Vaillant 637 + 180l Unistor

[ln1234]

Would like some advice on the following choice of boiler + unvented cylinder.

Vaillant 637 + vr65 / vrc430 controller
Vaillant Unistor 180L

We have a 3 bedroom house with 1 (soon to be 2) bathrooms, and 2 adults + 1 child living here. The flowrate on an open pipe is 26 litres per minute, and at a tap is 19 lpm

My thoughts for going with the 637 + 180L cylinder are to have a quick reheat time, and not store too much hot water that might sit there for ages if we don't use it. 180L seems like a good compromise, and I calculated this as follows (hope my maths isn't wrong):-

180L stored at 65 degrees + 180L cold = 360 litres blended hot water available (50:50 ratio at shower)

approx 20 litres per minute available, which means 18 mins showering before hot water depleted

Whilst hot water is depleting, reheat time for 70% of the cylinder is approx 21 mins at 37kw, which means that after 18 mins 50-60% of cylinder is hot, and another 10 mins or so of showering available

And so on

So in all, we could have continuous hot water of approx 30-35 mins at 20 litres per minute.

Does this sound right? What do you think of the 637 + 180l combo?

Cheers

 

[gas4you]

I don't think you will have any problems with this set up.

I've fitted the 637 with the 260 litre cylinder in a large house and it has always been very good.

 

[ln1234]

I don't think you will have any problems with this set up.

I've fitted the 637 with the 260 litre cylinder in a large house and it has always been very good.

Thanks

I think the boiler is oversized slightly, but the house is solid brick rather than cavity so heat loss is probably more than it should be. I've read some comments about the 637 only being able to modulate down to 12kw - we have 9 rads so I hope it's still efficient.

 

[cider]

You dont need 37k of heat in you home even if you walls were paper thin.
Size it up on line (google boiler sizing) and enter you house info.
If the 637 can only modulate down to 12 kw it wont like your system when its hot.
I bet a 618 will heat your place easily and more efficiently plus you probably wont need a new fas feed.

 

[ln1234]

You dont need 37k of heat in you home even if you walls were paper thin.
Size it up on line (google boiler sizing) and enter you house info.
If the 637 can only modulate down to 12 kw it wont like your system when its hot.
I bet a 618 will heat your place easily and more efficiently plus you probably wont need a new fas feed.

I just did the sedbuk calculation and it came back with a figure of 22.9kw. So that means I can use a 24kw vaillant boiler? Is there any harm in oversizing it for future expansion and faster coil heat up times?

 

[mickyg]

the coil won't take much more than 15-20kw so no point going bigger. a 24 kw boiler will cope with about 15 rads on most systems quite comfortably. Going bigger will only reduce efficiency. Small is best, right on the limit