MVHR and open fireplace

[Ronan 1]

Gents I've been reading a few threads on MVHR to try and decide if I want to include it in my build. Before i say something stupid I am completely ignoramt of the system but feel that for the fresh air benifts ive read about here id like to install it.I am building a 2 story 3430sq ft house heated by an oil condensing burner and UFH and I am going to have 2  open fireplaces and am wondering of having 2 open fireplace means it a bit pointless exercise. 

 

P.s The fireplaces are not for negotiation... or so I've been told ?

 

Appreciate the advice

[joe90]

3 minutes ago, Ronan 1 said:

having 2 open fireplace means it a bit pointless exercise. 

Yes, MVHR only works well in a relatively airtight house, open fireplaces are great big draughty holes in the building fabric.

Edited January 14, 2021 by joe90

[Ronan 1]

1 minute ago, joe90 said:

Yes, MVHR only works well in a relatively airtight house, open fireplaces are great big holes in the building fabric.

Thanks Joe I was kinda afraid that would be the case.

[jfb]

I have a burner and Mvhr and it works fine. 
Burners are much more efficient than an open fire - why the insistence on it?

[ProDave]

Why open?  What's wrong with a room sealed wood burning stove?

[joe90]

+1 with room sealed wood burning stove, I have one and MVHR works very well! (And they need not be black!)

 

Edited January 14, 2021 by joe90

[Jason L]

5 minutes ago, joe90 said:

+1 with room sealed wood burning stove, I have one and MVHR works very well! (And they need not be black!)

 

Does the Mvhr system overcome the need for the air bricks for the fire . ?  

[Ronan 1]

24 minutes ago, ProDave said:

Why open?  What's wrong with a room sealed wood burning stove?

Absolutely nothing wrong with them in fact I quite like them. I have a thing for open fires after been rared in a real old stone house with one in every room and moving abroad at a young age and it always was the one thing reminded me of home and the wife also has notions ?

Edited January 14, 2021 by Ronan 1

[Ronan 1]

12 minutes ago, joe90 said:

+1 with room sealed wood burning stove, I have one and MVHR works very well! (And they need not be black!)

 

That is nice Joe

[joe90]

5 minutes ago, Jason L said:

Does the Mvhr system overcome the need for the air bricks for the fire . ?  

if installing MVHR you need a room sealed stove, they have a ducted air input pipe extending to outside so it does not use indoor air.

[Ronan 1]

Joe would there be any benefit for it at all in my case if you were to forget about the heat recovery end of it and focused only on air quality and extraction.

 

I hate them drafty old bathroom extractors and would prefer not to have to have anything like window vents.

Edited January 14, 2021 by Ronan 1

[joe90]

Not sure it would work in a draughty house even as ventilation or worth the expense.

[Roundtuit]

1 hour ago, Ronan 1 said:

P.s The fireplaces are not for negotiation... or so I've been told ?

 

Sounds like you've got some negotiating to do ?

 

Room sealed woodburner and mvhr gets my vote.

[Jilly]

As an asthmatic, for air quality: just don't have a fire of any kind, they increase indoor pollutants.

 

But they are nice...

[joe90]

15 minutes ago, Jilly said:

As an asthmatic, for air quality: just don't have a fire of any kind, they increase indoor pollutants.

 

@Jilly I completely understand as an asthmatic but a room sealed wood burning stove must be a small percentage polluter compared with an open fire?

[Conor]

Open fires have a net cooling effect as they draw out more heat energy (the warm air) than they radiate out (don't know about back boilers). They have no place in our world anymore. There's a house (about 150m²) that's just got fpp across the road from us and they have three open fires and a wood fired pizza oven in their house design... It'll either be freezing or unbearably warm ?. Not sure how they'll pass their air tightness test.

 

And your MVHR won't work properly at all, esp when it's windy or the fire is lit. So you'll be better off with trickle vents and bathroom extractors. And you'll also need a wall vent in the rooms where the fires are, so even draughtier.

 

I think a room sealed stove is the obvious compromise.... You can always fire the door open for effect when the mood takes you.

 

Sorry to be negative, but that's the reality.

[Ronan 1]

Wonder would one of these glass doors make a difference 

[Roundtuit]

3 minutes ago, Ronan 1 said:

Wonder would one of these glass doors make a difference

Probably direct more of the heat straight up the chimney, but it might keep you warm cleaning the glass?

[Ronan 1]

4 minutes ago, Roundtuit said:

Probably direct more of the heat straight up the chimney, but it might keep you warm cleaning the glass?

Aparently they are designed to direct more of the heat out !!! But to be honest the fireplaces isint just for the heat and I don't think the fact it will leave the house non airtight will bother me that much,  I supposed it's not high on my list of priorities for the build. I will just ensure that it is good and airtight everywhere else and well insulated as I said I'm used to very old, very draught and VERY cold.

Edited January 14, 2021 by Ronan 1

[Adsibob]

On 14/01/2021 at 17:18, joe90 said:

+1 with room sealed wood burning stove, I have one and MVHR works very well! (And they need not be black!)

 

Beautiful stove @joe90. Which manufacturer and model is that?

[PeterW]

On 14/01/2021 at 19:17, Ronan 1 said:

I will just ensure that it is good and airtight everywhere else and well insulated

save your money. No point putting any more than BRegs level insulation in if you are having open fireplaces as the air test will be off the scale (I doubt it will actually depressurise the house enough to register) and you’ll need to add solar or something else to get a SAP Score to pass I expect. 
 

Open fires are a relic from the 18th century and should stay there. There are some beautiful new stoves that you could have and they would be both efficient and air tight. 

[Ronan 1]

Hi Peter, thanks for the heads up and I appreciate where your coming from but this will be my "forever" home and SAP scores really don't register with me. The Open fireplaces are important design features for both me and my wife so I'd prefer have the house we want than compromise for a SAP score or such like.

It's in northern ireland and I have a few relatives that built in the last couple of years and all have open fires  so I guess I'll just have to see what they did and what my architect says if he ever gets back to me with the final plans . ?

Edited January 20, 2021 by Ronan 1

[joe90]

9 hours ago, Adsibob said:

Which manufacturer and model is that?

https://www.ukstoves.co.uk/p/5kw-oakdale-gloss-cream-se-multi-fuel-stove

[Bitpipe]

43 minutes ago, Ronan 1 said:

Hi Peter, thanks for the heads up and I appreciate where your coming from but this will be my "forever" home and SAP scores really don't register with me. The Open fireplaces are important design features for both me and my wife so I'd prefer have the house we want than compromise for a SAP score or such like.

It's in northern ireland and I have a few relatives that built in the last couple of years and all have open fires  so I guess I'll just have to see what they did and what my architect says if he ever gets back to me with the final plans . ?

 

As a NI native I understand the appeal of an open fire  I had an old school friend who I had to stop coming round for a drink in the garden as after about 10 mins he wanted to 'get a fire going' ...

 

SAP scores may not register with you but you need to pass to get the building signed off, there is a recent thread where someone is now being advised to retro fit solar PV to bump up their score due to some lack of foresight at the design stage. Also forever homes have a habit of being sold at some stage so they need a valid SAP.

 

As Peter says above, if the open fireplace is a must have then don't waste money on airtightness, insulation and MVHR elsewhere as it will be pointless.

 

A house works as a system, doesn't matter how airtight the rest of it is when there is a massive hole in the envelope - two actually as you'll need a free air supply to compensate for the fire. All the heat you pay to generate elsewhere in the house will fly up that chimney.

[Bitpipe]

On 14/01/2021 at 17:39, Ronan 1 said:

Joe would there be any benefit for it at all in my case if you were to forget about the heat recovery end of it and focused only on air quality and extraction.

 

I hate them drafty old bathroom extractors and would prefer not to have to have anything like window vents.

 

For MVHR to work as a ventilation system you need a balance between supply and extraction, supply to living areas & bedrooms and extraction from damp / smelly areas like kitchen and bathrooms. You also need an air gap of 7600mm2 under every door to enable airflow between rooms.

 

MVHR units run at fairly low speeds for the majority of the time and only boost when triggered - manually (switch) or automatic, such as Co2 / humidity sensor or wired into the cooker hood or lighting circuit. When properly installed you should not really detect the airflow even when standing under a supply.

 

Their effectiveness as ventilation systems is dependent on being balanced and having the external intake and extract on the same face of the building so they are not affected differently by wind. Their effectiveness as heat recovery systems rely on the house having an airtightness of 2 ACH or less.

 

So having one or more fireplaces (with the associated free air supply) will rule out any heat recovery as your house will have negligible airtightness and may well rule out effective ventilation as, if there is airflow across the top of your chimney then that will pull air out of your house and out compete the pull from the extract fans in the bathrooms & kitchen.