Hi Arran

I'm not HVAC, but I was responsible for the training of "Mechanical" Building Services Engineers, for what was arguably the UK's leading major contractor in the field and historically a pioneer and leader of the discipline. I'm not a member of CIBSE either, but as The former "Institution of Heating and Ventilating Engineers", they would be interested. 

Engineers in training carried out manual heat loss calculations and radiator sizing during the ONC (first year) element, but aslo got a student license for "FACET". I think that this is the successor? https://www.iesve.com/software/ve-for-engineers .  I also seem to recall that "Building Physics" was a key component of CEng Accredited (which ours wasn't) MEng & MSc courses, so their material is out there. I get the impression that errors in the software packages used by design consultants and major contractors have been mostly ironed out? 

Because material is 1950s, or even Victorian for that matter doesn't necessarily make them wrong. Particularly during the post-war period the National College of Heating Ventilating Refrigeration and Fan Engineering, now part of South Bank University carried out much research.  There are also BRE , BSRIA & ASHRAE in the US. 

"Rules of thumb" are often "near enough" for everyday purposes, although it  might be of academic interest to evaluate them against an analysis from first principles. I would have a speculative punt with a pint on it, that the the best Victorian efforts were within 10% of today? http://www.hevac-heritage.org/

The issue here might be expecting an academic answer from a practically trained person. They are operating at different ends of the spectrum. Many smaller Heating Engineers are self-employed plumbers who have learned by experience, perhaps with some formal learning to Technician standard. More sophisticated approaches can probably only be justified on large multi-million pound jobs. I know that it irritates many of a more academic persuasion that they are even allowed to call themselves "Engineers", but they got there first.   

Roy Bowdler:

I would have a speculative punt with a pint on it, that the the best Victorian efforts were within 10% of today? http://www.hevac-heritage.org/

I can believe that because they built things properly back then! The problem is when faced with modernising a 1930s semi that had central heating installed around 1975 with an obsolete back boiler behind a gas fire from the same year and old fashioned single panel radiators. The house could have been upgraded over the years that improves energy efficiency - such as double glazing or thicker loft insulation - and the radiators could have been specified with a low power output as not to overload the boiler or even a suboptimal power output for the room to start with. Chances are that the radiators are in imperial or obsolete metric sizes so new radiators are unavailable in exactly the same dimensions. The replacements might also be double panel or a decorative variety. Therefore trying to match the power output or the physical size of the replacement radiators with the existing radiators is not always a sensible strategy. A replacement boiler can have a higher power output than the existing boiler therefore enabling replacement radiators to also have a higher power output. Older installations generally do not use TRVs so radiators were commonly selected with power outputs assuming only an averagely cold day in order to save energy but were unable to provide enough heat during a big freeze up. The modern practice is to be generous with the power output and turn down the heat with a TRV when full heat is not required. It's quite common for TRVs retrofitted to older installations to be on full power almost all of the time simply because the radiator doesn't provide sufficient heat to enable the TRV to operate on a lower setting.  

The issue here might be expecting an academic answer from a practically trained person. They are operating at different ends of the spectrum. Many smaller Heating Engineers are self-employed plumbers who have learned by experience, perhaps with some formal learning to Technician standard. More sophisticated approaches can probably only be justified on large multi-million pound jobs. I know that it irritates many of a more academic persuasion that they are even allowed to call themselves "Engineers", but they got there first.   

Perhaps if there was better information and better formulas that were widely disseminated then self-employed plumbers can use them to create better heating installations that are sufficiently warm and energy efficient at the same time. Modern day plumbers use websites and apps to compute all sorts of things but the output is only as good as the input data and whatever formula is used.


Even room temperature recommendations haven't kept up with the times. Bedrooms are specified to have a lower temperature than living rooms. The figures might be fine if bedrooms are just for sleeping or occasional use but if kids use them for study rooms, video games rooms, and entertaining friends for hours on end during cold winter days then really they should be as warm as a living room, or else they will plug in fan heaters and the electricity bill will skyrocket!