Gravity system advice

Discussion in 'Plumbers' Talk' started by Nick Ahmed, Apr 11, 2016.

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  1. Nick Ahmed

    Nick Ahmed New Member

    Gravity system advice

    Hi. I have a gravity fed system so when I have central heating on I have to have hot water on also. I have a potterton nettaheat boiler and a hortsmann c27 programmer. The programmer will only allow me to programme hot water and central heating to come on at the same time. I can have hot water separately but not the other way around.

    If I just want central heating on but have to have hot water on at the same time (when it's not needed) does this not mean that I am wasting hot water and increasing energy bills?

    Also, if I want to have a system that allows me to have each one on independently, do I have to have a new heating system metalled rather than just have a new programmer installed?
     
  2. kiaora

    kiaora Guest

    Hi
    You will need to rearrange the pipe work and add either a diverter valve or 2 zone valves, it's not too difficult.

    Will need a professional to give it the once over and tell you what's needed

    Regards
    Peter
     
  3. KIAB

    KIAB Super Member

    Simple job.
     
  4. Nick Ahmed

    Nick Ahmed New Member

    Thanks for the advice. So, am I wasting hot water if i have to have the central heating on for long periods?

    Thanks
     
  5. KIAB

    KIAB Super Member

    Very inefficent setup.
     
  6. Hi Nick.

    Looks like the C27 programmer will do both CH and DHW, so you'll still be able to use it after conversion (with a wee tweak so's they work properly independently).

    As said above, the flow from the boiler/pump (is it built in to the boiler?) will need to split and be fed into (ideally) two separate zone valves. One will control the flow to the hot cylinder and t'other to the CH. Both open will do both...

    In theory that's all that's needed - along with wiring them up. I'm guessing your hot cylinder will already have a thermostat on it? If not, it'll need one too.

    Parts are not expensive, tho' labour cost will depend on how your current system is laid out and how good the access is.

    Far better system, and your DHW will heat up faster too...

    As always, try and get around 3 quotes (unless you know someone you already rate).
     
  7. Nick Ahmed

    Nick Ahmed New Member

    Thanks very much Devil's Advocate. Appreciate your knowledge. I''m a novice so really don't understand a lot of this. Not sure if the flow is built into the boiler I'm afraid. All I know is that the heating is a gravity system as the boiler has 4 pipes running off it. Yes, the hot water cylinder does have a thermostat control on it.

    Its a very old setup and I'm not really sure why it was done this way. Its been fine for us for the last 4 years as wife and I work 9-5 so only have heating on in evening and morning, therefore not wasting hot water in the day. Now about to have a baby so wife will be at home more in the day and will therefore need heating on more in the winter but i am concerned that as we also need hot water on at the same time due to our set up we are wasting hot water
     
  8. kiaora

    kiaora Guest

    Hi
    With a heat loss around 2/3 kW per day, from a normal cylinder, that's around 10 -15 pence a day. Less if the heatings off at night.

    £40 a year? Ish?

    Just an observation, when considering your options.

    Regards
    Peter
     
  9. Nick Ahmed

    Nick Ahmed New Member

    Thanks kiaora. So if the hot water is turned to 'on' but the tank is full of hot water and not used, is it not actually costing me any more money?

    Thanks
     
  10. In theory, once the hot cylinder has heated up to the set temp on the thermostat, it'll turn the boiler off - so it shouldn't be costing you any more money.

    Very good point by Kiaora - although your system is, ahem, crude and slow, it still does what it's designed for.

    Silly me - if it's a gravity system, then it's unlikely the boiler will have a pump built in - instead it'll be on the CH flow pipe.

    The four pipes you mentioned going to your boiler, I presume again that two are for the CH and 2 for the DHW. In which case your plumber will know whether two need capping off, or if all 4 will still be used. I haven't a clue...

    Call in some plumbers, ask about the pros and cons of conversion, and then get a price.

    Then sit down and decide :)
     
  11. KIAB

    KIAB Super Member

    Get a Combi.[​IMG] [​IMG]
     
  12. Crowsfoot

    Crowsfoot Screwfix Select

    I think too much is made out of fit a combi and save money and "Doing The Maths"!

    Whilst your heating is on your hot water is being constantly topped up by gravity for free!
    You are also saving money on electricity because a gravity system requires no pump.
    Plus saving all that wear and tear on MVs and Pumps.

    If you've got some spare cash to flitter away I guess installing a combi is a good a method as any of spending your cash.

    My winter heating bill was actually £28.00 dearer after installing a combi!
     
  13. KIAB

    KIAB Super Member

    A gravity system is so old fashion today, & obsolete, a relic from the last century,so inefficent,you have a bath,draw off all the hot water from cylinder, you then have to wait for boiler to reheat cylinder, the op's system must be at least 30 years old & scaled up.
    With a combi it's constant hot water, no silly header tank(s) to freeze, even when well insulated.
     
  14. I don't understand that, Crows. From the simple fact that combis only heat the water you actually use, compared to a stored tank which will always lose a steady amount of heat to the air.

    Could it have chust been a colder winter?
     
    KIAB likes this.
  15. KIAB

    KIAB Super Member

    Exactly.

    Rip it out.:p
     
  16. Crowsfoot

    Crowsfoot Screwfix Select

    At the same time I upgraded all the radiators and re-piped the heating (replacing the old micro bore with a two pipe system.
    To be fair I have run the new heating system on a higher temperature setting than I ran the old boiler on.
    Hence, the house has been warmer since fitting the new combi; so perhaps it's not a fair comparison.

    However, I was eagerly awaiting my first February winter heating bill with the new combi and wondering how much money I had saved....imagine my disappointment when it actually cost me more money than the same time last year (this even included the BG a price reduction).:(
     
  17. Crowsfoot

    Crowsfoot Screwfix Select

    Maybe heating very cold water each time from scratch (which will consume a lot of energy very quickly) is not as money saving as heating the warmer stored cylinder water at a more steady pace.
    Only thing I can think of Devs cause I don't think it's been a colder winter.
     
  18. chippie244

    chippie244 Super Member

    It's been a warmer winter, I was only out of shorts for 3 weeks in March.
     
  19. The energy required to heat up a body of water from cold to, say, 60oC is the same regardless of whether it's done 'instantly' by heating a fast flow through a 15mm pipe or whether it's done slowly via a 22mm pipe and a heat exchanger in a hot cylinder.

    Pretty much.

    But, the water in the stored tank will always be getting cooler through heat loss, and that is all waste.

    No question that heating only the water you need - whether it's via a thrumming combi blasting oot 30kW or not - will always be more cost efficient than heating a 'store' of water which will always be getting cooler.

    The higher bill must have been down to something else - like your extra-warm toes... :)
     
  20. And for these three weeks you were in the nuddie...
     

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