I have been trying to fathom out the (presumably deliberate) lack of parameters to actually size a boiler under the new part L regs. At the moment these absurd guidelines say such ambiguous and vague comments as : boiler is not “significantly oversized” can modulate down to the “typical heating load of the building” and the boiler set to “match the calculated heat loss”
Well the last reg is not so bad and I assume it removes any boiler that can’t be range rated? Is this goodbye to the Ideal Logic boiler? You can’t range rate a Logic so I suppose it does. What are the house builders gonna use now then?
As to the other two phrases
I have scoured dictionaries encyclopaedias thesaurus & Wikipedia to try to get definitive meanings for words like “significantly” and “typical” in some sort of engineering capacity but to no effect. I can only think these ill-defined words have been specifically chosen to render these regs meaningless so it would be impossible to confirm if you had complied or not? Sadly these words have not come from politicians (who never want to be held accountable at the best of times) but from the tall forehead brigade with Engineering degrees. Why is that?
I live in the Midlands. I have googled the weather data for the last year.
If I add up all the average low temps for the 8 heating months it comes to 49 so then divide that by the number of months (8) it averages out at about 6 degrees. That’s an average winter temperature.
Let’s take an ordinary bigger house with a heat loss of 7Kw, at an outside temperature of -2 degrees (no ordinary new build is anywhere near this) and work out what the heat loss is at the “typical” heating load at outside temperature of 6 degrees.
This is a spread sheet using the Cibse method of heat loss
At the average or ”typical” temperature of 6 degrees, the house requires (what we have to assume is) the “typical Heating Load “of 4.6Kw.
At last, – some sort of figures to work with. But – – – this means the poor old Ideal Logic combis (and the many many other top brand names that have minimum outputs much higher than 4.5Kw) will now not comply with the new regs in the vast majority of properties.
All normal new builds have a much lower heat demand than 7Kw so are we going to see the launch of many new low modulation boilers? (Not before time but no chance really)
Looks like Baxi may have a serious problem complying as they have nothing small enough?
Baxi200C=5.2Kw Baxi200H=7.5Kw Baxi300C=5.2Kw Baxi400C= 5.2 Kw Baxi400= 7.5Kw Baxi600C=6.7Kw
Some other big brands that will struggle WB29cdi-7.4Kw WB Highflow=7.4 GW Energy=7.2Kw Ideal logic=7.1 Valliant EcoFit=6.1 Valliant EcoTecplus=5.8 to name a few.
An interesting side note to this – many of these boilers will be replaced by a ASHP with a MAXIMUM of 6Kw ( and that will also provide the hot water)
For those who may not fully grasp heat loss (required now in the new Part L) here are the figures for a typical 1970’s 4 bed house.
As you can see this 1970’s Four Bed needs about 5Kw at -2 degrees. Applying the same logic (no pun intended) to this property as the original one, the typical heating load would be about 3.5Kw @6 degrees leaving all but a few boilers compliant? Namely the V200, 100 & 050, Intergas X range, Vokera Alpha Ravenheat (honest!) WB 4&8000 & Ideal Vouge. Boilers that can achieve these low minimum outputs are not necessarily expensive either.
Is the era of the ‘bonfire in a box boiler’ coming swiftly to an end?
For boilers like the Logic 35 combi and Baxi 600C with a minimum output of around 7Kw you can work the figures back, to say it isn’t suitable to fit these type boilers into any dwelling with a heat loss at design temp of 11Kw or less. This is a large property, probably in the top 10% of all houses , before we can actually fit these old dinosaur boilers within the requirements of Part L.
To conclude. Let’s say I am fitting a new system into the 1970’s 4-bed house exampled above. I do a heat loss with proper heat loss software like http://heat-engineer.com/ Proof enough that I have complied so far. I then fit Logic Baxi 600 or similar type boiler where do I stand? Is it legal & compliant or not? If the Building inspector got involved (always good for a laugh) could I be sued for ‘not fit for purpose’ & non-compliancy?
I haven’t even started on what part L would determine as a “significantly oversized” boiler but maybe at least the days of fitting 35kw boilers in to two bedroom flats is nearly over.
Maybe I have got it all wrong but It’s a fair enough question, I think?
Lets see if I get a black & white answer from the Part L brigade.