Chimney System - Air Tight House

Jorus · 27-07-2008 10:28PM #1

Hi,

Just wondering if anyone knows about this or if they have done it in their house?
We are building a block house - hoping to get it as air tight as possible (putting in HRV etc).

We are just wondering what is the best chimney system to put in? We are putting in a free standing log stove in one of the rooms and also a insert wood burning fire ( http://www.fondis.com/dn_the_open_hearth/) in the other room. We will need a chimney system that has an external air feed and is also air tight ?

We are looking at the Scheidel system? Does anyone else know of other systems to compare prices with?

Also the insert fire by Fondis - are they any other alternatives out there (that must be capable of connecting to an external air supply) ?

Thanks,

cormacmul · 28-07-2008 09:16AM

Hello Jorus,

I am interested in the same types of systems. But I am finding it very hard to get good advice. I am looking at having two solid fuel stoves. And the only advice I have been given so far is to have an extenal fuel supply so that the fires are not taking air from the house. When the fire's are not in use, then vents would be sealable.

Have you met or seen anyone that has installed the systems you are taking about, if so I would like to talk to them too.

Talk later,
Cormac

Jorus · 28-07-2008 10:32AM

Also - do we even need an external air source for the fire / stove if we want an airtight house with HRV?

Is it sufficent to just close the air feed vents on the front of a standard fire / stove when they are not in use?

cormacmul · 28-07-2008 10:53AM

Hi Jorus,

Some people I talk to, say that you don't. That the air from the HRV would be enough to feed the fire. Other people say that you need an external air source.

But to me at the moment there are to many if's and but's and no proper answers.

My understanding of fireplaces/stoves is that they are complex to get right. I would love to meet or talk to people who have fireplaces/stoves with HRV. I have talked to some HRV installers and they say they have installed them with fireplaces/stoves but when I ask for some references they arent forthcoming.

Is it sufficent to just close the air feed vents on the front of a standard fire / stove when they are not in use?

I think this would depend on the stove, but yes I think this is OK.

Please talk to some HRV installers and if you get any good specific details please let me know.

Talk later,
Cormac

CJhaughey · 29-07-2008 08:24AM

We have HRV and a woodburning stove (Morso Squirrel)
All last winter we burnt wood and never had any problems.
The flue height must exceed the roof of the house by a few feet or you will have downdrafts in some wind directions.
Bear in mind that the stove is quite small and we run the HRV with a slight underpressure to avoid pushing house air into the fabric of the house.

cormacmul · 29-07-2008 10:45AM

Hi CJ

Can you explain a bit more

we run the HRV with a slight underpressure to avoid pushing house air into the fabric of the house

If you don't push air in how can the heat be recovered from the air going out?

Talk later,
Cormac

CJhaughey · 29-07-2008 12:18PM

Our HRV unit Temovex 480 has 2 fan speed adjustments, one for the intake fan and one for the exhaust fan.
If you run the exhaust fan at a higher speed than the intake fan speed the house will have an underpressure.
The air still moves in and out of the house but the extract is stronger than the intake.
The heat exchange works as usual.
If you set it the reverse way there will be over pressure and moist air could possibly be forced into the fabric of the house via electrical switchplates etc.

10-10-20 · 29-07-2008 03:17PM

Correct me if I am wrong, but a house running a negative pressure and a room-fed stove (as opposed to room sealed) will draw air back down the chimney and cause poor buring in the stove. It will also present a carbon-monoxide hazard.

True or false?

CJhaughey · 29-07-2008 04:08PM

Technically you are correct, In practice the fire works fine with plenty of draw and no smoke coming back down the flue. The negative pressure is only very low, and I haven't had any alarm from the CO alarm.
That said my stove is the smallest Morso make and the draw required is probably only small.
So I will say IME.
Small stove+ HRV running (slight) underpressure+ sealed house = No problems.
That may not be true for others with bigger stoves/greater draw and different HRV systems running different fan speeds.
ALWAYS have a CO alarm if you have a solid fuel stove.

cormacmul · 29-07-2008 04:43PM

Hi all,

I'm not very experienced with stove, does each stove have draw specifications.

If I was going to supply the stove with an external air source. Could I find out the diameter of the pipe needed by this draw specifications.

Thanks for help,
Cormac

Mellor · 29-07-2008 05:16PM

10-10-20 wrote: »

Correct me if I am wrong, but a house running a negative pressure and a room-fed stove (as opposed to room sealed) will draw air back down the chimney and cause poor buring in the stove. It will also present a carbon-monoxide hazard.

True or false?

In theory yes, but bare in mind that the extract will resist the under pressure also.
so it would likely make up the negitive pressure through the extract before the flue.
The under pressure is achieved by having a higher speed on the extract, the setting is fan speed not extract volume. This is key

If the pressure is equalised in the extract, that means that the resistance on the extract is equalised my the extra speed. Resulting in equal in and out and a balanced room. No air in through flue, and zero into fabric.
If then, due to athmospheric changes, the intake increases, the extract alters immediatly to cope.
Its a very good way to run in imo.

cormacmul · 29-07-2008 05:26PM

Hi Mellor,

So Mellor what your saying is that air is taken from the room and from the HRV extract pipe. So less air goes up these extract pipes, even tho the extract fan is running.

Thanks,
Cormac

Jorus · 30-07-2008 11:31AM

Just got a reply from a HRV company -

"a heating systems should have its own air source if the structure has very good levels of airtightness, If not air for outside will fill the negative pressure created by the stove."

cormacmul · 30-07-2008 11:41AM

Hi Jorus,

This is why I am so confused. So many different answers from different places.

If I do go with a air tight building and a HRV i will be providing access to external airsource. But the problem is here what diameter of pipe is needed to provide this air. I have been told it needs to be the same diameter as the chimney flue. I think this is 8 inches. That is a pretty big air source.

Does anyone have any comment on the above. Its a very complex area.

Thanks,
Cormac

30-07-2008 11:59AM

I would be looking at "roomsealed" stoves, ones that can be attached to balanced flues or can take air from a duct.

At least then it won't have any effect on the HRV.

sydthebeat · 30-07-2008 12:14PM

Deleted User wrote: »

I would be looking at "roomsealed" stoves, ones that can be attached to balanced flues or can take air from a duct.

At least then it won't have any effect on the HRV.

absolutely agree with the above statement. A room sealed stove with a balanced flue or feed from a duct woul dsolve most of the issues mentioned here.

If served from a duct this duct should be piped to the external and carried through the floor to the area where the stove is located

cormacmul · 30-07-2008 12:58PM

Hi lads,

I can't find any information or Irish suppliers of room sealed stoves. If you can't write them here then can you PM me the details.

sydthebeat in response to

If served from a duct this duct should be piped to the external and carried through the floor to the area where the stove is located

What diameter should the duct be?

Talk later,
Cormac

10-10-20 · 30-07-2008 08:38PM

It possibly should be the same size as the output.
The heat from the fire will cause expansion of the air, so any intake smaller than the output will possibly choke the fire.

cormacmul · 31-07-2008 09:25AM

Hi 10-10-20,

What do you mean by output. Is it the size of the flue?

Thanks,
Cormac

ollie30 · 31-07-2008 09:57PM

i spoke to a co. dealing in room sealed stoves,firebox inserts etc from galway and they told me to leave a 100mm duct for most air intake ducts ,but may depend on product your buying. you'd probably need to speak to them.i'll pm you incase you dont know who i'm talking about

d o'c · 12-08-2008 01:20AM

ollie30 would you mind PMing me that Galway Co details also please....

timmer3 · 30-06-2009 04:51PM

just saw this thread now, i know it's old but for anyone who's interested, i've been doing some research and got some very useful info from clearviewstoves.com on this topic.
the external air supply kit is a 3 inch stainless steel duct, which you can extend if you need to. even though the model in question (pioneer range) is advertised as room sealed, and sold with an external air supply kit as an optional accessory, when i asked for clarification on using the draught controls in conjunction with the external air supply, i got this response:

The box (external air supply kit) will only supply the secondary air outlet not the primary. So when the stove is first lit, and should you need to bring the stove back up to temperature then you will need to draw from the room.

these stoves are one of the top brands and as far as i can make out there is no completely room-sealed stove, they all take in air from the room to some degree, even with an external air supply kit. i guess once the draught control is closed as much as possible (i.e. when not in use, or overnight to keep the fire in) it's going to be pretty air-tight, at least compared to an open fire.

gman2k · 30-06-2009 05:47PM

Interesting...old thread reappearing..

I was in a stove supplier today (does various brands - Isle of Wight, Belgium, Chinese), and everything was going swimmingly until I mentioned that I had a MHRV in the build.
As I need a stove with a back boiler, the options seem very limited - at least with his suppliers.
There are 'snorkel' stoves available, where you feed in an external air feed, but he said he could not get any snorkel stoves with back boiler options.
He then rang his supplier as there was rumours that something was in the production pipeline. Apparently, it will be available in October (may push out to December though)

He advised fitting a 100mm dia SS duct from external to back of stove position, where this can then be connected to the stove. In my case, this will be a 100mm flexi duct, with various 90deg bends where necessary.
In most cases, this duct should be underfloor, but I've gone past this point!
I'll post back up some more information when it comes to hand, and I'll also consult with my MHRV supplier also.

timmer3 · 30-06-2009 05:58PM

i don't need the boiler option so that gives me more options. i have a combi boiler with rads but once the stoves are in place i intend to use them and rely on the HRV to distribute the heat to the rest of the house, and hopefully not use the gas at all. i'll post back here in the winter if this idea works! i'll use the boiler for hot water anyway, and as a backup if i run out of wood or get too lazy to light up the stove. apparently wood is the cheapest fuel (although those are 2006 prices).

Wally Runs · 06-07-2009 02:35PM

I hope this works. I am retro fitting a 1970's home with HRV (and all the air tightness bits). We have opted for a Morso 6000 with an external air source. Please find attached the fitting information for the kit form Morso. The cost of the kit is GB£25.00.

The project is on going so I cannot say if it works as yet. The use of the kit does limit the location of the stove (external wall) unless you can go through the floor.

timmer3 · 06-07-2009 02:41PM

i'm a few months away from buying the stoves and HRV system, i'll be watching with interest to see how well it works for you.
i'm sure you checked anyway but thought it no harm to mention that the air kit PDF doesn't mention your exact stove model "Morsø outside air kit: 3100's 3600, 7100 & 8100's"
good luck with it.

Wally Runs · 06-07-2009 05:34PM

Yes, saw that, have been through the hoops on this. It took us a while to convince the stove supplier that the 6000 came with an outside air kit ( because as you say it is listed againist other stoves in the range). I have been suprised how even with big suppliers you sometimes end up teaching them about their own products.

timmer3 · 06-07-2009 11:07PM

found the same thing myself with clearview stoves, they didn't advertise the outside air kit as an accessory for the stove i wanted but to be fair the chap i spoke to was quite the expert on their products.

MacTheKnife1 · 07-07-2009 08:14AM

I am looking for the same thing - a range and a stove that ideally should be room sealed (for the HRV).

I spoke with an Irish company recently that gave really excellent advice on these stoves. If anyone wants the contact please PM. I have absolutely no connection with the company.

timmer3 wrote: »

found the same thing myself with clearview stoves, they didn't advertise the outside air kit as an accessory for the stove i wanted but to be fair the chap i spoke to was quite the expert on their products.

fuchia · 07-07-2009 08:31PM

Hi Macktheknife1,

Could you PM me the contact info.

Thanks

Fuchia

miss indecisive · 07-07-2009 08:52PM

Hi mactheknife1

Could i get a pm of that company as well please.

Thanks

Chimney System - Air Tight House

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