Advice welcomed on DHW/Space Heating system

[catrionag]

Good morning, BH!

 

I'm looking for some advice/thoughts on our proposed space heating/DHW plan. The house isn't built yet and we're currently at Building Warrant stage so now is the time to think about what's going to work best for the space.

 

Some info about the house first of all:

Small 1.5 storey new build of approx 120sqm floorspace/300 cubic metres total space.

Based in Scotland (Midlothian)

Insulated to passive standards

No gas

3.7kw PV panels on the roof

Room sealed 5kw woodburner in double height living space

2 adults, no kids in terms of DHW requirements.

 

Our initial plan was to have the woodburner as our main source of space heating, with topup from electric radiators in the bedrooms if needed and towel rails in the bathrooms. DHW would be from a Direct Unvented Cylinder (tips on good brands of UVC welcome too!). 

 

We're installing UFH pipework as a 'just in case', so that if needed we could easily hook up a heatpump.

 

My partner and I are now of different viewpoints. My thoughts are to keep it simple and stick with the plan above: woodburner + rads for topup and UVC. He thinks that since we are already installing the pipework for UFH we might as well get rid of the downstairs electric rads and get a little direct electric boiler (separate from the UVC?) to run the UFH. His thinking is that the boiler would probably cost about the same as the electric radiators we would plan on getting anyway, so why not just go ahead and hook up the UFH from the get-go. It seems to me that's overcomplicating things, and that for the number of times we would actually use the UFH it's not worth it. 

 

Any thoughts/advice/criticism welcomed.

 

[jamieled]

Can't comment directly on your options as I don't know much about electric boilers, but your proposed setup is pretty similar to ours. We are not at passive standard, our main heating is via a woodburner in an open area. We have a couple of electric radiators downstairs but we haven't used them apart from checking they work. We have wired upstairs for electric radiators but based on experience so far I don't think we'll install anything. I did think about putting UFH loops in just in case but didn't bother in the end. When it gets colder we have the woodburner on most evenings for a couple of hours and that sorts us for a day. We're based in the highlands and the house gets quite a bit of solar gain due to its orientation. hot water from a direct electric UVC coupled to PV via an immersion diverter (which we still get some benefit from even at this time of year).

[ProDave]

Our house is just slightly larger and probably in a colder place, and a 5kW ASHP runs hearing (UFH) and DHW fine without problem and very cheaply.

 

We also have a 5kW room sealed WBS which is positioned so heat from that will heat the whole house.  Like @jamieled the WBS would do our entire space heating, but I would probably struggle keeping up enough wood to feed it if I used it all the time, and it does not have a back boiler to heat the DHW Plus you need to be there to manage it. No good for when you go away and come back to a cold house.  So I like the ASHP for it's "just gets on with it" automation but with the flexibility to burn some wood when we want to.

[catrionag]

Thank you both for your perspective!

[JohnMo]

There are others on this site, that charge the floor via UFH on cheap rate overnight electricity, basically an immersion heater in a tube.  Very simple plumbing and low cost parts.

 

DHW, is done in a similar fashion but in a cylinder, in summer excess PV will keep your DHW hot if you install a diverter.

 

Small panel heater in bedrooms if you want them warm.  Electric towel rads to dry towels winter and summer.

[Stones]

As you're putting in the UFH anyway, I'd go with a Willis heater and circulation pump connected to your UFH. 

 

Nice as WBS* are, processing endless amounts of timber will eventually lose its appeal!

 

*assuming of course the government doesn't prohibit them in pursuit of net zero