I’d like to seal and fill the chimney stacks in my Victorian semi. 

 

What would be the best way to block the fireplace flues?

 

And what to use to fill the chimney stack voids? Vermiculite/Perlite/Leca/EPS?

 

Got to seize the chance and do this quick as there’s scaffolding access to the top of the stack!

If the pots have been removed and the top capped off why would you want to fill the void?

 

My concern is filling the stacks with loose fill is if someone removes a blanking plug in a room containing a disused fireplace.

 

Vermiculite and Perlite both absorb water, so I wouldn't use them.

9 hours ago, twice round the block said:

If the pots have been removed and the top capped off why would you want to fill the void?

 

My concern is filling the stacks with loose fill is if someone removes a blanking plug in a room containing a disused fireplace.

 

I’d like to fill the voids to avoid having to ventilate them, and provide some form of insulation for the stack. 
 

Is Leca absorbent? Would be great to do a DIY pour down the chimney and swerve the cost of blown EPS…

I’ve heard to fill them to loft insulation height with EPS beads leaving them ventilated but covered with a chimney cap. 

Hello,

There are a few ways to do this -

Block the chimney with wool insulation. If the chimney flue isn't too wide, you should be able to seal it by simply stuffing some wool-type insulation into the opening. This will allow some air to pass through (good ventilation) while preventing uncontrolled loss of warm air. 

Fit a "chimney balloon". As the name suggests, these are inflatable bags which can be fitted up the chimney before being pumped full of air. If positioned correctly they will seal the chimney flue.  Bear in mind that they may need topping-up with air occasionally.

If you have access to the roof, the chimney can be capped to create a complete and permanent seal.

Further advice on draughtproofing can be found here: https://www.insulationadvice.co.uk/ia-draughtproofing

My chimneys had the stacks removed to loft level, and I filled the flues with eps beads. I did not want warm room air being vented into the loft space.  The chimney breasts are external (I.e. stick out of the outside wall) and I was surprised at the size of the void that was either side of  the flues. I needed more eps beads to fill those. 

3 hours ago, osprey said:

My chimneys had the stacks removed to loft level, and I filled the flues with eps beads. I did not want warm room air being vented into the loft space.  The chimney breasts are external (I.e. stick out of the outside wall) and I was surprised at the size of the void that was either side of  the flues. I needed more eps beads to fill those. 

 

Thanks; did you DIY the EPS fill, or use a contractor?

I DIY'ed it. I had house cavities done just before, but guys injecting the beads said they 'were not allowed to' inject flues, even if capped off, 'in case somebody wanted to use them in the future'. 

I was about to have the roof replaced, so I bought a few bags of eps beads (sadly not grey, but an individual cannot buy them for some reason) off ebay, climbed the builders scaffolding, and poured them in. They flowed easily, and it was quite enjoyable!

Hi @osprey

 

how have you got on with your EPS beads in your chimney? 
 

Any issues at all? 
 

I am going to be doing the same soon and trying to work out the best filling material. 

 

 

No problems at all!

 

If I could have found the grey beads I would have used them,  but had to make do with the ordinary white ones. I did put a thin layer of rockwoll lot insulation of top, prevent them blowing about, but probably not needed.

Great stuff. 
 

thanks for the reply. gives confidence I should be OK. 
 

I have managed to locate a company that will sell the grey EPS beads in 10m3 bags in Nottingham called polypearl if you ever need any further beads.