2 Quotes for new heating - what option should I choose - advice appreciated

[stardanny]

You really need to check the working pressure and the flow litre per minute of incoming water main before making decisions on which system is best.

IMO, you be better off with water tank, cylinder and sealed heating system.

Daniel.

 

[Agile]

Hot water heating should be timed to be for 30 min before heating start times so the full boiler output is available to reheat the cylinder.

The full heating power of 15 kW is only required when the temperature is at -1 C outside. That's usually only a couple of weeks in the year. For most of the time there is plenty of excess power available for water heating whilst delivering central heating.

 

[hztm2008]

Neither the independent heating engineer or BG engineer properly checked the incoming water supply. The independent did turn on the kitchen tap and say that should be fine.

I have just run off 5l in to a bucket from the kitchen cold tap and it took around 18-19 sec so I guess this makes the flow rate around 16l per minute but I have no way of checking the pressure. Would the flow rate sound ok for the combi or unvented cylinder suggested. Many thanks for all the help.

 

[DP]

Hot water heating should be timed to be for 30 min before heating start times so the full boiler output is available to reheat the cylinder.

The full heating power of 15 kW is only required when the temperature is at -1 C outside. That's usually only a couple of weeks in the year. For most of the time there is plenty of excess power available for water heating whilst delivering central heating.

So what happens when heating is on and cylinder has no hot water
If the cylinder needs 24kw, I cannot understand why you would underspecify

It is like boiler needs a 28mm gas line, but you feel it will could be 22mm because full loading will be rare

How can you have excess power when cylinder needs 24kw and you only have 15+ 3kw?

 

[MJGas]

So what happens when heating is on and cylinder has no hot water
If the cylinder needs 24kw, I cannot understand why you would underspecify

It is like boiler needs a 28mm gas line, but you feel it will could be 22mm because full loading will be rare

How can you have excess power when cylinder needs 24kw and you only have 15+ 3kw?

Also depends if Tony balances the cylinder to only recieve 3kw

 

[Doggit]

I have just run off 5l in to a bucket from the kitchen cold tap and it took around 18-19 sec so I guess this makes the flow rate around 16l per minute but I have no way of checking the pressure

As the Vailant 830 is rated at 13Ltrs per minute, then that would be fine, but as I said earlier, you're better off comparing against the current electric shower, which I suspect is about 9litres/minute. Water prices are only ever going to increase, but you may well be looking forward to a great shower.

If the cylinder needs 24kw, I cannot understand why you would underspecify

Where did the figure of 24Kw come from; an Ariston 210Litre cylinder is rated at 3Kw

 

[Roger928]

I think he means the coil heat exchanger is rated @24kw. Which would be from cold.
Most cylinders begin the reheat at a higher temp thus extracting less energy from the boiler and tailing off as the cylinder reaches set point.

 

[Doggit]

I think he means the coil heat exchanger is rated @24kw. Which would be from cold.

As a lot of system boilers are only 24Kw, I suspect someones got confused somewhere along the line.

 

[Agile]

Neither the independent heating engineer or BG engineer properly checked the incoming water supply. The independent did turn on the kitchen tap and say that should be fine.

I have just run off 5l in to a bucket from the kitchen cold tap and it took around 18-19 sec so I guess this makes the flow rate around 16l per minute but I have no way of checking the pressure. Would the flow rate sound ok for the combi or unvented cylinder suggested. Many thanks for all the help.

That's the mistake that so many plumbers make.

But it is the open pipe flow rate with no significant pressure in the pipework.

To use a shower you need a residual pressure in the pipework of about 1.0 bar to produce a nice high velocity shower to give that nice tingly feeling on your back.

A combi boiler also can have a significant pressure loss through the heat exchanger.

The only measurement which is useful is the dynamic flow rate which leaves say 1.0 bar pressure in the pipework.

Tony

 

[MJGas]

As a lot of system boilers are only 24Kw, I suspect someones got confused somewhere along the line.

Aint no confusion on DPs part. A lot of cylinders have large coils in now.

Google has failed you as a 210 litre "indirect" cylinder has a 27.2kw coil.

Worcester have one as large as 38kw in there 300 litre cylinder.

But what Ill do is allow 10kw for a large modern house. And +3kw for the hotwater and **** the reheat times on cylinder. Because @Agile says 3kw is adequate. And Ive been making so many mistakes before.

 

[Doggit]

It wasn't Google that failed, it was my eyesight. 3KW was the immersion rating so sorry guys, I have to apologise for that. I need to look in to this further.

 

[Steelmasons]

Hey Agile , unless I'm mistaken was it not you that recommended a heat load of 2kw for hot water cylinder?...it appears you've moved the goalposts and now recommend a heat loading of 3kw?....could you explain?

 

[DP]

As the Vailant 830 is rated at 13Ltrs per minute, then that would be fine, but as I said earlier, you're better off comparing against the current electric shower, which I suspect is about 9litres/minute. Water prices are only ever going to increase, but you may well be looking forward to a great shower.

Are you sure electric shower produces 9l per minute or do you think it does. Is that seasonal or consistent throughout the year?

 

[DP]

The only measurement which is useful is the dynamic flow rate which leaves say 1.0 bar pressure in the pipework.

Let us say I am a 10 thumb plumber, how do you go about doing what you say in above quote from your good self

 

[bernardgreen]

Google has failed you as a 210 litre "indirect" cylinder has a 27.2kw coil.

27.2 kW coil ? Does that imply it will transfer 27.2 kW into the water in the cylinder ? At what delta T is that measured ?. ( delta T being the difference in temperature between the water in the cylinder and the water circulating through the coil ). Quoting the value to 1% ( 0.2 in 27 ) requires similar accuracy in the details of when that performance is achieved