MVHR and log burner

[Tetrarch]

It looks as though two independent decisions may cause us a problem

 

I have a Riva 76 wood burner and am in the process of installing an MVHR system. I had (naively) assumed that I would be able to install a direct air supply, but this appears to not be possible

After consulting with Stovax they've sent me the following:

 

"Installation of products into rooms fitted with mechanical extract or heat recovery systems In general installing an appliance in a room that has mechanical extract ventilation or heat recovery systems should be avoided, and Stovax installation instructions state this. However sometimes this is unavoidable and it is acceptable to install Stovax appliances if all of the following criteria are met: • The installation is completed as detailed in the appliance installation instructions and complies with ADJ of Building Regulations (or other local regulations). • The flue system is suitable for the appliance and complies with ADJ of Building Regulations (or other local regulations) • Suitable ventilation is fitted to comply with ADJ of Building Regulations (or other local regulations), along with any additional air required to establish safe use when the extraction system is running at maximum output. (Some Stovax appliances can be fitted with a direct external air supply kit, which will duct air directly to the appliance) • A full spillage test should be completed to ensure safe operation of the appliance when the extraction system is running at maximum output, and be checked under the following conditions: o Cold Test – Appliance Door Shut o Hot Test - Refuelling o Depressurisation test (effects of extraction fans and mechanical ventilation systems) Should operational issues occur with the installation, unless identified as a clear mechanical fault with the appliance, Stovax will expect the installer to investigate and rectify the issues arising. 

 

Does anyone have any advice or experience?

 

Regards

 

Tet

[Tom]

2 minutes ago, Tetrarch said:

• Suitable ventilation is fitted to comply with ADJ of Building Regulations (or other local regulations), along with any additional air required to establish safe use when the extraction system is running at maximum output.

 

This pretty much makes the MVHR pointless. Can you not just get a different stove which can take a ducted air supply? 

[JohnMo]

Don't use or replace the stove. Worst case is you but an always open vent somewhere, defeats the intended purpose of MVHR.

 

if you don't you could have carbon monoxide spillage into the house etc, not good. A silent smell less killer.

[Tom]

Don't be put off by the woodburning stove naysayers, if you want a stove, go for it. Just get one with a ducted air supply, or forget the MVHR. All new installs by law must have a CO alarm anyway.

[JohnMo]

1 minute ago, Tom said:

with a ducted air supply

For primary AND SECONDARY air. Not all are so check before you buy. Soap stone is a good addition as it slows down the output but also keeps giving heat for many hours after the fire is no longer burning.

[Dave Jones]

ethanol stove. expensive but look and feel like a fire, dont need a chimney or external air.

[ProDave]

55 minutes ago, Dave Jones said:

ethanol stove. expensive but look and feel like a fire, dont need a chimney or external air.

Are you sure?

 

Using the spirit stove on our boat at the weekend, with the main hatch shut but front hatch open a crack and rear ventilator open. it set off the CO alarm.

 

I am happier that the WBS at home takes it's air directly from outside and all the products of combustion go up the flue, not into the house.

[Iceverge]

I would just install the MVHR and not worry about it. 

 

The whole risk is completely hypothetical. 

 

The arguement goes something along the lines of worst case MVHR supply side fails and exhaust side sucks fumes backwards through the stove into the room and poisons the occupants. 

 

Firstly that assumes that there's a one way damper on the MVHR (which there isn't)  which prevents the air freewheeling through the supply fan to balance the house. 

 

Secondly it assumes a completely hermetically sealed house. Our passive house had holes an equivalent area of 49cm² with a pressurisation test result of 0.31ACH.  More than enough area to supply a wood burner in reality. 

 

Thirdly tens of thousands of houses have powerful cooker extract fans, bathroom extractor fans and wood burners and don't suffer any ill effects. 

 

Fourthly an MVHR fan runs at something like 40w. A small stove will tip along at about 4000w. Theres something wrong with my understanding of physics if a fire 100 times more powerful than a fan can't overpower it.

 

 

Carbon monoxide poisoning is a real risk. My parents alarm when off when a whole load of soot fell and completely blocked the back of the stove. 

 

Keep your flue clean, burn dry timber and keep batteries in your CO alarm and you'll fine. MVHR or not. 

 

 

 

 

 

 

[JohnMo]

19 minutes ago, Iceverge said:

I would just install the MVHR and not worry about it. 

 

The whole risk is completely hypothetical. 

 

The arguement goes something along the lines of worst case MVHR supply side fails and exhaust side sucks fumes backwards through the stove into the room and poisons the occupants. 

 

Firstly that assumes that there's a one way damper on the MVHR (which there isn't)  which prevents the air freewheeling through the supply fan to balance the house. 

 

Secondly it assumes a completely hermetically sealed house. Our passive house had holes an equivalent area of 49cm² with a pressurisation test result of 0.31ACH.  More than enough area to supply a wood burner in reality. 

 

Thirdly tens of thousands of houses have powerful cooker extract fans, bathroom extractor fans and wood burners and don't suffer any ill effects. 

 

Fourthly an MVHR fan runs at something like 40w. A small stove will tip along at about 4000w. Theres something wrong with my understanding of physics if a fire 100 times more powerful than a fan can't overpower it.

 

 

Carbon monoxide poisoning is a real risk. My parents alarm when off when a whole load of soot fell and completely blocked the back of the stove. 

 

Keep your flue clean, burn dry timber and keep batteries in your CO alarm and you'll fine. MVHR or not. 

Not sure I could agree with any of the above.

 

Follow manufacturer guidelines -  nothing else, get a hetas installer and get them to complete the tests.

[Iceverge]

I have the "stranger on the internet" qualification, does that not count for anything 🤣?!

 

I am of the opinion that it a regulation that is based on the square root of an uneducated guess by someone without even a highschool understanding of physics. Regulations are what the manufacturers and Hetas copy and paste.  

 

Can anyone point to me a controlled study where there is any actual data on this? Any real world examples of carbon monoxide poisoning where MVHR was a contributing factor. 

 

 

 

[Andehh]

We installed a big Stovax, with an external air supply to underneath it. Mvhr in the bedroom area and seperate one for lounge/kitchen etc area (bungalow split in two halves)

 

During long periods of inactivity, I just stick a foam blocker in the outside. That being said in 18months I've remembered to do this never....

[Alan Ambrose]

I’m completely with @Iceverge on this. There’s a slavish regard of ‘manufacture’s instructions’ which can sometimes be written by idiots who are mainly motivated by fear. What they’re really saying is ‘we don’t know, we’re not familiar with this new technology and can’t be bothered to expend the effort to understand it, and we’re certainly not willing to accept any liability regarding it’. The whole world driven by an erroneous understanding of insurance and liability law.

 

i can’t see whether the Riva 76 accepts an external supply, I think it doesn’t? But … at 9kW it’s almost certainly too much heat unless you live in an enormous leaky barn with no insulation. Trade it in for a Scandinavian model, probably the smallest heat output you can find, say 3kW, which takes external air? Check beforehand that they’ve thought sensibly about MVHR.

[dpmiller]

If HETAS were a bit more open and transparent then things might be a bit different...

 

Our boiler stove is room sealed but still is in a room which only has a supply vent, and I have to MVHR commissioned to slightly pressurise the house

[Dave Jones]

11 hours ago, ProDave said:

Are you sure?

 

Using the spirit stove on our boat at the weekend, with the main hatch shut but front hatch open a crack and rear ventilator open. it set off the CO alarm.

 

I am happier that the WBS at home takes it's air directly from outside and all the products of combustion go up the flue, not into the house.

 

the burn process produces very little co2, normal MVHR is plenty the manufacturer advises. We have a co2 anyway so will test when we get it (they are £3.5k for the digital ones).

[Kelvin]

I assume you mean CO. The burn process, in theory, produces just CO_2. I wouldn’t have one in the house frankly. 
 

https://www.sciencedaily.com/releases/2014/09/140903091728.htm

[JohnMo]

43 minutes ago, dpmiller said:

 

Our boiler stove is room sealed but still is in a room which only has a supply vent,

A room sealed means the boiler takes air from outside the room. The combustion process and the air for it, is sealed from the room. It takes air via the flue.

[dpmiller]

/double post

Edited Friday at 06:44 by dpmiller

[JohnMo]

5 hours ago, Alan Ambrose said:

I’m completely with @Iceverge on this. 

 

 trade it in for a Scandinavian model

 

11 hours ago, Iceverge said:

The arguement goes something along the lines of worst case MVHR supply side fails and exhaust side sucks fumes backwards through the stove into the room and poisons the occupants. 

Not sure that is the argument. It's not at all to do with MVHR really, it's about where the stove gets the air and good airtightness houses.

 

The house and outside air pressure are assumed to be equal and the flue draw is about 10 to 20 pascals. If the house pressure becomes lower than outside, even by a few pascals the flue draw is lost and it's becomes easier for combustion gas to spill into the room. It becomes an issue when the air supply is convoluted MVHR ducts have a pressure drop of 20 to 100Pa and the 49cm2 is spread across the whole house not next to the stove. Most other appliances either gas or oil, can be switched off quickly if you need too, a stove burns until it runs out of fuel.

 

@Alan Ambrose why are you saying ignore the rules, but going on to say trade it in and get one with external air supply? Seems an odd stance.

[dpmiller]

hmm, looks like my double post *wasn't*...

 

1 hour ago, JohnMo said:

A room sealed means the boiler takes air from outside the room. The combustion process and the air for it, is sealed from the room. It takes air via the flue.

 

BRegs do not allow an uncontroled combustion appliance in a room with an extract vent.

 

AD L, 2012 (current for NI) states

 

"for a solid fuel appliance – a room extract fan should not be installed
in the same room. If mechanical extraction is unavoidable then seek
specialist advice from a mechanical/services engineer to ensure safe
operation of the appliance."

[JohnMo]

4 minutes ago, dpmiller said:

hmm, looks like my double post *wasn't*...

 

 

BRegs do not allow an uncontroled combustion appliance in a room with an extract vent.

 

AD L, 2012 (current for NI) states

 

"for a solid fuel appliance – a room extract fan should not be installed
in the same room. If mechanical extraction is unavoidable then seek
specialist advice from a mechanical/services engineer to ensure safe
operation of the appliance."

Not really sure what you are saying. Agree with the above, but you made a comment about your room sealed boiler being in a room only a supply vent. But a room sealed appliance, has no interaction with the room. It is only connected to the outside, taking combustion air from outside -just the same as a stove with external air supply.

[dpmiller]

8 minutes ago, JohnMo said:

Not really sure what you are saying. Agree with the above, but you made a comment about your room sealed boiler being in a room only a supply vent. But a room sealed appliance, has no interaction with the room. It is only connected to the outside, taking combustion air from outside -just the same as a stove with external air supply.

 

It's a woodburning stove with a heat exchanger, a "boiler stove". With an opening door it can only be room sealed when it's closed...

it's not a roomsealed boiler.

[JohnMo]

5 minutes ago, dpmiller said:

 

It's a woodburning stove with a heat exchanger, a "boiler stove". With an opening door it can only be room sealed when it's closed...

it's not a roomsealed boiler.

Sorry missed read - my bad

[Alan Ambrose]

@JohnMo >>> why are you saying ignore the rules, but going on to say trade it in and get one with external air supply? Seems an odd stance.

 

I was simply saying ‘if Stovax can’t figure out log fires & MVHR buy from someone (probably the Scandinavians as they’ve been making log stoves the longest) who can’.

 

 

[IanR]

23 hours ago, Tetrarch said:

I have a Riva 76 wood burner and am in the process of installing an MVHR system. 

 

What's your planned airtightness? If you have sufficient "natural" ventilation to feed the Wood Burner, I'm not sure you'll get any benefit from MVHR. Unless I've misunderstood the Riva 76 taking primary air from the room.

 

Maybe the answer is to save your money and not fit MVHR.

[Alan Ambrose]

>>> and not fit MVHR

 

At least in that room. Presumably it’s a supply outlet anyway?