Oso vs Megaflow
- Thread starter meldrew
- Start date
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Yes it's very true we don't need our bedrooms as hot as down south, and our shops are cooler. otoh we have more cold to overcome with our installations, and modern young couples seem to be as soft as southerners, so standards are becomeing more uniform up and down tut country lad.
If you chop your own wood you warm yerself twice.
You burn so much ebergy getting to the top floor of our house you have to take your wooly off when you get there anyway. You do wear wooly's indoors don't you?
OK I'll admit it, I can't go to work today because I have kids. Anyhow last night Halstead rep took us out for beer, pasta and Jim Davidson. A very good night was had by all. I might actually look at their boilers again.
If you chop your own wood you warm yerself twice.
You burn so much ebergy getting to the top floor of our house you have to take your wooly off when you get there anyway. You do wear wooly's indoors don't you?
OK I'll admit it, I can't go to work today because I have kids. Anyhow last night Halstead rep took us out for beer, pasta and Jim Davidson. A very good night was had by all. I might actually look at their boilers again.
silverback said:
Depends how they are utilised, if your demands on each are at the capacity of the boilers it makes good sense to have a seperate boiler for hot water and for heating. If you are running a big 3/4 bathroom house with power showers and plenty of occupants off an unvented system then I'm sure you would appreciate a heating boiler sepeate in the depths of winter.
No, Just install a good quality cylinder with the correct capacity and a fast recovery coil.
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I don't see an advantage in having one boiler on the HW and one on the heating.
An immersion takes a while to heat 300l!
Oh, what's a "wooly". Sounds rather primitive? Is it one of those things we used to give to poor people?
An immersion takes a while to heat 300l!
Oh, what's a "wooly". Sounds rather primitive? Is it one of those things we used to give to poor people?
ollski said:
Drain 500 l in under 10 minutes, I don't think so, if showers were capable of this we would have to heat a reservoir to keep up with demand
Ollski, your power shower must mix with quite a lot of cold, unless you have asbestos skin.
If we assume 10 degrees for cold temp (but would be higher in summer) and 60 degrees for hot water, 60% hot to 40% cold will give mixed temp. of 40 degrees (unless I've cocked up on the maths).
So you have to allow more like 15 - 20 minutes to empty hot tank, not allowing for recovery.
If we assume 10 degrees for cold temp (but would be higher in summer) and 60 degrees for hot water, 60% hot to 40% cold will give mixed temp. of 40 degrees (unless I've cocked up on the maths).
So you have to allow more like 15 - 20 minutes to empty hot tank, not allowing for recovery.
ChrisR said:
Chris Thanks for your comments so far, plus those of everyone else, it's got me thinking..
I'm having a new watermain fitted, I think it's 22mm? Or are they 25 - the standard blue pipe?
Pipework - I can specify what size I shuold run from the uv cylinder to the showers, would 15 be alright given that they run at mains pressure, or is 22 better?
Showers will probably be grohe thermostatic, the model 1000 or similar.
Gas meter - I hasd a look at this but it doesn't say anything like U6 - does this correspond to any other measure eg cubic ft per min (it's an old meter!)
Gas meter to boilers will be about 15m. The first 5m is in existing steel pipe which looks about 1.5"
Just a couple of flame effect gas fires run off the gas pipe, very rarely used.
I will ask my plumber about options on a single boiler, and if we use a pair, whether it'll be zoned.
Lots to think about!
chrishutt said:
Chris are you taking the pi55 now?. I'm more assuming worst case in winter with cold main 3-5 degrees and the usual hot water temp of 55. Ok I'll give it you maybe 13.6 minutes....I take it all back then there is no excuse to ever fit 2 domestic boilers.
If you have space, I'd use two boilers, why should you need an excuse!
Whether you use one or two boilers you can have whatever zoning you like. Making them supply different circuits though removes one of the advantages of having two so I can't see the point of doing that.
Your meter is probably a normal domestic one, designed for 6 cubic metres per hour. It'll have a type number on it somewhere, R5 and G6/P are others. The next common meter up is a U16.
If you measure the width of the meter and it's 200 or 235 mm, it's a 6cu m/hr one.
Those boilers use a maximum of 2.9 cu m per hour.
The specification in gas meters says that they can lose 2 mbar pressure at maximum flow. 2 x 2.9 = nearly max flow for a U6.
Meter output pressure at "normal" flow is allowed to be in the range 19 to 23 mbar. (Sometimes they're less and there's nothing you can do if the supply in the road is poor.)
So at max flow maybe 17 to 21 mbar.
One can calculate what pressure drop you SHOULD get in a certain length of copper of given diameter. Unfortunately the charts we're supposed to use are hopeless. The drop is always more than calculated. I recently used 28mm pipe (biggest we're allowed to use, with "domestic" qualifications) to supply a 33kW boiler TEN metres from the meter, and the drop was 2 mbar.
Those boilers cannot be expected to work (seriously!) if they get less than 18 mbar.
And, by the way, your gas fires will use the odd 14kW or so! Around 1.5 cu m/hour
Am I getting the point across? There is an issue here. You may need a bigger meter, or bigger pipe, or both. This takes you into "industria££y" qua£ified corgis. (Have used 2 pipes for 2 boilers before - not a solution for you here.)
As it appens I have used a Megaflo, at 3 bar, to supply a single Grohe 1000 shower. Shortish 22mm pipes, apart from the ones in the wall (and the hose, which is smaller and takes H + C together). The max flow rate with the Grohe multi head was 16 litres/minute, less than I thought it would be.
The later M'flos have a less restrictive valve arrangement, so it might be a bit more.
25mm is probably big enough for your supply pipe, but if you can, bribe the installers to use 32mm - assuming the official response is that you don't need it. They shouldn't object, imho, but they often do.
At sixty litres per minute you'll lose half a bar in 10 metres of 25mm, or 0.15 bar in 32mm. Not really something to lose sleep over, but the fittings lose (and cost) disproportionately more. Your plumber will be providiing the stop cock etc in the house - don't make the mistake of using small ones on cost grounds.
Someone might suggest putting a big "break" tank (cistern) in the ex-garage, with a 4 bar £500 pump providing your UV cylinder with all the water it can use.
Whether you use one or two boilers you can have whatever zoning you like. Making them supply different circuits though removes one of the advantages of having two so I can't see the point of doing that.
Your meter is probably a normal domestic one, designed for 6 cubic metres per hour. It'll have a type number on it somewhere, R5 and G6/P are others. The next common meter up is a U16.
If you measure the width of the meter and it's 200 or 235 mm, it's a 6cu m/hr one.
Those boilers use a maximum of 2.9 cu m per hour.
The specification in gas meters says that they can lose 2 mbar pressure at maximum flow. 2 x 2.9 = nearly max flow for a U6.
Meter output pressure at "normal" flow is allowed to be in the range 19 to 23 mbar. (Sometimes they're less and there's nothing you can do if the supply in the road is poor.)
So at max flow maybe 17 to 21 mbar.
One can calculate what pressure drop you SHOULD get in a certain length of copper of given diameter. Unfortunately the charts we're supposed to use are hopeless. The drop is always more than calculated. I recently used 28mm pipe (biggest we're allowed to use, with "domestic" qualifications) to supply a 33kW boiler TEN metres from the meter, and the drop was 2 mbar.
Those boilers cannot be expected to work (seriously!) if they get less than 18 mbar.
And, by the way, your gas fires will use the odd 14kW or so! Around 1.5 cu m/hour
Am I getting the point across? There is an issue here. You may need a bigger meter, or bigger pipe, or both. This takes you into "industria££y" qua£ified corgis. (Have used 2 pipes for 2 boilers before - not a solution for you here.)
As it appens I have used a Megaflo, at 3 bar, to supply a single Grohe 1000 shower. Shortish 22mm pipes, apart from the ones in the wall (and the hose, which is smaller and takes H + C together). The max flow rate with the Grohe multi head was 16 litres/minute, less than I thought it would be.
The later M'flos have a less restrictive valve arrangement, so it might be a bit more.
25mm is probably big enough for your supply pipe, but if you can, bribe the installers to use 32mm - assuming the official response is that you don't need it. They shouldn't object, imho, but they often do.
At sixty litres per minute you'll lose half a bar in 10 metres of 25mm, or 0.15 bar in 32mm. Not really something to lose sleep over, but the fittings lose (and cost) disproportionately more. Your plumber will be providiing the stop cock etc in the house - don't make the mistake of using small ones on cost grounds.
Someone might suggest putting a big "break" tank (cistern) in the ex-garage, with a 4 bar £500 pump providing your UV cylinder with all the water it can use.
I posted my last reply on the run. I should have added that one boiler could heat bigger of the two heatin zones and second boiler remaining CH zone as well as HW zone.
Such a connect would not need any special interface to fire one boiler with second kicking in if load demanded
Meldrew, not zoning the installation will is not an option. Your plumber may suggest only TRVs if he does not understand zone valves and roomstats controlled by programmers. Three zones as mentioned above, will make system operationally economical. Splitting the system may be a little troublesome though.
Such a connect would not need any special interface to fire one boiler with second kicking in if load demanded
Meldrew, not zoning the installation will is not an option. Your plumber may suggest only TRVs if he does not understand zone valves and roomstats controlled by programmers. Three zones as mentioned above, will make system operationally economical. Splitting the system may be a little troublesome though.
BUt why split the system to make one boiler just heat part of it, I can't see any advantage. It can of course be zoned with, er, zone valves!
All you need to wire up 2 boilers in tandem is a relay box (Danfoss do one for about £50) so the main room thermostat operates the relay and separate poles on the relay turn the boilers on. They come on together but the electrical supplies can still be separated that way.
You can have thermostats thoughout the house connected to zone valves, and the one relay box, if you want.
All you need to wire up 2 boilers in tandem is a relay box (Danfoss do one for about £50) so the main room thermostat operates the relay and separate poles on the relay turn the boilers on. They come on together but the electrical supplies can still be separated that way.
You can have thermostats thoughout the house connected to zone valves, and the one relay box, if you want.
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