boiler insulation

[Yorkie]

Hi Gents, I just thought I'd get some opinions from forum members.
I have a 30 year old Glo-worm gas boiler that works very well and is fitted to a fully pumped and controlled system with zone valves.
People are telling me to get a modern condensing boiler, but the need to totally change the system and remove the copper cylinder would give a long pay back period.
I also intend to fit a solar hot water collector of my design and feed it into the tank on a new coil as a feedwater heater. This I could not do if I remove the cylinder.

The idea is to insulate the free standing boiler to reduce heat losses from its water jacket by means of a modern insulating blanket that is a similar material to shuttle tiles. This will fit inside the boiler sheet metal casing and be clipped against the outside of the boiler, obviously leaving gaps where there are air intakes, flues and other combustion access. This should considerably reduce losses from the boiler shell.

Your thoughts Gents?


Ed


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You are confusing a condensing boiler with a combi boiler Ed.

To replace your 30 yr old Glow Worm boiler with a condensing boiler is about a day's job, assuming that your Glowworm is a balanced flue boiler on an outside wall and the new boiler is going in the same position. A condensing boiler retains your hot water cylinder and cold feed tank, but you will possibly find that to comply with current codes of practice, the installer will want to update your programmer and room thermostat.

A condensing boiler is about 95% efficient - your Glow Worm will at best be about 60% effcient, and also has a permanent pilot usding gas 24/7/365, which is not permitted on modern boilers. It will certainly be such a 'gas guzzler' that it would have been on the list of boilers elgible for the £400 'Gordon Brown grant' for replacing inefficient boilers with condensing boilers. My 20 year old Glow Worm was on the list, so I took advantage of the grant a couple of years ago.

A combi boiler is quite a different animal and the explanation that follows has no relevance to your situation, but may help to clarify what a combi boiler is: It doesn't use a hot water cylinder or cold feed tank so no hot water is stored - it is supplied on demand by the boiler when a hot tap is turned on on a sink or bath or shower. The heating system is sealed, and pressurised to 1 - 2 Bar (about 14 - 28 PSI). This is simply done by turning a bypass valve usually located near to or within the boiler while observing the pressure gauge on the boiler until it reaches the correct pressure, then turning off the valve. There is small pressure gauge on the boiler and the householder needs to keep an eye on that because very small leaks on radiator valves can cause the pressure to fall, and of course, if a radiator is removed to decorate behind, as soon as the radiator valves are tuned back on, the pressure is lost in the system. If the pressure drops too low, the boiler closes down.

The main drawback with combi boilers is the poor delivey rate of hot water. Not too noticeable if you only use showers, but very noticeable if you want to fill a bath. This is even worse in winter when the cold water from the mains is so much cooler, because to provided a constant output temerature with a fixed heat input to the boiler, the only way to maintain the temperature is for the boiler to slow down the water flow rate. Combis have their place, especially in single floored apartments where there is no 'head' for a cold water feed tank for a conventional boiler, and for a new installation, there is a saving on plumbing costs - not cold feed tank, overflow pipe, hot water cylinder etc.

None of that has any relevance at all to you Ed, so file it under 'burn before reading!.

More relevant to your situation are condensing boilers:

All current production gas boilers must by law be condensing boilers, and confusingly perhaps, that includes combis. (So while all current combis are condensing boilers, not all condensing boilers are combis!). Prior to condensing boilers, gas central heating boilers were about 65 - 70% efficent - the rest of the heat went out through the flue outlet in the form of water vapour and carbon dioxide at quite a high temperature. The heat exchanger of a condensing boiler is so efficient in extracting heat from the flue gases that while to carbon dioxide is emitted from the flue, the gases fall to a temperature at which the water vapour condenses into water, which is connected to a drain, which ideally should be indoors and connected to say the waste pipe of a sink, as for example would be a dishwasher, washing machine etc, but are often installed externally. That is very bad practice as the 22mm diameter pipe will freeze even if their is onlty a light frost. The reason for this is that when the boier is operating, the water goes down the drain in a trickle rather than a great gush, so will strat to freeze on the inside wall of the 22mm drain, mkaing the internal diameter progressively smaller, until it freezes solid, then the boier shus down.

Condensing boilers are room sealed - they take their combustion air from a concentric flue pipe with the inner pipe being the 'exhaust' and the outer concentric one being the freash air inlet. Because the flue is fan-assited, it is small in diameter (about 75mm) and can run for quite long distances of several feet horizontally or vertically, so the boiler siting can be more flexible that older balanced flue boilers, which had to be sited in an outside wall.

Rather a ramble, but I hope it helps rather than confuses!