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Heating and cooling: Heating Options During Refurb...

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    • CommentAuthorNRDigger
    • CommentTimeJul 19th 2020 edited
     
    Heating options during refurb

    Hi all, OK so new member here.... I've done a fair bit of reading but am starting from quite a low base knowledge wise, and would hugely appreciate any advice on the following!

    We currently live in a reasonably large detached 1920s house in Norfolk. Mix of solid and cavity walls. Good loft insulation. Double glazing. EPC grade C. Suspended floors which I plan to insulate at some point, and we’re looking at options for the walls also. Some of it is much newer construction so obviously much better insulated.

    Heating use currently is about 15000kWh/year currently provided by a 40kW Baxi Gas Combi boiler. Probably installed around 2011/2012. But unfortunately located in one of our upstairs bedrooms (lazy previous owner, builder who had clearly bought it and done things to a 'standard'... a low one...).

    No underfloor heating but rads are generally reasonably sized (and we are changing a few as we go anyway) and I ran the boiler at 50c flow temp over last winter and kept us warm enough. We are 18c people rather than 25c people, if that makes sense.

    We have a 4kW Solar PV array also.

    I have only ever lived in houses with combi boilers so have no experience of tanks or system boilers. Nor, indeed of ASHPs.... which is the reason I'm here!

    We are planning to do some reconfiguration work upstairs (resizing a bathroom, putting up some partition walls, etc) and at the same time I would like to get rid of the combi boiler in the bedroom and place it somewhere more sensible - possibly the loft?

    Except, of course, options seem much more complicated, as we'd also like to become a bit more green in the process!

    I came across the Daikin Hybrid Heat Pump system which includes both a gas boiler and 8kW ASHP and this seems a reasonable system. I reckon I could get the gas boiler in the loft and we’ve got a few potential sites for an ASHP which I don’t think would be too problematic for the neighbours. There's an Ebay seller who is putting these packages out at less than £4k which doesn't sound bad. The presence of the boiler gives perhaps a bit of comfort if things get really nippy outside and of course means no tank. Anybody used this set up? And are Daikin the only people making this pair in this way? Is Daikin a reputable company? Are these easy enough to get fitted?

    Of course we could also put in a tank somewhere and then presumably get an ASHP to run both DHW (??) and heating, and get rid of a fossil burner completely.

    Or I could get a hot water tank, some kind of system boiler (is that right?), and an ASHP as some kind of bivalent (?) system.

    Please be gentle if I’m using a vocabulary that stretches beyond my knowledge – I guess I really just don’t appreciate the various benefits of the different setups, and, before I go asking for quotes I really want to know what I’m asking for rather than to end up with the installer’s personal preference.

    So I guess my main question is, if you were in my shoes, what would you do, and why? I know experience is a great teacher and I suspect people on this forum are a lot further down that road than me...

    Primary considerations include:
    * Installation cost
    * Operational effectiveness and efficiency for heating
    * Longevity and need to service
    * Simplicity
    * Actual ‘green’ impact

    Thank you so much!
  2.  
    I'M not sure about the regs in the UK but I would not want a boiler in the loft unless the loft was within the heated envelop of the house.

    For my money I would not go for fancy heating options that run to thousands, I would look to the efficiency of the existing boiler and replace it (with another combi) if justified when moving it to a better location and then spend the thousands saved on extra insulation to reduce the energy demand of the house more than already planned.

    IMO if you are on the gas grid it is difficult to justify not using a gas boiler and spending any spare cash to insulate and thereby reduce the carbon footprint by using less energy.

    Over here at least there is very little difference in price between a system boiler and a combi and a lot of the time a system boiler will be more expensive than a combi of the same output.
    • CommentAuthortony
    • CommentTimeJul 20th 2020
     
    First the best approach is to reduce the heating load as much as you can first and I like your idea of 18c as this does a massive amount for you. Next is air sealing, draughtbusting followed by adding insulation. I like to choose a Target U-value And work towards that.

    If you can face it do the floor insulation this time round, absolutely essential with UFH. EWI is better than IWI and increase ceiling insulation to the maximum.

    As I don’t have a formal heating system I am not the best person to advise on your proposed set up and am sure that others will jump in.

    I have high hopes for you not needing a heating system 🙂

    Ask me about that route if you wish - spend on insulation - no more heating bills
    • CommentAuthorbhommels
    • CommentTimeJul 20th 2020
     
    Even if you don't / can't go heating system free, it is worth holding out replacing the boiler until you are done with the insulation and airtightness improvements.
    For various good reasons, I had to upgrade the boiler at the time when only part of the insulation was installed and airtightness was not very good at all. Unfortunately it will probably result in our boiler being massively oversized once the refub is complete. Luckily, boilers can scale back reasonably well when the heat load decreases. For heat pumps, oversizing means reduced efficiency, so these should be sized properly. If you can, it would be better to hold on to the existing boiler until you have a better idea what the heat load is going to be.
    •  
      CommentAuthordjh
    • CommentTimeJul 20th 2020
     
    As others have said, concentrate first on the building fabric. Decide how much insulation you want (i.e U-value) and how airtight you'll try to make it and only after that can you plan a heating system and also ventilation (which will be vital if you do much in the way of draught reduction, which is itself a very good thing to do).

    Personally I like hot water stores - thermal stores in particular - because it can be heated using the solar panels most of the year. But I do recognize they have higher standing losses that an instantaneous system like a combi.

    Start with the loft. Where is your insulation - along the rafters or along the ceiling joists? If the latter then don't even think about putting a boiler up there. In either case make sure there's at least 300 mm and preferably 100 or 200 mm more. Make sure that there's an airtightness layer wherever the insulation layer is.
    • CommentAuthorphiledge
    • CommentTimeJul 20th 2020 edited
     
    Personally, Id want any boiler/tank/pump etc on the ground floor in the centre of the house so the heat losses are all used to warm the house. Site them in the loft and all losses are exactly that.

    If youre reworking the plumbing I’d split the house into zones so you only heat occupied areas. Basic zoning would be upstairs and downstairs CH so you only heat the upstairs first thing in the morning and late evening.

    If you need/want to retain a heating system, then even if you super insulate and go for a heat pump, I’d keep the boiler as a back up as you already have it and a gas connection.
    • CommentAuthorMike1
    • CommentTimeJul 20th 2020 edited
     
    Posted By: philedgePersonally, Id want any boiler/tank/pump etc on the ground floor in the centre of the house so the heat losses are all used to warm the house.
    Except in summer, when you don't want it to warm your house :)

    Insulate it / them well, whether inside or outside the heated envelope.
    • CommentAuthorMike1
    • CommentTimeJul 20th 2020 edited
     
    1) Concentrate first on the building fabric, as above

    2) Move to an ASHP for space heating (not gas - see http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16654), ideally using underfloor central heating for lower flow temperatures & greater efficiency

    3) From an economic perspective, keep your boiler for now and seek to take advantage of the heat pump subsidy expected in 2022* (http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16542)

    4) For relative simplicity, heat hot water with electricity + your PV panels

    5) For added complexity, your ASHP could be configured to heat water too, though it would loose some efficiency

    *but be prepared to do it without subsidy if the Government impose criteria that your house doesn't meet, or installers jack up their prices. It's also possible that there may be subsidies this year under the Coronavirus scheme https://www.bbc.co.uk/news/business-53313640
    • CommentAuthorGreenPaddy
    • CommentTimeJul 20th 2020
     
    In your shoes I would...

    - insulate as much as you possibly can, and spend the say £8k on that rather than an ASHP. The floor insulation on the suspended floor is a must, irrespective of how you heat. My clients visibly wilt when I tell them that they are effectively living in a shed, thermally, if you consider the floor boards have no insulation under them, and so are essentially like a shed wall. Plus, your feet tend to be very good temperature sensors, and will give you a sense of discomfort, even if the room air temp is warm.

    - insulating walls and improving airtightness is an area that needs more thought, especially with solid walls

    - keep the existing gas boiler. It's likely over 90% efficient, as only 8/9 years old, and you should get another 10 years out of it (scrapping and buying new kit has a carbon footprint too)

    - locate it somewhere else in the house if you wish, but preferably not in the loft, not least of which because maintenance will be more tricky, and less likely to get done.

    - keep plumbing set-up as-is, with combi feeding DHW & CH. Rads should have their own temp valves, so you'll only heat the rooms that the valve permit. Presumably there is an existing wall thermostat, which gives the permissive signal for the CH to run

    - get the existing CH system cleaned out, and as you mention oversize any new rads. I always do a room by room heat loss calc, to be sure I know what over-sizing actually means.

    - in the future, you can hook up an ASHP to the CH system, and continue with the gas combi for DHW if you wish, or replace the gas combi with a DHW cylinder, into which the ASHP can add heat, plus the solar PV can feed into it. Consider the route for future ASHP insulated feed pipes, and allow for those routings now (ducts in/under floor, or through a wall, whatever, to get you to the desired location in the house).

    - The solar PV shouln't really have any bearing on our choice of heating, as it will be generating very little excess energy in the heating seasons, almost all output from April to Oct.
    • CommentAuthorNRDigger
    • CommentTimeJul 20th 2020 edited
     
    Hello everybody,

    My goodness I have just checked back to look at this post and am absolutely amazed with the hugely helpful
    responses. There is so much that is helpful in this thread!

    Did people say 'heat free house??'! That sounds incredible.

    So, yes, we started the year with 'project insulation' as one of our New Year's resolutions but it sounds like that will continue to be the direction as we continue to work on the house.

    It's a good point about trying to plan for an ASHP now even if we don't install one now. We'll have a lot of boards lifted throughout the process so we might as well take that opportunity!

    My one fright with wall insulation is what seems to be a debate that splits people almost wider than the Brexit vote - that is whether and how old houses need to 'breathe'. We've got lime plaster over the brick walls and my neighbour (experienced builder) recoiled in horror when I spoke about wall insulation. Yet plenty of online forums talk about sealing everything, etc etc. Interesting about EWI as an option though, this must be a collossal job though, no? We have painted concrete render on the outside.

    'How houses work' should be on the National Curriculum, I reckon, if we're ever going to get anywhere with reducing CO2 nationally. There's certainly a huge range of variables that seem to need to be balanced and counterbalanced and no end of conflicting opinion.......

    Thank you again for your helpful comments - any more of course hugely welcomed!!!
    • CommentAuthorNRDigger
    • CommentTimeJul 20th 2020 edited
     
    Posted By: djhAs others have said, concentrate first on the building fabric. Decide how much insulation you want (i.e U-value) and how airtight you'll try to make it and only after that can you plan a heating system and also ventilation (which will be vital if you do much in the way of draught reduction, which is itself a very good thing to do).

    Personally I like hot water stores - thermal stores in particular - because it can be heated using the solar panels most of the year. But I do recognize they have higher standing losses that an instantaneous system like a combi.

    Start with the loft. Where is your insulation - along the rafters or along the ceiling joists? If the latter then don't even think about putting a boiler up there. In either case make sure there's at least 300 mm and preferably 100 or 200 mm more. Make sure that there's an airtightness layer wherever the insulation layer is.


    Thanks for this - the loft insulation is I think done to 300mm. Some bits have been a bit dodgy though. Some bits were loosely boarded over with insulation chucked on top. In places I've begun to remove the boards, creating a raised platform for storage with Celotex both between the rafters then above as well... slightly stalled however when I found a bundle of lighting cables which seem to be hung together with gaffer tape, so wanted to get that sorted first (by a sparky I hasten to add) before going further.

    The biggest (?) problem we have are some sloping ceilings that cut up into the loft space - about 2ft diagnoally. Above which a void then tiles. I guess you might as well leave a window open...
    Plan was to try and insulate those bits from the inside, I reckon I could get at least 50mm insluation backed plasterboard or similar along there, and leave the middle empty or relatively empty to maintain ventilation... but again, all advice welcomed.....
    • CommentAuthorNRDigger
    • CommentTimeJul 20th 2020
     
    Posted By: Mike1
    Posted By: philedgePersonally, Id want any boiler/tank/pump etc on the ground floor in the centre of the house so the heat losses are all used to warm the house.
    Except in summer, when you don't want it to warm your house :)

    Insulate it / them well, whether inside or outside the heated envelope.


    Again this is actually extraordinarily helpful. Bizarrely I'd never actually considered the impact of putting the boiler in the loft, I'd just guessed not much heat would be lost at a boiler itself these days, and so long as the pipes were insulated it'd be fine!

    It sounds like a reasonable plan would be to try to generate some kind of airing cupboard/boiler room (which would have to be on the 1st floor given layout, but easily enough done whilst we are doing the refurb anyway), but then we do have some decisions still about whether to plunge into a heat pump territory now or not. In any case it sounds like a concerted effort on insulation is key.
    • CommentAuthorNRDigger
    • CommentTimeJul 20th 2020
     
    Posted By: tonyFirst the best approach is to reduce the heating load as much as you can first and I like your idea of 18c as this does a massive amount for you. Next is air sealing, draughtbusting followed by adding insulation. I like to choose a Target U-value And work towards that.

    If you can face it do the floor insulation this time round, absolutely essential with UFH. EWI is better than IWI and increase ceiling insulation to the maximum.

    As I don’t have a formal heating system I am not the best person to advise on your proposed set up and am sure that others will jump in.

    I have high hopes for you not needing a heating system 🙂

    Ask me about that route if you wish - spend on insulation - no more heating bills


    The only issue with the 18'c philosophy is when you turn up at work and I find I'm shedding layers when I get into the office!!

    I have to say I have (seriously) never heard about somebody in a modern house not having a heating system.

    You said 'ask me about that'... which sounds like an open invitation, so please tell!! Does this involve a heat recovery system as well? (again a term I know only through reading, not from experience). How key is that in the grand scheme of things?
  14.  
    Posted By: NRDiggerI have to say I have (seriously)neverheard about somebody in a modern house not having a heating system.

    Modern commercially built houses will need a heating system. They are built for profit not for the end user or the environment.

    Self builds done with care and designed not to need a heating system don't need a heating system.

    It is very difficult (expensive) to retrofit a house not to need a heating system.

    To get a house to the point where a heating system is not needed means that the heat losses must be less than the heat produced by normal living (cooking, breathing, DHW use etc.)

    Ventilation is necessary in a house to maintain a healthy environment however ventilation will involve heat loss as stale warm air will be exchanged for cold fresh air.

    Poorly built modern houses and older houses will leak air so much that ventilation is almost automatic and uncontrolled and thus a good amount of heat is lost - requiring replacement via a heating system.

    Well built houses will be air tight to avoid this loss but ventilation is still required
    Here the heat recovery systems come in (known as MVHR (mechanical ventilation with heat recovery)) MVHR uses the warm outgoing stale air to heat the cold incoming fresh air.

    As well as ventilation heat losses heat is also lost through the fabric of the house. This means the the fabric must be insulated sufficiently to avoid more heat loss than the heat that is produced by normal usage (living). fairly cheap to do (in the long term scheme of things) for a new build - much more expensive in a retro fit. But for a new build good design and great attention to detail are needed for a new build to achieve the no heating situation. Unfortunately attention to detail is lacking in most (all?) commercially built houses and good design is sometimes also lacking.
    • CommentAuthortony
    • CommentTimeJul 20th 2020
     
    Draughts, air tightness and the like see https://readinguk.org/draughtbusters/

    My house http://tonyshouse.readinguk.org/

    Have a read pick any good bits that you like
  16.  
    Posted By: NRDiggerMy one fright with wall insulation is what seems to be a debate that splits people almost wider than the Brexit vote - that is whether and how old houses need to 'breathe'. We've got lime plaster over the brick walls and my neighbour (experienced builder) recoiled in horror when I spoke about wall insulation. Yet plenty of online forums talk about sealing everything, etc etc. Interesting about EWI as an option though, this must be a collossal job though, no? We have painted concrete render on the outside.

    Old houses need to breath - which IMO means that the moisture created by living in a house will need to find a way out. In addition if the walls have no DPC then any moisture coming up from the ground will need an escape route.

    If your house has concrete render that has been painted the it is probably fairly well sealed (non.breathing) already. Concrete render is one of the more vapour closed renders in use and depending upon the type of paint used that could further seal the walls.

    EWI is the better way to retro-fit wall insulation to a house. The alternative IWI (internal wall insulation) is more disruptive and risks condensation (= mould) between the insulation and the wall. The usual EWI material is expanded polystyrene boards (EPS) this is sufficiently vapour open so as not to cause problems. (XPS (extruded polystyrene) is closed cell and not considered vapour open)

    I have a couple of houses that are built of stone walls with rubble infill (a couple of hundred years old) with no DPC that I have retro-fitted the standard EWI (EPS, adhesive and glass mesh then thin film acrylic render) with no problems at all and a much improved comfort level and reduced heating bills. (however the reduced heating bills won't recover the cost of the EWI in a lifetime!)

    For me the decision would not be whether to EWI or not, but rather whether to knock of the concrete render first or leave it on and EWI over. However if you are going to EWI cavity walls then you must properly fill the cavity with insulation (CWI) as part of the job otherwise the EWI will be a waste of money and effort.
  17.  
    Posted By: NRDiggerthe loft insulation is I think done to 300mm. Some bits have been a bit dodgy though. Some bits were loosely boarded over with insulation chucked on top.

    Hmm - attention to detail as mentioned above.

    Posted By: NRDiggerslightly stalled however when I found a bundle of lighting cables which seem to be hung together with gaffer tape, so wanted to get that sorted first (by a sparky I hasten to add) before going further.

    If they are all lighting cables and you are using LED lighting fittings there will be no problems with insulating around and over these cables, providing the cables are in good nick. LED lights use so little power that there is no chance of over heating by wrapping the cables in insulation. Undo the gaffer tape to spread the wires out and change the circuit breaker to one that is 50% of the existing, (down rating the may current available to the cables) this should still provide any amount of light needed given the lower power needed for LED lights and will give a safety margin for the insulation wrapped cables

    Posted By: NRDiggerThe biggest (?) problem we have are some sloping ceilings that cut up into the loft space - about 2ft diagnoally. Above which a void then tiles. I guess you might as well leave a window open...

    Skeiling ceilings - One of the reasons it is difficult to retrofit a house to negate the need for a heating system. A real pain to insulate.
    • CommentAuthortony
    • CommentTimeJul 20th 2020
     
    Insulate by underlining with 100mm sheet insulation and plasterboard

    I would have no hesitation with filling the sloping void with insulation either.

    I disagree with two previous comments, A) moisture does not come in from below

    B) breathable is not the same as draughty in this context, it really means vapour open as in open to the passage of water vapour outwards. Nothing to with ventilation.
    • CommentAuthorGreenPaddy
    • CommentTimeJul 21st 2020
     
    One issue with insulating inclined/skielings/coombes, is it normally has to be done from inside, which equates to mess/redecoration. Assuming you can live with that, a few options, you might consider...

    - strip off the existing plasterboard
    - fix battens to the sides of the rafters, immed under the felt, to ensure a 50mm ventilation cavity is left after insulation is installed between the rafters (you might consider reducing that 50mm cavity as the coombe is only 2ft, but that's a judgment call).
    - fit insulation between and under the rafters. Lots of options for that, but here are a few with Uvalue numbers, assuming the rafters are 50x150mm...

    1. PUR/PIR 100mm between and 50mm PUR/PIR underdraw - 0.147 W/mk

    2. Knauf Frametherm32 wool 100mm between and 50mm FT32 underdraw between perp battens - 0.205 W/mk

    3. Knauf Frametherm32 wool 100mm between and 50mm PUR/PIR underdraw - 0.175 W/mk

    Getting continuity of insulation on either side of the coombe (above to below) is vital, but I'm sure we can all give you chapter and verse on how to achieve that once you've decided on insulation materials.

    In terms of being breathable/vapour open, the wool above is extremely vapour open. The PUR/PIR with foil faces is extremely vapour closed. This is such a small area, and with a ventilated cavity at the rear, so I personally would not concern myself with that aspect. Save that conundrum for your solid walls.
    • CommentAuthorNRDigger
    • CommentTimeJul 21st 2020
     

    Old houses need to breath - which IMO means that the moisture created by living in a house will need to find a way out. In addition if the walls have no DPC then any moisture coming up from the ground will need an escape route.

    If your house has concrete render that has been painted the it is probably fairly well sealed (non.breathing) already. Concrete render is one of the more vapour closed renders in use and depending upon the type of paint used that could further seal the walls.

    EWI is the better way to retro-fit wall insulation to a house. The alternative IWI (internal wall insulation) is more disruptive and risks condensation (= mould) between the insulation and the wall. The usual EWI material is expanded polystyrene boards (EPS) this is sufficiently vapour open so as not to cause problems. (XPS (extruded polystyrene) is closed cell and not considered vapour open)


    Very brief reply - but again all incredibly helpful and will look at links posted in more detail later.

    The house does have a DPC and the walls internally seem pretty dry. I think the concrete render may be pretty old but really not sure how old.

    Does a MVHR help with the 'breathable' problem? Presumably less damp air floating around inside the house is also better for the walls?
    And - retrofitting an MVHR to an old house? - laughable or do-able? (or worthwhile??).


    Very interesting hearing about the 'skielings' - I knew there must have been a word for these things but never knew it!!!

    Lots of learning still....
    •  
      CommentAuthordjh
    • CommentTimeJul 21st 2020
     
    Posted By: NRDiggerDoes a MVHR help with the 'breathable' problem? Presumably less damp air floating around inside the house is also better for the walls?

    To some extent it helps, as you say. But it's better to solve the problem properly, either by making the whole construction 'breathing' or by making sure any vapour-impermeable layers are always warm enough to be above the dewpoint temperature (e.g. EWI outside the cement render could achieve that).

    And - retrofitting an MVHR to an old house? - laughable or do-able? (or worthwhile??).

    It's doable but might be quite a bit of work. It depends on the exact plan of the house and on which MVHR you install. Most MVHR systems require ducts from the unit to each terminal in the rooms and that's what can be difficult to do. There are a few that operate with one or more freestanding units though they have other requirements.
    • CommentAuthorNRDigger
    • CommentTimeAug 9th 2020
     
    OK - I'm coming back to this thread after a few busy weeks... having had a bit more thinking time, and most importantly time to discuss with my wife!

    1. EWI vs IWI. I *think* we've decided not to pursue EWI. Looking at the practicalities of drains, stacks, and eaves (with obviously a rather inexpert eye) I am essentially concerned this will be a way more massive job than I want to take on. The front elevation particularly does not have overhanging eaves/soffits (these are on the sides of the house but not the front and rear) which I guess will make this complex. Cast iron stacks and drains in inconsiderate places I guess are also going to need dealing with. It may be more straightforward on some walls, but a. I guess a partial solution is not worth the effort (?) and b. those walls are on the other side of the house from where we're currently re-furbing.

    2. So, in terms of insulation we are back to IWI- I guess. Which I think leaves me with a 'what's best' question in regards solid walls. I appreciate the logic about reducing the dew point within the wall; is there a way of trying to work out whether interstitial condensation will be a problem? I came across this wonderful looking tool, which seems to be slightly reassuring, but as I don't really understand what's going on behind the spreadsheet I'm reasonably sceptical: https://www.vesma.com/tutorial/uvalue01/uvalue01.htm

    3. So if IWI, what material? Insulated plasterboard with a foil layer? Something like Superquilt? (I have a friend who has used this with solid walls) or do you go for a natural option?

    4. Heating... So the above has definitely been very helpful:
    a. We will not be putting a boiler in the loft but instead building an airing cupboard on the 1st floor. Thanks for the advice on this one.
    b. Right now I am inclined towards keeping a gas boiler either by relocating the current one to the new airing cupboard or installing a new one whilst we're at it.

    If we keep a boiler but prepare for an ASHP later, are there any brands of boilers that will work better with this setup? And would you go for a combi or a system boiler if you had the choice at this point? Any recommendations for brands/models particularly something that would potentially work in blissful harmony with an ASHP if that is possible! (currently a 40kw Baxi combi).


    5. MHVR... undecided... wondering whether a decision to go to IWI makes this more worthwhile. We're going to have access to lift plenty of boards whilst we're doing the refurb internally so running some ductwork right now may actually be a reasonable possibility.

    With huge gratefulness!
    •  
      CommentAuthordjh
    • CommentTimeAug 9th 2020 edited
     
    I'm just reading your post and reacting, so it may not be of much help.

    EWI vs IWI, I'm not your man. Personally I'd always go for EWI, but I ran away from even that and built new instead. With IWI you need to be especially careful about condensation issues is about the most I can say.

    edit: Vilnis Vesma seems to be one of the good guys who knows his stuff, so I'd expect his calculator to be sensible.

    Boilers I don't know very much about.

    MVHR, I'd definitely recommend if you can find a way to fit one. Every house should have one.
    • CommentAuthorMike1
    • CommentTimeAug 10th 2020 edited
     
    IWI - Since you seem to have breathable external walls (based on your posts above), an easy solution would be to use one of the options mentioned in the Historic Scotland Refurbishment Case Study 4 - https://www.historicenvironment.scot/archives-and-research/publications/publication/?publicationId=651e6f16-087f-408b-ab3d-a59300fd971a - though there are many other possibilities.

    For u-value calcs I've used the BRE calculator for years, but it does cost £60 to buy. https://www.brebookshop.com/details.jsp?id=139470 However if you lift a solution from the above Case Study then you may well not need it.

    I'd relocate the existing boiler for now, and move to an ASHP when you can. From the environmental perspective there is no longer a case for installing new gas boilers, IMHO. See http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16654

    And I'd agree with djh that every house should have MVHR, where affordable and installable.
  25.  
    Good plan, we did IWi which transformed the comfort of the house, and ASHP which transformed the carbon footprint.

    Retrofitting MHRV, I am going for several small MHRV units dotted round the house, each supplying one room and extracting from the adjacent room. Rather than one central MHRV unit with ducts and manifolds, we don't have good routes for those.
  26.  
    Posted By: WillInAberdeenRetrofitting MHRV, I am going for several small MHRV units dotted round the house, each supplying one room and extracting from the adjacent room. Rather than one central MHRV unit with ducts and manifolds, we don't have good routes for those.

    How do the costings work out for several small units against one large one?
    • CommentAuthorNRDigger
    • CommentTimeAug 11th 2020
     
    Thanks all, would be very interested to hear more about the option for several small MHVR units as opposed to a whole system... And as with the other Peter (who I guess is in Hungary) an idea of costings?

    Mike, thanks so much for the IWI links. I will digest!
  28.  
    I don't understand why, but several small MHRV units are much cheaper than one bigger one:

    Eg 3x VAHR100r @ £250ea = £750, plus short ducts
    Or 1x sentinel kinetic @£2000, plus manifolds and long ducts

    This isn't apples-apples as the big unit is generally better and has more features, but if the small ones do the job then we'll be happy.

    Should say this is all work in progress that has been paused for lockdown, so no feedback whether it works.

    The small units can be installed piecemeal as we work our way round the house, so we might install more or fewer depending how we get on. Our main driver is lack of space for manifolds and duct, your mileage may vary...
    • CommentAuthorMike1
    • CommentTimeAug 18th 2020
     
    I'd be very cautious about usisng multiple MVHR units.

    On a central unit you have a single pair of holes to the outside, both on the same elevation, so variations in external wind pressure don't affect the system; if you have multiple holes in multiple walls / ceilings, I suspect that the ventilation rate might rise significantly as the wind causes cross-flow through the house.

    Not sure what size holes you need to drill for the VAHR100r, but I'd guess that the total cross-sectional for all the units might be higher than for a central unit, so greater heat loss.

    You'd also have multiple fans running all the time instead on one, multiple filters to change, probably no proper summer bypass, probably less effective suppression of external noise (they won't each come with a 1m long silencer), and maybe some other things I've not thought of...

    In short, better than no MVHR, but less efficient and effective as a central system.
    • CommentAuthorJonti
    • CommentTimeAug 23rd 2020
     
    I would have thought it would be very much site specific. In some cases it might be possible to have intake and exhaust on the same elevation and if the property breaks down into well defined spaces that can be seperated from each other then why not.

    I can see Mikes point on the silencers but as for the filters I would have thought uses/replacement would depend on the volume of air filtered not the number of filters.

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