MVHR - list of questions/thoughts

[mjward]

Hello

 

As per my other post with regards to ICF, I've returned from the Self Build show with a few questions I'm hoping the good folk on here will be able to assist with:

 

1) the marketing pitch I received was that no radiators/UFH are required and that MVHR will keep the house at a pleasant temperature just with the help of the odd towel radiator. In the real world how true is that? My research prior to the show was that its greatly aided by a more noticeable support and my plan was wet UFH in kitchen/bathrooms to be said boost (with no rads in any room).

 

2) linking on to that, how good are these units are balancing out influencing forces? i.e. if I want UFH in kitchen/bathroom as I like warm tiles underfoot, will that just ensure my house will be too hot or will the system be able to moderate it? and in turn, if its moderating it, am I wasting heat/power in doing so, i.e. best off with just the UFH in kitchen as a sole heat provider. I appreciate it's a length of string type question as depends on house size/thermal load etc.

 

3) For those that have MVHR installed and no UFH, does the floor ever feel cold in tiled/floorboard rooms?

 

4) I saw posi-joists for the first time at the show and it looks a no-brainer to be able to route MVHR ducting amongst other things. Is there a better product people have used or any downsides to posi-joists?

 

5) I was surprised at how many manufacturers were offering just a 5yr warranty. Seems very low given a boiler at a tenth of the cost can get you up to 8-10 years.

 

6) What issues/problems have people had with this setup and how did you overcome them?

 

7) Merits of all-in-one vs separate systems? Received ballpark quotes of 25-35k for all-in-one systems (i.e. inc ASHP, cooling & heating) and although appreciate the benefit of "the tech can talk to each other", it seems the components were cheaper than the sum of the parts and give you the added benefit of only replacing one element if it goes kaput. 

 

8 ) How much of an MVHR system can be installed by a DIYer? Was thinking to run the ducting unless more can be done.

 

9) Question from my wife...what is the water temperature like at the tap i.e. how does an ASHP & MVHR compare to traditional gas boiler for hot tap/bath water?

 

10) finally...what steered me to MVHR in the first place was the govt decision to ban gas boilers in new builders from 2025. I thought it made sense to future proof if that was the direction the govt is going. However, given it would be impossible for the govt to force every household to change from gas at a later date, and the fact we will have hydrogen boilers in 2025 that are apparently a straight swap for the gas setup, should I be viewing this as a window of opportunity to get the "cheap" gas boiler/traditional setup or as the consensus that an MVHR/ASHP investment is worth it for the utility bill savings alone (assuming a well insulated property). What I can't afford is another Crestron mistake i.e. spend 50k+ on equipment only for sonos/philips hue et al come out and do the same thing for pocket money a few years later.

 

That's all I've got for now, thanks for any and all responses. Much appreciated

Edited October 21, 2020 by mjward

[MJNewton]

Reading your questions made me wonder if you were confusing MVHR with ASHPs, but given you've mentioned both I'm not so sure. Suffice to say though; don't mix up MVHR with heating/cooling. MVHR is an approach to providing ventilation and whilst it does so in a way that minimises losses through heat recovery it is no substitute for heating/cooling as the air flow volumes are so low it has very little effect. Don't get me wrong, I think it is great and would definitely recommend it (I retrofitted a system here and so in answer to Q8 I can confirm it is *definitely* DIYable and would be even easier in a new build).

Edited October 21, 2020 by MJNewton

[Thorfun]

yep. as MJNewton said, MVHR is not a heating/dhw system! although it can be used for a bit of heating/cooling (from the reading I've done on here a few have a system that does a little heating/cooling) it is no substitute for a gas boiler or ASHP as a primary heating/dhw supplier.

 

take a read through the MVHR forum and ASHP forums for load more information on both subjects.

[ProDave]

MVHR is about providing fresh air into a building without wasting the heat from extracted stale air.  It is not on it's own a heating system, though some mvhr units are available with a heating function.  I think that is what you are talking about?

 

So your house won't heat itself.  MVHR is one ingredient to making a low energy house.

 

Having said that. we have UFH downstairs, but upstairs only in the 2 bathrooms.  We find we don't need heating upstairs because that does okay with what creeps up from downstairs. Most of that will be via the centrally positioned stairwell.

 

As part of your design process you should get a SAP assesment done that will tell you the heating requirements of the house.

[Conor]

MVHRs sole job is to maintain air quality, whilst recovering some heat from the exhaust air. There's no need to have MVHR and heating "talk" to each other.

 

Yes, there are some MVHRs out there that have integrated heat pumps and can heat domestic hot water and heat/cool incoming air. But as others have said, unless you are building a passive House with minimal heat load, these will struggle to distribute heat. I think the max realistic heat you can distribute through air is about 2kw. The peak heat load for my house is 2.5kw, so I can't reliable heat my house this way. Plus, you have to have higher air flow rates which often equals more noise. And when I did the sums, the likes of the Nilan compact P with ASHP was coming out nearly double the cost of a separate ASHP and MVHR.

 

If you go for a standard MVHR like a vent axia sentinal or a Zehnder Q series, and a separate monoblock ASHP, you should be able to do 90% of the install of both systems yourself. This is what I'm doing in my ICF passive House. My current estimate is about £12k for self install of both systems including DHW tank, ufh, but excluding commissioning. Ashps can get hot water tonl 50c + ... Tho most here seem happy with 45c.

 

Be aware there are lots of companies and people jumping on the MVHR bandwagon with limited expertise and will say anything to make a sale. It's like the double glazing boom of the 90s.

 

What ever way you go, your number one priority should be maximising insulation and air tightness. You can then spend a lot less on heating. I recommend you look up the passive House standards of you want a very low energy home.

Edited October 21, 2020 by Conor

[joe90]

I agree with all the above, the mantra here is insulation insulation insulation, fabric first approach, you only buy insulation once, all other things either have a life or need constant spend (electricity etc). My build is not to Passive spec but passive esc, in other words loads of insulation and attention to detail re airtightness. I have a small 5kW ASHP and MVHR, both bought through EBay and self installed, not rocket science. I too have UFH downstairs and only towel rads and electric UFH In bathrooms, no heating at all in bedrooms as the whole house is a constant temp.

 

re question 9, like others here with an ASHP I only heat DHW to 48’, most gas boilers are 60’ ish the standing losses from a hot water tank are much less when stored at this temp, it’s also too hot to hold your hand under (washing up) and bath /showers more than hot enough BUT, you will blend down the water less so the DHW tank needs to be larger.

[mjward]

23 hours ago, MJNewton said:

Reading your questions made me wonder if you were confusing MVHR with ASHPs, but given you've mentioned both I'm not so sure. Suffice to say though; don't mix up MVHR with heating/cooling. MVHR is an approach to providing ventilation and whilst it does so in a way that minimises losses through heat recovery it is no substitute for heating/cooling as the air flow volumes are so low it has very little effect. Don't get me wrong, I think it is great and would definitely recommend it (I retrofitted a system here and so in answer to Q8 I can confirm it is *definitely* DIYable and would be even easier in a new build).

 

I forgot to "follow" my own thread and missed this.

 

Apologies for confusion, it spent most of the show looking at all-in-one systems that had MVHR & ASHP but do appreciate they do different jobs.

[mjward]

23 hours ago, ProDave said:

MVHR is about providing fresh air into a building without wasting the heat from extracted stale air.  It is not on it's own a heating system, though some mvhr units are available with a heating function.  I think that is what you are talking about?

 

So your house won't heat itself.  MVHR is one ingredient to making a low energy house.

 

Having said that. we have UFH downstairs, but upstairs only in the 2 bathrooms.  We find we don't need heating upstairs because that does okay with what creeps up from downstairs. Most of that will be via the centrally positioned stairwell.

 

As part of your design process you should get a SAP assesment done that will tell you the heating requirements of the house.

 

Yes precisely, it was the all-in-one beasts I had been learning about but certainly not married to any particular setup at this early stage. With regards to your UFH, is that for the entirety of your ground floor or just kitchen? 

 

Will make a note re SAP, at this stage I don't even have a finalized design, just trying to learn as much as I can about the various parts that may influence said design.

[mjward]

23 hours ago, Conor said:

MVHRs sole job is to maintain air quality, whilst recovering some heat from the exhaust air. There's no need to have MVHR and heating "talk" to each other.

 

In your opening line you've just null and voided some of the sales pitch I had fallen for  

 

23 hours ago, Conor said:

 

Yes, there are some MVHRs out there that have integrated heat pumps and can heat domestic hot water and heat/cool incoming air. But as others have said, unless you are building a passive House with minimal heat load, these will struggle to distribute heat. I think the max realistic heat you can distribute through air is about 2kw. The peak heat load for my house is 2.5kw, so I can't reliable heat my house this way. Plus, you have to have higher air flow rates which often equals more noise. And when I did the sums, the likes of the Nilan compact P with ASHP was coming out nearly double the cost of a separate ASHP and MVHR.

 

Encouraging to hear and certainly seems the logical choice, cheaper than all-in-one with added benefit of being able to replace one faulty part down the line.

 

23 hours ago, Conor said:

 

If you go for a standard MVHR like a vent axia sentinal or a Zehnder Q series, and a separate monoblock ASHP, you should be able to do 90% of the install of both systems yourself. This is what I'm doing in my ICF passive House. My current estimate is about £12k for self install of both systems including DHW tank, ufh, but excluding commissioning.

Ashps can get hot water tonl 50c + ... Tho most here seem happy with 45c.

 

90% is music to my ears. Is this something you learnt from scratch or did you have a pre-existing plumbing/electrical skillset? Would love to be able to have both installed for 12k+commissioning, would make a huge difference. 50c is more than good enough for me so brilliant again, thank you

 

23 hours ago, Conor said:

Be aware there are lots of companies and people jumping on the MVHR bandwagon with limited expertise and will say anything to make a sale. It's like the double glazing boom of the 90s.

 

...on this note, don't suppose you have strong thoughts on the triple vs double glazing argument? I haven't approached this seriously as yet but from my initial research I'm getting a vibe that the thermal efficiencies aren't worth the cost differential. 

 

23 hours ago, Conor said:

 

What ever way you go, your number one priority should be maximising insulation and air tightness. You can then spend a lot less on heating. I recommend you look up the passive House standards of you want a very low energy home.

 

This is most certainly the plan. To be aware of PH standards but I'm not outright targeting PH certification. Going down the ICF route for airtightness, will pay close attention to property orientation for thermal improvements and will be mitigating openings as aesthetically as I can.

 

[mjward]

23 hours ago, joe90 said:

I agree with all the above, the mantra here is insulation insulation insulation, fabric first approach, you only buy insulation once, all other things either have a life or need constant spend (electricity etc). My build is not to Passive spec but passive esc, in other words loads of insulation and attention to detail re airtightness. I have a small 5kW ASHP and MVHR, both bought through EBay and self installed, not rocket science. I too have UFH downstairs and only towel rads and electric UFH In bathrooms, no heating at all in bedrooms as the whole house is a constant temp.

 

re question 9, like others here with an ASHP I only heat DHW to 48’, most gas boilers are 60’ ish the standing losses from a hot water tank are much less when stored at this temp, it’s also too hot to hold your hand under (washing up) and bath /showers more than hot enough BUT, you will blend down the water less so the DHW tank needs to be larger.

 

Sounds like we are very much on the same page. Again is your UFH across all of downstairs or just a kitchen setup? Seems like from yours and above the sweet spot is ground floor UFH and bathroom UFH/towel rads and thats your lot (assuming adequate work down on insulation and air flow).

 

In regards to the water temperature, that all make sense and is very useful, particularly the larger DHW tank part, hadn't occurred to me so thank you very much

[Conor]

28 minutes ago, mjward said:

 

 

 

...on this note, don't suppose you have strong thoughts on the triple vs double glazing argument? I haven't approached this seriously as yet but from my initial research I'm getting a vibe that the thermal efficiencies aren't worth the cost differential. 

 

 

 

There's no argument at all as far as I'm concerned, triple glazing is significantly better than double on many measures. Insulation, sound exclusion, solar gain reduction. There are a lot of basic window manufacturers that only make double glazing profiles and others who just don't want to work with heavy 3g units.

 

Of you have any significant south facing glazing, you pretty much NEED triple glazing to prevent over heating. Also, there's not much of a coat difference, I don't see the point in saving a few hundred or thousand of pounds when your ploughing so much more money in to the fabric of the house.

 

Re install... I won't be doing any electrics but I've a fair bit of plumbing experience (I'm an engineer in the water industry, so it's naturally familiar to me, just pipes are a lot smaller!).

 

I monoblock ASHP only has two water connections and one electric connection plus controls. I'll like have everything bolted and sat in place then I'll get the spark to do the reat and plumber to do the hot water cylinder.

[joe90]

1 hour ago, mjward said:

Again is your UFH across all of downstairs

Yes, all one zone but lounge has a slightly higher flow rate as it’s where we sit most.

 

1 hour ago, mjward said:

Seems like from yours and above the sweet spot is ground floor UFH and bathroom UFH/towel rads and thats your lot (assuming adequate work down on insulation and air flow).

yes, but if we did suffer a long very cold spell a couple of oil filed electric radiators in bedrooms are more than adequate (not needed them so far). If it’s that cold we light the woodburner and that heats the whole house nicely.

 

34 minutes ago, Conor said:

Of you have any significant south facing glazing, you pretty much NEED triple glazing to prevent over heating. Also, there's not much of a coat difference, I don't see the point in saving a few hundred or thousand of pounds when your ploughing so much more money in to the fabric of the house.

Not sure I agree there, ours is all double glazed and the company that made the windows uses a glass “technician” and with the coatings he got us very near triple glazing u value, I don’t like very heavy windows with triple glazing plus every pane of glass you add gives a little more “haze”. We do overheat a little but that is because of a south facing conservatory but that also heats the house very well in the shoulder months, even winter on a clear sunny day. (Saves me paying fir a holiday in the south of France!!!!

Edited October 22, 2020 by joe90

[mjward]

1 hour ago, Conor said:

 

There's no argument at all as far as I'm concerned, triple glazing is significantly better than double on many measures. Insulation, sound exclusion, solar gain reduction. There are a lot of basic window manufacturers that only make double glazing profiles and others who just don't want to work with heavy 3g units.

 

Of you have any significant south facing glazing, you pretty much NEED triple glazing to prevent over heating. Also, there's not much of a coat difference, I don't see the point in saving a few hundred or thousand of pounds when your ploughing so much more money in to the fabric of the house.

 

Got it, with that conviction it sounds like I need to do some serious research with a view to include. 

 

1 hour ago, Conor said:

 

Re install... I won't be doing any electrics but I've a fair bit of plumbing experience (I'm an engineer in the water industry, so it's naturally familiar to me, just pipes are a lot smaller!).

 

I monoblock ASHP only has two water connections and one electric connection plus controls. I'll like have everything bolted and sat in place then I'll get the spark to do the reat and plumber to do the hot water cylinder.

 

Definitely sounds doable. I'm a zero for both electric/plumbing experience but started studying the City & Guilds Electrical installations course at the end of August and hoping mid-2021 I am at a level I can approach most of the electrics (first & second fix) bar leaving the fusebox and mains incoming (as well as sign off) in the hands of a professional. I haven't started yet but I am also planning to take on similar for the plumbing side.

[mjward]

43 minutes ago, joe90 said:

Yes, all one zone but lounge has a slightly higher flow rate as it’s where we sit most.

 

Got it, current thought process is to wood parquet the entire ground floor which I believe would work well with a wet UFH system, the prices of which seem to have plummeted in recent years. Would I be right to assume one zone but each room independently reaching the manifold?

 

43 minutes ago, joe90 said:

yes, but if we did suffer a long very cold spell a couple of oil filed electric radiators in bedrooms are more than adequate (not needed them so far). If it’s that cold we light the woodburner and that heats the whole house nicely.

 

Interesting. When I started this enquiry in the summer I was reading about the problems of insulation + MVHR not being able to adequately cope with 30c heatwaves but sounds like both extremes could be an issue. I was planning to avoid the woodburner in order to nudge closer to PH standards, although I really like the look and heat from them. I wonder if it would make sense for me to fit a heat source like an electric rad in the upstairs hallway or even per bedroom that can be activated only in the extreme scenarios.

 

43 minutes ago, joe90 said:

Not sure I agree there, ours is all double glazed and the company that made the windows uses a glass “technician” and with the coatings he got us very near triple glazing u value, I don’t like very heavy windows with triple glazing plus every pane of glass you add gives a little more “haze”. We do overheat a little but that is because of a south facing conservatory but that also heats the house very well in the shoulder months, even winter on a clear sunny day. (Saves me paying fir a holiday in the south of France!!!!

 

This is what my initial research had thrown up, i.e. the proximity of some DG to TG with regards to U-values yet the significant disparity in cost. As per above, I'll need to do more research on it. Note overly fussed about the weight aspect as I was under the impression an element of the MVHR is that it encourages you to keep your windows closed?

[joe90]

55 minutes ago, mjward said:

Would I be right to assume one zone but each room independently reaching the manifold?

yes

 

56 minutes ago, mjward said:

current thought process is to wood parquet the entire ground floor

My lounge Is engineered oak but rest is tiled 

 

58 minutes ago, mjward said:

Interesting. When I started this enquiry in the summer I was reading about the problems of insulation + MVHR not being able to adequately cope with 30c heatwaves but sounds like both extremes could be an issue. I was planning to avoid the woodburner in order to nudge closer to PH standards, although I really like the look and heat from them. I wonder if it would make sense for me to fit a heat source like an electric rad in the upstairs hallway or even per bedroom that can be activated only in the extreme scenarios.

the thing with insulation is it works both ways, keeps heat in and out, I have large bi folds into the kitchen diner and lounge, during cold weather they are kept shut (no heating in the conservatory) and during warm weather they are open to help heat the house BUT in hot weather they are kept shut to keep excess heat out of the house. During this hot weather I open windows at night to purge the house and close them, and curtains during the day to keep the heat out. Some have put dedicated wiring in bedrooms fir heaters but a 3 pin socket works just fine heaters kept in cupboard in case (ever) needed. (P.S. we love our wood burner, better than watching tv at times) butvrarely lit, purely extravagance on our part.

[mjward]

17 hours ago, joe90 said:

yes

 

My lounge Is engineered oak but rest is tiled 

 

the thing with insulation is it works both ways, keeps heat in and out, I have large bi folds into the kitchen diner and lounge, during cold weather they are kept shut (no heating in the conservatory) and during warm weather they are open to help heat the house BUT in hot weather they are kept shut to keep excess heat out of the house. During this hot weather I open windows at night to purge the house and close them, and curtains during the day to keep the heat out. Some have put dedicated wiring in bedrooms fir heaters but a 3 pin socket works just fine heaters kept in cupboard in case (ever) needed. (P.S. we love our wood burner, better than watching tv at times) butvrarely lit, purely extravagance on our part.

 Got it, very clear. Re the 3 pin, you are absolutely right, in our previous renovation I wasted far too much time (ergo stress) on the "what ifs" and future proofing etc that you need to pinch yourself and remember that extreme scenarios by their very nature don't happen very often and a cheap but effective solution is the winner.

 

Re wood burner, if you can't build your own house with a pinch of extravagance then why bother although my wife has put her foot down on the fireman's pole from the master bedroom to the kitchen

[mjward]

One thing to add here is that I saw the below in a homebuilding magazine and was surprised that they say the running cost of the ASHP is comparable to a gas boiler. Given the larger equipment cost with ASHP, if the running cost is identical what makes people have a preference for ASHP?

[DavidFrancis]

My current gas cost is just under 2.5p/kWh. Electricity is just under 15p. So you'd need a very, very efficient ASHP to improve on unit costs. But then there's a standing charge of about £80/year for gas that could maybe be eliminated. Using an ASHP may produce less CO2, but I don't know enough about the current grid mix and efficiencies to comment. I think the ASHP installation costs could be greatly improved-on with shopping around. Look at @ProDave's blog for example.

[joe90]

I think ASHP is ideal fir a new build where insulation etc can be maxed out and UFH installed, we have no gas (apart from bottled for a hob) I bought my ASHP on Ebay and self installed for less than a gas boiler would have cost. Every case is different.

[ProDave]

The one thing against gas of course is for those who have no access to mains gas.  That's us.  So the only mains energy service available is electricity.  Otherwise the choices are LPG gas, oil, or sold fuel.

 

LPG gas is expensive, Oil is cheap at the moment but very volatile.

[Oz07]

It used to be a running theme on this forum people said if you had access to gas then use it. Regardless of how you build if you have mains gas is it not always cheaper? It's subsidised isn't it?

[Conor]

51 minutes ago, Oz07 said:

It used to be a running theme on this forum people said if you had access to gas then use it. Regardless of how you build if you have mains gas is it not always cheaper? It's subsidised isn't it?

I was part of that crowd. But once you factor in servicing, standing charges, and the fact that you can get electric from as little as 5p/kWh on flexible tarifs, ASHP has a lower lifetime cost. But the main thing for me is I'm not directly burning stuff and pumping it in to the air. With SSE airtricity here, 80% of the electric over the course of the year comes from renewables. That, paired with my own PV means my carbon emissions are less than a gas boiler.

[Levo]

2 hours ago, DavidFrancis said:

My current gas cost is just under 2.5p/kWh.

Wow, that is cheap! Which supplier do you use?

[Ferdinand]

18 minutes ago, Levo said:

Wow, that is cheap! Which supplier do you use?

 

I had 2.5p per kWh as a normal average figure for the unit rate on a decent tariff, but standing charge adds to that depending on usage. It is my current rule of thumb for comparisons in my head.

 

eg for one list (example not recommendation)

https://www.theenergyshop.com/guides/energy-prices-per-kwh

 

F 

[Bramco]

On 21/10/2020 at 14:43, mjward said:

1) the marketing pitch I received was that no radiators/UFH are required and that MVHR will keep the house at a pleasant temperature just with the help of the odd towel radiator.

 

This is something that has got me thinking.

 

Assuming we have our bathrooms warmer than the rest of the house and also have heated towel rails in the bathrooms, won't the returned warmth that an MVHR recovers as the air flows from the living spaces through the bathrooms to the outside keep the living spaces warm. 

 

So you can imagine that the heated towel rails are actually doing the heating which if these are electric are at a COP of 1....    

 

Is this an issue? And if so how do you prevent it happening.

 

Simon