MVHR system in new build

[deuce22]

Hi.

 

I am building a 3 storey 350m2 ICF property and have just been told, that I should install a MVHR system. I have heard about these in the past, but have no experience with them.

 

What I would like to know is:

1. Are they worth installing

2. Do they replace extractor fans in bathrooms

3. What would be a rough price to accommodate that size property

 

Thanks.

 

[Iceverge]

It depends. 

Yes. 

£3-9k.

 

 

 

[deuce22]

11 minutes ago, Iceverge said:

It depends. 

Yes. 

£3-9k.

 

 

 

Depends on what things?

I didn't realise they were that expensive. I have been told that I could get a system for around £1500 and they can be installed pretty easy. I've also been told that they are not worth the extra cost as it will take so long to actually get a return from the energy savings.

[Tom]

It's not so much about the energy savings - I think you're right, you'd probably struggle to recoup the cost - it's about the comfort. In the grand scheme of things even 10k is a small % of a 350m2 build cost to acieve this.

[Russell griffiths]

I don’t think you have a choice. 
for building regs you need to specify how you will extract damp smelly air and replace with fresh air. 
so what do you think you will do. Build a good quality house and then have trickle vents to let cold air in. 
then heat the inside of the house and blow it all outside when you turn an extractor on. 
if your building to a good standard I don’t really know of another solution except MVHR. 

[Marvin]

1 hour ago, Tom said:

It's not so much about the energy savings - I think you're right, you'd probably struggle to recoup the cost - it's about the comfort. In the grand scheme of things even 10k is a small % of a 350m2 build cost to acieve this.

HI @Tom I beg to differ about the energy saving. For 100m2 ours runs at about 17Watts per hour. Call it 20watts times 24 hours a day.

So half a kWh a day. 

 

During the winter we have witnessed the outside temperature of about 5C air, passing through our MVHR and the heat from the air being expelled, heat the outside air up to 19C before it enters the room at 30 litres a second.

Someone who knows the maths will tell me how much energy saving there is on heating 108m3 of air from 5C to 19C per hour.  I bet its not half a kWh per day!

 

Thing is you don't see the heat your not using.

 

 

[redtop]

We havnt put mvhr in, Air tightness at 4 and trickle vents. With Double the min levels of insulation and top quality double glazing house doesn't need a lot of heating anyway. When looking at the benefits most people compare with a standard build to min BC regulations. Half the air leakage and double the insulation and the benefits are far more marginal. Sure it would be even less with mvhr but the biggest gains are insulation

[ProDave]

Once you get down to good air tightness and good insulation, you will find that more heat is lost through ventilation, than through heat loss through walls etc.  That is where mvhr is worth it for cost savings.

 

But even before that point I think mvhr is worth is for the better comfort in the house.  I used to hate wind howling through bathroom fans and the cooker hood when it blows a gale.  You get none of that with mvhr, just constant controlled ventilation ensuring fresh air and no damp, without losing a lot of heat from the building.

 

Most of us here have tried hard to build our houses to way better than building regs standard, the target for most has been something close to passive house standard, and many achieve that with certified passive houses.  Others like me were not bothered getting it certified as a passive house but still wanted to aim to be close to that using all the same principles.

 

It all depends what you want. With the direction fuel costs are heading, it just makes sense to make the house as low energy as possible.

[JohnMo]

Not sure of the rules where you are, but in Scotland if your final airtightness is 3 or better you would have to have it installed. ICF builds tend to be quite airtight.

 

dMEV is a good option if worse than 3, anything from 3 to 5.  This would require trickle vents, and continuously running (silent) fans in wet rooms and kitchen.  This can be made to run on condition (humidity etc), so run at a low output, until required.

 

We have MVHR, my wife has COVID, and somehow I don't.  Not sure if it's the continuous ventilation or I'm lucky so far.

[Tom]

1 hour ago, Marvin said:

HI @Tom I beg to differ about the energy saving.

 

Eh? I didn't say anything about energy saving!

[Iceverge]

3 hours ago, deuce22 said:

Depends on what things?

I didn't realise they were that expensive. I have been told that I could get a system for around £1500 and they can be installed pretty easy.

3 hours ago, deuce22 said:

I've also been told that they are not worth the extra cost as it will take so long to actually get a return from the energy savings.

 

 

Airtightness, complexity of design. Insulation levels. The occupants value on air quality and comfortable .

 

£1500 sounds like a bargain, was that from a supplier? 

 

Theres a good few threads here where this has been debated to the nth degree. 

 

In short no it will probably never pay itself back in cost terms.

 

Then there are lots of things in our house that certainly have no payback. 

 

Footpaths, paint on the walls, skirting boards, windows, internal doors. Floor tiles, carpets, fitted kitchen, tumble drier. 2 of the 3 toilets, most of the furniture. Wife, children, etc etc etc. 

 

You must decide where the accountant on your shoulder gets told to bugger off! 

 

 

[TerryE]

3 hours ago, Marvin said:

HI @Tom I beg to differ about the energy saving. For 100m2 ours runs at about 17Watts per hour. Call it 20watts times 24 hours a day.

So half a kWh a day. 

 

During the winter we have witnessed the outside temperature of about 5C air, passing through our MVHR and the heat from the air being expelled, heat the outside air up to 19C before it enters the room at 30 litres a second.

Someone who knows the maths will tell me how much energy saving there is on heating 108m3 of air from 5C to 19C per hour.  I bet its not half a kWh per day

 

SH_air ~ 1 kJ/kg/K,  Dens_air ~ 1.2 kg/m3.  So 108 × 24 × 14 × 1.2 × 1 /3600 = 12 kWh 

 

Yes you are correct in that it is not ½kwh / day.  It is roughly 25× that.  Your inference is wrong.  In a near passive class house, air losses are by far the largest heat loss component if you don't install MVHR.

Edited March 13, 2022 by TerryE

[Mr Punter]

One advantage of MVHR is that the ventilation in an airtight house is controlled.  With trickle vents on a cold windy day there is lots of cold air entering and on a still day there may not sufficient air changes and the internal air may become stale.

[deuce22]

3 hours ago, Russell griffiths said:

I don’t think you have a choice. 
for building regs you need to specify how you will extract damp smelly air and replace with fresh air. 
so what do you think you will do. Build a good quality house and then have trickle vents to let cold air in. 
then heat the inside of the house and blow it all outside when you turn an extractor on. 
if your building to a good standard I don’t really know of another solution except MVHR. 

This hasn't been specified by building regs and I only found out about them a few days ago.

 

I was planning to do exactly what Redtop has stated. I have gone over on insulation and my SAP calculations have come back at 88 and I can't get it any higher, unless I add renewable energy.

They also added this and there is no mention of a mvhr system.

Other specification

• -  Ventilation via 5 intermittent extract fans, extracts from each kitchen and wet rooms.

• -  100% of the lighting is to be low energy.

[deuce22]

Iceverge

 

I was speaking to another self builder nearby. He told me it would be around £1500, but he may not have a clue. I'll speak to a few companies tomorrow and get some quotes.

 

TerryE

 

12kw per day to use? That seems expensive to run.

[Nickfromwales]

6 minutes ago, deuce22 said:

Iceverge

 

I was speaking to another self builder nearby. He told me it would be around £1500, but he may not have a clue. I'll speak to a few companies tomorrow and get some quotes.

 

TerryE

 

12kw per day to use? That seems expensive to run.

Recovered heat energy, not the electrical energy to run it  

If you would have been discharging huge volumes of heated air to atmosphere with regular extractor fans, you would be sucking in cold air to replace it. The HR element of MVHR would be preheating the incoming air with the otherwise wasted heat carried 'out'. Some systems can recovery up to 18oC of the 21oC that is 'leaving'. It's a significant energy saver basically. 

[Conor]

@deuce22 we've just moved in to our 350m² three story ICF house.

 

We have two MVHR units but they are not commissioned yet.

 

So we are relying on trickle ventilation from four 1sr floor skylights, and four 200mm diameter holes in the outside walls for the unit.

 

It's nowhere near enough. Air feels musty when it's warm, there's often condensation on the roof lights, and smells from the kitchen linger though the house (recirculation cooker). 

 

ICF houses are incredibly airtight and I wouldn't consider one without an MVHR or other controlled system. 

 

Mine cost £4k but that was for two passive House certified units and lots of galvanised steel ducting. You could do it for less.

 

You've mentioned no renewables... With cost of fossil fuels and energy going the way they are, I'd find the funds for solar PV and a heatpump. No better time.

[Nickfromwales]

45 minutes ago, Mr Punter said:

One advantage of MVHR is that the ventilation in an airtight house is controlled.  With trickle vents on a cold windy day there is lots of cold air entering and on a still day there may not sufficient air changes and the internal air may become stale.

Plus the fact that humans tend to close trickle vents in the cold windy depths of winter......PPM levels of CO2 subsequently go through the roof, plus humidity, and then comes damp.

It's a double-edged sword, where you build either to our dogshit British building regs and fit trickle vents, or go better and provoke a requirement for mechanical ventilation. All of my M&E clients who have MVHR all state that it is a very pleasant environment to live in. We engineer systems to be near silent also, but at £1500 you'd have a very cheap and nasty setup with a unit made from Chinesium. I pay more than that for just the bare units to be delivered, without any ducts etc. Budget for the £5k minimum for supply and fit for a 3 storey house, for a radial system. I'm not a fan of series run ducting because of the higher primary airflow rates and the noise from the attenuated valves closet to the unit. Also some have raised issues over cross-talk, the sounds transmitted from room to room via the interconnecting ducts.

[TerryE]

51 minutes ago, Conor said:

We have two MVHR units but they are not commissioned yet.

 

So we are relying on trickle ventilation from four 1sr floor skylights, and four 200mm diameter holes in the outside walls for the unit.

 

Conor,  You've got your commission order out of sequence.  MHVR should have been just be about the first thing to commission after 2nd fit as soon as you have a temporary electricity supply up.   Pretty much everyone here on the forum (at least those that have sized and commissioned their MVHR systems correctly) agree that you live in a house that always smells fresh and  that never have problems with damp or condensation.   The tickle vents and four holes will be a PITA to seal properly once your MVHR is commissioned.

 

The MVHR system was one of the things that Jan and I did ourselves.  The sizing calcs are straightforward as is a star manifold installation, though to do need to properly calibrate and commission the system.  If done properly, the B Insp will accept a self-certified commissioning report.  It performs really well.

Edited March 13, 2022 by TerryE

[Nickfromwales]

2 minutes ago, TerryE said:

The tickle vents and four holes will be a PITA to seal properly once your MVHR is commissioned.

The trickle ventilation, I believe, is being created by setting the skylights to be just ajar  The 4 holes ( 2 per MVHR unit ) will be the pre-installed insulated ducts coming in to connect to the unit, perhaps?

[JohnMo]

Out of interest what airtightness figure was used to get an 88 from SAP?

 

1 hour ago, deuce22 said:

 SAP calculations have come back at 88

 

[Adsibob]

7 hours ago, deuce22 said:

I have been told that I could get a system for around £1500 and they can be installed pretty easy.

I think you'd really struggle to find a unit big enough for your house that cost less than £2400. You want to oversize the unit so that you can run it really low. Add all the ducting and some nice looking lindab airy valves, booster switches and humidity sensor and you're going to getting close to £4k in materials. If you design and install it yourselve you could save a few thousand, though I think I'd want a professional to design it for me. Some do basic designs for free as part of their "marketing". 

Edited March 13, 2022 by Adsibob

[Nickfromwales]

Brink Flair 400 would be suitable. Change of £2.5k. PH certified and very quiet / robust. I've had great feedback from clients we've fitted these for, and the guys at CVC Ltd have provided the units, associated materials and design support with excellent results every single time. Very quiet units, but we always fit silencers ( aka attenuators ) in every instance for near inaudible operation, often inaudible at trickle rate and only slightly notable during boost.

[Rishard]

Another learner venturing into mvhr systems. I’m also very early in our project, planning passed and working towards building control application stage/demolition of existing structure.. we are 200m2. Any other recommendations for supplier designs to quote for our system? I will be installing as I’ll be doing most of the build (builder) along with good plumbing/electrician friends. None with much mvhr experience on low energy housing, yet! 

[TerryE]

1 hour ago, Rishard said:

Any other recommendations for supplier designs to quote for our system?

 

We used these guys: BPC.  I got them from others on this site who recommended them.  I downloaded all the manuals, installation guides, etc, and dis my own design but passed it past them for validation.  They suggested a few tweaks on vent placement, but OKed the rest.. Others just shipped them their house plans and asked them for the layout and equipment list.  They then shipped us everything on a palette. Based on a couple of spot-checks, they were pretty competitive (this was ~5 years ago).

 

As I said above we did the install ourselves as part of 1st fix and commissioned the system pretty soon after the the internals were plastered out.  All pretty straightforward, really.