UKC

Does anyone have any experience of living in a house that is very energy efficient?  EPC rating A.  I'm in the process of downsizing and have put an offer in on a one year old property with solar panels and an air source heat pump and no gas.  The cluster of houses in the cul de sac also contribute to the upkeep of a septic tank that serves several of them.

The owner says they have zero energy bills as long as they use things like the dish washer and washing machine during the hours that the sun is shining and there are times when the electricity supplier pays them.  It all sounds too good to be true, is it? Is it warm enough in winter? Are there any disadvantages?

Flip that question - is it cool enough in summer?  Particularly important if you’re not happy leaving the house unattended during the day with windows open downstairs.

I don't live in an A rated house (noting that amongst A rated houses there will be differences because some may be very large or very small (relevant to actual heating bills), some will only just achieve the rating, and some may surpass it by some way) but am familiar with some of the discussions. 

Electricity suppliers will pay for exported solar power but the rate is normally very poor (old 'feed in tariffs' stopped being available in 2019). Better off using the power yourself if you can (running appliances while the sun shines as suggested etc). 

As long as the heating system was designed for heat pumps, which it probably will have been if its a one year old house with no gas supply and heat pump already installed, should be absolutely no problem keeping it warm.  You tend to hear about problems using heat pumps when the houses they heat aren't well insulated, or when the heating system isn't designed for low temperature circulating fluid (eg radiators are too small and pipes too narrow to allow enough flow). Sometimes they can be inefficient if sited poorly too. 

He's probably exaggerating about not paying any energy bills though. Unless the solar panel installation is exceptionally large the small payments for exported power won't outweigh the costs of usage after dark and when they don't keep up with demand (eg a dull winter's day), and the standing charge for connection.  Especially when electricity is used for heating too, likely at times when solar power will be limited. 

If he has a large solar panel installation and a large home battery then it might be possible not to pay anything I suppose.

Poor ventilation can be a disadvantage, so unless the house has a Passivhaus style heat exchanger system for ventilation you will want to keep vents open on the windows, and make sure you have a decent extractor fan in in the bathroom and above the hobs to get rid of water vapour (which to be fair is the case in all but the draughtiest houses anyway).

Don't know much about septic tanks and likely costs etc. 

No direct experience but is it effectively sealed from the outside world?  I quite like, for example, hearing birds in the morning which quadruple glazing would prevent.

Just asked for details of any maintenance/service costs.  They appear to be minimal.  His electric bill for the months November to March was £146.  There is a charge of £35/month for maintenance of the septic tank and the shared block paving road.

As long as there's blinds on the windows, a well insulated house should stay nice and cool in the summer.

In reply to Shani:

No, it's a perfectly serious reply.

Insulation does indeed work both ways, but a house is not made of insulation alone, and a house is not a passive box.  

• "Insulation alone" - a house is also made of glass, and the flow of energy through glass is not symmetric - there's a reason the effect of excess CO² is called the "Greenhouse effect".  A significant flux of energy enters windows as visible light (where glass is transparent), is then absorbed by the contents of the house (furnishings, furniture etc) heating it.  Some of that heat is re-emited as MWIR light, which does not pass back out through the windows.  It also does not pass out well through insulation
• "Passive box" - boilers, appliances and people in the house all generate waste heat, and if. house is well insulated, it can't leave.

Unless a well insulated house is seriously well thought out with things like external sun-shades (precent direct sun-light ingress), whole house PIV ventilation (push hot air out in summer), significant extra thermal mass inside (even out diurnal variation) or air conditioning (burning money in a climate like the UK's) they can become too hot in summer.

Hope that clarifies my comment.  Our house is not sufficiently well insulated for winter but - aided I think by a stupidly located and designed conservatory - it can become inhabitable hot in peak summer.  Opening windows doesn't work well for sleep given traffic noise outside the bedrooms; at some point I'm going to look in to a PIV system that can use a heat exchanger in winter (refresh air, reduce mould in a couple of corners and keep the heat in) or just blow fresh air in (cool in summer).  Or we could wait until everything on the road is a BEV and the noise drops significantly...

In reply to Ciro:

Rumour has it people have windows in part because they like to look outside however, and rather like the sunlight streaming in to their houses.  I'm more of a fan of outside sun-shades but I only ever recall seeing them on commercial premises in the UK.

I live in an “A” rated house, 110m2 on the Isle of Mull. We have an ASHP but no solar. Our monthly electricity bill has increased from  £120 to £160/month. It may be that the house in the OP is insulated to a higher standard, plus we are in a relatively exposed spot. The house is warm enough in winter, but I wouldn’t fancy trying it with no heating. You’d need to look at the size of the PV array and feed-in tariffs to support the low bills claim - what does the EPC say? Although we have minimal windows facing the sun, it only needs a small amount of warmth to increase the interior temperature to over 23C - in the summer we often have the vents open on the Velux windows all the time.

How!?? Our bill in a drafty Victorian house is £80-90/month. 

I’m always surprised by how high some peoples gas and electric bills are, but £1000 a year for a drafty Victorian house, assuming it’s not a 2 up 2 down, very low.

It is, largely through not heating (or using wood). £120/month for a passive(ish) house is huge, however. 

Passivhaus require 15kWh/m^2.yr max. So with 115m^2, you'd expect something like £300-400yr.

In reply to Shani:

And windows work one way. I live in a passivhaus apartment in Scandinavia and I can assure you it gets real hot when the sun comes out. But we have used zero heating all winter, soooooo….

But an A rated house is up to 50kWh/m² (unless the UK uses a different scale after Brexit).

One of the "cool" effects of using ASHP and underfloor heating is the possibility to cool the floors down using the reverse cycle. A friend of mine did this once and spent the evening mopping the floor dry!

Interesting. So not very good, really. 

Indeed, but you cannot simultaneously be looking out the window, and not in the house and therefore afraid to leave the windows open.

If you want to keep the windows shut and the curtains open, any house with a conservatory on a sunny aspect is going to get unbearably hot in summer.

An A rated house isn't anything very special, to be honest.  Our mid 1980s townhouse has had 'sensible' upgrades - cavities filled, loft insulation topped up to 450mm, decent double glazing, and we have a biggish (5.7kWp) PV array.  According to the EPC it's A(94) and installing our ASHP brings it to A(97).  

Does this property have a massive PV array and a serious battery?  If not, I struggle to believe that the energy bills are genuinely anything close to zero.  We still import an average of 3kWh a day to run the house (not counting what we need to charge the car). 

Unless they are subtracting the export payment from the bill..?  

No idea about the battery.  It has 11 panels. The house is 1 year old and the bill for the period November - March was £146.00 which sounds quite good.

Ah, that's a bit more believable.  Four months - 120 days - about £1.20 a day.  If they are on a decent fix and paying 25p SC and 15p/kWh then they're importing around 6kWh/day.

11 panels suggests a typical 3.7kWp system.

When he said zero I think he was anticipating the summer months. My wife and I are both 74 and she has some cognitive impairement issues.  I have 2 choices. 1) spend £20,000 to £30,000 converting my garage to a bedroom with en suite (it already has 3 bedrooms which would become surplus to requirements 2) downsize to this almost new 2 x bedroom 2 x bathroom bungalow with solar panels and ASHP.

IMO it's a no brainer option 1 costs me, option 2 will leave me with a small surplus and lower running costs. I simply want to make sure that I am not taking on board unaffordable future maintenance and service costs not to mention the practical issues.

Right, understood.  It certainly wouldn't be putting me off.  A new build house designed around an ASHP will be as easy to keep warm (probably much easier) than a typical house with a gas boiler.  It's slightly different - you keep trickling heat in all the time rather than having defined heating on/ heating off periods.

Could there be unexpected maintenance issues?  Yes, but no more likely (possibly less likely) than with a gas boiler.  An ASHP is just a big fridge, and fridges go on for ages.

Bills won't be zero during the summer - there will still be standing charge, and the cost of electricity used during the night - but I can well believe that your annual bill might be in the region of £2-300 if they've only used £150 during the coldest and darkest four months.

As several have said, if this is a very well insulated house then you want to consider comfort during the summer months.  I'd be asking them what it is like in July and August.  Mind you, worse case is you use some of your PV to run an aircon.

Separately, I'd want to know a lot more about this septic tank.  Is it only a year old, along with the house, or is it older?  They aren't cheap when they have to be replaced.

Is the septic tank a septic tank or actually a modern sewage treatment plant?

What type is it? Does it have moving parts that agitate the sewage? Or does it just bubble air through the mixture? Or is it an old-style anaerobic system?

Generally modern plants will rarely need to be emptied and should be very reliable for a long time to come if it is a year or so old like the house.

But!

If the plant is a lot older, it could be past due for replacement of parts or other types of maintenance. Any time you share infrastructure with several neighbours, it is a headache. You _will_ have to accept there will be disagreements when it comes to maintenance, upgrading and maybe even just paying the electricity bill for it (modern plants use electricity but in very small quantities) and you may find that at least one of your neighbours puts stupid things like bleach and condoms and tampons down the drain with knock-on effects on your treatment system. In the worst case you might have one neighbour from whom you simply cannot extract money. Usually you can muddle through in the end. 

There is a pretty simple way to put the owners electricity claims to the test - ask them to show you the last 12 months of electricity bills. Just be aware that they might have spent a month away on holiday in the middle of winter or kept the thermostat pretty low and always worn heavy sweatshirts indoors.

Everything is less than 12 months old. It's a small development of about 8 bungalows in a small village who each contribute to the maintenance of the septic tank.  The only electricity bill the occupants have is for £146 for November to March I don't think they were in occuption in August. They are an elderly couple who have to move for health reasons and need to be in the centre of town.

For windows getting direct sunlight, I'm pretty sure that would only really be the case if the blinds are outside the windows,  not inside them. 

Shutters have been a solution to this for a long time.