Venting from en-suite shower into chimney

[Paul Shortman]

Hello all,

I've been lurking on this group for ages and always google to find info first, but can't find anything to help with this query. I'm building an en-suite shower room into our front bedroom and due to the room layout the wife wants it to go at the farthest point from any external walls. My problem is ducting from the extractor fan to the outside. To make matters worse, we have three floors and the room in question is on the middle floor, so no easy exit upwards. However, right next to where I want to put the fan is the chimney breast. The house is Victorian, mid-1880's and has fireplaces in all three front rooms. I don't know which flue is on the right-hand side next to where I'm putting the fan, but if the chimney was properly ventilated, I wondered if venting the fan directly into the chimney would cause any problems? Only the downstairs fireplace is being used, and that has a gas fire installed. I'll be glad for any advice you can offer. Thanks in advance.

Paul Shortman.

[Set Square]

It sounds like a pretty *bad* idea!

The grill on bathroom extractor fans provides nothing like a perfect seal. Any time when the downstairs gas fire is on and the en-suite fan isn't on, there is a high probability that fumes from the fire will end up in the en-suite.

I would be very surprised if your proposed solution would comply with the relevant building regs, anyway. Others can probably quote chapter and verse on this.

[IMM]

Why would it? It doesn't do now, so why should it do it if a vent is run though it?

I would run flexible ducting up the flue to the chimney pot and terminate with a normal flue terminal. It may require two fans in series to push up that far. There are non-return flaps available for ducting, to prevent any draw on the flue and any fumes from the gas fire entering the vent duct. See the vent ducting makers for these.

[Owain]

"Paul Shortman" wrote | I'm building an en-suite shower room into our front bedroom | However, right next to where I want to put the fan is the chimney breast. | The house is Victorian, mid-1880's and has fireplaces in all three front | rooms. I don't know which flue is on the right-hand side next to where I'm | putting the fan, but if the chimney was properly ventilated, I wondered if | venting the fan directly into the chimney would cause any problems? | Only the downstairs fireplace is being used, and that has a gas fire | installed. | I'll be glad for any advice you can offer.

Very bad idea. If the chimney is that used for the gas fire, your extractor fan could blow the combustion products from the gas fire back into the room.

Even if it's an unused chimney, the air from a shower room will be moist. That moisture will condense out of the air inside the chimney, leading to rot.

You may be able to use an unused chimney to continue the extractor fan duct up to roof level, terminating at an appropriate terminal (not sure of regulations if there is also a gas flue terminal on the same stack). But you will have to use a centrifugal fan to overcome the duct resistance, and probably also provide a condensate drain-off for the duct at the bottom.

You can get rectangular cross-section ducting so if you have front-back floor joists may be able to take a ducting through the floor cavity above the bathroom to the outside wall.

Owain

[Peter Taylor]

Hi Paul The original bedroom fireplace will have its own flue and chimney. It does NOT share a flue with downstairs, as some people have remarked. I have never heard of two fireplaces sharing a flue (unless someone has been messing about with them of course). Sometimes the wall separating separate flues in the stack (called by various names depending where you are, but what I call a withe or withy) has become damaged and allows smoke and gases to pass between flues, but this is fairly rare as the soot tends to block up any gaps.

The problem about using a flue for shower ventilation is the condensation that will occur when the warm moist air hits the cold air and brickwork in the flue. The moisture will dampen the soot and cause a black tarry stain internally, which will ruin decorations and be very difficult to eradicate. The damp soot is very acidic and attacks various materials, particularly any copper pipes or lead flashings.

The way over this is to use a plastic duct to suit the size of your fan, and drop it down the flue from the chimney pot until you can reach it through the hole you make for the fan. Ideally the duct should be rigid (eg 110mm dia uPVC soil pipe) as this has maximum air efficiency, but you can use a flexible duct but may need to upsize it slightly. Then seal the duct securely to the fan and a proper flue outlet at the top. Condensation will still occur inside the duct and needs to be able to drain back into the shower room, but insulating the duct will minimise this. Get yourself a decent fan catalogue, such as Vent Axia, and talk to their technical rep if necessary.

you thought about having a ceiling fan with a duct in the loft going up through the roof? Might be a lot easier.

Best of luck Peter

[BigWallop]

These might help:

[Owain]

"IMM" wrote | > Very bad idea. If the chimney is that used for the gas fire, | > your extractor fan could blow the combustion products from | > the gas fire back into the room. | How?

^ fumes rise up chimney | | | ^ | | | | | | | | ^ | | | | | | | | | | | ^---FIRE

__| |_

[Owain]

"Peter Taylor" wrote | "Paul Shortman" wrote | > I don't know which flue is on the right-hand side next to where | > I'm putting the fan, | The original bedroom fireplace will have its own flue and chimney. | It does NOT share a flue with downstairs, as some people have remarked.

However the OP's wording seemed to suggest that he might be breaking into whichever flue in the chimney is nearest.

Owain

[Peter Taylor]

Fair cop guv. I didn't read it properly. Sorry Peter

[John Stumbles]

Missed the original message (NTL newservers playing up again? :-().

Even discharging into a separate flue I think it's a bad idea because the warm wet air is liable to condense and cause damp in the chimney.

[IMM]

They are two separate flues, not one.

[IMM]

[Peter Taylor]

IMM wrote

He still doesn't get it, does he Owain? :o)

Peter