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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthormoogaloo
    • CommentTimeApr 10th 2007
    I have just purchased a new house (which is currently being rewired) and as I have not moved in at the moment and all floor coverings are in I am getting wet underfloor heating installed under the floor. The house currently has a newish condensing boiler.

    I am planning on getting solar hot water system installed and a couple of wood burning stoves in the two main downstairs rooms.

    I am also considering an Air Source Heat Pump to drive the underfloor heating leaving the condensing boiler to top up any lack of solar heating in the water tank.

    Other considerations might be a Thermal Store that could be topped up by Solar/wood burning stove back boiler/heat pump.

    The question is which way to go? The wood burning stoves will be primarily decorative, so I am quite happy to leave them out of the equation and any time I do use them, the rest of the heating system should not work so hard.

    So any advice here? Which direction should I go in? What should I look at?

    Also can anyone give me any idea of how much an Air Source Heat Pump for a 3 bed semi would cost including installation (Ball Park)?


    • CommentAuthorPeter A
    • CommentTimeApr 10th 2007
    Moogaloo, Have a look at NIBE website, they do a combined ASHP with Heat Recovery, you're probably looking at about £5-6K installed, the heat recovery bit will mean a bit of upheaval.
    • CommentAuthormarionhaste
    • CommentTimeApr 11th 2007 edited
    Have you thought about having a wood-burning stove which also powers radiators? This will be the second house in which we have used this sort of system - and you also already have a back-up gas boiler to use when you don't want to light a fire.

    I think you should try to simplify your approach. Aside from anything else it will cost a small fortune to do everything you describe.

    Under floor heating (UFH) isn’t necessarily a green option although it does sit well with condensing boilers. Primarily you should look to reduce heat (energy) consumption by insulation and fastidious draught proofing. With an existing property you wont be able to achieve the near zero level some aspire to, but every move in that direction will help. The building requires heat in direct proportion to the heat lost and this is regardless of the delivery method (eg UFH or Radiators or even electric fire – whatever). The UFH works well with high occupancy levels requiring constant back ground heat, but if you and your family are mainly out during the day and you like to come home to a very warm house then a quick blast from any heating system might be as effective as the UFH as this would have had to have been fired up many hours earlier to achieve that warmth level. Which in the end probably would consume the same power? So it has to match lifestyle as well.

    The wood burners could go unless you expect to use them daily. The reason is that each will require an open flue and a fresh air inlet to the room of a similar size. Roughly like having a window cracked open the whole time in each room. The cause’s quite massive losses of your warmed air and thus a massive loss of heat. Unless you use them every day the heat lost when not in use will outweigh any benefit from using wood etc. Clearview stove do a balanced flue model which is completely room sealed which solves this problem, but must be on an outside wall.

    The stove would probably upset the heat recovery system anyway as there would be uncontrolled air flow.

    The solar will be good and can feed an indirect cylinder or a thermal store, but would still require a boiler for top ups. You can run the boiler directly into the thermal store which can reduce cycling in fixed output oil boilers. For gas no need as a modulating boiler will automatically turn down as the rooms’ heat up to reduce consumption. Like wise weather compensation will also do the same in response to increasing outside temps. This in many cases can be added as you have a boiler.

    The heat pump should do the heating ok, particularly if you lower your heat requirements as much as possible, but it wouldn’t do the water heating, so you’d still require a boiler (more £).

    SO – Renovate to the highest standard you can achieve, and a use condensing modulating weather compensated gas boiler with solar coil DHW cylinder probably represents the best £ for £, that is reasonably straight forward (this might be complicated enough as it is) and maintainable, and can be installed by local folk easily. That’s my advice for the layman.

    Unless of course you want to invest in making your house an showcase for green technology on a money no object basis (sorry).

    Cheers good luck

    • CommentAuthormoogaloo
    • CommentTimeApr 11th 2007
    Thanks for all the info. Obviously greenness is not our only consideration and the wood burning stoves and underfloor heating certainly fall in to the catogary of wanting them for other reasons, not just for greenness. I will obviously be insulating and draft proofing. I think heat recovery might also fit into the "too much" category for a retro fit.

    So reading everything you have mentioned maybe running the underfloor heating using the Wood Burning Stoves with the existing condensing boiler as backup, might be a good solution. Then I can just try and use the wood burners as much as possible. The only problem I guess would be in the mornings when I would need to use the boiler.

    Can anyone give me any further insight as to how this would work in terms of using a gas boiler as a backup to a wood burning stove back boiler?

    Your gas condensing boiler is probably sealed and has an expansion vessel, the stoves/fires can only be connected to an open vented system for safety reasons - which means there would be a feed and expansion tank in the loft. If the boiler can run as vented then they can be joined, but control is important to prevent the boiler from heating the stove and vica versa. Alternatively if vented both can be run into the thermal store. This is where thermal stores come into thier own as they can combine various sources. Failing that the stoves can run gravity feed to DHW, but that requires the DHW pretty much above the stove which isn't always possible. You could always run a separate pumped circuit to supply some rads from the stoves, this would still require a heat leak radiator directly above, in case the power goes off the heat will run up by gravity to this radiator - this is a mandatory requirement.

    • CommentAuthormoogaloo
    • CommentTimeApr 16th 2007
    OK I have got the man in, he is going to install some underfloor heating with a Thermal Store and a large water solar panel. The thermal store will also accept an input from my existing Modern Condensing Boiler and can also accept input from a wood burning stove back boiler (when I save up my pennies to get this done too). I also have the option of swapping my boiler for an Air Source Heat Pump in the future, depending on how much use my boiler ends up getting.

    Before next winter all my cavities and loft will be well insulated. So I will let you know how I get on.
    • CommentAuthorGuest
    • CommentTimeApr 23rd 2007
    I am installing a Marshall 120,000 btu oil fired boiler and a 12.5Kw Clearview wood burning stove in a new build property. The Rayburn will run the underfloor heating and hot water via one of two coils in a 'megaflow' mains pressure 300L cylinder. The woodburner will heat the water in the cylinder via the second of the two coils. Has anybody else installed this system design? Does anybody have a drawing illustrating both the pipework required and the wiring for an appropriate control scheme?
    Posted By: GuestI am installing a Marshall 120,000 btu oil fired boiler and a 12.5Kw Clearview wood burning stove in a new build property.

    That must be one of (a) a huge property (b) poorly insulated (c) in an extremely cold climate or (d) massively oversized

    How did you determine that you need 47.5kw of capacity (162,663btu/h)? That's around 3x what I need for a 185sq m old house in a climate with a design temperature of -20C? Or around 2.8x what I need for a 325 sq m new house (which also has underfloor heating) in a climate that's slightly colder (-21C)?

    If you oversize your oil boiler, its efficiency will be significantly lower than the faceplate steady-state value.

    Paul in Montreal
    • CommentAuthorTerry
    • CommentTimeApr 24th 2007
    Mike (up north) said:
    "The wood burners could go unless you expect to use them daily. The reason is that each will require an open flue and a fresh air inlet to the room of a similar size. Roughly like having a window cracked open the whole time in each room. The cause’s quite massive losses of your warmed air and thus a massive loss of heat."

    As far as I understand it, the modern way is to feed combustion air via a duct from outside directly to the wood burner.(Clearview and others have this option) the flue then goes up the chimney from the burner. If the wood burner has a properly sealed door on the front, you effectively have a closed system with no negative impact on airtightness.
    • CommentAuthorGuest
    • CommentTimeApr 24th 2007
    My tuppence worth.
    Given that you are going to improve the u values of your house (wall/window/insulation/details etc) first.
    Dependant on the extent of this work the most effective, economic and life cycle combination for heating your house is something like as follows;
    Retain your newish conventional gas boiler and flush out all the systems connected to it to renew its maintenance cycle (if unknown)
    Install a twin coil calorifier to store the heat produced by it and couple this to a solar thermal array orientated due south.
    By including a three port valve you can also connect your wood burning back boiler to the system.

    The installation is hassle free simple and does not disrupt any external surfaces (GSHP).

    I notice from your other postings that your enthusiam to include technology based solutions although well founded may not be as effective as passive measures.
    To summarise heat is no problem for housing whereas electricity is more problematic.
    good luck though.

    • CommentAuthormoogaloo
    • CommentTimeApr 24th 2007
    I am already on my way now with my solution as it was cheaper to get a solar system now and get my underfloor and pluming work done at the 5% rate, rather than split into seperate jobs.

    For now I am simply getting a Hot Water Solar Panel, Thermal Store and Underfloor heating. The reason I am keen to do this now is not simply that i like technology based solutions, but because I currently have an overlap before mooving into my new house and that it needs redecoration and refurbishment, so it was a kind of now or never approach.

    For most people the best thing they can do is to insulate and get an efficient boiler, but I do earn enough money to put it where my mouth is and make choices that should reduce my impact on the environment. My car runs on biodiesel, I buy local meat and veg where possible, pref organic and freetrade, I recycle, compost etc etc. But the kind of questions I post tend to be at the more techno end of things I guess.

    As far as technology goes though, I do think that it does hold the key to cracking climate change as the masses are unlikely to change their ways too significantly, I think paper recycling has largly been used as a distracton tool as apart from the production process it is largly carbon neutral as well oil is not. Also some technology is been sold as green when clearly it is not. The current range of petrol hybrid cars are a good example as my Diesel car has a better MPG return.
    • CommentAuthorGuest
    • CommentTimeApr 29th 2007
    The comments about woodburning stoves not being viable due to requiring an open flue and a fresh air vent is slightly missleading. A correctly installed wood burner should be sealed at the bottom of the chimney. When the woodburner is not in use you simply close the vents thus stopping any air flow through the chimney. Wood burners are one of the most efficient ways of heating your home. Your looking at around 75% efficiency. Any forms of electric heating are very inefficient and gas prices are pretty dear nowadays. Also if you have a power cut you can still heat your home, have a shower and boil a kettle.
    • CommentAuthorGuest
    • CommentTimeApr 30th 2007
    This is all very interesting for a novice who has moved into an 1950s detacted property which is not warm without the heating on. I have a condenser boiler and I discovered the radiator pipes under the ground floor were not insulated, but are now. I would like to boost the heat input into the house without turning the heating on if possible and to get heat from a solar source without spending a fortune. What would you recomend for underfloor insulation? Is it possible to heat the rooms independently of hot water. The hot water cyclinder is no long attached to the system, but left (by the previous owners) in the loft, can it be put to some use? I have a bricked up chimney into the dining room and the garage attached to the same wall. Any ideas or pointers to useful websites to do further research would be appreciated.
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