Ask The Trades - Combi boiler & booster pump?

Welcome, Guest. Please Login or Register

	May 2^nd, 2024, 7:36am
View recently thanked users View top thanked users

Quote: A rock --> me <-- A hard place

Ask The Trades › DIY Forum › Plumbing Questions › Combi boiler & booster pump?

(Moderator: thescruff) - (Moderator Group: Board Moderator)

< Previous Topic | Next Topic >

Pages: 1

Combi boiler & booster pump? (Read 7354 times)

stressedout

GDPR opt-out

Combi boiler & booster pump?
Jun 10^th, 2005, 2:13pm

At present I have a conventional oil-fired boiler, hot-water tank, etc. Everything is gravity-fed from a cold water tank in the loft which, in turn, receives water directly from a reservoir (i.e. no mains water). Water pressure is low as it enters the house.
As part of a kitchen redevelopment my plumber suggests completely removing the existing system, except for the cold water storage tank. He then suggests I install a booster pump at the 'mains', to feed a combi-boiler. I would then get pressurised cold water to all outlets from the pump and pressurised hot water from the combi. A thermostatic mixer is planned to prevent unpleasant surprises in the shower.
Keeping the cold water tank is meant to provide a standby supply for taps, toilet, etc. in the event of electrical power failure (not uncommon in the country).
I have been given conflicting advice by 'armchair experts' so, before I commit myself to relatively expensive modifications, does this plan sound reasonable to you?
Thanks.
Stressed

IP Logged

billythekid Trade Member Offline I love YaBB 1G - SP1! Posts: 3402 Total Thanks: 0 For This Post: 0 Trade: Plumber	Re: Combi boiler & booster pump? Reply #1 - Jun 10^th, 2005, 7:30pm you cant pump the mains, not allowed. btk
Back to top	IP Logged

supersparky Administrator Trade Member Author Offline Posts: 6097 Total Thanks: 3 For This Post: 0 Gender: Trade: Electrician	Re: Combi boiler & booster pump? Reply #2 - Jun 10^th, 2005, 7:45pm reckon he means pumping from the tank in the loft? hence hes keeping it.... pump from there to get a pressurised supply? maybe? if he was intendingto do that its ok aint it? aslong as tanks big enough ? ss
Back to top	IP Logged

billythekid Trade Member Offline I love YaBB 1G - SP1! Posts: 3402 Total Thanks: 0 For This Post: 0 Trade: Plumber	Re: Combi boiler & booster pump? Reply #3 - Jun 10^th, 2005, 8:10pm on re-reading it i reckon you are right! lol. sure pump it, why not, just make sure your reservoir can supply your tank. also, how would this "emergency supply" bypass the pump? I see no problem with boosting tank water, we often do it for showers... btk
Back to top	IP Logged

thescruff Global Moderator Trade Member Author Offline Who said plumbing was easy. Posts: 6037 Total Thanks: 147 For This Post: 0 Gender: Trade: Plumber	Re: Combi boiler & booster pump? Reply #4 - Jun 11^th, 2005, 2:04am Better still have an unvented cylinder installed and pump that from the tank, cold can be connected to the balanced pressure valve.
Back to top	IP Logged

CWatters

Super Member

Offline

"Daddy fick it" says James

Posts: 5150

Total Thanks: 58
For This Post: 0

Gender: male

Re: Combi boiler & booster pump?
Reply #5 - Jun 11^th, 2005, 10:22am

I don't think I would swap a conventional boiler for a combi but perhaps they've improved since I last lived in a house with one.

I did the sums (below) and calculated that it takes around 35KW to heat 20L/min of water from 10C to shower temperature. That's some boiler. If you need more than one shower or a shower and a washing machine then it seems a H/W tank is needed to provide a reservior of heat for the peak demand flow.

This is how the numbers went...

I believe an average shower uses upto 20 liters of water per minute at about 35C. So we can easily work out how big a heater you need...

Assume the water starts at say 10C in Winter. This means the heater needs to raise 20 L by 25C in 1 min.

The equation needed is..

Q = cmT

where
Q = Energy
c = specific Heat of water
m = mass
T = Temperature rise

Now power = energy/time so

Power = Q/t

where t = time in seconds so

Power = cmT/t

Google says:
C= 4.2 Joules/gram C or about
= 4200 J/L C

and we can assume 1L of water = 1KG so

Power (in Watts) = 4200 x 20 x 25 / 60

= 35KW !

eg a decent 20L/Min flow would need a 35KW heater!

Or put it another way a 7KW shower heater can only manage a wimpy flow rate of 22 x 7/35 = 4.5 L/Min

If my numbers are right that explains why you never get as much water out of a 7KW electric shower heater.

« Last Edit: Jun 11^th, 2005, 10:30am by CWatters »

IP Logged

Lectrician

Administrator
Trade Member
Author

Offline

Ask The Trades
Posts: 8814

Total Thanks: 109
For This Post: 0

Braunton, North Devon
United Kingdom
Gender: male

Trade: Electrician

Re: Combi boiler & booster pump?
Reply #6 - Jun 12^th, 2005, 10:11am

I have seen a house with 4 combies installed!

One for the kitchen/util, one for an annex, one for the main bath and 1 ensuite, the other for the other ensuite!

two are in the airing cupboard, and two are in the utility. HUGE gas pipe!! (does do the pool boiler aswell!)

Plumber reckoned it was more economical this way, as the boilers where close to the supply points, and no wasted hot water.

Also seen a huge boiler heating several tanks via stats and valves in different areas of a house.

Need to post a picture? Click HERE for info!

IP Logged

scotspark Trade Member Offline mmmmm it's gonna cost you!! Posts: 3074 Total Thanks: 10 For This Post: 0 scotland Scotland Gender: Trade: Electrician	Re: Combi boiler & booster pump? Reply #7 - Jun 12^th, 2005, 12:07pm to save the problem of wasted hot water could he jus not have had an unvented hot water cylinder with a secondary return on the hot water with a bronze pump??????????????????? thats what i have wired up for the plumbers in the large houses i have done
Back to top	brown to red and blue to f****&&&&ommited!!!!!!!!!!!!!!!!!!!!!!!!!!! IP Logged

Lectrician Administrator Trade Member Author Offline Ask The Trades Posts: 8814 Total Thanks: 109 For This Post: 0 Braunton, North Devon United Kingdom Gender: Trade: Electrician	Re: Combi boiler & booster pump? Reply #8 - Jun 12^th, 2005, 2:46pm I have done similar - but you need to lag the pipes well - otherwise you have underfloor heating I don't question plumbers - just whack in the cables Some plumbers just love combies, other just love cyclinders! Just as some love copper and other plastic!!
Back to top	Need to post a picture? Click HERE for info! IP Logged

stressedout

GDPR opt-out

Total Thanks: 109
For This Post: 0

Re: Combi boiler & booster pump?
Reply #9 - Jun 12^th, 2005, 7:57pm

Hiya. Thanks for the responses so far. Actually I have been offered two solutions by different plumbers.
One is as described above - to fill the CW tank from the mains and then pressurise it to the boiler. From the responses, I guess this is OK as long as the tank is big enough.
The other suggestion is to pressurise the water just after it comes into the house. I hear what you say about not being allowed to pressurise directly from the mains, but this is a gravity-fed system from a local reservoir (a well, if you like) down a LONG pipe under my neighbour's field - hence the low pressure. Would it still be illegal to boost this? Even if it is legal, would it work?
Does it make any difference that I am in Scotland?
Thanks (sorry if the questions are stupid)
Stressed.

« Last Edit: Jun 12^th, 2005, 8:02pm by stressedout »

IP Logged

billythekid Trade Member Offline I love YaBB 1G - SP1! Posts: 3402 Total Thanks: 0 For This Post: 0 Trade: Plumber	Re: Combi boiler & booster pump? Reply #10 - Jun 12^th, 2005, 8:06pm if the main is yours alone then its not the water main from scottish water and you can do pretty much what you like to it, make sure there's plenty of water in the reservoir tho! lol Quote: Does it make any difference that I am in Scotland? makes all the difference in the world m8 btk
Back to top	IP Logged

stressedout GDPR opt-out Total Thanks: 0 For This Post: 0	Re: Combi boiler & booster pump? Reply #11 - Jun 12^th, 2005, 9:16pm G'day Billy But would it work? ??? Stressed. P.S. I pay Council Tax for the water supply, so I guess your first response stands.
Back to top	IP Logged

Pages: 1

(Moderator: thescruff) - (Moderator Group: Board Moderator)

< Previous Topic | Next Topic >

Ask The Trades › DIY Forum › Plumbing Questions › Combi boiler & booster pump?