6 bed 240m2 detached house
I'm figuring that is building-footprint, not floor area over 2 floors? I'm struggling with the maths to get 6 beds in otherwise ... but maybe my bedrooms are "excessively generous"
Im busy renovating my 1967 detached property ...
My house is 1960 and pretty much solid concrete. Relative to now, let alone then, its very airtight as a consequence. It had flat roof (concrete with some insulating stuff mixed in) on top of which previous owner put pitched roof (all the 60's flat roofs leaked ...) and so we now have masses of insulation in the loft too. Decent cavity, which we filled, modern (but only double glazed) windows.
All of that led to less heat needed Hooray! ... and more damp Boo-Hiss
We then retro fitted MVHR (Ducted air, exhaust air passes through heat exchanger and warms incoming air, reducing losses). This is only even the slightest bit worthwhile if the air tightness is very good (otherwise some/most of the air coming in escapes elsewhere, and the exhaust air volume is too low, so the amount of heat that can be recovered is "poor"). That fixed the damp problem and the living conditions are perfect. We did not replace the aged skirting radiators ... and I have huge regret that we didn't (we suspect asbestos int he concrete floors insulating the old pipes, so didn't go the UFH retro-fit route for that reason).
So, as everyone else has said, plan to insulate and also make it air tight. Also make sure you have no cold bridging. The better you insulate the more dramatic they become, and will lead to condensation and that will lead to damage to materials.
I recommend having an air tightness test done to see where you are. If it is good that test will tell you where the leaks are (they use a smoking joss-stick type thing, and you can see the smoke charging for the tiny gaps
) so you will be able to plug them, and if it is rubbish then you will need to prioritise doing something about it. Otherwise you will basically just be heating outdoors, rather than indoors.
We set about bringing the old house up to passive house standard and decided it was impossible ...
Where did we get to? We built a Passive House extension and prioritised living in that end. It has kitchen / snug, and master bedroom above, so is all Wifee and I need in winter and we drop the thermostat for main house (unless we have guests staying). Extension has increased house size by 30%, and even allowing for some heat in the extension we have reduced our Winter fuel by 50% (combination of lower temperature, MVHR, more roof insulation and also insulation around window reveals to prevent cold-bringing).
Would I do it again? Nope, absolutely not. I would either knock-down-rebuild or build on a green field site (or, poor third choice, move out and gut the place to do a proper job). I knew nothing about Passive House 5 years ago when we started, I absolutely would not consider living in a house that wasn't now. We haven't had a winter cough or cold in those 5 years (known benefit), and it is SO comfortable. Don't believe people who tell you its like living in a plastic bag, the MVHR pumps a huge amount of air through, and that air gets everywhere - so no damp spots in a poorly ventilated corner etc. - people who come here remark on the air quality in the house. We've never had a cooking smell persist or travel into adjacent rooms.
Couple of points that have come up on here before:
In response to Folk saying "I'm going to insulate as best I can" the replies have been "Yeah, I have done that. Several times now. Just do it the once"
And in response to "I'm tight, I keep it at 19C" or "I'm Eco, it must have zero energy" (I was the second) I would say "Be comfortable". I have friends in Passive Houses that just put on an extra sweater in winter. I've changed my stance, what;s the point of that? Plan to be comfortable. We keep the kitchen/snug at 22C in winter. It takes SO little energy (reminder that we are using only 50% of previous energy and house is 30% bigger) it is easy to do. You are 30-something, but if you are staying for 30 years, maybe more, you won't want to be living at 19C then ... and doing so will take a toll on your health.
UFH / heatpump: Consider reversible heat-pump to put cold water through UFH in summer. That's back to "comfort" again, and not cooking in the house and having trouble sleeping in the heat etc. etc. Last summer heatwave highest temperature was a few miles from here, so a good test of Passive House. The Max indoor temperature we hit was 25C, but that's too hot to sit still in, and we have to night-vent to achieve - which is fine, but little-by-little the temperature of the internal fabric of the house crept up day by day over the several weeks heat wave. You can't night-vent when you are away, and it lets the flys / moths in etc. Would have been much easier to cool the UFH, and we of course there is unlimited PV during a heatwave of course
I will look into Thermal stores and unvented cylinders, however with many sources of heat I guess a TS is more appropriate (and the fact Im not sure living out here on the end of a water main gives me the best water pressure, and Im up a hill)
I have huge thermal store (5,000 L). It has multiple heat inputs (Log batch boiler, Solar Thermal, and 2x18kW immersion if everything else breaks!); I could add Heatpump (except that I need HOT water for radiators in old part of house).
It ups the capital outlay, and increases the flexibility. I could, for example, have an oil boiler speced to produce kW for worse day in the year but running 24/7 at that time, rather than sized for "now heat the house from freezing to comfortable in 30 minutes". The Thermal Store buffering would get me the "heat house quickly" and would also allow the boiler to run in condensing mode pretty much all its running hours.
If mains pressure low you can add a "buffer" pressure vessel if you want to have direct feed DHW. Its nice to have the hot water at same pressure as cold (mains). No tanks in the loft is nice (hot water is potable, no dead rats falling into the tanks etc.). The Continent doesn't do open-vented (AFAIK).
My DHW (mains feed) is pre-heated through TS, so I am not heating DHW from very cold mains temperature. The central heating and UFH is drawn off the TS. The UFH is direct, the old (open vented) Rads are through a heat exchanger (wasn't confident they would convert to pressurised without something blowing ...) so basically just a small heat exchanger box exactly where the oil boiler used to be, no other changes to CH circuit
The swimming pool is heated direct by (separate) Solar Thermal, but can also be heated from Thermal Store - if I have excess heat to dump in summer, or I want the pool hot early in the season.
yes, lots of flexibility, but quite a lot of capital cost too, and plenty of plumbing complexity
But you have the perfect solution if you are keeping your oil, you just have a control problem where you need to use the ashp when not so cold out, and the oil on the coldest days.
My local plumber hates the idea of multiple heat sources onto a heating circuit (that's not the same as a TS of course). For example, he is very against having ASHP for cold water in UFH in the summer, and TS for heat in the winter.
OTOH both my heating engineer and passive house consultant have no problem with it ...
Sounds like I need a full system expert in..... good luck finding one! (Warwickshire - anyone?)
The passive house consultant I used is in Milton Keynes, I expect he would travel to Warwickshire. He is not cheap, but his advice would most definitely tell you what you could achieve (building improvements vs. energy cost for the lifetime of your occupancy) ... personally I like huge amounts of data before making decisions, but I'm not "everyone"
I want to do it right and once.
I'm an old codger. That is definitely the right approach ... the money I have spent achieving that in my lifetime made me wince, at the time. All my mates went "Ha!Ha!Ha! Look at him he's off on one again" ... and, thankfully!, followed a few years later by "I wish I had done that"
I'm not sure that most plumbers would think that way, more likely they want to put a system in without the flexibility you may want in the future. Even teh heat calculations carried out by the plumber are likely to be very rudimentary and include a large margin to ensure it is warm enough regardless of whether that costs more to operate than is should or not.
Mine have been a disaster. The plumber employed by builder did heat calculations which were ridiculous for a Passive House. He said he used standard calculations, based on the u-values the Passive House guy calculated, and I have no doubt that he did that correctly. He installed seeming very big radiators in bedrooms upstairs, based on his calculations. We didn't use them, not once, in the first winter so we took them out and got all that wall space back ...
As said earlier, my local Plumber doesn't want to install second-source of (cooling) on UFH so I'm going to have to find someone who will.
I've had the cost of Heating Engineer (I mean a proper, qualified, engineer
) as well as Passive House consultant to get to where I am now ... but the house is lovely, and SO comfortable all year round. And healthy
(Id consider thermal but I think PV is the way to go now)
I have Solar Thermal for DHW/TS and separately for Pool. Both of them have required plumber visit almost annually when air gets in. not everyone has had problems, but I would
not do it again. I agree, PV + Heatpump, although for HOT water a Heatpump is not great. Boosting DHW with tubular immersion on pipe might be acceptable if in practice achieving decent DHW temperature is hard (we have very long pipe runs so starting at 60C isn't much COP <sorry!>)
[UFH] needs to be set up so that it runs most of the the time to maintain house temperature with the water temperature varying inversely to the outside temperature. People expect to run it like gas fired central heating and leave it off all day and then turn it on in the evening expecting to get a warm house, and when that doesn't work they turn up the water temperature, the COP drops and the bills go up.
I'd go so far as to say that if the house is unoccupied for a lot of the time I wouldn't choose a heat pump.
Very important point on house occupancy. UFH needs to be on long hours each day, response time is very slow, if you aren't there all that time it will seem nuts.
But ... if you insulation is good maybe it won't matter and won't bother you.
If we go away for 24 hours, turn everything off, in mid winter, my Passive House bit loses 1C per day. A 3 bed passive house has a heat requirement of something like 1kW in the depths of winter.
So if you can get heat loss down to "nothing" the UFH approach may not matter, even if you are out at work during the day.
Run the hot water off Solar PV
As said I would skip Solar Thermal if doing it again ... but getting water up to 60C+ with heatpump is not ideal.
With Solar Thermal you can heat DHW tank (I do) but then what when that is hot? I divert the heat to my Thermal Store - which is huge, because designed for Winter heat, and I can then shift that "free" heat into swimming pool ...
The need for a plan to use up excess Solar Thermal is one of its problems. But if you've always wanted a swimming pool don't let me stop you
... but PV + Heatpump much better for pool - no shortage of Sun during the swimming season, and if you want to heat the pool early/late in the season you can just use the Grid. But with Solar Thermal you would need "a second heat source"
If you read this far well done!
I highly recommend "
The Passivhaus Handbook - A practical guide to constructing and retrofitting buildings for ultra-low energy performance.". It is written suitable for both laymen and engineers and will tell you everything you need to know about why Passive House works, and what compromises you make if you only do THIS or THAT. Also about managing a project of this type (Will the builders forget to do X? Will they pull the wool over your eyes on Y? that type of thing)
