@newby

Sorry to hear about your problems

Can I just check my understanding.  Firstly a question about the situation:

Is this 'built for you' or a house built by a developer 'on spec' and then sold to you?  Are there other houses of a similar kind and are they experiencing the same problems?

Secondly just to confirm the problem as you appear to have described it:  

Both the areas with UFH and the areas with radiators are heating only to 14-16C.  This is the case even though

• You are operating the heat pump 24x7
• thermostats and trvs are turned up well above the target value so that they are not limiting in any way
• The weather compensation curve has been turned up to (what settings?)
• the mixing valve on the UFH manifold, if there is one, has been turned to max
• room influence on the heat pump has been disabled or the target room temperature on the heat pump controller/maduka have been turned up well above the target value (say to at least 25C)

Is this a correct understanding in relation to space heating and what is the situation with DHW? 

What is the floor area of the house, and which Daikin heat pump is it? 

Do you know if there is a buffer tank/low loss header/plate heat exchanger between heat pump and emitters?  It would probably look like a largeish tank in addition to the DHW tank

Its must be a pretty serious error if a new build is only getting to 14-16C, possibly even UFH at the wrong spacing and, as you surmise, undersized radiators, or undersized pipework both requiring fairly disruptive work.  If you can answer the questions above it might suggest next steps.

@newby — can you say what your estimated heat loss is, how it was calculated (eg speardsheet, if so which one) and what you installed heat pump power output is?

@jamespa

Thanks again for your help — here’s a clearer and more detailed breakdown of the situation, including the temperatures we’re seeing when the outside temperature drops to 7°C or below.

1. Type of property

It’s a developer‑built new‑build, not a custom build. I bought it completed, so I had no involvement in the design, sizing or installation of the ASHP system.

2. House size

The total internal floor area is 164.25 m² (4‑bed detached).

3. Heat pump model

The data plate confirms it is a:

Daikin EDLA08E2V3 (8 kW class)

• CAP (HEAT): 7.5 kW @ A7/W30‑35
• Real output at winter design temps (‑3°C to 0°C) is typically 5.5–6.5 kW

For a 164 m² detached house — especially with confirmed insulation defects — this is almost certainly undersized.

4. Actual indoor temperatures when outside is ≤7°C

When the outdoor temperature drops to 7°C or lower, these are the indoor temperatures:

• Utility, main bathroom, cloakroom, hallways: 12–14°C
• Bedrooms: 16–19°C
• Two en‑suites: 16–18°C

This is with:

• Heat pump running 24/7
• All thermostats/TRVs turned up high
• Weather compensation curve increased significantly
• UFH mixing valve fully open
• Room influence disabled / target temp on Daikin controller set high
• No schedules limiting anything

So the system is effectively running flat‑out and still cannot heat the house.

5. Emitters

Upstairs radiators are:

• Single‑panel, boiler‑spec
• Not sized for 45–55°C flow temperatures
• Bathrooms have towel warmers, not radiators

This alone makes it extremely difficult to heat the house at low flow temperatures.

6. UFH

UFH is:

• Lukewarm
• Loops appear unbalanced
• No commissioning data provided
• No flow rates
• No ΔT readings
• No screed commissioning evidence

7. Hydraulic layout

From what I can see:

• No buffer tank
• No low‑loss header
• No volumizer
• Straight from heat pump → manifold → emitters

The builder refuses to provide any drawings.

8. The core issue: the builder will not provide ANY documentation

Despite repeated requests, I have been unable to obtain:

• SAP (design or as‑built)
• BREL report
• Airtightness certificate
• Room‑by‑room heat‑loss calculations
• Emitter sizing
• UFH commissioning pack
• Daikin commissioning data
• Zoning/control documentation
• Hydraulic design or pressure‑loss calculations

Their position is simply: “The system is working as intended.”

9. Thermal envelope

Thermal imaging and intrusive works have already confirmed:

• Missing insulation
• Cold bridging
• Loft defects
• Wind‑driven heat loss

This increases the heat load significantly.

10. My concern

Based on performance and the lack of documentation, I strongly suspect:

• The heat pump is undersized
• Radiators are undersized
• Bathrooms have no proper emitters
• UFH was never commissioned
• Heat loss is higher than SAP assumed
• The system was never properly designed
• The builder is withholding documents because the design won’t stand up to scrutiny

11. Why I’m here

I’m trying to understand:

• Whether this looks like a fundamental design failure
• Whether others have had similar new‑build ASHP issues
• What the next steps should be (NHBC, independent M&E engineer, etc.)

Any guidance you can offer would be massively appreciated.

@cathoderay

I don’t have an accurate heat‑loss figure yet because the housebuilder hasn’t provided any of the required design data (SAP, BREL, U‑values, airtightness, emitter sizing, UFH pipe layout, etc.), so I can’t run a proper calculation in Heat Engineer or the MCS spreadsheet.

What I can confirm is:

• House size: 164.25 m²
• Installed heat pump: Daikin EDLA08E2V3 (8 kW class, 7.5 kW @ A7/W35)
• Likely winter output: around 5.5–6.5 kW at 0°C to –3°C

When the outdoor temperature is 5°C or below, indoor temperatures are:

• Utility / main bath / cloakroom / hallways: 12–14°C
• Bedrooms: 16–19°C
• En‑suites: 16–18°C

This is with the heat pump running 24/7, all thermostats/TRVs high, weather comp increased, and UFH valve fully open.

Given the performance and confirmed insulation defects, the actual heat loss is clearly higher than the heat pump can deliver. I’m planning to get an independent M&E engineer to carry out a full room‑by‑room heat‑loss calculation since the builder won’t release the design pack.

@newby — thank you for the extra details. It is rather ominous that the developer/builder wont release the heat loss calculations. You could save yourself a bob or two with a DIY heat loss assessment eg use the Freedom Heat Pump spreadsheet (a version can be downloaded here), mostly you only need to enter dimensions and make selections for U-values and air changes etc. It is subject to the caveats that apply to all spreadsheet calculators, but it would at least give you a starting point.

@cathoderay

Thanks, yes, it’s definitely a red flag that the developer won’t release the heat‑loss calculations or any of the design data.

I’ll give the Freedom Heat Pump spreadsheet a try, but at the moment I can only estimate because I don’t have the key inputs (U‑values, airtightness result, SAP figures, emitter sizing, UFH pipe spacing, etc.). Without those, any DIY heat‑loss number will be a rough guess.

What I can confirm is:

• House size: 164.25 m²
• Heat pump: Daikin EDLA08E2V3 (8 kW class, 7.5 kW @ A7/W35)

Given the indoor temperatures I’m seeing when it’s 7°C or below (12–14°C in utility/bathrooms/hallways and 16–19°C in bedrooms), it’s clear the actual heat loss is higher than the heat pump can cover. But I agree, running a spreadsheet will at least give me a ballpark until I can get an independent M&E engineer involved.

Posted by: @newby

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8.  

Despite repeated requests, I have been unable to obtain:

• SAP (design or as‑built)
• BREL report
• Airtightness certificate
• Room‑by‑room heat‑loss calculations
• Emitter sizing
• UFH commissioning pack
• Daikin commissioning data
• Zoning/control documentation
• Hydraulic design or pressure‑loss calculation

I bought a new build property some 2 years ago.  I was able to get most of the documents you cited above.  However, it was a battle, and I had to get my solicitor to obtain these.

Thank you for your response. 

Assuming that the house has been built to current building regs, and once the insulation defects are fixed, it'm a little surprised its undersized to the extent of causing rooms to heat only to 16C, unless you are in a very windy area or the house is long and thin or otherwise departs significantly from a cubic shape.    Do either of those apply?  In the absence of these (and with insulation properly done) I would have expected your loss to be perhaps 6kW or less, so something isnt stacking up!

For comparison I have a 200sq m 1930s house with partial fabric upgrades to perhaps the standards of the early 2000s, and its measured loss @-2 is 7kW or a touch under.  Data on heatpumpmonitor and elsewhere tell us that surveyed/calculated heat loss is generally overestimated realtive to actual (ie measured) loss.

That said finding data on Daikin heat pumps is difficult (their stock answer if you ask any questions is 'ask your installer'), so I dont actually know what its output is at your design temp (presumably -2 or -3).  

Your results clearly indicate something is at fault, but various bits dont quite stack up so I am going to ask some more questions

• You state that the oversizing factor for the rads was 0.33, which corresponds to a deltaT rad to room of 21C, requiring a flow temp of 45C, assuming DT of 5 and room temp of 21.  What are the actual weather comp settings?
• Is it possible that the screed under the UFH is uninsulated - that would certainly sink heat
• Do you have any records of electricity consumption or better still measured heat output from the Daikin from which we might get a handle on measured loss?
• What are the sizes and material of the pipework leaving the heat pump and feeding the rads?  How many primary pairs (ie flow and return to rads/UFH) do you have ?  How are the rads and UFH connected to the heat pump/each other and are there any secondary water pumps (a sketch would be ideal)
• Are there uninsulated lengths of pipe (particularly buried lengths) between heat pump and emitters?
• Is DHW working OK?

Based on what you have said so far and pending answers to the above questions my tentative advice would be

1. Focus first on getting the insulation defects fixed (and confirming that there is proper insulation under the UFH screed).  Until this is done (or it has been decided that it wont be done) a heating engineer cant do a design because they don't know what they are designing to. 

• If the insulation is not going to be fixed you may have to have actual heat loss measured since, in that circumstance, there are no proper drawings from which to do calculations. 
• If you cant confirm that the screed has been properly insulated and there is any reasonable suspicion that it hasn't, then the UFH may never work properly and even a measured heat loss wont do, because it wont take into account the downward heat loss from the UFH pipework

2. Make sure that the developers/NHBC/anyone else you may be able to sue know that the heating is also defective.  There is no need at this stage to go into detail nor to speculate on the reason or discuss missing documentation (in facrt its probably unhelpful to do so).  Just a summary of how you are operating it, steps that the developers have taken to rectify it, and the current status is sufficient, together with a clear statement that it is not fit for purpose and must be fixed.

2. Once the situation with insulation is resolved, turn the spotlight back onto the heating

If you are able to answer the further questions (ideally keeping answers short) about the ASHP above I may be able to provide further comment

Posted by: @newby

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I’ll give the Freedom Heat Pump spreadsheet a try, but at the moment I can only estimate because I don’t have the key inputs (U‑values, airtightness result, SAP figures, emitter sizing, UFH pipe spacing, etc.). Without those, any DIY heat‑loss number will be a rough guess.

You only need dimensions, U-values (the spreadsheet has some standard ones built into it) and air change assumptions to use the calculator, some of the variables you mention come later, when designing the system. At this stage you only need a ball park figure for the heat loss, while acknowledging it is only an estimate.  

Posted by: @cathoderay

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Posted by: @newby

↑

I’ll give the Freedom Heat Pump spreadsheet a try, but at the moment I can only estimate because I don’t have the key inputs (U‑values, airtightness result, SAP figures, emitter sizing, UFH pipe spacing, etc.). Without those, any DIY heat‑loss number will be a rough guess.

You only need dimensions, U-values (the spreadsheet has some standard ones built into it) and air change assumptions to use the calculator, some of the variables you mention come later, when designing the system. At this stage you only need a ball park figure for the heat loss, while acknowledging it is only an estimate.  

I would be willing to bet that, with a sensible value for ACH it will work out at 4-8kW, ie not a value that helps us a lot given the uncertainties, absence of precise output tables for the Daikin, and in particular the insulation defects.  Im not sure its worth doing in this case. 

If we could get a measurement or alternatively identify obvious major sources of loss or some other reason then that might be better.  However Im open to being proved wrong.

Posted by: @jamespa

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Im not sure its worth doing in this case. 

Heresy!

Unless the property is huge, which it isn't, it won't take long to do a heat loss (half a day or so for a first timer, particularly with modern laser measurement tools which make getting dimensions a doddle), and it really is one of the most basic requirements. You can also run it with and without the 'insulation defects' to get an idea of what difference they might make, and generally get a feel for what does and doesn't affect heat loss.