Baxi Duotec 40 vs Vaillant 837

ed110220

What is your central heating demand? That Vaillant is a big boiler, the minimum CH output is 12 kW.. that is more than the maximum CH demand of my average 3-bed semi. Do you really need such a high output, as oversizing a for CH boiler is inefficient as it makes the boiler fire up, switch off, fire up etc when a more appropriately sized boiler would run continuously at the lower level.

A bit like two people could drive between two places in the same length of time, the one racing along for a while and then stopping every so often and the other driving continuously at a moderate speed.

Ed

diywhynot

ed110220 wrote: »

What is your central heating demand? That Vaillant is a big boiler, the minimum CH output is 12 kW.. that is more than the maximum CH demand of my average 3-bed semi. Do you really need such a high output, as oversizing a for CH boiler is inefficient as it makes the boiler fire up, switch off, fire up etc when a more appropriately sized boiler would run continuously at the lower level.

A bit like two people could drive between two places in the same length of time, the one racing along for a while and then stopping every so often and the other driving continuously at a moderate speed.

Ed

The Vaillant and Baxi boilers mentioned by the OP are combis, modulate and are sized for DHW demand. Useful boiler jargon guide here.

ed110220

diywhynot wrote: »

The Vaillant and Baxi boilers mentioned by the OP are combis, modulate and are sized for DHW demand. Useful boiler jargon guide here.

Indeed, which means unless the house is large and/or poorly insulated or the inhabitants are used to Singapore it's high minimum CH output will mean its operating less efficiently as it's oversized for the CH. This may be a necessary compromise if there is a high DHW demand, but one should at least be aware of the downside as many people just think the more hot water it can heat per minute the better.

330d

diywhynot wrote: »

And how did that go?

His opinion was the current boiler should be sufficient for the property and the flow rate problem is due to plumbing problems I may have.

He did a flow rate test on an outdoor tap and it was over 28 litres per minute. Don't know the exact figure as his scale only went to 28. He then tested a the kitchen and bathroom cold tap and was only getting around 11. The hot water was even lower at 6.

As the boiler should have a hot water flow rate output of 11, he reckoned its a plumbing issue with the pipes.

diywhynot

ed110220 wrote: »

Indeed, which means unless the house is large and/or poorly insulated or the inhabitants are used to Singapore it's high minimum CH output will mean its operating less efficiently as it's oversized for the CH. This may be a necessary compromise if there is a high DHW demand, but one should at least be aware of the downside as many people just think the more hot water it can heat per minute the better.

OP says

it's a 4 bedroom house with 2 bathroom and 13 radiators.

What do you think the heat requirement would be?