Hi Everyone,

Newbie here. First post. It is a big one, so I very much appreciate any advice given in advance. Thank you.

I live in Oxford and I have commissioned an architect to transform our 3 bed 1929 semi into a 4 bed EnerPhit home. Overall the house will end up at around 160m2. The architects have done many retrofits to EnerPhit standard.
The house is in a flood plain, with an immediate drop at the back of the house of 1.5m down to land that regularly floods. Side access is narrow. For this reason I would prefer not to have an external ASHP unit.

We have been back and forth on how to ventilate and heat the house, and supply hot water.
We have had multiple quotes but all seem alarmingly expensive.
Total Home Environment want £37K to design, supply at Pichler PKOM4 all in one unit, install and commision. VAT free but no BUS grant.
Williams Energy Design want £14 to design, supply a Zehnder ComfoAir Q600, install and commision. VAT payable but no heating / cooling or hotwater. To add the Comfoclime unit is an additional £6K plus VAT (but my understanding is that if an ASHP is attached then it can be zero rated). But still no hot water or cylinder, and would also need to additional heating through electric towel radiators and/or IR panels. The architect says Rod Williams is particularly good at the design so that there is no unnecessary boxing of ductwork.
Energy My Way want £26K for MVHR and separate external ASHP, hot water cylinder with a small amount of UFH and towel radiators. No VAT, and this has already taken into account BUS grant.
Heat Space and Light were cheaper but do not install and could not give me the name of a reliable installer in the Oxford area.
All of the above will also be subject to main contractor builder's 10% overhead and profit charge.

The first question is about approach. How would you knowledgeable guys go about heating and ventilating the place?

Secondly, it is feeling very, very expensive compared to the indicative prices I see online, but maybe I am missing something.
I am a competent DIYer, but I feel this might be too big a job, and as it is instrumental to meeting Enerphit and having a comfortable home it is not something I want to get wrong.

Am I being over-changed? Is there an architect's premium? Does anyone have any advice, or details of a reliable Passivhaus MVHR that covers Oxfordshire.

So many thanks in advance.

Tony

BPC Ventilation will design the layout for you based on your plans. Fitting is easy, it’s not rocket science. Especially if you are a competent DiYer. I am an incompetent DiYer and I managed it. Hired an anemometer and commissioned it myself as well. You can do this!

Sorry don't know your heating load, but guessing Enerphit would be 2.5kW on the design coldest day, so 1-1.5kW most days of the winter?

That's great and less than most homes so normal rules don't apply!


The annual heating load would be about 4000kWh so a heatpump would save maybe 2/3 of that.
Assuming you are fitting some PV and use an offpeak tariff then your electric cost would be maybe 10-15p/kWh, so £4-500/y for direct electric heaters, or save £250-300/y by using a heatpump.

There are no air-water heatpumps suitable for such low demand, smallest is about 5kW. But the savings are not going to amount to much over its lifetime, especially if the upfront costs of underfloor pipes etc are being added to a mortgage and costing interest. Not worth spending 10s of £k on.


Overall you might be better starting with minimal direct electric heating, perhaps a few panel heaters and towel rails and mats under any tiled flooring . Tweak this once you've lived in it and know better what the consumption is. You could consider an air-air heatpump in the living area, get a local air con fitter to quote?



Hot water, hard to beat a cylinder with an immersion on offpeak tariff or PV, your plumber can fit if you're not going for air-water heatpump for heating.

For ventilation, what others said, or also look at push-pull through-the-wall units which might be easier to fit than threading ducts though the existing joints.


Many PV installs these days have a battery to maximise export tariff, but also might help collect offpeak import for use in the winter.

On costs, you're in a very affluent area so prices you see "online" need to be related to jobs in your area. The same pack of work in less affluent areas is likely to be way cheaper.

If you use an ASHP and set it on a small plinth level with the interior FFL a flooded £4k HP will be the least of your worries!!

If you're having any tiled areas then definitely go for underfloor heating, electric or wet, but definitely have it:)

Just had a quick look at the Heat Space and Light website and what they say about costs seems sensible. They also seem to have a reasonable approach to brands and DIY.

My $0.02 worth.

I have a Komfovent MVHR system - really happy with it - I can access it via MODBUS and control it with HomeAssistant. I fitted it myself - my only caution is I suggest getting it commissioned properly to balance the system.

The post heater works well, but I would not rely on it for heating, it simply means the air supplied to the house (after the HR has done it's job) isn't colder than the supply setpoint.

The Komfovent unit does that well varying the power in fairly small steps.

Perhaps consider investing more in batteries charged off peak or with associated PV and using direct heating.

It also depends on your level of comfort. Ours is at a fairly high temperature compared to friends and family . The calculations tell you one thing, but actually using tends to be a different story

Final thought is a split A2A HP. I would be inclined to fit this in at retrofit time in preference to doing it later. Things like the condensate pipe can be a pest to retrofit! You also get the advantage of cooling if you need it.

I used BPC for my place, which has two systems as there was no practical way of linking it all into one. Bpc were very generous with their allowance for the semi rigid ducting ( and i did’nt check) so ended up with 3 coils left over. Also in their quotes you’ll find lots of bits and pieces (125mm ducting and fittings, insulation and fixing strap etc) are considerably cheaper locally. Plus you only end up picking up the bits you actually need rather than bpc’s best estimate from your drawings.
Installing it really quite simple, an extra pair of hands will save plenty of time when feeding the ductwork through ( assuming you go with the semi rigid)
Currently doing another on a bungalow renovation for a family member. This i’ve planned myself , will use lots of bits left over from my place, additional bits ordered from bpc where sensible.
Really quite satisfying job to do.