gas boiler v wood boiler v electric water and space heating (as winter top up to PV system)

Turtle42 · 26-04-2022 2:55pm #1

Hi! I'm about to do a big extend and renovate jobbie and need to decide on an energy system. We have until now been heating the house with one dry woodstove in the winter, rarely used in the summer. Water heating has been all electric... shower, washing machine, dishwasher, kettle, occasional immersion if im feeling flahulach. We are connected to gas and have been using it to cook only.

I am leaning towards solar PV with battery storage and an eddi, to cover as much of our electricity as possible, and hot water in the summer, and i need some form of boiler to top up in the winter.

It is a small terraced house and I will be extending it and hugely improving insulation and airtightness, so it's hard to know how much heating I'll actually need. To get us through the winter, I have three options as far as I can see, to woirk in addition to solar PV.

1: Dry stove in the new extension. It will be the living room and on the north of the house, so will have no sunlight in the winter.. I want to coziness of a stove. We have a great wood supplier and it's from local sustainably managed woodland. A small condensing gas boiler to heat water and a few rads on cold mornings.

2: boiler stove in the extension to heat water and a few rads in winter. no gas.

3: No water tank and just get a decent sized battery, have a dry stove for space heat in the extension and use electricity to heat water as needed year round, and some top up space heating in the original house. no gas

We may need very little space heating after the renovation. The original house is directly south facing and gets good solar gain in the winter even now, and we will hold on to that heat even better after insulating the walls really well, new windows and doors, etc. I dont want to over do the energy system, if I could better spend the money on other measures like insulation but of course I dont want to under do it either.

any advice gratefully received

the_amazing_raisin · 26-04-2022 6:58pm

So one thing to consider with the wood stove and back boiler combination is that it'll need to be an unsealed system. Basically you need an open attic tank connected into the boiler. This is in case the hot water isn't circulating (due to pump failure or power cut) the water in the boiler could turn to steam. In a sealed system this is usually followed by a fairly spectacular boom

This isn't anything new, this type of system predates the more modern sealed system, but it is a design consideration. It might also limit the options regarding how you pump water to the radiators, a lot of modern boilers are designed around sealed systems

If you want the flexibility of both, then you might need a dual coil water cylinder, one coil for the stove and another for an alternate fuel source if you want one. You'll only get hot water instead of space heating though

A third option might be to ditch the boiler and install a stove that can circulate warm air. Fondis stoves can do this, but they're not exactly cheap. There's probably other options out there

Since you mentioned improving air tightness in your house, it's probably best to look for a stove which is sealed and has a fully external air supply. Otherwise you might find the stove starts consuming the oxygen in the room you need to breathe 😱

Turtle42 · 27-04-2022 6:46am

Oh yes, the external air supply to the stove is definitely the plan! As it will be going in the new build section it shouldn't be a problem. Where we have the stove now, we have had to crack the window nearby for air supply!

We actually have an attic tank at the moment, connected to the old electric immersion tank.

gas boiler v wood boiler v electric water and space heating (as winter top up to PV system)

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