:58

can you post a pic of the fan you have?

Does it go straight through the wall? If not, how long is the duct?

Take a torch and peer in. Can you see dust and cobwebs? When turned on, do the blades spin too fast to see?

Have you got scope to fit a fan above the ceiling, with a duct leading outside (you must not blow steam into a loft or other cavity)?

PausingFlatly Tue 21-Oct-14 22:09:12

And erm, what's with this idea that water vapour is "lighter" than air?

EarSlaps Tue 21-Oct-14 22:18:46

One very boring picture smile

It is a bit dusty, I do clean it sometimes but tbh it was always pretty rubbish. It's about 4 years old and we've always had steamy bathroom issues. Vents straight to the outside through the wall. 1970s cavity walls. Makes one hell of a racket with extra drones sometimes iyswim.

I'd ideally prefer a ceiling extractor but I guess it would be cheaper to get the current one replaced.

PigletJohn Tue 21-Oct-14 22:19:42

Clouds are formed by water vapour rising into the sky, which it does because it is lighter than air. It also rises from cooling towers. In bathrooms, ceilings are always worse for condensation and peeling paint (subject to temperature of walls).

I had a look for an alternative source

PigletJohn Tue 21-Oct-14 22:25:40

how near the ceiling is that fan?

I think it might be this one Note the price.

I haven't yet been able to find its extract rate in cubic metres per hour.

If it is noisy the bearings are probably worn out and it might be running slow.

EarSlaps Tue 21-Oct-14 22:25:47

I am thinking maybe a humidistat one this time, or is that just more to go wrong?

This one is timed, seems about 5 mins after lights off but we leave them on if needed. But opening windows works better.

Is it worth getting one with a constant trickle function as our windows don't have trickle vents?

EarSlaps Tue 21-Oct-14 22:26:49

It's about a foot down, can't go higher if out to wall as we have a low roof.

EarSlaps Tue 21-Oct-14 22:27:16

Yes, price confirms how crap it is.

PigletJohn Tue 21-Oct-14 22:45:16

found the rating. It is nominally 80 cu m/hr which is typical for a small fan.

We had another 'snetter earlier who was pleased with her Airflow QuietAir (half way down which is nominally slightly more powerful at 90 m/hr, but is a quiet fan with ball-bearing motor. I have noticed over the last couple of years that people are turning away from the budget throw-away fan.

I do recommend one with a timer, I would suggest a 20 minute delay. A good fan is very quiet so I don't think it will keep you awake. The power usage is only 5 Watts, so it would run for 200 hours on 14p worth of electricity, which I think is fantastic. It is a bit expensive to buy.

Also consider this one which is slightly more powerful.

Look at the noise ratings. Your old Silavent was rated at 32dB(A) when it was new.

When you have a new fan fitted, wipe out the duct when the old one comes out, and feel the outside terminal in case it is jammed or blocked. It will either have a grille, or some kind of flappy vent. I recommend the Cowl Vent, which has one large flap and is much quieter and more durable than the sort with a plastic venetian blind.

I did look at the wholesaler for Centrifugal fans, which tend to be quieter and more powerful, but couldn't find one.

PigletJohn Tue 21-Oct-14 23:06:37

And here are some inline fans like you would put in a loft, or out of sight in an airing cupboard. Read the reviews, you will see one big brand comes out better than the other.

Also look at the extract rate. If you buy one of these you should be looking at about 250 cu m/hr, which is three times the power of a little fan.

Use rigid ducting, not flexible, and flop loft insulation over the duct to prevent condensation inside it.

EarSlaps Tue 21-Oct-14 23:11:00

Thank you for your help!
I like the look of this as it's very powerful but it has a hefty price tag. Still, we'll have installation costs too so not much point going too cheap.

PigletJohn Tue 21-Oct-14 23:20:10

123.3 cubic metres per hour is quite a lot, yes. See if they do a mains-voltage one which (presumably) is the same as you already have so would swap in.

Have a look at this

EarSlaps Sun 26-Oct-14 17:49:18

Had the electrician round and he suggested ceiling inlets for an inline fan in the loft. The location of the fan on the wall means it will never clear the steam at the top of the room. Plus it is 240v when it should be 12v (in zone 1).

He suggested two inlets- one over the bath/shower and one over the loo area to make sure it gets all the steam. Plus a run on timer. I'm going to get this beast.

I'm guessing once we've cleared the bathroom steam it would be amazing for airing the rest of the house- just open the windows everywhere but the bathroom and internal doors and pop the fan on for a bit.

We're going to go for a lo Carbon Tempra in the downstairs loo as there's currently no ventilation in there and that will help the downstairs air quality without making that room even chillier!

Personally I'd love a whole house mhrv system like there was in a flat I lived in in Finland, but they are so expensive. I might consider on upstairs at some point if prices drop.

EarSlaps Sun 26-Oct-14 17:50:44

And thank you for all your help. I feel like a true MNer now I've had PigletJohn responding to one of my threads smile.

PigletJohn Sun 26-Oct-14 17:53:47

that looks great.

ask him to mount it on a thick ply board with synthetic carpet (or some kind of rubber mat) between the board and the joists, it will reduce vibration to the ceiling.

The duct should slope slightly downwards towards the outside so that condensation runs outwards, but if you flop loft insulation over the duct it will not get much condensation.

EarSlaps Sun 26-Oct-14 18:15:29

Thank you! I will ask him to do that. He's hoping to run it out of the soffits but said it's not always possible.

I'm looking forward to an end to having the upstairs windows open all bloody day and still having a mouldy bathroom. Once we can clear the steam better I'll treat, stain cover and repaint the ceiling and redo the sealant. The bathroom will look nice again.

I'm considering one of those windows vacs too to clear the tiles and screen as that should lower humidity in the room, but I'll see what difference the decent fan makes before I invest.

EarSlaps Sun 09-Nov-14 08:41:54

An update- had an inline fan added on Friday. It's very powerful and he mounted it on board and foam as requested so it's really quiet. A long hot shower later and the mirror was clear before I left the room and the windows not much later. No more steamy damp bathroom.

Also had a single room heat recovery ventilator but in the downstairs loo. It runs on a constant trickle and can be boosted if needed. The air feels a lot nicer in there now.

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