Complete new DHW / CH System - what type?

[ed1178]

I have just bought a large victorian property in need of total renovation. Part of the work will involve total replacement of all plumbing, including installation of an entirely new HW / CH system. So far I have had different advice from each of the three heating engineers who have visited!

The property is a 5 bed 3 bath / shower detached house in which four adults will be living. We need to heat the whole property comfortably and in addition provide sufficient hot water for at least 4 showers in quick succession (the morning rush hour)

Initially I thought a traditional vented system with a large cylinder would be the best bet however a mega flow has been suggested. I can see the argument for one, however with a 15mm supply pipe I am concerned that flow will be inadequate for running two outlets at the same time, hence my preference for a tank in the loft (a big one!) I understand that the toilets can also fill from the same loft storage tank to avoid pressure loss in the DHW when they are flushed - is this true? We have plenty of loft space to accommodate tanks etc. Also if my incoming water flow is not great won't my baths take ages to fill with a megaflow? I don't want to mess about with pressure boosting pumps etc.

To further complicate matters we are considering installing a woodburning boiler stove. While this will not be the primary heat source we would like it to feed in to the DHW / CH when it is in use, as we have access to free logs. I want to be able to run both the DHW and CH on just the woodburner should I wish too, although I realise its output will not be enough to heat the whole house properly, it should just take the edge off. The stove output will be around 12kw to water. Is it possible to operate the CH pump independently of the CH boiler to circulate this heat? In early autumn I may light the stove but not want to operate the CH proper, but without the pump on it may boil, and with the pump on won't the boiler kick in? Would a mega flow be able to accommodate two heat sources?

I have also considered a thermal store which seem ideal for feeding the woodburner into. However If I am operating only on the woodburner, switch on the central heating pump and deplete the stored hot water I presume I will have no DHW either - the woodburner would never catch up. Is it possible to set the CH pump to only come on when there is sufficient stored hot water, and to operate for just enough time to leave me some hot water? Also I don't understand how a thermal store which operates at 90+ degrees is able to return water to a condensing boiler at a low enough temperature to enable it to operate at its most efficient. I am concerned that with 3000 sq ft to heat, solid walls and original single glazed sash windows that my heating bills are going to be high enough already.

Any advice greatly appreciated!

 

[bengasman]

Old fashioned open vent tank is disgusting with dead flora and fauna floating in what you use to clean your face and brush your teeth. It will do the job though if you don't want to spend money to upgrade your incoming mains.

Best solution is 32mm pipe back to the water meter and than branch off from that inside the house. BIG megaflo, and Bob's your uncle.

Why are you so intent on making things complicated by hooking everything up to the woodburner?

 

[ed1178]

Thanks Bengasman. i hadn't considered the prospect of floating dead pigeons but now you come to mention it...

The size of the pipework inside the house is not the issue, it can be as big as required as all is being replaced, but the supply itself is small (I estimate 15mm) It is the original lead pipe and I don't think replacement is an option due to the distance to the street and the fact that it runs down the side of the property under an original tiled path which I want to retain and then under the drive. I guess it could be rerouted. Would the water company pick up the cost for a new connection in the street - I can see them charging a fortune to dig a hole in the road if not!

The only reason I was thinking of connection a woodburner was because we have access to free logs, and as I work from home most of the time feeding the thing is not a major issue. If I can get 12kw if free heat (more with space heating) for most of the day it seems silly not to. 12kw for 10 hours a day equates to about £4 in gas? Over a winter that would add up quite nicely!

 

[ChrisR]

Full answer would be longer than you're likely to get from a DIY site!.

With no pumping, you're going to need a bigger mains pipe, 15mm (old lead or corroded steel?) won't ever do. Tanks in the loft may provide the store big enough , at least 600 litres though. If you use the right sort of pump, the noise will be very low and if it stops, gravity will still work. Pumps have moved on! I'd use something like a multi-stage inverter driven Lowara, for around a £grand. 2-3 bar pressure independent of flow, up to 80 litres/minute, sorted. For just loos and basins, so quiet you wouldn't hear it if it was in a cupboard with a good door.


I'd probably go with a thermal store, so you can use the wood, but you'll be looking for one in a thousand or so plumbers who's happy and competent with them - unless you want to learn a fair bit yourself. May be more in Yorks with mixed supplies??

Condensing boilers are only 10% or so less efficient when they're operating too hot for condensation, so don't get too hooked up on that.
While the water in the store is less than 76 (ish), they can condense. It can go in at 20º hotter than it comes out, depending...

only on the woodburner, switch on the central heating pump and deplete the stored hot water I presume I will have no DHW either

It would be controlled by temperature sensors, so the boiler would cut in and if done right you wouldn't be short of anything.

Is it possible to set the CH pump to only come on when there is sufficient stored hot water, and to operate for just enough time to leave me some hot water?

So you don't want hot water if it's going to cost you too much?? Bloody Yorkshiremen! JUst get the thing set up right and you won't have to think about it.
Grief, suppose you can't be bothered, or are too ill to feed the woodburner? It still has to WORK!.

Before you add the complication of the free wood supply, do the maths on how much it's really going to save you in energy, considering the regular effort, extra maintenance and upfront cost.

I'd spend money on controlling the heating into zones, so it looks after itself. You will have people who think you can control the whole thing with a cheapo thermometer in the garden. All right for factories 50 years ago. Look for Opentherm room sensors. You'll end up with an outside sensor as well, because that's the way the manufacturers have gone. A sore point with some of us.
My pet hate is inadequately insulated underfloor pipes, ground floor. Recently I measured 10 degrees drop across the radiators, and 5 degrees drop across the uninsulated pipes. 33% waste! You need thick insulation, done well.

 

[ed1178]

Thanks ChrisR.

I may not have made myself very clear in my original question regarding the woodburner. Basically I want one as a focal point in the sitting room which is where I will spend most of my time. As I have free logs it makes sense to use them, and as I am at home most of the time feeding the woodburner is not a problem. Seeing as I am feeding the thing every hour I thought it would make sense to have it help heat the water and rest of the house too. My concerns were more around how exactly the pumping would work - obvioulsy 12kw is a lot to go into the system if nothing is being drawn off, so surpless heat would have to go into the radiators. I don't mind this as it will help spread the heat around the house, but what I don't want is to light the stove only for the heating to kick in as well when I don't really need to - does that make a bit more sense? My other thoughts were to have a couple of large radiators acting as a heat sink in the hall directly behind the stove and on a landing above, operating on a separate, independent circuit, obviously making sure the rads were big enough to cope with the stove output, these could possibly be gravity driven? I could go for a smaller stove but as logs are free I would like to take advantage if possible...

I totally agree on the insulation - we are having the windows renovated and draughtproofed, the roof will be well insulated and suspended ground floors will be insulated from underneath. If the budget allows we may also excavate the solid kitchen floor and insulate that properly too, otherwise it will be some kind of insulated board under wood flooring. Her indoors is planning to undo all the good work by buying an AGA however. Perhaps someone can tell me if they are cheaper to run on gas or used £5 notes

 

[bengasman]

....Would the water company pick up the cost for a new connection in the street...

That is a good one. Water companies are in the business of charging, not paying.
Doesn't have to be that expensive, if you let ditch diggers dig the hole, not the plumber. Pipe can go anywhere you want, nothing to do with where the old one is.

The only reason I was thinking of connection a woodburner was because we have access to free logs, and as I work from home most of the time feeding the thing is not a major issue. If I can get 12kw if free heat (more with space heating) for most of the day it seems silly not to. 12kw for 10 hours a day equates to about £4 in gas? Over a winter that would add up quite nicely!

What also adds up quite nicely is integrating dhw and ch, provided you want it done legally and safely.
I'd forget about integrating it, and spend a little bit extra on top notch ch controls. That way, the gfch will automatically come on when needed and equally automatically turn of when satisfied.
Integrating ch plus dhw with a woodburner is very complicated as it can create very dangerous situations if not done perfectly.

 

[bengasman]

... Her indoors is planning to undo all the good work by buying an AGA however. Perhaps someone can tell me if they are cheaper to run on gas or used £5 notes

AGA's are dreadful things, god knows why people are so keen on them. Probably because the neighbours have one. Pump out loads of heat, whether you want it or not. Mostly not.
It's the girl's version of a Chelsea Tractor, completely impractical for an average of 50 weeks per year.

 

[Norcon]

Hire your self a good time served and experienced plumber to install your wood boiler and inter linked system.
A simple gravity circuit and twin coil cylinder+heat leak radiator/s and T'ing into the existing circuit is all thats needed and need not necessarily break the bank.
Hi-Lo stats and a relay interlocking the oil boiler.

Have a look at these.....
http://www.broseleyfires.com/Technology.html

Which will simplify the installation even further and allowing (wait for it)...........
Solid fuel integration with a sealed heating system.

European stoves with SCWS fitted are already on the market here in the UK.
DPS also supply units for retrofitting with scws integrated.

 

[ed1178]

I know - I'm not a huge aga fan - I take her point about them looking good, but that's where it ends as far as i'm concerned. The brochure says they are the green option as they are made from recycled iron and that you can bin the electric kettle if you buy an aga - then two lines later they tell you that it "only" uses 425kwh a week! imagine how many kettles full that is. Anyone who believes they are saving the planet by buying one of these monsters needs thier head examined.

Have been reading up on the boiler stove thing a bit, and it does sound like it could get complicated and possibly unreliable. I may keep the woodburner just for space heating, I guess with proper central heating controls I will still be saving as the rads will not come on when the room is warm. Can always open the doors to heat upstairs!

Will be calling Yorkshire water first thing about upgrading supply pipe. Hopefully second mortgage won't be required...

 

[bengasman]

...will be calling Yorkshire water first thing about upgrading supply pipe. Hopefully second mortgage won't be required...

Don't have them do it, it will cost the world. Sometimes they are helpful/reduced cost if you mention getting rid of a leaking lead pipe. But only let them do the connection to the mains, not the rest. Unless they offer to do it for free as a xmas special.

 

[rompers1978]

Could be an idea in to looking into getting your sash windows draughtproofed as well. If you're a DIY enthusiast it is relatively easy to do with basic instructions or call in the specialists. It's something that English Heritage endorse and means you keep your original windows.

 

[ed1178]

Just a quick update and thanks to all who offered advice initially.

Complete new system was installed and has now been running for the best part of a year, perfectly!

In the end we opted for a thermal store, more for convenience of link up and to ensure plentiful hot water than anything else.

Heat is provided by 20kw (14kw to water) wood stove and 40kw gas boiler. Store can operate on wood only, gas only or both. Generally we run on auto (both) and find that the stove really does make a difference to how often the boiler fires up. We did experiment and found the stove is not quite sufficient to heat the house alone, but we never expected it to, however once the house is warm and the store is back to temp after initial start up of central heating, the stove alone can just about maintain the temperature if we keep it burning quite hard. For convenience more than anything we just let the gas boiler do it's thing!

We upgraded the water supply pipe as although we had very good pressure before, it was so long and narrow that flow was poor. Now we can easily run two powerful showers together no problem. We have never depleted the store to such an extent that the heating has turned off to preserve hot water temperature. Even when we had 16 people staying at Christmas (never again, but that's another story!)

I suppose the mild winter has not really been a true test of the system but so far we are delighted with the economy of it. We do burn a lot of free wood, but we do like the house warm, and our gas direct debit is only £55 a month. Not bad for a big 5 bed victorian place - in fact better than my old 3 room flat!

Sorry not much in the way of technical detail, I let my heating engineers specify the whole thing as they saw fit. Initial costs were highish, but this was mainly due to the store which was almost £2000. However economy wise I can't complain and provided our free wood supply holds up we will recover the additional costs over a more conventional system in a year or two. As all the controlls, store etc are located in an attached garage access for future upgrades or maintanance is easy and should keep costs down.

A final update on the Aga saga - after much digging in of heels from both parties the better half agreed to give up on the aga dream. A compromise was reached in which the chimney breast was left clear for possible future instalation. However my thoughts are now turning towards a wood fired rayburn and an extra coil in the thermal store..... It's scary how easily one can become obsessed with free heat!