New CH system underpowered/ wrong layout?

[SimonG]

To the op.

Just as an example, measure a room (length x width x height) and measure the radiator and the type of radiator and let us know.

 

[chris watkins]

Thanks vern, don't know much about WB (only that they are hard to work on LOL) much easer to have these adjustments on a combi rather than heat only but still it must have an effect if/when the heating load is so low doesn't it ?

 

[vern]

To the OP, I would be 90% certain your rads are undersized, probably due to installer using an heat pack from his suppliers, which limits the outputs of radiators before you pay more! At £7K you should be sweating!

 

[vern]

Thanks vern, don't know much about WB (only that they are hard to work on LOL) much easer to have these adjustments on a combi rather than heat only but still it must have an effect if/when the heating load is so low doesn't it ?

You can do this on all CDI range heat only and system and obviously combi, but you have to know what you are doing, I spent a day learning this alone, the pump can even be adjusted to suit micro / mini bore systems too obviously not heat only in this respect.

Never had trouble with low loads, as said if all parameters are set up correctly, if you are pushed you can fit an ABV across flow and return, to balance load, never had, always managed, using the 2 level installer menus.

 

[Alex100]

I have said it before but here goes COMBI'S ARE EXEMPT FROM WHOLE HOUSE HEAT CALCS!.......
due to many reasons but the main one is that their outputs are based upon hot water production, obviously this should be matched to incoming mains water pressure and gas runs from a responsible installer but often are not!

To get round this good manufactures get round this by allowing range rating.

Worcester bosch get around this on the junior and Si with a code plug that down rates from 24kw to 12 kw, the CDi can be adjusted from 30kw to around 9 kw on 38 and 42 CDi and 30 kw to 7 kw on 29 and 34 Cdi (this can only be accessed via installer menus, I am not posting how as the menu contains all stuff that should not be touched unless you are trained by WB, pump maps, turbine delays, and much more!

the 38 Cdi is actually 40 kw on DHW NOT 38 marketing bluff as not to pull sales from 42 cdi

i actually look after some trendy apartments that have 42cdi's and 2 rads and a towel rail! 42 kw for hot water due to silly sized baths!

Very interesting. Does this mean just the heating output and not the hot water heating rate can be downrated?

 

[chris watkins]

Very interesting. Does this mean just the heating output and not the hot water heating rate can be downrated?

Yes ......

 

[vern]

Very interesting. Does this mean just the heating output and not the hot water heating rate can be downrated?

Correct get your installer back......

 

[Alex100]

Many many thanks to all those helpful posts - and good to see people enjoy what they do too. In response to request for sizes, here are room sizes.


Room size examples:

Lounge - 3.45m x 4.25m x 2.5m high, two external walls of 18inch stone & rubble, 3.2m of double glazed and draughtproofed sash, timber floor with space beneath. In here he has placed a Stelrad K2 compact (450 x 1200mm) which gives about 5615 BTU

Dining - 3.45m x 4.2m x 2.5m high, one external wall, one single glazed window into the conservatory (so not really a window). In here a compact stelrad K2, slightly smaller, 450mm x 1100mm, giving about 5100 BTU

Kitchen - I wanted to get a rad and the installer didn't calculate what I'd need. I got a vertical semi designer thing from B&Q (i know, i know, but it was a weak moment) giving 2800 BTU. Looks alright but gurgles if turn TVR up beyond 3. Kitchen is 2.7m wide x 5m long x 2.2m high, one small double glazed window, one external wall (short side) and one wall has a door and window into the conservatory (antarctica).

Conservatory - a few installers who quoted suggested not trying to fully heat the conservatory but I though to put something in at least to take the edge off the cold. I suggested something under the interior window, so he put Stelrad K2, 300mm x 1500mm giving 5026 BTU. It's 2m x 5m long, and over 3m on high side. Also, that rad is teed off the dining room rad flow & return, not from the main flow/return circuit.

Hall & upstairs landings - incl stairs it's about 15 to 16 m long (horizontally) x 0.9m wide x 2.5 m ceiling. No outside walls (just party walls) or windows. There is one K1 downstairs (600mm x 11000mm = 3678 BTU) and one upstairs (600mm x 900mm giving 3009 BTU)

Master bed - 4.35m wide x 4.2m long x 2.4m high - he put in a K2 600 x 1000mm long, giving 5910. There are two external walls, like lounge, and three single glazed sashes but all secondary glazed so no draughts. There is about 75mm of loft insulation.

2nd bed - 2.55m x 4.2m x 2.4m high. Rad is K2, 450mm x 1100mm = 5100BTU. Two outside walls, one double glazed window, roof space insulated with 75mm insulation.

Bathroom - installer was arguing that I asked for a towel rail which he pointed out isn't as powerful as a panel radiator. I pointed out I never told him how big to make the towel rail! He installed one 500mm x 1200mm giving only about 1400 BTU. Bathroom is about 2.7m x 2.3m x 2.2m high, two external walls, one double glazed window.

Study - small room about 2.2m x 1.7m x 2.2m high. No radiator, just the boiler. One small dg window, one external wall.

That's it, so about 37600 BTU of radiators in house. Sounds like I need ask if he limited the boiler heat output yes?

 

[Alex100]

Hi Steve and others who can advise on the flow/return circuit

So just having two pipes to all rads is good enough? I expected to see two pipes passing close to every rad, and then tees going off to the rad from the circuit, one to each end of rad. As some of these branches/tees are 2 to 8 metres long (the flow/return circuit not coming near some rooms even), and one or two have a second radiator teed off mid-way, I was a bit worried the system may have curious eddies/turbulence and be difficult to balance.

Can I at least forget about this issue and not be expecting to see a nice two pipe circuit flowing round the house? It looks more like a set of long branches from a limited ring main.

 

[Alex100]

Is the boiler continually turning on and off while the house is heating up?

Did the installer measure the incoming cold water flow rate and dynamic pressure before recommending a 38kW boiler?

I haven't checked that. Do I need to just listen to the boiler? I assumed it would turn off every few minutes whilst the hot water pumped round, then come on again. What am I looking out for?

I asked for adequate hot water and he specified a 37CDi - I pointed out that had been discontinued and replaced with a 38CDi, which I said I presumed he would then get. He never mentioned matching a boiler size to house size, and I doubt he did that measurement - would it be in my commissioning booklet?