Home Heating. How it feels. ASHP, UFH and MVHR

Sorry for all the initialisms in the thread title.

TL;DR – does an airtight home with good insulation and MVHR feel like living in an office? Will we regret it.

Full post:
Does anyone in here have any experience of combining an Air source heat pump, underfloor heating, and a mechanical ventilation heat recovery system?

We are about to almost fully knock down and rebuild our house, and considering our heating options.

We live in the South East and currently have the widows open from pretty much when the heating goes off in the spring to when it goes on again in the autumn. In winter, we’ll often keep the doors open when in the house during the day if the heating is off as we seem to like fresh air.

The house, although it will not quite be to Passivhaus standards will be really well insulated and pretty airtight. The construction method will allow for MVHR to be in the ceiling/joist voids. We are proposing UFH on both floors, paired with an ASHP with flow temperature of about 35-40deg.

Quotes for supply of the three systems (excluding fitting and commissioning), with control systems and hot water tank are coming in at about £30-35k+vat.

From this we should get £5k back from the government fire the ASHP.

If we go down a traditional gas boiler and radiator route, it will be about £15-20k in materials, as the house will be quite large, we need all new pipework, radiators etc and we will still likely want UFH on the ground floor.

Will we feel it is a worthwhile investment, or will it feel like we are living in a climate controlled office with a near constant temperature and fresh airflow throughout the day/year? We would like carpets in some rooms, but with UFH we will be limited to thinner tog carpets, possibly further enhancing the ‘office’ feeling.

Have been reading lots of great posts on Buildhub, but everyone is a bit geeky on there, and the majority of people are happy to comment on the efficiency figures, costs/savings and installation process, but there is not really much chat about the ‘feel’ of a house with these systems.

Thanks.

I regularly stay in my brother’s passive house, it does to me feel very hospital like and I wouldn’t want to live there. Temps are less stable than I imagined, there are several digital readouts around and it’s interesting to see what happens on a sunny day for example. Windows and doors are ‘always’ closed.

My own house is conventional but massively insulated. Lots of solar gain so windows and patio doors generally open, this allows the heat to come in but also be drawn through. Typical temps are 20/21c on a normal day.

Gas boiler for hot water only outside winter months, we have a wood burner too but since topping up insulation it’s use has dropped to one load in the evening. Gas heating is typically on for 30 mins on a cold morning but that is Highlands cold.

To be honest I am utterly amazed at the difference our insulation project made – usual loft standards plus underfloor insulation, some minor wall cavity, draught and leak elimination. Best of all the house feels lovely, there are cooler areas in the bedroom, toasty areas in the lounge. So compared to passive, it’s far preferable for us in terms of ambience and I think we have done a good job in terms of energy reduction

My brother’s home is very much the classic white box, and I think this goes a long way towards how it feels inside. It could be very different with good use of colour and furniture choices that do not resemble a dentist’s waiting room. This is all subjective of course but I am sure a lot of the ambience could be addressed with nicer decor, but not all of it.

There are regular organised open days through the passivhouse trust. Next one is November.

https://www.passivhaustrust.org.uk/event_detail.php?eId=1151

Failing that you could google stalk your nearest one and knock on the door / leave a note to ask if you could pop round.

Another route is to go down the breathable materials route with sheeps wool, woodfibre and hemp.

I have no experience of it but have always been attracted to the air filtration aspect of MVHR. Less air pollants and pollen in the home.

Also are you not able to tune these systems to your liking to an extent to get the ideal moisture and air change figures?

x.

+1 on Passivhaus trust.

I have been in a few and stayed in a couple of PassiveHaus/AECB gold houses. All felt perfectly pleasant, had a homely feel and carpet. I wonder if your brother has gone all ‘white box and sterile’ instead of ‘efficient but homely’.

Last week we stayed in a newish holiday cottage that was built above Scottish building standards for insulation, with ASHP and UFH. It was properly lovely and nice.
It was however too warm for mrs_oab and i and we spent a lot of the week with doors and windows open – but that may be as it was lacking MVHR.
My brother in NZ has just retrofitted his house to around Passivhaus. BUT, they had damp issues forming in just the one winter before he got the MVHR fitted. In the space of a month he said the house was transformed – feels like fresh air and yet toasty warm. They are aiming for no heating other than the MVHR he installed has a heating coil – bear in mind they are in Auckland.

We moved into our self build two years ago, as an architectural designer I designed and specified the build throughout to be as close to a passivhaus standard as possible whilst utilising traditional build methods i.e masonry cavity wall, beam and block floor etc to appeal to as many builders as possible for build speed and tendering, I needed to get the house built v quickly for our disabled son and to get it done before brexit pushed material prices up, that was the plan and then the pandemic hit which made things interesting.  Anyway, some rambling thoughts to hopefully help you out:

Our house is pretty airtight (2.5) considering this type of build is prone to being leaky. We have an ASHP, MVHR, UFH, Solar PV and rainwater harvesting (wc’s and washing machine). Triple glazed windows/rooflights and increased thermal insulation throughout. We were very keen not to have a new build feel internally (white box) and do have some rooms with carpets – lounge, study and all bedrooms. Oak window cills, window and door frames with a light grey finish, most importantly – colour on the walls! Have fun with it.

Regarding internal comfort, we were coming from the complete opposite, a 17th century cob cottage which we renovated. The cottage was always cold, damp and draughty. The new house is obviously the complete opposite and has taken us a while to get used to, it is far warmer and dryer than we were used to but not unpleasant – just different. The air always feels fresh inside and its really nice not worrying about mould/condensation anymore. I would not hesitate going for this spec again and now have the info to pass on to my clients. In terms of how we use the house, generally we have windows and doors open during the summer months day and night as you would in a traditional house (except in a heatwave). The MVHR is kept running all year – summer bypass mode during warmer months, in the colder months we begin to close the house up more so we then utilise the heat recovery. In winter we have found the MVHR to create quite a dry environment despite hanging clothes to dry in one of the bedrooms over night. If I was doing another build I would be speaking to the MVHR designer about how this can be factored in (Green Building Store designed ours and were excellent). Make sure the MVHR is designed with acoustic baffles to each habitable room, this reduces the risk of noise. We cannot hear our system at all.

Internal temperatures stay around 21 to 22 most of the year, dropping to 19 during the colder months with some heating. The biggest issue with a well insulated house is the potential for overheating, I put our design through the passivhaus software (PHPP modelling) and reduced the areas of glazing considerably, choose good quality triple glazed windows (G value important, less transmission = reduced overheat risk). Keep rooflights to a minimum, we have two with external roller blinds that are electrically operated and can be closed during heatwaves.  Carpets/underlay – just go for ones that are suited to UFH, it wont be quite as reactive but it will be fine.

Unlikely that you will need to run the ASHP flow temps that high, were at 28 to 38 (weather dependant).

Cost seems about right.

Some more photos of builds/bikes on my insta if interested

I’m doing similar myself on a new build. UFH down, and in the upstairs bathroom, radiators in the 3 upstairs bedrooms.

My total materials cost is going to be £18k ish, 8kW ASHP and integrated tank from Nibe is £10k, MVHR is roughly £3k, UFH is around £4k, rads and pipeworks and ancillaries will add another grand, so your total of £30k is about right if they are installing too.

There are more budget options available, Nibe are at the top of the tree price wise, Baxi etc are a lot cheaper, the integrated tank at £4k costs roughly double the equivalent from Gledhill etc, but it fits in really well where I want it.

Some of the MVHR units are f-ugly, if in the attic, not a problem, but if on show, have a look at them first, we’re probably going for Duco, they have good controls too, some are very basic.

Keep rooflights to a minimum, we have two with external roller blinds that are electrically operated and can be closed during heatwaves.

@nt80085 Do you have further details on these blinds please? Brand name or link perhaps?

House was built 2 years ago – timber frame with a high level of insulation. ASHP with UFH downstairs and radiators upstairs. Did consider GSHP with MVHR but at the time, the payback for the extra cost was in excess of 10 years. Even though we’re on the Isle of Mull, any sunshine and it gets pretty warm – most of the summer the windows are open all the time – it’s very quiet, so noise isn’t an issue. It doesn’t feel at all like an office, but that’s as much to do with the decor and furnishings.  The heat is very much ambient and consistent throughout rather than the warm spots created by traditional heating.

@jolsa Velux rooflights with their roller blinds, hard wired at blind, wireless remote on wall. Would defo use again.

What an odd question. Is it going to be full of bland desks with loads of people sitting at computers? If not, it probably won’t feel like an office.

I’ve stayed in a Passivhaus. It was nice because it was big and well lit. The temperature was just normal.

We lived in a certified passive house when we were in Germany (3 years). If it’s true passive it won’t need heating, that’s the point!

In Bavaria ,even when the temperature outside was -15, the house didn’t need the heating on and stayed at a comfortable 20-21°C.

MVHR was superb and any washing would dry very quickly.

Building fabric was concrete with about 60cm thick external insulation stuck to the walls and triple glazed. We watched the rest of the estate be built.

Superb place to live, then we had to move back to the UK………

I live in an antipodean house with an ASHP? (a what???) – a ‘heat pump’ I think you mean – and a ‘mechanical ventilation heat recovery system’??? wow! you Britishers and your funny verbose terms*. I think you mean a ‘DVS’ system, as we call them here.

These systems are pretty much standard for all Kiwi houses. In a typically poorly insulated antipodean house, a heat pump barely provides enough heating for the house. It’s noisy relative to the quiet cosy ‘glugging’ of a UK central heating system. And it blows air in your face, which is not very restful. And, unless you are very rich, there’s generally only one of them to heat the entire house. Ours is in the living room. The living room is warm and windy. The rest of the house is cold.

The DVS ventilation system is absolutely essential in a typical poorly insulated antipodean house, otherwise mould will be quite literally climbing the walls. The ventilation system makes the house colder than it should be in the winter and warmer than it needs to be on a baking hot summer day. At some point, during middling spring or autumn outside temperatures, it works well at driving warm air in from the roof to moderate the house temperature during the day and night, while providing an endless stream of fresh air that mould won’t tolerate.

Underfloor heating would be some sort of dreamlike fantasy. I could see that possibly providing the requisite level of cosiness in a bespoke designed, well insulated house. It would probably overcome some of the vast shortcomings of a heat pump, anyway.

* I’m from the UK, originally.

Thanks all, some really useful and informed replies.

I’m reassured that my numbers feel about right. It really isn’t a cheap option, but as we intend to be in the house for a long time we should enter the payback period. I think that as we have the opportunity to do this now, we may regret it in the future if we don’t, and are trying to retrofit in 20 years.

We will most likely pair it with solar and battery storage which will help even further.

I’ll register with the Passivhaus trust and try to attend an open day.

My next issue is where do I site all of the plant for the systems.

We have a utility room of about 3.7mx2.6m. Located at the side of the house with the majority of the bathrooms and kitchen, but due to a 1.2m path alongside them house and then a retaining wall up to another area of garden, there is no suitable area for the ASHP. This is also directly above the main bedroom, so not sure that we will want to keep all the manifolds, hot water tank and MVHR system humming away in there.

We have enough space at the other side of the house to snip about 1.5m off the end of a sitting room to create a ‘plant room’. This has a suitable space against the external wall for the ASHP, but I then worry that if we also locate the hot water tank in there, it is a minimum of 10m horizonal distance to any taps that we will want to be fed with hot water, so will be waiting an age for it to draw through, plus it may be really inefficient.

@no_eyed_deer they are called air source heat pumps in the UK to differentiate them from ground source heat pumps, and any other type of heat pump.

I think you mean a ‘DVS’ system, as we call them here

DVS is different to MHR (at least in the in uk)

@peekay – we located our ASHP approx 6m from the house, the flow and return pipes run underground into a highly insulated pipe specifically for this purpose, this may give you more options. Our hot water cylinder is in an airing cupboard at first floor level and a long distance from the ASHP, this is silent. We have our hot water on a programmed secondary return pump so when turning the hot tap during those times = instant hot water, you can now by hot water pumps with flow sensors built in which would be a better more flexible option. Our Zehnder MVHR lives in a large cupboard in the utility room and is silent. Hope this helps.

<p style=”text-align: left;”>Thanks @nt80085</p>

For some reason when designing the house I was trying to keep everything located together in a specific ‘plant room’ type place. I’d never really considered distributing through the house. I think I’ve got a few areas that we could create a void, cupboard or larger service riser that we could fit some kit in.

Time to get the pencils out again.

Our ASHP is quite distant to the cylinders and that isn’t really a problem. The central heating pump and buffer tank are a little noisy (can hear them in the downstairs loo next door) but as mentioned previously the hot water cylinder is silent and needs to go near the demand (our kitchen sink is miles away and it is very wasteful).

The ventilation ducts should ideally be in internal voids to keep them warm and prevent condensation (I dabbled with a DIY system and it was crap trying to properly insulate ducts and unit in a cold attic). Ducting also needs some proper design to prevent noise. We stayed in a Swiss chalet last summer with a fancy system but it was still a bit noisy in the bedrooms.

We have MVHR with a 2kw heating coil that struggles to make a big difference to the temperature in the house. Heating from electric underfloor, which is absolutely not what we would have chosen. We still open the windows in the summer and the insulation really helps to keep the house cooler than a “normal” house.

One alternative you could consider is a ducted air to air heat pump. This would give you heating in the winter and cooling in the summer. The ducting needs to be insulated so you don’t get condensation so we can’t retrofit to ours. You’d have to have alternative water heating system and you might not get the 5k grant. Maybe the blowing air would be less comfortable than warm floors too. Noisy air vents.

Actually, this is a terrible idea!