Does the length of flow and return pipes to a boiler affect the system's efficiency? I'm considering having our boiler replaced and want to know whether moving its location will have any benefits. My central heating is unconventional to say the least and I'm trying to find out which would be the most efficient way to improve it. And then the best value for money... Currently a 13 year old Gloworm 100E combi boiler is in the kitchen by an external wall, 6m away from the utility room where the three motorized 2-port zone valves, underfloor heating manifold, unvented megaflo tank, expansion vessel and wiring centre are. It has long 22mm flow and return and gas pipes from the utility. It supplies hot water directly to the kitchen sink only which is adjacent. (If anybody wants to know why we've that arrangement, that's another two paragraphs!) Option one is replace the boiler with a condensing combi in the same location. Option two, replace with a system boiler and run a new 7m pipe for kitchen sink hot water from the utility. Option three, locate new boiler in utility with extended 6m flue to either front or rear of house, adding new hot water pipe for kitchen sink as well (or reusing c/h pipe). Efficiency wise, Is it true that shorter runs from the boiler to the tank and valves is better? A new boiler will be ninety something % efficient which is better than ours (81% at new) Cost wise Modern boilers can cope with long flue runs but not sure of cost of 6m flue! Moving boiler location will mean a small amount of pipe jiggery pokery, and several metres of pipe no longer needed. Running a new hot water pipe to kitchen is a relatively minor cost. Our boiler is Category D and our house has an EPC of B. Any tips, advice, or places to go looking for them is much appreciated! Thanks, Dave.
The length of the CH flow and returns will make no difference. The length of flue will make no difference. The best location is for you to decide. The length of the DHW outlet will, because of the long dead-leg. Have all pipes insulated and maybe an instant electric, or small 10-15 litre electric storage under-sink water heater that takes in the hot combi water and outlets to the kitchen/bathroom/downstairs toilet hot tap. This gives instant hot water at the taps and is filled by hot water from the combi fuelled by cheap gas to keep electricity usage to a minimum. The combi serves the bath and shower directly because the dead-leg time wait is not an issue with these hot outlets.
Wow, thanks for the reply Walt! I was beginning to think my post was beyond comment. Thank you for the info about what'll make no difference, whether to change those aspects will be down to install rather than running cost then! I'm struggling a little on the DHW idea tho. Do you normally fit a combi and then run two hot water feeds from it? One to bath/shower and one via an electric tank to all taps? This seems a bit time consuming and uses twice as much pipe? Or am I getting it wrong. In my case, I'm not sure if it'll be helpful - maybe I wasn't clear in my original description. We have a 210l unvented hot water tank already. It supplies the bathroom showers, sinks, bath and downstairs toilet sink. The combi sees it as just another heating zone. Basically when we switched from a combi system to an S-plan we didn't replace the combi as it was only 4 years old. Made for many head scratching moments I can tell you! The combi is essentially being used as a system boiler, albeit with it's instantaneous hot water being used solely for the adjacent kitchen sink. I take what you say about insulation though - might be worth fitting some on the long runs! Thank you.
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