Increased Combi KW size vs running cost

ThisIsWeird

Torque79 said:

Thank you for taking your time to respond.  

1 adult (he says!) in a semi-detached, 2 bed, 1 bath (no shower but shower mixer on taps), 2 sink (kitchen / bathroom)
Glow worm F55 conventional boiler with cylinder and loft tank,
9 radiators (2 very small, 1 very small double, 4 small, 1 long, 1 long double)
Only gas appliances are the boiler and the cooker. 

Currently CH upstairs however no CH downstairs (somtimes one rad has a little warmth) and HW is intermittent!  


From the engineers that have been suggestions are: 
"replace air vent on cylinder + new pump and may need new valves won't know till start OR Main 30kw or baxi 30kw" 

"change pump (I believe re-balancing as well) OR Main 30kw or Baxi 30KW"

"Main 30kw or Baxi 36kw" 

The flow rate has not been checked by an engineer.  

In your house, I'd settle for a 30kW combi, if combi is the route you are taking. That's what I have in a 3 bed, 3 bathroom house. Yes, if someone runs a tap/flushes a loo during a shower, it affects the flow a great deal, but a thermostatic mixer should prevent shivers and scalds. Other than that, it gives a great shower.

But, if you are happy with the performance of your current setup, and the small mods suggested by the plumber will keep the cylinder going, then I think I would stick with the system you have, and just go for another heat-only boiler. Cheaper, guaranteed results, and you retain the cylinder and its plumbing, ready for upgrading in the future to suit PVs or a Heat Pump.

Any chance of a photo of the current cylinder?

BikingBud

ThisIsWeird said:.  

In your house, I'd settle for a 30kW combi, if combi is the route you are taking. That's what I have in a 3 bed, 3 bathroom house. Yes, if someone runs a tap/flushes a loo during a shower, it affects the flow a great deal, but a thermostatic mixer should prevent shivers and scalds. Other than that, it gives a great shower.

In this day and age why would anybody install a system that performs likes this?

FreeBear

Torque79 said: Heat Pump - I have just been reading / watching a video about them:
Ground HP: seems to be very expensive and compromises land as you can't then build on-top, there is a bore-hole option which is even more expensive.
Air HP: seems to be the more financially viable option but then your home needs to be efficient re no draughts. 
Conclusion: HP are for new build homes where they are designed with HP in mind and not for old draughty homes.  

GSHP - If you go for a ground collector (slinky), you need lots of land and it needs some serious trenching (typically, 2m deep). If the coils are not deep enough, the winter frosts will lower the amount of potential energy that can be collected. And as you point out, the land can not be used for building on. Boreholes require less space as long as you can get a drilling rig in - I would have thought there isn't much difference in cost between boreholes or slinkies.

ASHP - The efficiency drops when the air temperature drops which is when you need the heat inside.

Both air and ground need larger radiators and/or UFH so that you can actually heat the property. Adding extra insulation and killing the draughts reduces the amount of heat required, so you can get away with a smaller heat pump. But even with a conventional gas/oil boiler it still makes sense to insulate & draught proof as best you can.

ThisIsWeird

BikingBud said:

ThisIsWeird said:.  

In your house, I'd settle for a 30kW combi, if combi is the route you are taking. That's what I have in a 3 bed, 3 bathroom house. Yes, if someone runs a tap/flushes a loo during a shower, it affects the flow a great deal, but a thermostatic mixer should prevent shivers and scalds. Other than that, it gives a great shower.

In this day and age why would anybody install a system that performs likes this?

Well, in my case it was because we'd had a loft conversion, and lost the cylinder space. And the flow issue is a very minor and temporary hindrance - the combi performs really well.

NannaH

You don’t need a 30kw in a 2 bed, we have a 28kw in a 3 bed, one bathroom,  pressure is brilliant for the shower off the bath taps.  My Daughter only has a 32kw in a 4 bed with 2 bathrooms.
Baxi, Vaillant or Worcester Bosch are all good and easy to fix,  parts aren’t extortionate and they have good warranties.   Just make sure your rads are flushed prior to new boiler fitting,  makes all the difference,  doesn’t have to be a power flush,  buy a bottle of fernox etc.  stick it in and leave for a week or two then drain the system,  the crap that will come out is unreal.  

BikingBud

ThisIsWeird said:

BikingBud said:

ThisIsWeird said:.  

In your house, I'd settle for a 30kW combi, if combi is the route you are taking. That's what I have in a 3 bed, 3 bathroom house. Yes, if someone runs a tap/flushes a loo during a shower, it affects the flow a great deal, but a thermostatic mixer should prevent shivers and scalds. Other than that, it gives a great shower.

In this day and age why would anybody install a system that performs likes this?

Well, in my case it was because we'd had a loft conversion, and lost the cylinder space. And the flow issue is a very minor and temporary hindrance - the combi performs really well.

??

"It affects the flow a great deal"
 
and

"The flow issue is minor"

Don't you just love subjectivity  

ThisIsWeird

BikingBud said:

ThisIsWeird said:

BikingBud said:

ThisIsWeird said:.  

In your house, I'd settle for a 30kW combi, if combi is the route you are taking. That's what I have in a 3 bed, 3 bathroom house. Yes, if someone runs a tap/flushes a loo during a shower, it affects the flow a great deal, but a thermostatic mixer should prevent shivers and scalds. Other than that, it gives a great shower.

In this day and age why would anybody install a system that performs likes this?

Well, in my case it was because we'd had a loft conversion, and lost the cylinder space. And the flow issue is a very minor and temporary hindrance - the combi performs really well.

??

"It affects the flow a great deal"
 
and

"The flow issue is minor"

Don't you just love subjectivity  

Just about as much as I like 'olery.

The flow is affected a great deal at these limited times, but the resulting issue is not a biggie.

Of course, you know this.

Torque79

plumb1_2 said:

Torque79 said:

change vent on cylinder 

do you have a small header tank in your loft?

If not and there’s a small vent on the cylinder, you’ll have a primatic cylinder.
If your gonna upgrade then fit a indirect cylinder if using heat only boiler 

There is a tank in the loft, F&E? I am not sure on size.  
I can't locate a vent on the cylinder but there appears to be a vent of sort on the pipe flowing into the cylinder. 

Torque79

I got a flow rate cup...

cold kitchen sink tap - if I turn it open on sensibly it is about 12l per minute, however if open fully it just splashes everywhere, probably way more than 15l per minute.  

The water stopcock tap is 1 full turn clockwise from fully open, is this correct? 
thanks.  

ThisIsWeird

Your flow rate sounds 'adequate'. A 30kW combi should be fine with this, delivering a full DHW rate, with some cold in reserve - you'll be using both in a shower, for example.

Yes, your mains stopcock sounds correct, essentially fully open, but given a turn towards close to help prevent it from seizing. It will be effectively fully open.