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Architect advice. Do we need this or not?



After my OH's reluctance to go for PV  soon, I needed a plan.  We had already talked and visited a local Eco Architect company when researching for our planned Passivhaus for the time we thought we had a plot.  I therefore got in touch to see what they offered.  We had a zoom meeting when i explained my plans.  Basically i wanted someone to help me plan the stages we could do now to help improve the parents comfort, with the intention to do the whole extension renovation when they don't need the bungalow anymore. So I was thinking cavity wall insulation/triple glazed windows to the front bedrooms (we wouldnt change this when extending) and PV with battery. 


But on talking to the architect, it was suggested for them to help, we needed the long term plan finalised first, which i guess makes sense.  They suggested they help us come up with a plan for the extension and then they could make suggestions for several levels of build - Passihaus, AEBC retrofit standard at 50kWh/m2 and EnerPHit.  they produced a proposal;-




Helping to prepare a phased approach will be a further cost which could be up to £2k.  


But when I said that my planned budget for the whole job was £100k, I was astonished when the architect suggested we'd need up to twice that!  That just would not be doable - the place would never be worth that much being spent on it.  I dont mind spending a good amount to make it a lovely place for us to live into our old age but at that rate, it would be cheaper to just make it comfortable with a standard extension and spend the rest on additional heating to keep us warm.  We'd never get anywhere near that back, even with lower bills. 


My calculations -


PV and Battery                                                               10k

new windows to front and cavity insulation                10k

new extension to rear                                                   80k  including airtightness tapes, underfloor heating in the rear half, MVHR.  


But maybe I am being unrealistic.  It woud not be a huge extension and we'd keep most of the internal walls.  



The plan above shows the extra space we have to work with.  When he did the shower room, Patrick moved the wall out slightly in the porch, and when he put in the window, he added a lintel suitable for the front door to be moved to the side, leaving the old front door as the door into the new utility room.  we were already thinking ahead. 


The plan now is to have a chat with our builder, Patrick, and see what he suggests.  I know he has done a Passivhaus and so knows how to build well.  I trust him to do an excellent job and with the advice of folks on here, I hope to be able to come up with a plan for the extension then a phased scheme of work which hoepfully Patrick can help with.


And I am going on an airtightness tape workshop soon so I can help with work too. 






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Have you considered fitting air to air heat pumps (A2AHP) to warm up your parents?

Probably the cheapest and most cost effective thing you can do.

Insulating the floor, if you have the room, is effective as well.

If no stairs to worry about it is a lot easier.

I would not worry too much about the windows, and bless they are really dreadful i.e. rotted through timber. May be possible to just replace the glass.

Edited by SteamyTea
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4 hours ago, SteamyTea said:

Have you considered fitting air to air heat pumps (A2AHP) to warm up your parents?

Probably the cheapest and most cost effective thing you can do.


Forgive my ignorance, but how would that heat them?  By heating the storage unit during the day?  If so, I'll take a look.  We didnt think we would change the ehating system until we did the whole renovation and are hoping the storage unit will carry on for a few more years.  It is about 50 years old already and one electric coil did break recently so it is being heated by 2 coils.  But as the place doesnt have radiators, we hoped to not have to install them with a change to a new heating system. Particularly as I would like UFH in the new extension and kitchen.  I'd leave the bedrooms and bathroom as is. (ie no UFH).


I would like to insulate the floor and would look to dig out the kitchen but leave the rest (bedrooms and bathrooms) so we can add insulation and UFH to the rear half.

The windows are okay at the front - maybe I'd just need to add airtight tapes to minimise draughts/airflow, being in mind I would like MVHR.  The bedrooms are next to a fairly busy road and I would hope to be able to have fresh air without having the windows open as I am a very light sleeper.

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7 hours ago, TheMitchells said:

Forgive my ignorance, but how would that heat them?

They just heat the air in the building, but with a much improved CoP.


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On 12/03/2024 at 05:58, SteamyTea said:

They just heat the air in the building, but with a much improved CoP.


It has taken a while but i have just realised that air to air heat pumps are quite different to ASHP which is what i thought you were recommending.  Air to Air ones sound like a possibility.  I am hoping to speak to CVC soon as recommended by @Nickfromwales and shall see if they think air to air would be suitable.  And I'm off to the NEC on Saturday for the renovation show so am hoping there will be plenty there to research. 

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22 minutes ago, TheMitchells said:

has taken a while but i have just realised that air to air heat pumps are quite different to ASHP which is what i thought you were recommending

It is down to terminology.

What we call an Air Source Heat Pump is an air to water heat pump combination.

There is Ground Source and Water Source, which are both Water to Water Heat Pumps.


They all work the same way really.

The down side of an A2AHP is that the heat emitter is generally a wall mounted fan unit. These are not the prettiest things, and have to be located in a place to get good air circulation in the room, and not be where the noise of the fan is an annoyance.

What they do offer is a higher CoP, and cooling (they are just air conditioning units after all).

They are well rested technology and cheaper.

Quite a few people on here have fitted them, the fact that we don't read about how dreadful they are says a lot.


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Not sure I would pin myself to passivhaus, but instead follow the principles.


A2A you still need a heater for the DHW, so I would stick to a normal ASHP.


MVHR several ways to do it, the normal way with a duct and terminal in every room, or cascade, generally duct to each wet room and a couple of supplies only that suit the layout. You will have a demand activated fan through a wall or two for awkward layout rooms that do not lend themselves to being cascaded.


An example of said fan



Get yourself a thermal camera and see where all the cold bridges are, so you can focus on fixing.

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1 hour ago, TheMitchells said:

air to air heat pumps are quite different to ASHP 

But they are not.

I have found I can best explain it as two circuits which interact at a heat transfer 'box' in the building.

A sketch on a blackboard  helps but I'm not doing one.

Anyway, it is 2 circuits passing through a shared box.

Improvements or corrections to this analogy are welcome.


Air source or ground source grabs energy from outside, heats up a liquid and this is circulated into  the building.

Once in the building, the warm heat supply has the heat taken from it in a plenum or a radiator or a tank by warming the internal circuit of liquid or air.

2 separate circuits.


For air to air it is rather simple with internal air being blown over the heated pipes, either straight into a room or through ducts.


Air to air.(but liquid moves ig around)

Air to water.

Ground to air (via liquid again)

Ground to water.


There are other circuits of air through the heat pump or replacement water flow in the ground but that might show as another loop on the sketch.


Phew that was hard to write. Easier at a client's white-board. There will be some corrections or clarifications needed.



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29 minutes ago, saveasteading said:

Improvements or corrections to this analogy are welcome.

PV/T = C


So all heat engines, which a heat pump is, follow this rule.


So you can think of it as the outside air/ground/water having a lot of volume (V) and by increasing the pressure (P) via a pump, you are in effect squeezing the energy out of it.

This raises the temperature (T).

As the inside of the house is a lot smaller in volume than the outside world, you can redistribute that raised temperature inside.


(it is slightly different as phase change can take place which allows a a smaller amount of energy to heat a gas than a liquid, but as energy cannot be created, the efficiency, which is hidden in the constant, C, evens that out)


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