Heating System for New Build

[Lucy Murray]

Morning all,

 

We're building a 1.75 storey, 236m2 & are looking at different heating systems...

 

What would you recommend? Our U value will be 0.16

 

Thanks guys.

[PeterW]

Depends on the availability of services ..??

 

If that's the wall uValue, you would need to get floor and roof and then calculate the overall loss but with some good airtighness work you could end up with quite a low demand. 

 

The issue with low demand is most gas boilers can't modulate low enough so you're into buffers for underfloor heating - assuming you are having it - and DHW will become your main demand for heat. 

 

If you are planning solar PV then look at SunAmp units and consider Air Source Heat Pumps, both of which can be DIY installed. 

[Jeremy Harris]

It's highly likely that heat loss, and hence heating requirement, will be dominated by the ventilation heat loss, rather than the fabric heat loss, so to get an idea of how the two impact on the total heating requirement you really need to do some sort of heat loss modelling.  It doesn't need to be very complex in order to size a heating system, and I would suggest not using SAP for this, as that's not what it's designed for at all; you need to know what your worst case heating requirement is likely to be for the coldest weather you are likely to get, so knowing how heat loss changes with outside air temperature and chosen room temperature is key.  I wrote a fairly simple spreadsheet in order to be able to see what effect trading off different elements of the build would have on the heat loss.  It's a bit crude and no where near as comprehensive a PHPP or SAP, but others have found it pretty accurate, and it came within about 10% of the full PHPP model for our house, which seems pretty reasonable for such a simple model.  It's here if you want to play around with it: http://www.mayfly.eu/wp-content/uploads/2017/01/Fabric-and-ventilation-heat-loss-calculator-Master.xls

 

As @PeterW has mentioned, it's quite probable that hot water will need more energy than heating, and it can be challenging to get a combined heating and hot water system to work well.  It may well be better to split the two requirements into separate systems, so each can be sized differently.  If you have mains gas, then using that, at least for hot water, makes a great deal of sense, as it's both cheap and relatively low CO₂ (which, incidentally, makes getting a decent SAP EPC easier).