CH system design advice please (no Gas or Oil option)

[texasholden]

Hi all,

Brace yourselves for a borathon but I'm guessing devil is in the details with system design.

I have an old stone cottage in Somerset, no gas in village, no room for an oil tank - 3 bed, 2 bathroom. Currently heated by storage heaters and an old, tiny woodburner (all downstairs). DHW is provided via a small tank with a 3kW immersion.

My girlfriend and I love the place. Love the single glazed wooden windows, old stable doors, stone unplastered feature walls etc. I know that I need to insulate as much as possible and I am in the process but the bottom line is that trying to keep this place to a constant 20 degrees without destroying the reason we bought it would probably require enough kWhs to warrent building my own nuclear power station.

So we're going to be cold. Fine. Luckily we work long hours and the offices is heated.

What would suit us is a system which can provide high output heat when we need it. The upstairs is less of an issue (at present we sparingly use oil filled electic heaters when it's too cold to sleep) so anything is better than them. I would be happy with 3 x 3kW upstairs (one in each bedroom) - which would only be used sparingly.

The woodburner's had it, and the chimney is slap bang in the middle of the downstairs so I'm thinking double-sided stove. We also lack a DPC so in the process of putting one in, I'll be insulating the ground floor and so I have the opportunity to install underfloor heating - which although isn't anywhere near enough to heat the place, will take the chill off the floor.

So, I'm not sure whether I just install electric underfloor heating downstairs (for the mornings) and put some electric rads upstairs (forget storage heaters we're both working 12 hour days and those things always trickle the heat out during the day no matter what).

OR, whether I install wet underfloor heating and get a stove with a back-boiler to run the underfloor heating (via a vented cylinder which has back-up immersion heaters). I have looked at a Boru stove which is supposed to give 14kW to water and 4kW to the room which as we sit real close to the stove, sounds like a reasonable option.

Or, shall I go for loads of Propane bottles and a massive Combi? (not sure if I've got space for the bottles)

I'm happy for you all to laugh at my predicament, but no abuse please or I'll go electric only and destroy the whole planet with my carbon footprint.

 

[SimonH2]

Well if you have to use lecky, then cost wise you'll be wanting some form of storage so you can use an off-peak tariff. I agree with you that brick filled storage heaters are "far from ideal" - we have them in the office at work and they are absolutely sh*te though I gather modern ones may be slightly less sh*te.

A large tank of water will allow you to store heat, and then pump it round a wet system (whether UFH, rads, or fan heaters). But, it will need to be quite large to hold the amount of heat you might need.

Is there any garden ? If so then you might be able to bury an LPG tank which whilst expensive, will probably be better that lecky in terms of "instant heat available NOW" with a decent boiler.

Might also look into an air source heat pump and UFH. While they are "not cheap" to run compared with mains gas, I believe they are cheaper than LPG. However, read the small print (performance tables) carefully as their efficiency drops off in cold weather and they can fall back to an immersion heater at some point.


And don't forget the socks, slippers, and wooly jumpers

 

[Aquilani]

Electric boiler perhaps?

 

[Agile]

You need to look at the cost/benefit of each arrangement.

Off peak electricity is not too expensive so underfloor heated during the early morning will cater for getting up warm with a thermal lag of about two hours after the off peak time has ended.

Upstairs an off/on peak air heater will provide rapid heat up as air has a low SH.

Sleeping needs an electric blanket and a very good eiderdown, probably two and with a thin one UNDER the sheet.

Heat pumps can give about three times the power input during the day and therefore the cheapest heating during the on peak time but they are expensive to buy, have a very limited warrantee and become very inefficient when its colder outside which is just when you need the most heat.

Its all very well living in old properties but heating is a problem!

Tony

 

[texasholden]

Thanks all for the comments - much appreciated.

Initially I was keen on the ASHP but I agree that they offer best performance at the wrong times of the day / year for me.

I'm esging towards a large tank with immersion heaters working overnight. At least I won't need to worry about servicing etc. Sounds to me like I may as well go unvented and plumb in a back boiler on the woodburner while I'm at it.

Any advice on using a plate heat exchanger to take the DHW off the tank?

 

[Agile]

Traditional wood burning is always a good idea if you want to be bothered with all the manual labour needed.

But to give the ventilation required its not very efficient.

Good at keeping a damp property aired though!

Tony

 

[SimonH2]

If feeding it with a wood burner, you really want to stay open vented (I suspect you meant to write that). You can DIY a pump and PHE - just look up "heat bank" and you shoudl see plenty of diagrams of all sorts of arrangements - most of which you can buy for a price
If you wanted to go for the full bingo card, you could consider a heat bank (or thermal store), plus ASHP, plus solar thermal panels on the roof, and with immersion heaters part way up for "topping up" - with DHW, wet UFH and rads (for a quicker heat up) running off it. That's going to add up in cost quite quickly though.

Design it right and you should be able to get the ASHP warming the cooler bottom of the store, and so on.

All a case of weighing up the pros and costs of each option.


One thing that does come to mind though. Beware of relying too much on leaving the place cold and heating the air quickly when occupied. It's a good way of suffering from condensation damp in the walls - which leads to mould.

 

[Norcon]

Thanks all for the comments - much appreciated.

Initially I was keen on the ASHP but I agree that they offer best performance at the wrong times of the day / year for me.

I'm esging towards a large tank with immersion heaters working overnight. At least I won't need to worry about servicing etc. Sounds to me like I may as well go unvented and plumb in a back boiler on the woodburner while I'm at it.

Any advice on using a plate heat exchanger to take the DHW off the tank?

I'm fitting a Stanley Tara multifuel boiler model into my own gaffe at the moment.
I'll plumb three high output Quinn Adagio column radiators to the upstairs rooms only.


Will eventually have an unvented cylinder on the gravity circuit which will probably be an ACV SLME.
But that's for another day as I have a few walls to bash down and re build.

Keep in mind when you mention unvented cylinders and solid fuel you probably won't find a plumber to marry the two!

I'm doing it the easy way as I like the simple concept of gravity circulation and also means I'll have hot water even if the electric is down.

 

[texasholden]

Sorry guys, yes I did mean vented cylinder - like those plumbers referred to in the previous post, I also don't want to try a solid fuel / unvented cylinder combo.

2 questions:

1) If I put the tank in the loft (basically 5m directly above the ground floor stove) should I use 22mm, or is 15mm fine for a gravity circuit between the burner and the cylinder?

2) I presume I'll need to be very careful about crud in the system getting into the underfloor heating pipes. Will straightforward gauze filters be sufficient?

 

[Agile]

Its normal to use 28 mm for gravity heating circuits!

But worse, you need a special cylinder with a 28 mm coil and they are not normally available off the shelf because everyone uses a pumped circuit for most installations.

A gauze filter fitted horizontally with the opening downwards is cheaper and better as it catches everything. If you think there is a lot of dirt then fit an oversize gauze filter. I use a 28 mm one on 22 mm tube in some cases!

Tony

 

[doitall]

A heat pump and buffer tank would be ideal, with a log burner to supplement it.

 

[SimonH2]

Just another option to toss into the mix, from the "dunno, but I bet it ain't cheap" catalogue ...

When someone was building a new house just round the corner, he had two holes bored down <some long distance> and put coils down for a ground source heat pump - no space for the more usual "large area of garden" heat collector. Dad happened to speak to him the other week and he said it was working very well.

 

[texasholden]

thanks to doitall, Tony and Simon for the info.

I have also dreamt about a GSHP, which is probably possible given a big budget. My neighbours have old wells in their gardens which are still full of water so I presume the water table is quite high - which I'd assume would help?

Still really unsure about the ASHP. If they were maintenance free then maybe. Thing is with only underfloor heating downstairs the stove will be used most evenings (I don't recall a single "evening in" in the past 6 months in which we haven't got the current one going) - so I'm thinking the heat-pumps might end up being supplementary to the stove!

At the risk of incurring the wrath of those more experienced than I, I have an idea for a system which I am certain will NOT work. The only problem is, I don't understand why it won't work.

What would happen if I plumbed the stove, the underfloor heating and a coil-less tank together? so the stove directly puts hot water into the top of the tank and a cold return from the base of the tank goes back to the stove - there is also a feed from the top of the tank to to the underfloor heating circuit (pumped with non-returns etc) where the return breaks into the cold return to the stove.

So when the CE is off, the tank is getting hot (normal precautions on water boiling etc) and when the CE pump is switched on the main flow is via the CE/stove/tank.

Now don't get mad, I don't seriously think it'll work - only I'm very curious.

 

[doitall]

You can connect multiple heat sources to a large buffer tank and feed the heating and hot water from it.

For GSHP you need an area of unshaded ground approximately twice the footprint of the house, and the collectors need to be roughly 1200mm cover.

We had 2 ASHP heating our offices that worked very well, did need to suppliment it somedays with a lot of in and out traffic.

Do you have an outbuilding most if not all the plant could go in.

Why not look up "eaton" in the search box and see if he could give you a few ideas and perhaps a quote. Details in his profile.

 

[dcawkwell]

Easy.
Because the place is relatively small.
Gas lpg combi boiler about 30kW with 2 or 4 47kg bottles.
About £3k to install depending on choice of boiler.

I would also go for a lpg gas fire so you can just heat the lounge
and keep heating to a minimum for the evenings/weekends.
Sorted.