Boilers - natural gas, heating oil and LPG - what do you need to know?
OK so boilers come in a massive variety of colours (yeah really - I have photos of red, white, orange and rust coloured - well ok rusty - ones), shapes and sizes but for the majority of purposes there are two main types that you need to be aware of - Atmospheric and Forced Draft (or maybe called Pressure Jet) - I'll chat about steam elsewhere - haven't decided where yet!
Atmospheric Boilers are simply those within which the combustion air and flue gases are drawn through the boiler without a fan wheras Forced Draft boilers - you may have guessed - use a fan to boost the combustion gas pressure prior to ignition. Ok it's a very simple analysis and I know - there are low pressure and high pressure boilers, LTHW, MTHW and steam etc etc but let's not get tied up in details.
A boiler is where water gets heated up by a flame derived (usually) from a fossil fuel for distribution round pipework to feed radiators or fan coils or underfloor heating or to a tank for storage or to a heat exchanger for some other purpose.
What a lot of these boilers have in common is inefficiency which is where my interest gets piqued! By the way - one thing that I find all too often and you should watch out for this 'cos it's important - is a failure of boiler engineers to stick the efficiency report on the side of the boiler. Now there are lots of reasons this might be omitted, from simple forgetfulness (yawn!) to outright dishonesty (in other words failure to do an efficiency check at all) but this information is useful and should be available to you, me and anyone else who cares - so ask for it!
Inefficiency I hear you shout - not my boiler! Mine is an all-singing, all-dancing, fully condensing with bells on, optimised and compensated, heat recovered, balanced flued, triple insulated, ideally located, regularly serviced gizmo with in-built XBox 360, SKY TV and tea making facilities! Hmmmmmm, nice - there are some of those out there but most boilers can benefit from some degree of improvement. I mean, take a look at these beauties.......
Whether it is down to lack of insulation, poor servicing, badly set time-clocks, utter lack of sensible control, inappropriate design, over-sizing, under-sizing, failure to split heating and hot water, heat loss from unlagged pipes in the boilerhouse etc etc - the list of potential improvements justs goes on and on.
Here are a few things that you may be able to take advantage of - but may I suggest you speak to me first - on-site.......
| The importance of good maintenance cannot be over-emphasised |
| All combustion equipment is prone to an element of energy loss as not all the energy in the fuel can be effectively used to generate useful heat. These losses can be minimized through robust maintenance. Let's look at a stylised boiler - this bit gets technical so if you don't like details just email me for help. Most of the heat released from the fuel is absorbed by the water in the boiler, but some escapes in the flue gases and some is lost by radiation from the boiler casing of the boiler. The picture below shows the overall energy balance: Energy enters the system as fuel at F units per hour Heat is lost up the flue at S units per hour Heat is lost from the casing at C units per hour U units per hour is the balance of useful energy generated
Flue gas loss is a percentage of fuel input F and the ratio (F-S)/F is known as ‘combustion efficiency’. S is never zero because the flue gases have to be maintained above a certain temperature to ensure the flue functions effectively and to prevent corrosive condensation (condensing boilers are an exception – see below). How high or low the actual efficiency is depends on various factors that affect S, including how well the burner is tuned. Excessively-high exhaust temperature will increase losses because of the exhaust gases carrying more energy away. Excessive exhaust-gas volumes will also waste energy (even if the temperature is OK) and this will occur if the fuel:air ratio is too “lean” – that is to say, if more air is fed in than is necessary for complete combustion. Conversely if too little air is supplied for complete combustion, some unburned fuel will escape up the chimney (as smoke, soot or carbon monoxide depending on the fuel). Damaged burners can cause incomplete combustion even with considerable excess air. Different burners can achieve different efficiencies, but a figure of about 80% - 85% would be typical in a heating boiler. The burner in a condensing boiler can achieve close to 100% because the exhaust gas is discharged at low temperature and latent heat is recovered from the water vapour, in the exhaust. By contrast, a burner on a high-temperature furnace would usually be much less efficient because of the high temperature at which heat is exhausted up the chimney. Correct adjustment of air:fuel ratio, combined with measures to minimise the exhaust temperature (like keeping the boiler internals clean, Figure 2) will between them ensure that the maximum useful heat is extracted from the fuel. This could yield a saving of several percent on boiler fuel, depending on how bad the situation is to start with - perhaps of the order of 20-30% in the worst cases. Moreover, these savings could be achieved at little or no cost since combustion testing and adjustment of burners ought to be part of good routine maintenance. Every boiler maintenance visit should include a combustion test, which can be done by sampling the exhaust gases (figure 3) and its results should be reported. Combustion efficiency can be tested (see typical kit) by taking the following measurements:
If you don't do the tests yourself, you should check that the reported percentage combustion efficiency is consistent with the recorded 'raw' measurements. A spreadsheet is available that can help you do this (download it). It is based on something I did when I was energy manager for a large organisation, and had checked through a batch of test reports from our boiler maintenance contractor to find about half of them somewhat suspect. I went out and did some spot checks with my own equipment, and stumbled over evidence of falsification: in some cases, previous test results were chalked up on the boiler, obviously with the intention of saving the technician the bother or doing a real test next time around. But the most susprising evidence of cheating was that flue-gas tests has been reported on some installations where there wasn't a probe hole in the boiler flue. In summary: poor maintenance of burner equipment will cause avoidable losses. Minimising costs is just a question of getting the maintenance right: and that will only happen if you monitor performance and insist that things are done as they should be. |
"Back in the day" as they say - I used to sell something called the IFC FuelSaver - a clever wee box of electronics designed to cut fuel consumption of indirect fired warm air heaters. We sold thousands of these wee beauties into factories and warehouses and averaged 20% fuel savings across the board - Reznor still fit them to their heaters supplied to B&Q, presumably under some kind of license!
I also sold a clockwork boiler control called the Sigma Economiser until I realised that the sophistication of the IFC unit would offer far more benefits to users and so persuaded the manufacturers (BBC Industries) to build a boiler control using proper fuzzy logic control algorithms and thermistor return flow sensing and again we sold masses of them. It was a great piece of kit that basically inhibited the burner circuit until it was actually needed - as determined by suitable drop in circulating water temperatures. It also spawned many copies and copies of copies until such time as - mid '90's - the market was saturated and BBC Industries closed. The Managing Director - Bob Holman - now sells very good cheese and wine, his own roast coffee beans and extreme chilli hot chocolate! If you are interested email me).
For years now I have been waiting for someone else to take over in this key area of energy efficiency - and I am glad to advise that the time has arrived - now is the dawn of the Boiler Load Optimisation control. What the heck am I on about? Why does a boiler need extra control?
Let's take a typical example of something I come across all the time - but this is an actual quantified case study if you like.
Three boilers were observed as part of an energy survey of a major secondary school for a Scottish Council. The boilers were shown to fire up when Return Flow reached 165oF or 74oC which was a very small drop from the output temperature of 170oF and is indicative of a phenomenon known as ‘dry cycling’.
During dry cycling the efficiency of the boiler is zero.
These units are much more than just simple clockwork timers that you (and I) may have come across before to eliminate dry cycling. The logic behind the systems is water temperature intelligence. A fuel saving unit is required for each boiler and strap on sensors are attached to flow and return. A microprocessor collects water temperature values from the flow and return every ten seconds and averages these readings out every minute. If the boiler thermostat or BEMS (Building Energy Management System) calls for heat the M2G will evaluate whether or not the burner needs to fire at that precise moment. The M2G will be able to detect the exact type of demand based on water temperature fall versus time and will fire the burner when its intelligence instructs it to do so.
So, first things first, think about the fact that as a rule 40%-ish of your radiator faces and therefore directly heats the wall on which it sits - heat which will inevitably be lost due to conduction to colder parts of the structure and eventually exit the building at a thermal bridge somewhere. What can you do?
Invest in a roll of heavy duty aluminium / silver foil and create a home-made reflector - it will have some effect but in 99.9% of cases look like a dog's breakfast - c'mon this is your home or office we are talking about!
Simple HeatKeeper panels are a very good solution that I have used in many hundreds of properties with tremendous success.
There are cheaper things out there and the claims for savings take your breath away but at the end of the day I reckon if you can cut 10-15% off your heating bills for less than £60 that seems like a pretty good investment to me!
The nice people at HeatKeeper have put together a couple of convenient pack sizes and have kindly allowed me to distribute them at discounted prices to anyone clever enough to be viewing this website! All packs are complete with self-adhesive tape and fixing instruction. Just email me to place an order.
A 10-panel pack delivered UK mainland costs £40 and a 20-panel pack £50.
The panels have recently undergone a wee re-design to make them even more user friendly and now come in a standard 580mm x 450mm size with lots of flat bits so you can cut them to suit any radiator size whatsoever or join them together very easily to cater for larger radiators. The panels are 8mm deep. Fitting the first one is a bit fiddly but once you have done one then the rest go very smoothly - trust me I know. I have fitted them in my own home and I am renowned for my DIY expertise - not - just ask my long suffering wife!
The value of this simple measure has been tested and proven over and over.
The UKAEA labs in Harwell tested the panels and observed "a heat saving, and a beneficial effect on flow pattern, due to the presence of the panel, especially when radiation is taken into account. Overall savings in the range of 22% to 27% can be expected".
BSRIA stated "the variation in output and hence reduction in losses is 15% to 13% based upon mean water minus room air temperatures from 10oC to 60oC. This figure relates to the losses through all surfaces and not just external wall"
It is all a fancy way of saying that they like them and found them to save fuel!
HeatKeeper panels simply stop heat loss through the wall - the circulating water therefore returns to the boiler hotter, reducing energy wasted in unnecessarily heating colder water. The air curtain created by the panels rises 2-3 metres above each radiator reducing the energy lost through windows and walls above radiators as well as just behind them.
These are UK-manufactured and comply with all required BS Fire and Safety requirements applicable within the EU. HeatKeeper panels are easily fitted using double sided tape or on uneven surfaces, using a standard readily available elastomeric adhesive. On average 2 panels per radiator are used in domestic use.
If you are still unsure email me with your queries
UFH comes in two forms - wet and electric.
Lets look at wet systems first - fed by the circulation of hot water through pipes under floors. These systems warm the floor structure by conduction causing the surface to radiate heat into the space above and the primary source of heat is typically a boiler - although many other options now apply which i will deal with later. The boiler heats water to 40-50oC and this is distributed in plastic pipes to one or more manifolds each of which comprises a flow and return header from which loops are taken to serve areas of the building to be heated. In a simple two-storey office for example there would be one manifold serving the ground floor and one for the first each feeding UFH loops in the individual rooms on that floor.
Getting good conduction between the UFH loops and the floor structure is the key to success. Different methods of transferring heat from the pipes are applied for different floor structures. The pipes are usually fixed to the floor insulation and a concrete screed poured over them further to which floor tiles, carpets or other surface finishes are applied. Where floor tiles are used heat radiates into the "treated space" at roughly 100W/m2. The design output achievable with suspended timber floors averages slightly lower at 70W/m2. Note the use of the word radiate - UFH is more akin to radiant heating than is for example the use of radiators which are mostly convection. Radiant heat means less rising heat lost to the roof void as convection - indeed with UFH the reverse is probably true - that is temperature inversion where the floor is hotter than the ceiling.
All of this means that the boiler operates at a lower temperature which promotes good combustion increasing efficiency. Typically a condensing boiler serving UFH would be operating at 90% compared to 87% for the same boiler feeding radiators.
These low operating temperatures also means that UFH is the ideal partner for "renewables" such as ground source heat pumps and air source heat pumps (where the heat exchanger carried out an air to water transfer). Why ideal? Well, simply because these systems tend only to heat water to 40-50oC and although some people like to boost this with a small boiler or an electric immersion element it seems a bit daft to me so I prefer to use the water at the temperature the heat pumps produces it in UFH systems - but heck what do I know?
Pro's and Con's of Under Floor Heating | |
| Pro's | Cons' |
| Lower running costs and CO2 emissions | Slower response time |
| Optimises thermal comfort | Heat output limited to 100W/m2 |
| Enhances decor by concealing heating | Supplementary heating may be required in small rooms & bathrooms with two external walls, small conservatories and corridors with large glazed areas |
| Flexible for use with renewables and CHP | Remains a "novel" technology, despite recent growth which tends to lead to uncompetitive pricing |
| Ease of access to manifolds for maintenance | Can restrict floor finish |
| Concealed heat emitters improve access for cleaning floors and skirtings | Pumps can be noisy so need sound damping or remote siting to avoid nuisance to occupiers |
| Enhances property value | Deep floor required to accommodate pipework and insulation |
| Common on continent - becoming more popular in UK | Not really much of an option for existing properties unless flooring is being replaced |
| Extended warranty of up to 25 years available on pipework loops of most UFH systems | Risk of damaging pipework if flooring is penetrated, leading to potentially costly repair works |
Conclusions: if you are building a new property then potentially great in terms of using new renewable technology. Initially expensive in terms of material costs and requires specialist labour (not just any old plumber can fit this stuff) but long term your running costs are likely to be substantially lower than with traditional boiler fed systems.
Electric UFH
I have to confess I have some of this in my own home - and very effective it is too.
We installed it in a wee lean-to conservatory underneath slate tiles and have control via an Aube TH132-F floor sensor stat.
Our space is just over 6m2 so we installed a mat rated at 750W.
The thermostatic control and timed management keep running costs down to a bare minimum and I reckon an entire winter costs us £50-ish.
