I am considering using a floor standing gas boiler and coupling to an existing (ex Rayburn range cooker) lined brick flue.
Assuming the flue is suitable, can combustion air be drawn through a pipe from outside rather than the room as current? Probably 20-25kW or so.
I think condensate can be routed to waste through the underfloor insulation.
Any particular gotchas?
Think you need to check with your boiler's installation instructions. What is and what isn't permitted is usually all listed.
What boiler is it?
Tim
Have a look at
Owain
+1 Many manufacturers let you download the installation instructions FOC.
Unknown at this stage:-)
I am planning to re-model what was my sister's timber frame, chalet bungalow. Technology has moved on since it was built in 1994/5. I have no interest in retaining the large lump of gas fired cast iron cooker which has done nothing other than a few rice puds.
With the planned enlargement, finding wall space where the exhaust plume will not be an issue conflicting with distance run to DHW cistern etc. Tempting to make use of the existing flue.
I rather wondered if anyone had come across a *room sealed* floor standing boiler where the combustion air is supplied by a duct separate from the flue.
The current arrangement involves knee height draughty vents!
The proposed location would suit a rectangular duct along a wall to the outside.
If it takes air from the room, it is hardly "room sealed".
Your problem may be to find a boiler which can work with a conventional flue and a ducted air supply if you want what might be called 'room sealed'.
OK chaps. There is a fair bit of information on the Viessman site about drawing combustion air down a conventional flue fitted with a duct for the exhaust.
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Yes, I fitted a Keston 15 years ago which uses 50mm muPVC (plastic) pipe for the inlet and the flue. I'm not sure if you'd find a floor mounted one, but you can wall mount it low down. (They used to do a floor standing mounting frame, but that was to mount it high up where there was no wall or where the wall wasn't strong enough, with space for a hot water storage cylinder under it.)
I did consider putting the exhaust pipework up an unused chimney so the steam plume appeared to come out of a chimney pot, but didn't do this in the end. Nowadays, flue pipes have to be accessible for inspection/maintenance which would be a problem if threaded up a chimney, although that wasn't the case 15 years ago.
You will need to use pipework the manufacturer specifies. If the flue length is long, it can pay to choose a boiler which uses standard muPVC pipe rather than (much more expensive) proprietary flue pipe extensions, which can end up costing more than the boiler itself when long lengths are required.
Or have a CO monitoring system in the void
Owain
He never mentioned taking air from the room.
So somehow modern boilers need to be looked at but old ones don't? I find that hard to believe.
Why, they run closer to stoichiometric mixture and therefore more likely to produce CO?
Old boilers had excess air in the exhaust. Rules have of course tightened up though I don't see much difference between a chimney and a flue in terms of access.
In message , Andrew Gabriel writes
Ah! That might be an issue. The Rayburn and its flue pipe was installed
20 years ago. Is inspection anything more than an access hatch?I guess what is there will be spiral wound stainless suitable for gas.
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You'd think they'd be made to produce LESS of the harmful gases.... health and softy and all that shit.
My boiler was fitted before I moved in 15 years ago. I've done nothing to it ever. No repairs, no servicing. Works fine.
The flue inspection requirements are retrospective, if you need a gas safety certificate (e.g. landlords).
Modern boilers pass all the air through the burner as the gas/air mixture. Older boilers have additional air passing through the chamber which didn't come through the gas/air mixer. I suspect that means thae chance of a modern boiler producing excess CO is actually significantly less, as lack of air is more likely to prevent the burner even igniting than is the case with lack of air in an old boiler, which can easily continue burning with a sooty/CO flame.
Some boilers get away with that. Two that I look after, a Potterton Profile and a Potterton Suprema, need almost no servicing. I've done them once in 15 years, and they didn't actually need it. I do check with a flue gas analyser every 1-2 years though.
Other boilers (such as the Keston C25) really do need at least some simple servicing regularly, or they would fail expensively. These are well known for the condensate drain from the heat exchanger blocking with debris, and this is easily avoided by pouring a couple of pints of water into the flue (*not* the air intake!) 1-2 a year to flush out the debris before it builds up. The burner gasket has a life of 2-3 years, so this needs changing and the top of the heat exchanger can be checked and cleaned when doing that. The internal fexible flue pipe has a limited life, and can be checked and replaced before it fails, and does lots of secondary damage. Also need to regularly check for any condensate leaks, as these will quickly write off the case, which will cause the boiler to fail a safety check.
Can't you just bribe them or get a mate to fill in the form?
So what they've done is make something more dangerous than it used to be. That is not the way of health and softy.
It's a Baxi WM 30/3 RS. The flue gases go outside, like with every boiler, so why would I check what's not going to end up in my lungs?
If a boiler fails like that it's not fit for purpose and should be returned under warranty, and some bad reviews filled in to make them lose business.
You will have a problem finding a small conventional flue boiler these days. Best forget about the existing flue. Only industrial/commercial sized boilers use conventional flues nowadays.
You might as well buy a wall hung room sealed (ie "normal"boiler)
Some have concentric flue/air intake pipes, some have separate flue and air intake. There are restrictions on the length of these pipes and how many bends you can have.
I was speculating the opposite (although the reasons are not for safety, but for efficiency). Heating up excess air which is not used for combustion is a waste, which old boilers did in a big way. So you might think you can measure the air so the oxygen is exactly the right amount to burn the gas, but that doesn't work because not not all the oxygen will get found by the burning gas so you'll get CO given off. It's thus a balance of providing enough air to minimise the CO, without providing so much you're wasting energy on heating up air which isn't needed.
If dust gets into the air mixer or burner jets, the efficiency drops, which means you're wasting money. If it gets really bad, you will be giving off CO too. You want to service a boiler before it gets anywhere near this bad.
CO poisoning needs two things to go wrong:
1) burner is not operating correctly, and 2) combustion products being breated in.The general priciple is that you prevent either of these happening. If you allow 1) to happen, then your risk of 1) and 2) happening together becomes much higher.
Most owners have not managed to keep their Keston C25's working for anything like the 13+ years I've managed by nurturing it - I heard of many which were chucked out after 3-4 years. No, it was not fit for purpose for the general public. Mine still looks brand-new inside, because I service it myself and I'm aware what it's problems are. (It might also help that mine runs at a very low temperature of typically 45C/32C flow/return, because I designed the heating system to run at low temperature with the condensing boiler, although that does mean it produces more condensate that is typical.)
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