Hi all,

I now have a very stupid question for everyone.

I have UFH in the main part of the house, rads in the (hardly used) guest extension and a desire to add solar or ghsp at a future date. In the meantime though, I need to chose a boiler setup for the house - something that I know sweet fa about. I've recommended a greenstar 30CDi linked to 250l unvented indirect cylinder. What I'm after is a system with low running costs, high efficiency and easily adaptable in the future. Will this do it, or is there a better system?

And now for the silly question. Is it better to have one boiler for all three, or three boilers where each does just one thing? In an ideal world what would be your perfect setup?

(I told you I knew nought!)

P

I think you've been recommended a very standard setup. Two questions are a. would you be really happy with 250l of pressurised hot water in your house and a cylinder requiring an annual inspection. b. Would you be willing to go for something a bit less "standard" which is more efficient but which far fewer plumbers have experience with.

If you are on mains gas then there's little point in considering gshp now or in the future.

Hi pantasarus

First thing to do is to look backwards through the recent threads on this site with thermal store in the title (there have been some recently). Then perhaps do a search to look at older posts. There's alot of information there. Then go and have a look at the web sites from some of the manufacturers e.g. DPS on www.heatweb.com, which has a load of background information. Then your brain will probably hurt from information overload so sit in a darkened room for a day or two. Try not to rush a decision! The technology gives mains pressure hot water but its completely different from an unvented cylinder. There are different types of store, fully vented systems are the most flexible in terms of heat in or out but you will need a boiler that will run on a fully vented system (fortunately these are generally the simplest kind). They work really nicely to integrate both rads and UFH, and also will enable your boiler to work at its most efficient as the return temperature can be controlled to ensure its condensing at all times and the boiler burns for longer periods less often, rather than cycling, and if the store is not up to temperature you can still get hot water out within a few minutes of the boiler turning on. Solar heat input is via a coil (or >1 coil - see previous posts). There are also stores where the main boiler heat input is via a coil, these are less flexible.

Main issue is finding a plumber who knows the technology (rare) or who you can educate. They are actually really straightforward but because they are not common it's easy for a plumber without an open mind to dismiss them.

Re GSHP this is a bit of a dirty word on this site I think. The efficiency drops as the temperature requirement increases so they are great for UFH but not for much else. They cost quite alot to buy and install so may not payback within the lifetime of the unit itself. Have a look at the housebuilder's bible for examples looking at costs of various heating solutions. Hence if you are not on mains gas it might be worth considering but there are still probably better things to spend your money on, difficult to comment further without knowing more details of your situation. Again there are alot of previous posts on this topic so have a hunt through the archives.

regards

Mike

Thanks for all the info. I've spent the past few days reading about thermal stores/banks and I think I've got my head around it. I've also been following some of the threads about space heating and read Crusoe's paper from the CAT conference. The heatweb site is slightly confusing for me since they talk about the benefits of one system over another and, at the moment, I don't know enough to really follow what they're on about. However, I'm glad for all the pointers and gratefully appreciate people taking the time to educate me.

At the moment the output of the boiler is split into three feeds, one for the rads, one for the UFH and one for the DWH. These are all controlled by a timer so that you can set the on/off times for each individually on a weekly basis. So the rads and the hot water are on for a couple of hours in the morning and evening whereas the UFH is set to on all the time.

All the rads have TRVs fitted and there's a room thermostat for them as well which turns them all off once (or is that the boiler off?) once the hallway gets to 16ºC.

Each room that has UFH also has a thermostat and 7 day timer so you can set each room's target temperature and on/off times independently from each other. However the UFH never really switches off since I've been told that it's more efficient to use setback temperatures of around 17ºC than to turn it off (is this true?). So this means that the kids' room has a profile of 18ºC for a couple of hours in the morning and at bedtime, a setback of 16ºC during the day and 14ºC during the night. So when it's cold, this means the UFH is effectively on 24 hours a day.

This is where I get confused. It seems that I have three different hot water requirements; water at around 40ºC 24 hours a day for the UFH, water at 60ºC for a couple of hours a day for the rads and water at 80ºC for DHW for half an hour or so (15mins to run a bath twice a day?). The thermal store designs I've seen seem to keep the water at 80ºC presumably for the DHW, but water at this temperature is only needed occasionally.

Why not have the thermal store at 60ºC instead and use it just for space heating? Would I then use 25% less energy as a result of having a lower temperature? Obviously I would still need to somehow provide DHW, so why not use a separate combi boiler for this? In other words, would two boilers be better than one?

P