Integrating an MVHR to our build

[djcdan]

We're considering specifying an MVHR system for our build and have some general enquiries which I hope others who have installed one will be able to help with and answer.

 

- We'll be having UFH on the ground floor and previously had specified radiators to the upstairs. By installing MVHR, could the upstairs be heated by i) rising heat from downstairs and ii) the MVHR to replace the needs to install rads?

 

- By installing MVHR, this replaces the need for other forms of ventilation to kitchen and bathroom areas, which would typically be extractor fans? I assume this is correct since any additional ventilation system would reduce the airtight seal on the property and decline the efficiency of MVHR.

 

- We're having an ASHP installed and had been expecting to have something in the region of an 8KW unit installed for our 200sqm property. As the heating would be supplemented by MVHR, would this reduce demand on the ASHP enough to allow us to install a smaller (5-6KW) ASHP unit? If we decide to go ahead with MVHR, our SAP calculations would need to be recalculated - as current calculations are based on without MVHR - but it would be ideal to have a rough expectation on this prior to making the decision to install to calculate potential cost savings on the ASHP?

 

- I have seen mentions to slight noise during a 'boost' period, and to ensure the correct unit/ducting is sourced for long term maintenance reasons? Other than these, does anyone have any negative experiences/feedback for MVHR.

 

Which unit to install?

Our budget is most likely mid-range. Based on own experiences, can other users recommend which brands/models to consider and which to avoid?

 

One local contractor installs NIBE units only and has based his quote on the NIBE F2040 ASHP. NIBE also offers MVHR which, according to their site, would integrate to the ASHP to create a single heating solution that works on one system with a single smart control panel to improve efficiency of the heating system. To me, this seems like a logical thing to do if the option is available in comparison to having the ASHP and MVHR on separate heating systems. Does anyone have the NIBE ASHP/MVHR installed and able to give feedback on this? 

[Mr Punter]

If your house is well insulated you may find that heat from downstairs means upstairs rads are not needed.  MVHR will not impact one way or the other and does not move heat around the house.

 

The MVHR will do the bathrooms.  In the kitchen I prefer a separate extract as I like to fry / char.

 

The MVHR will not supplement your heating system, it is just for ventilation.  It may have a small impact on your SAP calcs.  The main benefit is controlled ventilation with lower heat losses.

 

Like most mechanical ventilation there can be some noise when it is at full tilt.  A bigger system with larger ducting can minimise this.

[Conor]

Don't have time to respond in detail, but an MHVR is primarily there to maintain good air quality - you should pick one for that reason alone. In short, you don't need any other forms of ventilation (except kitchen extractor) and if you improve your airtightness to <3, you'll see a big improvement in your SAP and therefore heating demand. Finally, they don't move any heat around the house. You'll have much more heat movement through natural convection. Consensus seems to be in a airtight, well insulated house, heating on upper floors is not required. Re noise - over size the MVHR so the fan runs at lower speeds. in my 300m2 house, that means two units.

 

The exhaust heat pump MVHRs are a good solution... just quite pricey and when I looked at them, not viable for a large house as flow rates not enough.

Edited December 16, 2020 by Conor

[djcdan]

Thanks @Mr Punter @Conor

 

Ok, so a combination of both replies is that:

 

- rads upstairs won't be needed. We're having a closed panel Scotframe construction. The U-value for external wall insulation is between 0.13-0.15, with glazing @ 1.2. I presume this would be enough to qualify for insulation levels?

- The MVHR doesn't move the heat. Does the heat exchange simply take the chill from incoming fresh air before it's sent through to individual rooms rather than apply temperature? 

- Whilst there may be a minor impact on SAP calcs and heat demand, this wouldn't be enough to lower the sizing of the ASHP.

- Oversize the system to reduce noise output.

- Bathroom extraction isn't required, but kitchen is advisable.

 

With regards to units, are there any that you would recommend, or any that you've had experience of which should be avoided?

 

 

[Conor]

42 minutes ago, djcdan said:

Thanks @Mr Punter @Conor

 

Ok, so a combination of both replies is that:

 

- rads upstairs won't be needed. We're having a closed panel Scotframe construction. The U-value for external wall insulation is between 0.13-0.15, with glazing @ 1.2. I presume this would be enough to qualify for insulation levels?

- The MVHR doesn't move the heat. Does the heat exchange simply take the chill from incoming fresh air before it's sent through to individual rooms rather than apply temperature? 

- Whilst there may be a minor impact on SAP calcs and heat demand, this wouldn't be enough to lower the sizing of the ASHP.

- Oversize the system to reduce noise output.

- Bathroom extraction isn't required, but kitchen is advisable.

 

With regards to units, are there any that you would recommend, or any that you've had experience of which should be avoided?

 

 

 

0.13-.015 is great. That's passive house levels. Have you had the house modelled in PHPP? It will give you a better idea of heat load compared to the SAP. For a 200m2 house with passive levels of insulation, a 5kw ASHP is more than enough- we're going for that in our 300m2 house.

 

What's your glazing? 1.2 is quite poor. Its not much money to go to triple glazing and get 0.7-0.9. you'll really notice that, esp for summer over heating. If you get your airtightness and glazing right, you've an opportunity to reduce the size and complexity of your UFH system. E.g. we're only having it in bathrooms and one other room per floor.

 

I have been looking at Zenhder but they are quite pricey. Now leaning towards Brink. Have a look in the forum and you'll see the discussions.

[djcdan]

3 minutes ago, Conor said:

 

0.13-.015 is great. That's passive house levels. Have you had the house modelled in PHPP? It will give you a better idea of heat load compared to the SAP. For a 200m2 house with passive levels of insulation, a 5kw ASHP is more than enough- we're going for that in our 300m2 house.

 

What's your glazing? 1.2 is quite poor. Its not much money to go to triple glazing and get 0.7-0.9. you'll really notice that, esp for summer over heating. If you get your airtightness and glazing right, you've an opportunity to reduce the size and complexity of your UFH system. E.g. we're only having it in bathrooms and one other room per floor.

 

I have been looking at Zenhder but they are quite pricey. Now leaning towards Brink. Have a look in the forum and you'll see the discussions.

 

We've currently speced Rationel double glazing units for the windows, which have a rating of 1.2. The velux's in the bedrooms (it's a 1.5 storey) have a rating of 1.3 and there are two in each room.

 

I've not had PHPP modelling. Is this something that could be calculated myself, or best left with the architect?

[Russdl]

46 minutes ago, djcdan said:

I've not had PHPP modelling. Is this something that could be calculated myself, or best left with the architect?

 

You can, but it's not an afternoon exercise, I did my own which took yonks but I was able to try lots of different iterations to get the figures looking good. You could get a PHPP consultant to do it for you but make sure you get one who is properly qualified to take your money - there are some chancers out there.

 

@Jeremy Harris produced his own spreadsheet as he found PHPP to be overly complex iirc, there's probably a copy kicking around on here somewhere which I think several BuildHubbers have used.

[Bramco]

1 hour ago, Conor said:

What's your glazing? 1.2 is quite poor. Its not much money to go to triple glazing and get 0.7-0.9.

 

We had heat loss calculations done for both 0.7 and 1.2 and the difference in terms of heating required was actually quite small. Walls will be 1.4 and roof and insulated slab 1.

 

You have to weigh up the additional cost of going to 0.7 against the expense in terms of lekky for the ASHP with 1.2. When you work it out, it's not a lot - for us it would be £100 a year but a LOT more to do the windows at 0.7.

 

Having said that we may well go the extra mile to get an A rating - daft?!!!....

 

Simon

[Conor]

1 hour ago, djcdan said:

 

We've currently speced Rationel double glazing units for the windows, which have a rating of 1.2. The velux's in the bedrooms (it's a 1.5 storey) have a rating of 1.3 and there are two in each room.

 

I've not had PHPP modelling. Is this something that could be calculated myself, or best left with the architect?

 

Go triple glazed. It won't cost that much more. Same for the velux.

[MikeGrahamT21]

Agreed, theres so much more to triple glazing than just the energy savings, its a game changer

[djcdan]

On 16/12/2020 at 17:47, Conor said:

 

Go triple glazed. It won't cost that much more. Same for the velux.

 

On 17/12/2020 at 08:56, MikeGrahamT21 said:

Agreed, theres so much more to triple glazing than just the energy savings, its a game changer

 

I've sent across a quote request to compare the costs of triple compared to double. We have a decent amount of south facing glazing, so reduction of overheating would be a nice addition on top of optimising u-values.

 

I have read a lot of content on MVHR systems over the past few days on BH and now leaning towards installing a standalone system like the majority here tend to do rather than a system integrated with an ASHP. In practice, it doesn't seem to be any benefit other than having one control panel.

 

I am in the process of processing calculations and designing ducting routes, which I'll plan to have checked by BPC prior to purchase - which I have seen others mention on other threads. It has been mentioned numerous times on BH that a flow velocity greater than 2.5m/s will result in potential for increase noise from the system. I'm not sure whether I'm being dim and it is really simple, however I cannot find the equation to calculate this. In my head I can understand that the velocity will be the speed which is required to pass through the ducting in order to deliver the necessary flow rate to each room, but Maths is failing me! I'd use this to ascertain whether I'd need to double duct on certain runs.

 

Installation near-enough to the mid point of the attic space would be desired to keep this central to all runs. But this would take the unit further away from either gable than the optimal distance for the main inlet/outlet. I'm therefore looking to take the inlet and outlet through the roof. We're having a Cambrian 'slate' roof and they offer a Hi-Flow ThruVent tile that offers a ventilation rate of 15,000mm2. Would this be suitable for a 193sqm property? Alternatively, we'd need to install closer to one gable, have a 'traditional' inlet/outlet on the gable, but the runs are longer.

 

Cheers, Dan

[PeterW]

2 hours ago, djcdan said:

however I cannot find the equation to calculate this. In my head I can understand that the velocity will be the speed which is required to pass through the ducting in order to deliver the necessary flow rate to each room

try this

 

https://www.engineering.com/calculators/airflow.htm

 

Just watch for the units - ducts are sold as internal diameter and this calculator uses radius 

[djcdan]

Xmas has been well spent working on MVHR research and calcs. Does someone mind having a quick check over my calcs?

 

A few points of note:

- I've narrowed it down to four possible units, each with a max rate of between 300-350 m3hr. Based on the calcs, this would be a 36%/67% usage of unit capabilities (regular/boost) for 350 m3hr units, or 42%/78% for 300m3hr units. Is 78% in boost mode still acceptable if we were to choose a 300m3hr unit?

 

- I'm aware that rooms under 4sqm don't need to be included in the extractions. However, there are two rooms in the property that are smaller, but will be damp rooms. The drying room is small, but will be used over the winter months to dry clothes. The cloakroom will be on the groundfloor, so will have UFH and will be used to store boots/coats etc, so there will be water vapour in the room. I presume it is ok to include extraction points in these rooms? I have these spaces with a minimum extraction rate of 8L/s. Is this correct, or is it better to categorise these as WC's, which only require 6L/s as per building regs?

 

- Is it best to leave the hall/landing/vestibule areas - which are centrally located to rooms with extract/supply points - as transfer space? Or can supply valves be added to these spaces? Through my research, I've noticed that these areas don't usually contain supply outlets.

 

- The longest ducting run is just under 15m, so each run is based on single ducting as, based on calcs, it seems our velocity is well below the 2.5m/s advised here on BH as a maximum so each run is single duct. This, in addition to the unit usages in point one should result in low noise output from the unit?

 

[jfb]

Sorry not a detailed response to your last post but some few thoughts

- noise: install a sound attenuator on both supply and exhaust 

- kitchen extract as an extra not needed if you go for recirculating hood

- what air tightness are you aiming for? Ashp sizing will be affected by how airtight it is. If it is a leaky house Mvhr will be less use and you may need rads upstairs. Clearly you appreciate the need for airtightness but does the builder?

[DavidO]

We'll be having UFH on the ground floor and previously had specified radiators to the upstairs. By installing MVHR, could the upstairs be heated by i) rising heat from downstairs and ii) the MVHR to replace the needs to install rads?

 

- By installing MVHR, this replaces the need for other forms of ventilation to kitchen and bathroom areas, which would typically be extractor fans? I assume this is correct since any additional ventilation system would reduce the airtight seal on the property and decline the efficiency of MVHR.

We did exactly what you are describing in 2013 in a 195msq timber frame build. Our architect said it was “brave” and his energy consultant said we were “bonkers”. Both were wrong; it has worked perfectly and 7 years on we have no regrets whatsoever. Omitting the heating, other than heated towel rails in the bathrooms upstairs, saved £1,100 which was a significant contribution to the £2,600 cost of the MVHR system. We also negotiated a £600 discount from our window suppliers as we didn’t need trickle vents and saved another £800 or so as we didn’t need a cooker hood or any bathroom extractor fans, so the “net” cost of the MVHR was pretty minimal.

 

Unlike others our experience is that there is an element of heat redistribution from the MVHR, you can feel slightly warm air coming in through the vents. It’s difficult to quantify, but our bedrooms maintain a pretty constant 19 degrees in winter from the combined contributions from the ventilation system and the “migration” of heat which you mention from the ground floor, probably enhanced by an open plan layout downstairs which is also open to the stairwell. 
 

As regards your noise questions, our experience is yes you can hear it when it’s on boost, but not if the TV or radio is on, and in reality the boost level is so infrequently required it just isn’t an issue. We’ve also found that we can run the fans at much lower speeds than recommended by the manufacturers so in reality the system is virtually silent most of the time. Rigid rather than flexible ducts are supposed to help with this, as well as trying to keep your duct runs as simple and free of bends as possible. 
 

We located the intake/exhaust ducts on a north facing gable wall rather than through the roof in order to benefit from shaded/cooler air in summer. It’s amazing how hot a dark coloured slate/tiled roof can get with the sun on it, and the thought of sucking any of that heat into the house in July/August was unbearable, even in Northumberland. We also sited the exhaust duct downwind from the intake, which was a no cost option which which we thought might have (unquantifiable) benefits for both air quality and intake temperature in summer.

 

Good luck. Hope it works well for you!

 

 

[joe90]

12 minutes ago, DavidO said:

Our architect said it was “brave” and his energy consultant said we were “bonkers”.

I hope you have told them what you have posted here, we too have done the same as you and it works!!!

[djcdan]

@DavidO Thanks for this info. It seems your situation is similar. Ours is 193sqm with generally open plan living downstairs, stairs roughly in the centre of the property and central to all rooms upstairs. Others have suggested that MVHR plays a minor role in distributing heat, however if a constant supply of air is supplied to upstairs rooms - enough to complete an air change in that space every 3 hours at normal flow - at circa 18-19C, this must contribute to the overall climate control in these rooms... This, combined with the layout of the property, which promotes heats funnelling up from a continually heated downstairs and improved u-values to the glazing by improving from double to triple glazed, I think we'll scrap the rads upstairs, but keep rads in the bathrooms as you mentioned.

 

Our SAP is being recalculated next week, and I'll request the calcs be produced based on no rads upstairs and see if they balk at the idea. 

 

 

[SteamyTea]

55 minutes ago, djcdan said:

Others have suggested that MVHR plays a minor role in distributing heat, however if a constant supply of air is supplied to upstairs rooms - enough to complete an air change in that space every 3 hours at normal flow - at circa 18-19C, this must contribute to the overall climate control in these rooms.

Do the numbers, if the ACH are a small fraction of the total losses, then there is little to be gained i.e. say  2 kWh/day via air change and 30 kWh via fabric losses.

[Bitpipe]

Great advice above.

 

MVHR will distribute heat but in a very limited way that may or may not move the needle in your home depending on the overall heat requirement and performance of your fabric etc.  Best to think of it as a trim function vs the main source.

 

We have a large passive standard house that only has wet UFH on GF and electric under tile in bathrooms upstairs (plus towel rads). If a bedroom has been closed up for a few days (e.g. spare room) then it will feel cooler when first entered but leaving the door open for an hour or so (or just spending some time in it) will soon bring it up to same temp as rest of house.

 

If you're really paranoid about cold bedrooms, put a spare fused spur in each room and you could install a panel heater in the future if needed (it won't be).

 

We don't have sound attenuators on our Vent Axia system and get a slight drone when it goes on boost - most noticeable at night if someone gets up to use the loo.

 

We have a supply outlet above our bed which was maybe not a great idea but I got an attenuator specifically for that vent and its made a big difference.

 

We have a recirculating cooker hood and I positioned an additional extract vent directly beside it  - works well and no cooking smells in house.

 

Centrally locating your unit makes balancing easier but ours is in the basement on one side of the house and still works fine. Make sure you can get to it for filter change and annual cleaning the exchange unit.

 

 

[djcdan]

Thanks for the advice @Bitpipe
 

17 minutes ago, Bitpipe said:

If you're really paranoid about cold bedrooms, put a spare fused spur in each room and you could install a panel heater in the future if needed (it won't be).

 

I'm sold on the idea of no rads. Our u-values seem strong enough to support this. However, my partner is a bit of a 'traditionalist'! We've never lived in a well insulated or airtight home so is a little concerned she'll be freezing in bed at 12C on winter nights ?.

 

20 minutes ago, Bitpipe said:

We have a recirculating cooker hood and I positioned an additional extract vent directly beside it  - works well and no cooking smells in house.

 

 

This is the direction we'll probably take. I had planned a gap of 1.5m between recirculating hood and extract vent. This should be ok, shouldn't it?

[Bitpipe]

2 minutes ago, djcdan said:

Thanks for the advice @Bitpipe
 

I'm sold on the idea of no rads. Our u-values seem strong enough to support this. However, my partner is a bit of a 'traditionalist'! We've never lived in a well insulated or airtight home so is a little concerned she'll be freezing in bed at 12C on winter nights ?.

 

You really wont be. You will be comfortable, not hot or cold.

 

We have a Dyson fan from when we lived in the caravan. On the very rare occasions a bedroom is cool, usually a room that has not been entered for a few days like a guest room, a few minutes of the fan gets it back to comfortable temp. It's also noticeable how quickly a room warms up when you start doing the vacuuming or using a hair dryer.

 

Your focus should be on minimising overheating - even in spring & autumn, this can be a challenge if the sun is low in the sky and coming in through a window.

 

Think on shading and cooling strategy - we have external electric blinds on east and south aspects and can create 'stack ventilation' with roof windows on summer evenings.

 

I wish we had made provision for split air con for warmer summer days. If you have ASHP and UFH you can actively cool the slab which can make a big difference.

 

2 minutes ago, djcdan said:

 

This is the direction we'll probably take. I had planned a gap of 1.5m between recirculating hood and extract vent. This should be ok, shouldn't it?

 

Yep, we have about a 1m gap.

[DavidO]

4 hours ago, djcdan said:

 

Our SAP is being recalculated next week, and I'll request the calcs be produced based on no rads upstairs and see if they balk at the idea. 

Dont get too hung up on the calculations. Remember that, at your stage of the process, they include some important assumptions rather than realities, which, in effect, means they are (hopefully intelligent) guesswork. The prime example in our case, which was where the architects energy consultant slipped up, was airtightness. Her calculations were based on 3 (cu.m/hr/m.sq @ 50Pa) which,  as first time self-builders, was the very best she was prepared to believe we could achieve, whereas the actual result was 0.296. Fortunately we had stuck to our guns as regards omitting the bedroom heating (significant cost saving + Yorkshire genetics) but still ended up over speccing the boiler and including a wood burning stove which we have lit less than a dozen times in 7 years.

 

[DavidO]

4 hours ago, djcdan said:

This is the direction we'll probably take. I had planned a gap of 1.5m between recirculating hood and extract vent. This should be ok, shouldn't it?

Our experience is that you shouldn’t need any sort of cooker hood....we put 2 extract vents in the kitchen area and have no smells....no condensation and the boost hardly ever kicks in

[Gone West]

13 hours ago, DavidO said:

Our experience is that you shouldn’t need any sort of cooker hood....we put 2 extract vents in the kitchen area and have no smells....no condensation and the boost hardly ever kicks in

The only problem with that approach is that if in the future a lot of frying of food takes place the oil droplets will condense on the inside of the ductwork. Not an easy job to clean.

[joe90]

11 minutes ago, PeterStarck said:

The only problem with that approach is that if in the future a lot of frying of food takes place the oil droplets will condense on the inside of the ductwork. Not an easy job to clean.

for that reason I used a recirculating hood with charcoal filters and the extract 2 mtrs away. Works well

 

18 hours ago, djcdan said:

she'll be freezing in bed at 12C on winter nights ?.

Aint going to happen

 

18 hours ago, Bitpipe said:

If you're really paranoid about cold bedrooms, put a spare fused spur in each room and you could install a panel heater in the future if needed (it won't be).

 

Why, I just made sure 13amp sockets were in position for a small portable electric rad if required (and they haven’t).

Edited January 6, 2021 by joe90