Hi - I'm new to this forum but would appreciate some helpful advice. I live in a flat and am having the kitchen refitted, which means moving or replacing our existing boiler (Alpha Ocean Style FF - about 12 yrs old). I'm told that if we replace it we have to have a condensing boiler (new building regs), but I understand that there are problems with the plume from this type of boiler as we have a balcony roof above where the flue would exit, and it's close to a door and a window. The cheaper option is to just move the Alpha, but I'm worried this may affect it (cause leaks). Or can we get a new non-condensing boiler fitted? I've spoken to 4 different heating companies (incl BG) and have had different comments and advice from each. Any help much appreciated. Thanks.
Limitations on proximity to doors and windows are not that different to existing boilers. There are some issues with distances to neighbouring properties though since some folks may find the plume objectionable.
What you have been told is correct basically - in that in order to meet the energy efficiency requirements of the building regulations, you will need a condensing boiler.
However there are exemptions allowed in certain circumstances. You can find out if these apply to you by reading this:
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The cheaper option is to just move the Alpha, but I'm worried this may
Moving it would count the same as installing - so unless you are prepared to do it yourself (or can find a CORGI who is prepared to ignore the regs) then you would be back to requiring the exemption as above.
See above.
Hardly surprising - the regulations in this area are a bit of a pigs breakfast.
Provided the regulations and the manufacturer's instructions re distance from windows/walls are complied with there is no "problem" with the plume - it's only water vapour - apart from aesthetically. Personally, I don't see why people object, providing you aren't blowing it into straight into other people's faces/windows/gardens.
There are boilers with more flexible fluing arrangements than straight through-the-wall, some using twin lengths of high-temp small(ish) diameter plastic wastepipe, which you might be able to route around and above the balcony.
You can move an existing boiler (it has been confirmed by the BCO to someone here recently) but a new boiler must be condensing (a boiler in a kitchen is unlikely to be able to claim any exemptions).
I've often wondered why manufacturers don't fit a much longer insulated co-axial flue. This would reclaim much more of the heat lost in the exhaust by using the counter-current priciple to warm the incoming air to the boiler. Warmer incoming air would surely reduce the work the boiler has to do to heat the water?
Sounds too simple so there must be something wrong with the idea although I can't see it.
In effect, this is what some early UK designs of condensing boiler did
- manufacturers added a secondary heat exchanger. The trouble was that the whole set up was not well designed to cope with the acidic condensate and corrosion resulted; leading to a poor reputation in the trade for condensing technology in general. German and Dutch designs which were made from the ground up as condensing, did much better and have been in use for many years.
The second aspect is that balanced flue boilers with no fan are not designed to have an extended flue because they use natural draught to bring in air and expel exhaust. Even those with a fan may not be designed to run with a long flue since the fan may have been selected to run with a designed and limited length flue.
- People may not *want* to have a long flue even though the boiler may be able to support it.
- Condensing boilers have a low exhaust temperature. Since the rate of heat transfer would depend on the temperature difference between incoming and outgoing air, this would be a lot less than on a conventional boiler in the first place.
- Plastic flues are not good conductors of heat
Because of these first issues, to make this worthwhile whould probably need something similar in concept to a plate heat exchanger where there is a lot of contact area between the incoming and outgoing flows. There needs to be good conductivity as well. There would be additional condensation from outgoing flue gases and this condensate would be acidic. There would be an increased resistance to flow for gases in and out, and the fan would need to cope with that.
The net of all of this is that I suspect a physically large heat exchanger with quite large stainless steel plates would be needed in order to make much differene as well as standing up to the conditions.
Cold air is denser so you get more air per unit volume to support combustion so they also fit intercoolers to cool the air before it enters the engine.
Yeah but cars are internal combustion engines, not CH boilers so I'm not sure the argument's the same. Intercooling in a car maximises the power output which isn't the desired object of pre-warming the air in a CH boiler.
True but they might be convinced if the savings were worthwhile.
Again true but there is still wasted heat going out that could be regained. I've no idea of the amount but there's no technical reason why the exhaust temperature couldn't be cooled right done the the incoming air temperature. Surely that's got to be worth something?
Which would be good for the outer intake pipe. The inner exhaust pipe could be made of stainless steel.
I think that without testing designs it would be premature to dismiss a simple coaxial counter-current heat exchanger. Keeping it straight & relatively long would keep it cheap making the payback period proportionally shorter.
Duh...
So the stuff that condenses at the moment and trickles back through the boiler isn't acidic? I would presume that the boiler's materials already take that into account.
Well that's true and might limit what can be retro fitted to an existing boiler but many boilers can already accept quite long flue extensions.
A company in Plymouth, Zenex, has come out with a "top box" that fits on a condensing boiler's flue - out of the boiler into the box and out again to outside. Not new as Johnnson & Starley has one for their forced air units converting them to condensers. This appears a leap though making condensers more efficient.
They announced it pre-Xmas, but now it is on sale.
It extracts even more latent heat from the flue of a condensing boiler. They claim, with some independent validation, that a "condensing" boiler can improve fuel consumption by 30%. Currently the best non-condensing boiler is 80% SEDBUK, and the best condensing 92% - only 12% leap. They claim it will go to the near 109% available (yes you can get 109% efficiencies from a condensing boiler). There are no moving parts.
They claim that a combi can deliver 50% more water flow for the same input - so a 12 litres per min job will be 18 litres, a big hype that fills a bath pretty fast instead of a leisurely fill.
They are developing a 15kW combi that delivers 12 litres/min - a little better than the average combi around. 12 litres is normally only achieved by a 28kW boiler. So, at 15Kw it is not oversized for the CH in flats, and the case size can be kept down.
They plan one for a non-condensing boilers too, that will bring non- condenser into condesning territory.
They claim the price will fall from £595 as production gears up. If it get to half, and it does what they say, then this can save a lot of fuel, the bigger the house the more fuel saved.
They may have versions available for oil and LPG boilers. The version available may suitable for LPG boioers. This box may well make an LPG boiler equal, or better, than an oil boiler to run and with £600 on top probably still lower capital costs of installation.
Worth looking at and assessing.
Buy here for alimted flue implementation. More flues to come.:
Another way of eliminating a plume and yet have higher efficiencies than non-condensing boiler is to intall a bledning valve on the boiers flow-return, set to 60C. The returning wtaer will always be about dew-point.
A long plastic mPVC flue can have a pipe around it. A pipe in pipe arrangement. This is legal as the inside of flue is not touched at all. It could run for 10 to 15 foot across a loft and have water in the gap between the pipes. Feed cold mains water through this and it pre-heats the water. Zenex, pre-heat water this way with their top boxes and claim 50% greater flow rate through a combi. So, a 12 litres/min combi can be zipped up to 18 litres/min. Big jump.
Using a pipe in pipe means it is cheaper than their top box. But they are incorporating it all inside one combi box. They are talking to the big boiler manufacturers to licence their technology. If a 12 l/min combi gives
18 litre/min for the same kW input then this combi will sell like hot cakes. Also, the plume is eradicated.
Councils are now having to deal with complaints of nuisance pluming. This appear to be the answer.
I'm not sure that warmer air would improve combustion efficiency - cars are reputed to run better in cool weather as the air is denser. Re the flue, ISTM that the problem is that if heat can easily migrate from the flue into the room then the reverse will be true too, and when the boiler isn't running the flue would act as a heat sink losing heat from the room.
Are there any scientists here who can tell us how much heat could potentially be recovered if you could condense all the water vapour in the combustion gases. I remember enough school chemistry to know that it's CH4+ 4O = CO2+ 2H2O - so every 12g of gas burned makes 36g of water vapour. And the latent heat of water is easy to find. But I couldn't find what gas weighs given that it is under pressure when metered.
In co-axial flues the incoming air is heated by the exhaust air. Two pipe flue systems are more efficient as the incoming cold stays cold until burnt.
On large trucks there were experiments to us heat pumps to cool the incoming air. The larger the engine, and more fuel used, the more cost effective these things are.
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