Real world feel of MVHR +heat system

[MPx]

We've got a tricky decision coming up.  We're planning a Passivehaus standard timber frame build.  We've engaged with Total Home Environment for their MVHR +Heat systems.  I understand the calculations and can see a decent headroom for the minimal heat needed to overcome losses, etc.  So the numbers work...but I'm interested in how that might "feel" in practice.  I've seen a few threads discussing feel on here - some preferring what I'd call cool, other relatively hot so obviously interpretation is going to be tricky.  Our past experience is with a GSHP feeding wet underfloor heating which was nominally "on" 24/7/365 at low flow temp and kept the house at 21 degrees which we found our ideal.  What we are being offered I can see will be able to keep the house at a measured 21 degrees.  But there is no thermal mass of the type we were used to.  If we again opt for stone/tile floors but without UFH will that then "feel" cold despite the room being the same temp that we're used to?

 

Important because we have the option now to have underfloor heating pipes built into the floor "just in case" we later want to add another heat source (eg ASHP).  But I hate waste.  If I wont need it I dont want to build it in, even as just an insurance premium.  So just asking if there is any real world experience of this type of MVHR +heat set up out there and how it "feels".  Thanks

[ProDave]

I am not familliar with the heating system you propose.  Is it warm air heating delivered by the MVHR?

 

If so previous discussions suggest to deliver enough heat it will have to run at much faster flow rates than normal mvhr.

 

I would put those UFH pipes in and go that way.  You will almost certainly only need that on the ground floor as we have.

 

What do the heat loss calculations say is the heat input needed on the coldest winter day you can expect?

[JohnMo]

Been plenty of discussion on here, "we have a passivhaus so we don't need much or any heating".

 

Even to passivhaus spec you have a heat load of 10W/m², which isn't much, but is still some.

 

Heating element in mvhr can supply that (passivhaus heating spec, is designed around it). But if it's a heating element on direct electric, costs can soon stack up. So 200m² house at 10W, is 48kWh a day on your coldest day, or £13 in money terms. A well sized heat pump should be doing better than a CoP 3 on the coldest day, so now you are down to £4. Plus air heating you are going to need additional heat in bathrooms, I would think?

 

Do UFH on 200 to 300mm centres, and a small good modulation ASHP. Looking at about £4k in materials, plus the cylinder. Plus the ASHP can do your water heating and it costs a third it would, via direct heating. DHW heating could be costing £600 a year on direct electric, or £200 via a heat pump.

 

I would rather spend an amount up front, get a proper heating system that's cheap to run for ever more. 

[Russdl]

Also trying to sell a house (who knows what the future will bring?) without any heating may be problematic. That was one of the reasons we opted for UFH. The lived experience is that if we were living without UFH during these cold spells there would more than likely be a bit of grief with ‘er indoors. 
 

As an aside, our downstairs north facing toilet has two short loops of UFH pipes going in and out. The UFH is never on for more than 6hr (cheap rate electric) and it can feel cooler than the rest of the house during these cold spells. One or two tea lights is all it takes to keep that room snug and warm. 

[Russell griffiths]

Ufh pipes will cost a grand to buy, if you don’t put them in you need a serious word with yourself. 
 

I don’t understand the figures like some on here, but I know I’m sitting in the most comfortable house I’ve been in for a long time, just a gentle warmth in the tiles emits to every point of the house. 
 

it’s just an absolute pleasure. 

[Redbeard]

2 hours ago, JohnMo said:

Heating element in mvhr can supply that (passivhaus heating spec, is designed around it). But if it's a heating element on direct electric

 

If it's the same system I looked at via T.H.E for a client some years ago then it's a small exhaust air HP in the MVHR system.

3 hours ago, MPx said:

But I hate waste.  If I wont need it (*U'floor loops*) I dont want to build it in, even as just an insurance premium

 

But you do ask how the THE system (via the MVHR) might 'feel'. If there's any risk that, while the sums (heat in via the MVHR to replace heat loss) might work the 'insurance' might be worth it in case it doesn't 'feel' right *to you* in practice. It's going to be much cheaper doing it at screed stage 'at risk' than digging up the floor.

 

[Gone West]

3 hours ago, MPx said:

So just asking if there is any real world experience of this type of MVHR +heat set up out there and how it "feels".

I designed and built a PH that didn't need conventional central heating. It was heated using an electric towel rail in each of the three bathrooms and by warm air heating from a Genvex Combi 185. The temperature of the whole house was kept at 23C. It only worked because the house was only 130m2, had good air tightness and very good levels of insulation. It was a very pleasant environment to live in.

[saveasteading]

We were discussing what to do with rooms that should be cool. Larder/ cupboard etc. and does the Utility room need to be warm?

The current decision is to put the ufh pipes in anyway but not connect them, so we have full flexibility if (when) there is a revamp.

 

I think the same logic can be applied to the whole house if ufh is a likely addition in future. If diy'ing the cost isn't great at this stage but simply wont be done at a future stage.

[MPx]

Many thanks for the responses @ProDave , @JohnMo, @Russdl, @Russell griffiths, @Redbeard @Gone West, @saveasteading

 

And yeah...our prejudices are exactly the same hence my asking the question about feel.  The numbers are fine.  Requirement under 6kW - 10 available and more if we need a short burst.  The THE system uses a micro HP within the MVHR unit to generate the heat so its not an element - and will be (within margins) a similar cop to any other HP.   I want the house to be relatively "efficient", but I'm not overly concerned with running costs - it will be a fraction of our last house whatever we do.  I guess we will therefore be able to market that we have "heating" - although we're not planning to sell (accepting that you never know) but the design is for an old couple and takes into account likely eventual outcomes on health etc - so its intended to see us out and changing circs not force us to move ever again.  Also we will effectively have a "flat" on the 1st floor - where we would expect to spend 99% of the time.  The ground floor is services/utilty/gym/garage/and guest suit (which could eventually become accommodation for a live in carer if required).  So I don't really want to concentrate any effort on heating downstairs - its all about maintaining a comfortable feel on the first floor.  But as we're likely to have stone/tile floors on the 1st floor, rather than carpet (because that's what we like), I can see that we may achieve the numbers but still not "feel" cosy.  We had an ideal set up before with wet UFH so its would be easy to replicate that....but we didn't have a passivehaus spec, we didn't have MVHR, and we did spend a fortune on both installation and running.  I'm trying to embrace something new rather than falling back on what I already know.

 

Hence I'm really asking for what others with a similar set up have found in practice rather than what each of our attitdues to risk is.  

Edited 6 hours ago by MPx

[ProDave]

15 minutes ago, Russell griffiths said:

Ufh pipes will cost a grand to buy, if you don’t put them in you need a serious word with yourself. 

How much did you use in your house?  No more than 500M in mine, if that, and by buying new offcuts you can get it pretty cheap.

 

e.g 90 metre "offcut" for £60 with postage https://www.ebay.co.uk/itm/316187121886?

 

5 of those would have done my entire house.

 

At that price, just put it in, it gets used, or if not, you have not wasted much.

 

 

[Gone West]

2 minutes ago, MPx said:

The THE system uses a micro HP within the MVHR unit to generate the heat so its not an element - and will be (within margins) a similar cop to any other HP. 

As I mentioned, the Genvex Combi 185 is a MVHR with a built in EASHP. The HP heats the 185l hot water tank and provides warm air through the MVHR. I bought my Genvex direct from Denmark many years ago at a fraction of the cost from THE.

[MPx]

Thanks, I asked about future maint if they went bust...and was told it was a largely a badge engineered Genvex system with nothing exceptionally complex in it - so its good to hear that you've been happy with yours.

[JohnMo]

52 minutes ago, Russell griffiths said:

Ufh pipes will cost a grand to buy, if you don’t put them in you need a serious word with yourself. 

Gee you were either wrapped off, massive house and or tiny centres. I have 600m in the floor (192m²), so about £350 today.

 

43 minutes ago, MPx said:

Requirement under 6kW

That must be a massive house? If it's passive?

 

45 minutes ago, MPx said:

micro HP within the MVHR

I would definitely not do heat and ventilation as individual items. One dead both dead, when combined. Also look at the hot water generation time with your combined unit.

 

52 minutes ago, MPx said:

Requirement under 6kW - 10 available and more if we need a short burst

How are you getting that much energy out of a micro HP? Any links to the product?

[Adrian Walker]

You should be looking and considering an insulated concrete slab with UFH. UFH pipes can be used to both distribute heat and cool. 

[Andehh]

I find MVHR moves so little air the cooling impact of full boost on a cool summer night after a hot day, for an hour or two......nuffin!!

 

So I'd be nervous at relying on it for heating, based on no real knowledge other then my own experiences. 

 

100% UFH pipes in, pipes from manifold at where you 'could' do an ASHP, and put wiring in for it. Leave all capped off. 

 

So easy to do now, impossible in future! 

 

[MPx]

15 minutes ago, JohnMo said:

 Any links to the product?

https://www.totalhome.co.uk/ventilation/?pid=615

https://www.totalhome.co.uk/ventilation/?pid=595

 

9 minutes ago, Adrian Walker said:

You should be looking and considering an insulated concrete slab with UFH. UFH pipes can be used to both distribute heat and cool. 

Yes it will have an insulated concrete slab (down stairs).  I'm considering a lewis deck and screed upstairs too (where we'll actually live) but more to support the weight of the flooring than to house UFH. 

 

I dont want to put in stuff I dont need.  Any experience of how it might actually feel - not what you'd do in my place?

 

6 minutes ago, Andehh said:

So I'd be nervous at relying on it for heating, based on no real knowledge other then my own experiences. 

Its real life experience I want...so thank you.

[Adrian Walker]

1 hour ago, MPx said:

https://www.totalhome.co.uk/ventilation/?pid=615

https://www.totalhome.co.uk/ventilation/?pid=595

 

Yes it will have an insulated concrete slab (down stairs).  I'm considering a lewis deck and screed upstairs too (where we'll actually live) but more to support the weight of the flooring than to house UFH. 

 

Lewis decking is a good idea, but it won't need UFH.

 

1 hour ago, MPx said:

 

I dont want to put in stuff I dont need.  Any experience of how it might actually feel - not what you'd do in my place?

 

Its real life experience I want...so thank you.

 

 

I wouldn't use air to heat the house, it's a poor way to put heat into the slab.  You want a uniform and constant temperature that only UFH can provide. I have visited a certified passive house that didn't have UFH, it's was a disaster. 

[JohnMo]

1 hour ago, MPx said:

dont want to put in stuff I dont need

So based on the flow rates, it's around 400m² property - that's a big retirement pad. If it isn't that big you are going to massively over ventilate and maybe suffer a very dry indoor environment in winter to get 6kW.