4 Aug 2011

How do you assess a product like Oxyvent?

Here's an interesting press release that just landed on my desk. It's for a new plumbing product called Oxyvent. It's a box that you add onto your radiator or underfloor heating system that helps it run better, and it promises huge savings in fuel burned.

According to the PR lady, Paul Worswick, director of Oxyvent, is "very keen that Oxyvent isn't seen as some magic box of tricks as the physics behind the product is straight forward when explained." There's lots of information about on the website and a YouTube video sequence showing Paul himself with a Pimlico Plumber who is busy installing Oxyvent in someone's house. There's an FAQ and there is a brief summary of some tests carried out by Dr Tony Robinson, a lecturer at Trinity College, Dublin (the kit hails from Ireland). And there are some ringing endorsements from satisfied customers.

But what there isn't is any simple to understand explanation of what makes Oxyvent so special. It seems to turbo charge the flow rates of water through the radiators, which enables them to run cooler, but to my mind that doesn't equate to making them more energy efficient. Some where in this system there must be a trade off - an extra pump or two, another heat exchanger, something unexplained.

I'm quite prepared to accept the claims at face value, but only if there is a coherent explanation of how it all works. As it stands, the publicity poses more questions than it answers. Installing one of these is going to set you back the best part of a grand: that's an awful lot of money for something being sold on trust.

So I looked up Tony Robinson, the Dublin academic who has been testing Oxyvent. He was easy to track down so I emailed him. He got back to me in a couple of hours and what he wrote was very illuminating.

The simple answer is that under the conditions that we tested in my lab the Oxyvent system did something useful; and there is no questioning this because our experiments were well thought out, they were accurate and we are experts in this field.

We observed two things: (i) when the radiators were balanced (to give approximately 11°C temperature drop at around 75°C boiler setting) the radiators we tested showed major non-uniform distribution in temperature, i.e. very large cold regions, due to the low water flow rates, and (ii) there were large fluctuations in the radiator temperatures and power outputs due to the boiler switching on and off which caused the inlet water temperature to cycle hot and cold.

He went on. For this scenario the Oxyvent system made a difference by smoothing out the fluctuations in the main inlet water temperature and thus the power output of the radiators. It basically added thermal inertia to the system so that the radiators did not react to the switching of the boiler. Now, the water flow rate can be increased i.e. unbalancing the radiators, without large excursions in the power output, so that for a given water set point temperature the radiator power output is nearly constant with time. The knock-on effect is that with the higher flow rate the temperature distribution of the radiator is much more uniform (we used thermal imaging to show this) so that, for a given inlet temperature, the unbalanced radiator would output more power since it would be, on average, hotter. Thus, the even temperature over the radiator provides more heat (for a given water temperature) and the Oxyvent tank ensuring that there are no severe cycling of this heat combine nicely, in the sense that the boiler water temperature can be reduced, which reduces fuel consumption, whilst still outputting adequate heat that is not pulsing over time.

One might ask then why use the Oxyvent tank for this; why not just reduce the water temperature (thus saving on fuel) and turn up the flow rate (thus improving the heat spreading on the radiators and thus the power output)? The answer is that for this case, the water inlet temperature is still cycling due to the on-off nature of the boiler so that the radiators may well reach the same peak power output but will also drop to a very low one, so that on average over time the power output is much lower than the case with the Oxyvent tank which provides a much more constant inlet water temperature to the radiators, even though the boiler is cycling.

Are you any the wiser? I'm not sure I am. It makes it look like it does something, but what exactly is still hard to tell. Other experts I know had reservations, but perhaps the best comment I got was from Michael Holmes of Homebuilding & Renovating magazine. He wrote I suspect that this product is a large heat exchanger/store, so the boiler flow and return go direct from this box, which acts as a thermal flywheel. Any benefit in terms of energy saving is likely to come from increasing the amount of time the boiler is in condensing mode, and by setting the boiler to a lower output temperature so it gradually heats up this thermal store. It is not clear whether it offers direct DHW too.

I suspect there are ways to achieve the same using controls. A boiler with a modulating burner that has a second low temp output for UFH etc. might achieve the same results without the expense. A thermal store cylinder can also work as a thermal flywheel, and provide DHW on demand.

So there you have it. A product that does something but we are not really sure what. It doesn't come with any 3rd party accreditation, like a BBA certificate, so we are left with lots of customer feedback and the observations of a Dublin academic. My hunch is that there are some installations where Oxyvent may make a huge difference, but others where it may do very little. And I realise that's not very helpful either.


  1. it's a simple buffer tank with auto aif vent on top.

    you often find them with renewables like GSHP were you need a high flow rate to gain efficiency out of it.

    lots of manufactures make them. often they come in 50L,100L,200L sizes.

    You can buy a 100L one for £150-£200.

    as for why you would want one. it is really a solution to a problem you should not be having. if the boiler was correctly size and have a good modulation range. then the boiler on/off cycling is not a problem.

    also the idea of just firing water though pipes faster is not wise.

    the ideal speed for water through pipes is 0.5m/s to 1.5m/s. faster then 1.5m/s you get water velocity noise and erosion corrosion(ie the water is striping the metal for the pipe surfaces)

    to be honest this oxivent will have little use in a domestic setting and if you did want to use it(ie you boiler is way oversize for the house) then you could get the stuff need for way cheaper then £1000 price tag

  2. Dave HoworthAugust 05, 2011

    I didn't understand the bit about 'unbalancing the radiators'. I thought the purpose of balancing the radiators in a system was to get the correct heat distribution around the system. So you can't just arbitrarily 'unbalance' one or more without making somewhere in the house too hot.

  3. Mark, thanks for taking the time to look at the Oxyvent Tank and share it with your readers.

    As it performs several functions and delivers multiple benefits it’s hard to condense an explanation for how it works into a couple of sentences; there is nothing on the market which achieves all of these things in one product.

    1) It is probably the best de-aerator on the market. Air really is the enemy of central heating systems - problems from corrosion and sludge build up to poor efficiency heat transfer and pump cavitation

    2) It does act as something of a thermal flywheel - thermal videos from the lab testing can be seen at www.youtube.com/user/oxyvent/ From these it is clear the impact on the radiators from a heat consistency point of view as well as much superior uniformity or heat across the radiator.

    3) Faster flow removes the need to balance radiators. All balancing does is restrict flow through the radiators nearest the boiler otherwise the ones further away don't heat up properly. So conventional plumbing says to restrict flow meaning that the radiator doesn't heat up properly from top to bottom. With an Oxyvent in place this conventional thinking is thrown out of the window and radiators work much better.
    To check your raditors measure the difference from the top to the bottom and you'll see between 12 and 18 degrees difference! With Oxyvent in place this can be as low as 2-8 degrees.

    4)With the faster flow and more uniform temperature you can set your boiler to 60 degrees for a combi boiler or 65 with a hot water cylinder - this is where the major savings come in - most boilers we've seen are set at 75+!

    As we launch to homeowners over the next couple of months we'll be getting more and more testimonials and feedback from customers in the UK - we'll be keeping the website - www.Oxyvent.com - updated with all the latest.

    Thanks again,


  4. Mehran,

    We installed the first Oxyvent Tanks in Ireland 10 years ago and have overwhelmingly positive feedback -certainly no problems with faster flow as you mentioned.

    The £1,000 you're referring to is a rough estimate of installed cost - we are selling it for £495 ex VAT as an introductory price.

    If you'd like to talk more please do contact me - details on www.oxyvent.com.



  5. Hi Dave,

    This is a common question we receive from the professional installer market.

    Balancing a system is restricting flow to the radiators nearest the boiler to ensure that there is still sufficient heat to warm those furthest away.

    With the faster flow rates this is unnecesary, individual radiator temperatures should be controlled by Thermostatic radiator valves and not by balancing - once the room is up to temperature the TRV will switch it off.

    Balancing restricts flow and virtually stagnates water in radiators which is why they do not heat up evenly from top to bottom - with Oxyvent this is transformed - have a look at the thermal images at www.youtube.com/user/oxyvent.

    If you have any questions please contact me at www.oxyvent.com.


  6. *and there is no questioning this because our experiments were well thought out, they were accurate and we are experts in this field.*

    Working for a certification body that does take pride in it's work, alarm bells ring whenever any expert feels the need to talk like this.

    99% of the time it leads to BS.

  7. I agree with what Mehran said in that Oxyvent appears to be a simple buffer tank fitted with an auto air vent.

    As such it is similar to the Dunsley-Baker neutraliser which is the standard method of connecting two different heat sources to the same circulating system.
    Theory of operation is on their website.

    Used with a single heat source there may well be some theoretical benefit to specifying the gadget in a heating system, but in practice any saving is often minimal.

    It would certainly take a long period of time to recoup the initial outlay for the Oxyvent and for most domestic situations I remain unconvinced of it's cost effectiveness.

    There are plenty of electronic bolt on gadgets on the market which cost far less and their effectiveness to make worthwhile savings is already well documented.
    These come under the category of load compensator's and also weather compensator's marketed by several renown controls manufacturers.

    So effective are these compensator's that some boiler manufacturers are starting to build in such circuitry to their products as standard.
    As an add on they do not require draining down of the the system.

    I'm now a retired heating engineer but as yet have seen no convincing evidence which would have convinced me to have recommended this as a value for money product.

  8. A control system that automatically decreases the CH water temperature when the property is close to the target temperature and a fully modulating boiler may be a better solution.

  9. combi boilers are usually fully modulated,are they not? the combi boiler is sealed and pressurised. So how does air get in? something called an Oxypod removes air from central heating systems. So what is the difference.?

    1. Most heating experts do not know where the excess air in heating systems come from. The air is formed in the boiler, and yes, there is air present in every wet heating system. Oxyvent apparently reduces the delta T which gives a more balanced temperatures in the boiler and radiators. I can see how oxyvent would create uniform heat from the radiators and this would explain its fuel savings.