External Boiler Houses: A waste of heat

By The Helpful Engineer / On / In Energy Conservation

The madness of having external boiler houses is very clear now that a heavy fall of snow is covering the ground. The photographs below show the amount of heat being lost and wasted from the typical external boiler house. The first photograph below shows that heat from the boiler has melted the snow on the roof of the boiler house. The second picture shows the boiler house located at the rear of a garage. What seems to be a path which has been cleared in the snow has actually been caused by below ground heating pipes linking the boiler to the property, warming the surrounding ground and melting the snow. The last photograph shows cozy cats using the wasted heat from the boiler house to keep warm. What a useful investigation tool snow can be!

In these energy conscious times why are we still locating boilers in remote buildings/ boiler houses? One of my friends has positioned his boiler in a green house close to his house to try and put the, otherwise wasted, heat to some use.  He has also installed extra insulation on the pipework between his house and the boiler. But the best solution in my opinion is to locate the boiler inside the property thus protecting the boiler from rust and reducing any heat loss to a minimum, but within a fire proof and externally vented room. Building designers and self builders take note.

Reasons to avoid building a separate boiler house

  1. There is heat loss from the pipes transporting the hot water from the remote boiler house to the property.
  2. The boiler itself releases heat during operation, it is better to have this heat released inside the property rather than outside.
  3. The humid external air will be in contact with the boiler and associated pipework and shorten the life of the boiler, (by rusting).
  4. The longer lengths of pipes hidden from view by being buried in the ground increase the likelihood of leaks.
1. Heat from boiler has melted the snow on the roof
2. Heat from underground pipes has melted snow above
3. Cats keeping warm on boiler house roof.

18 thoughts on “External Boiler Houses: A waste of heat

  1. sure, heat loss is a given…..you have spoken entirely of negatives and have overlooked the reasons why anyone would want an external boiler in the first place.
    Maybe a person wants to burn wood……have you ever had to constantly clean up the debris that always occurs with carring wood inside the house?
    How about the ash that invariably floats away inside the house when you clean out the fireplace or stove?
    What about the labor involved in carrying the wood inside? With an outside boiler the wood can be stored right next to the boiler and who cares if ash floats away during cleaning?
    Another factor is that in the pictures you have posted the installer quite obviously didnt insulate the underground pipes…a very amatuerish installation like that gives potential people who would consider such a heat system the wrong idea.
    You mentioned rust…..maybe you think that boilers inside a home last forever? todays boilers have a lifespan of about 20 years or less…..they might not be externally rusted but inside their time is up anyhow after that time.
    How about fire hazard? You didnt mention how much safer an external boiler is than having a coal, or wood boiler or stove inside the home. Many insurance companies also increase premiums for houses containing any wood burning devise. An external wood fired boiler does not increase insurance costs

    1. Hi Harry,

      Thanks for your input. Good point about the wood boiler and insurance premiums. If you want to locate the boiler outside, go ahead, but take precautions against heat loss and corrosion, and in my experience builders don’t seem to be taking these precautions. Interestingly since I wrote that post I have heard of the flow and return water pipes feeding an outside boiler freezing because the pipes weren’t deep enough or insulated sufficiently, another negative. I was writing in particular about oil boilers which would be fed by a pipeline, with no physical carrying of fuel, the oil tank would be located outside or in a fire proof room. But this can also be done with a wood boiler, i.e. an internally located wood pellet boiler could be auger fed from an external wood store. I completely agree with you as well that any internal boiler should be installed in a fire proof and well ventilated room and I will adjust my post to highlight this, thanks.

    2. Hi,
      Does anyone have any ‘written’ information on the noise levels of external boilers? We want to install one and have included it on our planning application for an extension, but the council are concerned that the noise levels will be too loud for adjacent neighbours – we are appealing the refusal but we need more information and to date have not been able to get any ‘written’ information from any vendors – any help with this would be thoroughly appreciated – thank you 🙂

      1. unfortunately I don’t. Does anyone else?

        It is interesting that they raised this as it can be a problem. We can hear our own external boiler when its on as well as our neighbours. But our boilers are older models.

  2. what if the boiler is already in place and the underground pipes are melting the snow as in your picture? we had that problem last winter and it seemed a mad waste. I suspect we would have used half the oil if we weren’t heating the outside yard.Is there an easy way to insulate the pipes.?

    1. Not really. You need to get a contractor to dig up and replace your existing external heating pipe with a sleeved and insulated one. Alternatively you could relocate the boiler. I hope that helps.

      1. AlexYour query about the MVHR. We were concerned at an early stage of MVHR noise, we even tearvlled to Austria to stand and listen in a couple of passivhaus’s. Our fears were quickly dispelled, there was the very slightest sound when stood near an inlet. As for our Denby Dale passivhaus, the Paul Thermos 200 is completely inaudible in the house, the loudest noise is the gas heating boiler and that is only really audible in the study next to the plant room where the boiler is situated. The Paul MVHR unit is one of the quietest certified by the Passivhaus Institute.The main reason for the inaudibility I think is the integrity of the design, the mvhr, the quality steel ducting, the mounting of the ducting, having unobstructed runs and the right attenuation ( attenuation is the internal silencing of the system to counter any extraneous sounds being transmitted through the system i.e. voices or sounds from room to room etc.), system commissioning by qualified and competant people to tune in correct parameters, fan speeds and balance, duct velocities, outlet volumes, etc , the list is goes on! The MVHR unit is actually located in the garage, mainly for access and to save space in the house, but its quiet murmur is outside and not inside the house. This all contributes to system efficiency and is neccessary for good MVHR reliability and comfortable performance.The user programming is minimal once the system is correctly commissioned, we can and have adjusted, through trial and error to optimise our comfort, the desired running temp at 20-21c, night lowering, summer by-pass and of course we have a boost switch to boost the system when needed.In the extreme conditions of the last few weeks the system has really been tested and has performed well.

  3. Hi, great website! So useful to get correct costs for various fuel. Incredible that many older folk were persuaded to replace their coal systems with oil (many losing their back boilers) in the name of efficiency. Most people I know in Donegal are using coal more than oil now and it’s hard to get cheap wood… We’re lucky to have both options. The oil is used only minimally for winter mornings, gales and arctic freeze.
    RE outside outside boiler. Four years ago when being installed, I queried the builders several times re the rust factor, waste of heat etc etc and I hadn’t even researched it but was talked down as though I had silly notions. Turns out I was right. Our wet climate has caused rust that is getting worse, to the point of near corrosion. Luckily boiler is flush against back wall so no underground warm pipe to freeze. I took precaution of lagging the pipe to oil tank though, a few metres away although have been advised that that one never freezes?? Have now put “build round the boiler ” on To Do list for this year. At least, the wasted heat can keep some equipment and store stuff dry and my gardening clothes warm. Will make it into a useful store, allowing flue out and up through roof of course.
    PS Particularly enjoyed your “future house design” shared material. Keep up great work!

  4. I have seen some shocking boiler houses, but a good, well insulated one built as close to the house as possible can be a better option than an interior one. Purpose built kabinpac units are great. Interior boilers have a habit of becoming choked with dust, clothing fibres, pet hairs etc. I’ve even seen a mouse corpse clogging a burner. This can cause CO to be produced inside the property which is a worry.

  5. We have an outside oil tank and we want to move it into an outside garage for security reasons (oil been stolen from tank at weekend). I wan to know is it safe to put the oil tank into the garage as there is the oil burner in there as well.
    Please advice

    1. It depends on your specific circumstances, but in general oil tanks cannot be in or close to a property in case of fire. Refer to the building code for your region for particular rules and set backs etc.

  6. Hello. I have a question a bit off topic: can I install an external oil burner without installing additional flues? I have a downstairs flat in a semi-detached house, the first floor being occupied by council tenants. I would need to know it the vent in the burner is enough as I am concerned about fumes.

  7. I would not recommend to anyone to put a boiler inside. We had a boiler inside for 20 years and decided to upgrade. Due to negligence of fitters we lost 500 ltrs of oil under the house, we were all sick for 3 mths, the company were negligent at coming out, we have been out of the house almost a year, and just informed last week that there is also damage to the substructure of the foundations. I am at my wits end. There is no way, if I ever get back into my home that I will place the boiler inside. Nor would I advise anyone to do so. We had good insurance but to my dismay this has also posed a problem due to our insurance company just paying out minimal cost for items. The only person losing out is me, as the customer.

  8. Really helpful discussion. Can anyone point out possible drawbacks to the following:

    Problem: my “Ideal” gas boiler is mounted in a bedroom against the outside wall. It is noisy and I am paranoid about fumes tho I am assured it is safe and there is a carbon monoxide alarm. Needless to say, we don’t sleep in that bedroom or we turn the boiler off.

    Solution: I want to move the boiler so it is outside the building mounted on the other side of the wall. I am trying to source a boiler housing for it. The pipe run will only be the width of the wall the pipes travel through so minimum heat loss. Fumes if any can ventilate to the outside. Any ideas about a housing to contain the boiler once mounted on the outside wall?

  9. What is the benefit of insulating the external boiler housing?
    I have a combi boiler oil fired boiler and was thinking of putting Mylar sheets on the walls on inside of housing but can’t really see what difference it would make?

  10. Hi we have a external home heating oil burner , we’ve had it for several years , and get it serviced regularly , over the years the door although wooden had lasted until very recently , the last time we got the burner serviced , the engineer , said that we needed to replace the door to the housing , as a lot of heat would be lost .
    I’ve tried many sites to find a door with pvc covering the outside , and can’t find a supplier with these doors , they keep trying to Pam of a full housing saying it all would need to be replaced . What can you suggest?

  11. Hi, we’ve our oil combo boiler outside. Is there an easy way of finding out where the cold water in/hot water out pipe is leads in/out underneath ? It’s on a slab. Just to avoid digging random deep holes all the way around every side of the boiler!

  12. My oil burner is located about ten metres from rear of house in back garden. Flow and return pipes run from there under lawn into house, under kitchen floor to hot water tank in kitchen. I’m thinking of getting a small extension built at rear of house. Is it ok to leave these pipes in situ and lay concrete floor and foundations over them or have them re-routed overground along garden partition wall with insulation. Any suggestions greatly appreciated.

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