New boiler, new radiators

[danoid]

hello,

Bit of background info, got a small 2 bed house, 1 bathroom and 8 radiators. Conventional ideal classic boiler with hot tank and cold tanks in loft

all our radiators and the boiler is the original since circa 1991 although its chugging along fine, we want to do a complete refresh as sick of "do you want hot water tomorrow morning?" Yes we can upgrade to a proper programmer but its not going to last forever

Question 1, ive seen a combi boiler i quite like. Its a worcester greenstar 42cdi, which is going to be massively over spec, but its got high water output for showers and our mains water pressure & flow seems powerful but not measured. We'd probably go into the loft at some pointer so will add 3 more radiators and most likely an en suite so ive taken this into account with the beasty boiler.

Are there any negatives to having an over specced boiler? Other than costs? (looks like its only £1500-1600 anyway) In my mind its like buying a bigger engined car, probably wont need the power but if i do i know ive got it.

We'd be changing all the radiators from single radiators to the type 22.

The kitchen doesnt have a radiator, it use to but when the extension was built, they put in more kitchen units and the pipes behind some units (done before we moved in)

In the extension (kitchen doesnt have a full wall leading to the extension, kinda round arch where you walk then another arch over the worktop) theres a radiator probably 600x1200 single radiator which heats both rooms or tries its hardest as walking from the front room into kitchen you can feel probably 5-6 degrees difference.

So im thinking big solution, one of those beasty type 33 radiator, 600x1800.

Would that be enough to heat both rooms? Roughly 8m long by 4m wide, but the radiator is in the extension.

The only problem I see is the dining table is quite close to the radiator and I could imagine sitting next to it and basically turn into human scratchings!

I'm not rulling out fitting a radiator in the kitchen but where it'll go will be basically 600x600

 

[danoid]

Also the 2 original radiators down stairs have fairly skinny pipes going to them, measuring left to right is its 10mm.

The one in the extension is bigger so thats okay

Does this change anything in regards to fitting double radiators?

 

[oldbuffer]

1. You need to measure the pressure and dynamic flow rate of your incoming cold supply. You won't get any more flow out of the boiler than the flow going in to it.
2. 42Kw is way over the top for heating. It will modulate down to 9.4Kw, but even that's almost certainly much more than you need once up to temperature. The boiler will keep cycling on and off which is inefficient.
3. You could consider putting plinth heaters in under the kitchen cupboards. Can't tell from your description what size radiator you'd need. (Wall construction / insulation, windows, doors etc.)
4. 10mm pipework is quite limited in the heat it can pass. You need to do the calculation of Kw output of new radiators, and also need to know what feeds the 10mm pipework.

 

[muggles]

Takle the opportunity to increase the size of all your radiators if you have the wall space and you're changing them anyway - it's much more gas efficient to run big radiators at a low temperature than small ones at a high temperature

A 42CDi will use an enormous amount of gas and will be inefficient for heating. Using your car analogy, if you try to drive a high powered supercar through a busy city, you'll find it's really quite difficult to do. The clutch is heavy so you need a lot of revs to get it moving, but this can cause you to lurch forward meaning that you then need to jump on the brakes and possibly repeat the whole manoeuvre almost immediately. If you had a small city car, you'd be able to pull away gently and probably sit in first gear tickover for quite a while with much less braking needed. Result - you're much more efficient and comfortable in your appropriately sized car than one that's way too powerful/you'll be much more gas efficient and comfortable with a boiler sized more appropriately for your heating system. If you have a large hot water requirement, you need a hot water cylinder.

 

[danoid]

Thanks for that and clearing up the overkill situation.

We dont really have a high water need at all, just big dishes every few days and showers every few days (yes were dirty)

Would a greenstar si compact 25 or 30 be good? I was looking at these and we'd be able to hide it behind the cupboard like our existing one, which is nice.

Im just concerned as the boiler is downstairs and shower upstairs the water coming out would be quite weak, so thats why i'm think bigger has more flow so better shower.

Its probably been asked a million times now plus 1, but whats the best way to measure the flow do i need something like this?

http://www.screwfix.com/p/monument-tools-mains-water-pressure-test-gauge/82412

I can do the test and report back

Although i could change all the radiators sizes i dont fancy seeing the expense of lifting all upstairs boards up, especially my bedroom as im not undraining the water bed :0

So i think doubling up to type 22 will do. The house is fairly warm as it is anyway, only had the heating on 6 or 7 times since behinning of december

 

[empty-seat]

Just leave your heating alone then? You hardly use it and everything is working fine. Why are you faffing with all this.

 

[oldbuffer]

While flow and pressure are related, they are not the same thing.

The device you listed would be fine for testing the pressure. It should go on, for example, an outside tap. Close all other taps and open the outside one, and that will give you the static (no flow) pressure. Then open the kitchen tap as well, and that will give you the dynamic pressure (while water is flowing).

To measure the flow rate, you could use a flow cup, but for a one off, the easy way to do it is to time how long it takes to fill a 10litre bucket, then pro rate the figure to litres per minute. For example, if it takes 30 seconds for 10 litres, your flow rate is 10 (litres) x (60 / 30 (minutes)) = 20 litres / minute.

 

[danoid]

Although the boiler is producing good heat and heats the hot water, it doesnt always sound good bit wheezy sometimes and hear loads of bubbles when it fires up for the first time, sounds like its probably got a year or so left

when we go combi we can remove the airing cupboard to make the second bedroom bigger and get room back in the loft for that to be converted too

Does this sound right for measuring flow and pressure?

1. Connect pressure guage to outside tap and write down pressure

2. With guage still attached, turn on kitchen tap and check pressure guage result, dynamic flow?

3. Find a bucket say 15l, and if it takes 1 min to fill up with outside tap then thats 15l per min.

Thanks

 

[danoid]

While flow and pressure are related, they are not the same thing.

The device you listed would be fine for testing the pressure. It should go on, for example, an outside tap. Close all other taps and open the outside one, and that will give you the static (no flow) pressure. Then open the kitchen tap as well, and that will give you the dynamic pressure (while water is flowing).

To measure the flow rate, you could use a flow cup, but for a one off, the easy way to do it is to time how long it takes to fill a 10litre bucket, then pro rate the figure to litres per minute. For example, if it takes 30 seconds for 10 litres, your flow rate is 10 (litres) x (60 / 30 (minutes)) = 20 litres / minute.

Once I have the rates and say for example i have 11l per min.

Would i get the greenstar si compact 25si hot water flow 10.2l per min

Or greenstar 30si hot water flow 12.3l per min.

I know you said earlier my house probably only uses 10kw when up to temp, but the si compacts min is 24, but almost half the monster Initially said, but should be good for adding on 3 more rads plus shower in loft (future dev)