futureproofing gas central heating for solar thermal?

[pixelwitch]

Hello there,

I'm hoping to get some central heating put into my flat next year (2 bedroom 1st floor 1930s maisonette, with access to attic), and I'd like to know if there are things that I should specify now that would make it easier for me to upgrade to having solar heated water as well in the future?

Because its just a small flat, currently with just me in it, (though in the future probably a lodger too), I'm mostly being told that a combi boiler would make the most sense, and certainly it would take up less room, and be cheaper. But I have a more or less south facing pitched roof that faces onto the small back garden (so not visible from street), and with a school playing field behind it, so its not in shadow at all. It seems pretty much ideal for solar. Plus, I figure gas will only go up in price, and I um... read a book that talks of peak gas, so I'm thinking it'd be good to not always have to be completely reliant on it, (Yup.. may have some questions about woodburning stoves in smokeless zones a bit later too :-D ). And now I've finally got a place of my own to live in, I'd just really like to set it up as sustainably as I can anyway.

I can't do the solar thing right now though. Don't have the money, and would have to get permission from the freeholder (who seems to have gone missing), for the panels on roof stuff as well, and yeah... when I do manage to get more cash together, I probably ought to be sorting out the attic insulation first, but eventually maybe...

But I've been reading a few online forums and it sounds like a combi could really limit what I do later. It sounds like really, if I want to have solar in the future I should not get a combi now. I should get a big water tank put in the attic, and create some sort of airing cupboard in the bedroom and put a cylinder with 2 coils in it. Does that sound about right?

And if that's so, does the cylinder absolutely have to go in my living space or could it actually go in the attic instead? I suppose, I mean, does it have to be below the water tank or could it be on the same level? Sorry if this is a silly question. I am trying to read up on it all, but am just at the start really. Oh and will it matter if the cylinder had this extra coil in it that would go unused for a few years? Is that okay?

And then as there's currently no central heating infrastructure already there, should I maybe be considering other options like a thermal store instead? Would that be better than putting a dual-coil cylinder, or just different, and is there a big price difference? Is it right that a thermal store could help solar contribute to the central heating as well as just showers and baths?

Hmm. This has turned into a bit of a long mish mash of questions, so I think I'll leave it there, and save some of my other questions 'til another time. Sorry I've rambled on so much. But any recommendations for condensing boilers, cylinders, or advice about anything to do with it all is welcome really. :-D

[Annpan]

I dare say Martin will be along soon with some great advice but for now here are some questions answered.

The reason for your cylinder being in your living area is 2 fold...1. The tank will be fed by your cold water tank which needs to be higher than it for gravity to do its job. 2. Your regular cylinder will give out some heat wherever it is in, it makes more sense to use this heat than to have it going straight out through the roof.

Thermal stores are more expensive than regular cylinders, but they can hold the heat for 48h+, you may also find them named as accumulator tanks.

It does mean that your solar could assist with central heating but chances are the heat will be there more in the summer and not when you really need it in deep winter. (you do still get some heat in winter but not much)

Thermal stores also provide hotwater at mains pressure, meaning you don't need a pump on a shower.

They are larger than a regular cylinder but can go in your loft as they are super insulated (thats how they work)

They are ideal if you have a woodburner, but maybe not so cost effective if you use gas, and if it is a small household.

HTH, basically I reckon it is a bit of a balancing act if you are serious about solid fuel heating in the future it might be ideal, or (given the size of the flat) it might be more cost effective to have a cylinder.

[Martin]

Generally speaking combi boilers and solar don't mix too well - it CAN be done, but really isn't recommended -if you're ~"starting with a clean sheet of paper" I'd go for one of the new condenser boilers with a good old-fashioned vented system with a thermal store with two coils in it - again, it can be sited in the loft if pushed
here's a good faq on the subject! - http://c-zero.co.uk/e107_plugins/faq/faq.php?0.cat.1.12

[colhut]

I looked into this for our place, solar panels are certainly on the cards here when I get round to it. There are combi boilers that can work with pre-heated water and in my opinion this is the best logical system. even if in the depths of winter the solar panels only heat the hot water tank to tepid and you want a shower, thats probably 10 or more degrees of heating you don't have to burn fuel to do. All that is special about the combi boiler is that it senses the incomming water temp and can adjust the burner output to heat the water to the required temp. It seems ideal to me as every ounce of heat energy obtained from the panels directly offsets you water heating bills. If I remember right ATAG do a combi boiler that accepts pre heated water.

[Martin]

here's chapter and verse..........
http://navitron.org.uk/ihatecombiboilers.htm

[pixelwitch]

Wow. Lots of replies. Thank you ever so much. I'm sorry to have taken so long to come back and check. Been a bit of a busy week at work etc... Yawn..

Well thanks, Colhut, for letting me know about combis. Its good to know that there are options. As I'm not doing it straightaway though, and have a bit of a blank slate, I think I should take this opportunity to get my head round the non-combi options.

Lots of information there, Annpan. Thank you. I see that Martin too recommends the thermal store. So, I thought I'd just go over the issues you raised about their usefulness.

I am indeed a small household. Just me. Probably only ever would be two people. Its just a flat, so only one floor - 2 small bedrooms, one living room, a small bathroom and a small kitchen.
I can't speak for any future lodgers, boyfriends :-D or whatever, but personally, I'm not really that fussed about having a powerful shower. I mean, they're nice, but its not a really big issue for me, and I wouldn't want to be using too much water and all. Was quite used to just having a shower that came off the mixer tap in my Mum's home.

Woodburners are something I've only thought of quite recently, through reading forums like this one. I like the idea that they're kind of carbon neutral, of not being totally reliant on gas, and hell yeah... I quite fancy the romance of them too. But I do live in a smokeless zone, which seems to mean that I can only get the more expensive (sigh) smoke-exempt models like Clearviews and Hwams, and none of them seem to be small. Which seems to mean that there wouldn't be any point attaching it to the central heating, as it sounds like it would probably heat the whole flat up okay anyway. I mean... I have to do the maths and all, but that's my initial impression. And I probably wouldn't use it all the time, as I wouldn't want to have to use up all of my small garden for log storage. Want to grow some veg!

So, given all that, perhaps just a dual-coil cylinder would financially make better sense for me. But I do like the fact that you both reckon a thermal store could possibly go in the attic. Space is an issue for me in my bedroom, but the attic is a decent size. I guess I will look into costs a bit, which I'm curently a bit hazy on. I hope to live in this flat for years and years, so it may be worthwhile that I just put on another jumper and wait as long as I have to until I can afford to do it the best way for the place.

One thing I wonder about is if I get a thermal store - which is not what most people seem to have, will I run into trouble if something goes wrong with it and I need to get a plumber/central heating engineer in to sort it out? Do they tend to know about non-standard stuff like this?

Anyway, this all gives me some info to start looking into and thinking over, so thank you. And cheers, Martin, for that Navitron website link as well. Looks like a good site with lots of info and a forum to lurk on and everything. I shall have a bit of a browse around. :-)

[Martin]

if you go for a "vented" thermal store as I would recommend, as far as any plumber is concerned it's a perfectly straightforward hot water tank with lots of insulation, and two or three coils rather than one!
ps, don't lurk - join! - they're a good helpful bunch, many of them extremely well versed in all the different ways to design a system - and enjoy helping people like you!

[Annpan]

I don't know as much about it all as Martin does... he's been around in the business for a while where as I am currently doing my own research into what is available just now for our situation. (just to let you know where I am coming from )

I was talking about a kind of thermal store called an 'accumulator tank' - widley used on the continent, state of the art, covers all eventualities, EXPENSIVE solution. It is UNVENTED and needs a plumber who knows about this stuff to install it.

Martin is talking about a regular hot water tank with 2 or 3 coils, widely available, affordable. It is VENTED and easy to install, needs its own cold water tank which would sit beside it or above it (gravity and that) What makes it a thermal store is the super insulation that you would put around it - some of the stuff on the market now is really great.

I think that the vented option is what I would go for in your situation. It would be the more reasonable approach for a small flat IMO.

As for your wood burner, we have a clearview (no, not the cheapest option) and it does suck up the wood at a fair speed. You probably wouldn't need to link it up to central heating, as you say, it would do the job it's self, though you might want it to heat water for you... so if you had the radiators running off of the same tank you might have to heat radiators too... do you see what I mean? (I swear I confuse myself half the time ) OH has just piped up that you can't have a back-boiler on a smoke-controlled model... you had better check that out before makeing anymore discissions on it

If I were you I'd get mains gas condensing boiler type thingy (we have no gas or oil.. so I don't know alot about that) link up solar to the same super insulated hot water tank and think about a stand alone wood burner in the future (when there might be smaller models on the market).

Good luck

[Martin]

I was talking about ready-made vented thermal stores - no need for any extra insulation on the tank at all

[snapdragon]

I'm convinced - we were about to replace the old and rather scary boiler with a combi - but it will be a condensing one now - we have a south facing roof that will (when funds permit) be a good home for solar panels - and a fireplace thats awaiting a woodburner - but in the meantime we are keeping calor in rolls-royces

[Muddypause]

Just to add to the confusion; a 'thermal store' is a specific type of hot water tank. It's not to do with the amount of insulation it has, or whether it's vented or unvented; it's to do with the way the heat is exchanged and stored.

There are variations on a theme, but at its simplest, in a boiler-heated installation, the main body of water in a thermal store is heated directly by the boiler, in a closed circuit from boiler to tank and back.

This stored hot water never comes out of the taps; it is just there as a heat store. A secondary circuit supplies the water for the taps, and passes through a heat exchanger immersed in this stored hot water, where it picks up heat. In this way it can be at mains pressure, and because it never comes into direct contact with the stored water, is of potable quality.

The heat in a thermal store is exchanged the 'wrong way round' compared to a conventional tank. There are variations to this, which have the stored water heated by a coil from the boiler (more like a conventional hot tank - multiple coils would be the best approach if there is more than one heat source), ones which are heated electrically, and even ones that have an external heat exchanger, with the stored hot water being cycled through it by pump to heat the tap water.

The tank itself can be either vented or unvented, depending upon design. Often, the header tank of a vented store sits right on top of it, as a combined unit. An expansion vessel would be needed for an unvented installation.

[Martin]

another point to bear in mind is that you are not allowed to attach an "uncontrolled heat source", like a woodburner to a pressurised system - add to that the necessary once a year inspection of pressurised systems..........
(I wouldn't have a pressurised system in the house - they are intrinsically dangerous, relying for their safety on two or three valves....) - the main reason they are often fitted nowadays is that they come in "one lump", so it's cheap and easy to install for the property developers.........

[Annpan]

I was talking about ready-made vented thermal stores - no need for any extra insulation on the tank at all

I stand corrected. We still can't decide what we are going to do... this extra information is just making it all yet more confusing