DREG

Air permeability from SAP report

I think the specified room temps are incorrect: they should be 21C, according to NHBC TECHNICAL GUIDANCE 8.2/01. External temp should be -3.3C.

Asked for air test result but none found. Was sent the SAP report. The bathroom and en-suites have switchable fans with isolator.

Two further calculations…..

There have been other heat calcs done….. heat loss 29-1-25.pdf

I’m doing this retrospectively as house was built in 2021. I’ve been trying to get hold of the data but it’s like pulling teeth. I believe this is the heat calc that was used by the heat pump supplier/installer

If you have a heat loss/load calc that says 10.3 kW, what output heat pump would be recommended (new build house, EPC B) The MCS MIH documents don’t state clearly how many kW you need to allow for DHW and defrosting. Appreciate you do not want to oversize it; but equally is there a danger of under specifying it?

Thanks for that, John.

If the rad is producing 285 watts and the calculated total heat loss for the bathroom is 643 watts, does that mean the rad has been incorrectly spec’d? Or someone has not accounted for the corrected output.

Why would the inlet temperature be higher than the output temperature? That would give a negative answer to the Q (power) = Flow x SHC x (Flow-Rtn Temp)

Top to bottom. 60L buffer.

House has UFH on ground floor. Rads in bathroom, bedrooms and en-suites on upper floors. Flow temp into bathroom rad is about 37-40C. Screenshots of temp gauge on dining room (bifold doors) UFH manifold and the outlet/inlet temps on heat pump controller from yesterday.

Used 93kW in last 24 hours. Vast majority of that will have been heat pump; apart from lights, TV for a few hours, oven 1 hour, small electronic devices recharge. Outside air temperature between 0 and +4C.

Would it be possible for someone with knowledge of this to confirm these figures, please, in relation to an aluminium vertical radiator in a bathroom: Water temperature going into rad [flow in] is 40C and water exiting [flow out] is 35C. Average temp in rad is 37.5C. Target temperature of bathroom is 22C. DeltaT is 37.5-22= 15.5C DeltaT correction factor is 0.179 [from manufacturer] Radiator Output at DeltaT 60C is 1661 Watts [from manufacturer] Corrected rad output is 1661 x 0.179= 297.32Watts Many thanks.

Here’s the calculator, results and deltaT correction from the radiator manufacturer’s website…. Yes, made me suspicious too. The three houses are similar design, yes.

I do not have an in-depth knowledge of SAP reports. I got it 2 days ago and it’s the first one I’ve seen. Can you please explain what you mean about the built house being I don’t have in-depth knowledge of SAP reports. This is the first one I’ve seen and it was sent by builder on Friday. Can you please explain the built house being less than building regs and, if so, how it would be signed off. My understanding is they work out the heat loss as per photo attached showing calculation.

The rooms with rads are ok in terms of temperature, except for the main bathroom. That’s always been cold as detailed in original post. It’s a vertical panel aluminium rad. It’s rated at 5668 BTU but it can’t be emitting anything like that as the water going into it is about 37-39C. When the other rooms heated by rads are at 21C, the bathroom is 19C maximum. Its design temperature is 22C. The dining room with all the glass has its own UFH manifold. Appears to have a mixer valve. Photos attached.

ABSAPD_1.pdf Here’s the SAP report

Several different heat loss calcs done and all give heat loss of approx 10.3kW. I assume 11kW heat pump specified on that basis. But there’s no allowance for DHW heating or defrosting. Should there be? You recommend setting everything to 21C for 24hrs daily with no set-backs. Is that right?

Adjacent house (250m2) like us finds it costly to run and not particularly warm. They use a log burner to supplement the heating. The other (220m3) house occupants say they like to be cool 🤷🏻‍♂️. Do not have a heat meter. I think it would cost about £1200 (£600 for meter, £600 for labour) to install and nobody seems interested in doing the work. Assuming the WATER INLET and WATER OUTLET temps shown on the controller (photos below) equate to RETURN and FLOW temps, I could estimate POWER as: 1.66/3.666 X 4.2 X (46-43)=5.70kW. Is that correct?

It’s a development of 3 houses (280m2; 250m2; 220m2-all with same 11kW heat pump). Unfortunately, the glass in that room is only double-glazed.

The plumber found the temp of the water entering the rad to be 37C. The design temp of bathroom is 22C. Based on rad manufacturer’s table (see photo) the deltaT is 15C, I think-perhaps less if you allow for the temp drop across the rad. It’s a big rad (1800x575mm) with output of 5668BTU/1662W. I’m assuming the reduced heat output and less than design temperature in the bathroom is down to the temp of the water entering the rad. This is the second rad that’s been put in the bathroom. Previously it was a chrome type towel rad. When developer changed it they said the aluminium column rad would be more than adequate but they don’t appear to have taken account of the temp of the water in the rad.

I asked developer for SAP report and air leak/test report. Got the SAP but they said “cannot locate air test at this point but house would not have been able to get CML if it had failed an air test”. There is a large 4 pane double glazed window with no opening lights in the dining room. I did a test with a small candle and there appeared to be a draught. That’s the room with bifold doors and about 40m2 of glass.

Hi JohnMo There are 6 Heatmiser thermostats on the ground floor which has UFH. The schedule is: 06-0900 21C 09-1600 20C 16-2200 21C 22-0600 20C That is to have the heat pump running 24/7 and to reduce the warm up load, based on the advice I was given. Weather compensation is set on the YUTAKI controller, photo below. Upstairs radiators controlled by a single Honeywell thermostat located on the landing. Schedule is very similar to that of the ground floor.