Not signed in (Sign In to the Green Building Forum)
Categories
- General
- Essential for Newbies
- Building Regulations and Standards
- Commercial build
- Data and monitoring
- Downshifting
- Energy Assessment
- Events and Courses
- Fundamentals
- Green Building Bible
- Green Building magazine
- Green Living
- Heating and cooling
- Housing - New Build
- Housing - Renovation
- Offers and wants
- Politics
- Products
- Renewable Energy
Vanilla 1.1.4 is a product of Lussumo. More Information: Documentation, Community Support.
Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications:: Apply now.
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications:: Apply now.
-
- CommentAuthordovecote
- CommentTimeAug 15th 2012
I am looking to install two new chimneys as part of a refurbishment (7.1m floor to roof ridge). As open fires I see that the flue diameter is a factor of the fireplace opening area.
But what if I want to put a wood burning stove in there? Must I install a flue that is constrained by the stove outlet. I understand that most stoves have a 125mm outlet, but this can be adapted to a 150mm flue - but could a 125mm outlet be safely joined with a larger flue - say 200mm or more? -
- CommentAuthorjamesingram
- CommentTimeAug 15th 2012
I'm no expert , other here are more informed.
Depending on kW size, flue is usually suggested to be 150mm for stoves . If its to larger you can get drawing problems.
Build your chimneys to suit open fires then you can pop a 150mm liner down it if you have a stove. -
- CommentAuthorJTGreen
- CommentTimeAug 16th 2012
If you are building new and green, there's no reason to size your chimney flue to suit an open fire as you won't be having one. just start as you mean to go on, with the flue sized and lined for a stove. -
- CommentAuthorJoiner
- CommentTimeAug 16th 2012
And then only if alternative forms of space/dhw heating aren't available.
-
- CommentAuthorfinny
- CommentTimeAug 16th 2012
Hey Dovecote,
as above, open fires should be out of the question..a 150 mm flue will cover most installs, if there is any chance you will be wanting a monster stove then 175 mm may be necessary. Either way you should have some idea already of stove required. Remember to specify a vent for the appliance. -
-
CommentAuthorfostertom
- CommentTimeAug 16th 2012
Posted By: finnyRemember to specify a vent for the appliance
He means a gurt big open outside-air inlet to the room, to supply combustion air to the appliance. Which knocks a huge hole in all your other expensive heat-conservation measures. Poor idea. -
-
- CommentAuthorfinny
- CommentTimeAug 16th 2012
Not quite sure I said put a gurt big anything in there Tom..
As I am sure you aware, in this situation an appliance of 5 Kw or under requires no dedicated vent.
An 8 Kw appliance requires a circular hole 46 mm in diameter.. Gurt..no..ventilation, yes.
With the option to connect the appliance directly to the vent can't see the bad idea..oh and it's required by Part J -
-
CommentAuthorfostertom
- CommentTimeAug 17th 2012 edited
Posted By: finnyWith the option to connect the appliance directly to the vent can't see the bad idea
No, that makes it a good idea - but very few appliances offer that facility, yet.Posted By: finnya circular hole 46 mm in diameter.. Gurt..no
Gurt..yes - that's a disastrous hole, if you've spent lotsa money on sealing up all other leaks. If you haven't done major airtightness, then yes, a bit more makes little difference. Except that any kind of chimney/flue + inlet is a very efficient air-changer, compared with casual cracks and holes. -
-
- CommentAuthorWillInAberdeen
- CommentTimeAug 17th 2012
A 46mm dia hole is 1700 mm2.
This is the same air leakage area as:
a 0.3mm gap all round the edge of an external door [2*2100 + 2*900]*0.3 = 1800mm2
a 0.1mm gap all around the perimeter of a room (2*4000 + 2*5000)*0.1 = 1800mm2
a 0.02mm gap between osb sheets on a roof (2400 + 1200) * 30sheets * 0.02 = 2200mm2
All are undesirable! Some are more avoidable than others.
Yes, a round hole will leak more air than a long thin crack, of same area.
Our house still has one open fireplace c/w chimney balloon, we light the fire at weekends (homegrown logs, remove the balloon). Over a year I'm convinced we loose more heat in draughts than we get out from the fire. Does look nice, but will replace it with stove when possible.
For unused fireplaces, we boarded them over, builder was keen to put a vent to ventilate the disused chimney with air drawn from room. Convinced him to ventilate them with air drawn down from roof void instead. -
- CommentAuthorEd Davies
- CommentTimeAug 17th 2012
WIA, how do you work out the air leakage for the various sized holes? -
- CommentAuthorWillInAberdeen
- CommentTimeAug 18th 2012
<scratches head and searches internet for long forgotten fluid theory>
In theory the Darcy weisbach equation can give air flow if you know pressure difference and hole diameter.
http://en.m.wikipedia.org/wiki/Darcy%E2%80%93Weisbach_equation#section_7
If the hole is not circular then you convert it to an equivalent "hydraulic diameter" based on area and perimeter. A crack has longer perimeter so comes out with less hydraulic diameter.
In practice you might be better measuring the air loss, calculating it is heavy going !
1 to 11 of 11
