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Critique my gas ducted heating plan - sketch attached

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  1. #1
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    Default Critique my gas ducted heating plan - sketch attached

    Hi all.

    Currently our old late sixties brick veneer is heated (well, at least the lounge room is) by a single gas fireplace.

    I have the opportunity to pick up a brivis he20i from a friend of a friend who has recently upgraded. The unit is about 6 years old and by all accounts has been running well and 'serviced' annually. Having done some research on the forum I'm a little apprehensive, given the issues encountered by others But for a hundred bucks (plus cost of controller) I figured it's worth a crack.

    That said, I'd like some feedback on what people think about my rough sketch for duct installation. You'll have to ignore the window dimensions. I rough did that plan on my phone using magic plan, so while positions of doors and windows are correct, sizes are rough only (none of the windows are floor to ceiling). Room dimensions are pretty close though.

    duct-rough-sketch.pdf

    The unit has to be installed in the roof as, while the house is on stumps, there is no room to install under-floor (the back of the house is about 4" from the ground to the bottom of the bearers).

    Note that I'm not sure what the supply size is for the he20i (could be 12" or 14" depending on model). If 14" then the section to the first BTO will obviously be 14" with a 14-12-12 BTO.

    The other issue I have at the moment is positioning of the return. While I'm loathe to give up valuable storage space (of which there is little) I'm pretty much resigned to having to do it.
    x y and z on the plan show some rough spots for the return grille. There is an option to put it at z as that wall doesn't have any plaster on it as yet and could utilise the space between the joists. Having done some quick calculations though, the volume of that space is less than that of a 14" duct so I'm concerned it could throttle the return too much. Option y could also have the return grill mounted on the dining room, or entry sides.

    Looking forward to hearing your thoughts and ideas, good, bad or otherwise.

    Cheers.

  2. #2
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    Hot air will follow a path from the vent back to the return, so we were always told to put our ducts at the furthest point from the return possible.
    The outer edges of your kitchen and living room will not warm up (according to your duct placement).
    Also - have you thought about putting the return grille on the ceiling? I've seen this done.
    The other piece of advice I got was to always ensure you have at least 10m of duct from the return grille to the unit. It stops fan noise from coming out of the return.

  3. #3
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    Thanks davegol for the reply.

    Quote Originally Posted by davegol View Post
    Hot air will follow a path from the vent back to the return, so we were always told to put our ducts at the furthest point from the return possible.
    The outer edges of your kitchen and living room will not warm up (according to your duct placement).
    You're right. I was a bit sloppy with those couple of duct positions. The living room one will probably straighten a little and move a bit closer to the kitchen wall, and the kitchen one will also be extended.

    Also - have you thought about putting the return grille on the ceiling? I've seen this done.
    The other piece of advice I got was to always ensure you have at least 10m of duct from the return grille to the unit. It stops fan noise from coming out of the return.
    I didn't think about putting the return grille on the ceiling as I thought it was a bit of a no-no for roof ducting. I could put it in the ceiling at the x or y positions.

    Yeah I'm aware of the idea for longer ducting to help cut down fan noise (I also plan to use a filtered grille for noise and dust control).

    I know that straight runs and no sharp bends are the ideal, but is there anything wrong with snaking the return a little to gain some length? As it is there's only about 4 metres between the preferred grille locations and the heater.

  4. #4
    1K Club Member paddyjoy's Avatar
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    Agree with dave, need to push those living room and kitchen outlets right over to the other side if possible to avoid cold spots. Also might be worthwhile putting one in the other living room since you are going to all the hassle of installing the system?

    Probably wouldn't use X for the return grille because there are two doors that can be potentially closed which would restrict the return air flow, could be same issue with Y, if you can get it in an open area it is better I reckon.

  5. #5
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    For a unit mounted in the roof space the return air is normally mounted in the ceiling and

    commonly doesn't have a filter as there is very little dust up near the ceiling

    Around that central dining area would be ok

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    Quote Originally Posted by paddyjoy View Post
    Also might be worthwhile putting one in the other living room since you are going to all the hassle of installing the system?
    Good pick up! Hadn't even noticed that one had dropped off my first rough copy.

    Probably wouldn't use X for the return grille because there are two doors that can be potentially closed which would restrict the return air flow, could be same issue with Y, if you can get it in an open area it is better I reckon.
    Yes the door is a concern. To clarify, the return at 'X' would be facing into the dining room, so there's only that one door to the front of the house that could be closed ... I say 'could', as no-one seems to close any doors in this place

  7. #7
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    Quote Originally Posted by goldie1 View Post
    For a unit mounted in the roof space the return air is normally mounted in the ceiling and

    commonly doesn't have a filter as there is very little dust up near the ceiling

    Around that central dining area would be ok
    Didn't know that about the ceiling mounted return, the only other place I've been in with ceiling registers had the return at floor level.

    Thanks for the tip on the filter, makes sense if the return is up there not to have to filter it.

  8. #8
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    Our return is high on the wall with 3.3 metre ceilings, there is still a lot of dust that gets caught by the filter, if you want to minimise the fine dust that gets caught in the ducts I would install a filter.
    The location of the heater unit appears to be in the middle of a large open living area, you may get a lot of noise from the unit, ideally you place the unit over a utility area to help reduce noise.
    Some of the ducting looks like you may have close to 6 metres run in 6", also tee's in the middle of a 6" run, this may not provide much flow at the end of the run. I would use larger duct until closer to the registers and also step the duct down at the BTO's for the run to the master bedroom I would use 8" and step down to 6" closer to the registers and at the tee.

    Here is a copy of a design guide for Braemar systems the ducting and location principles should be the same.
    section4_systemdesign.pdf

  9. #9
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    Quote Originally Posted by droog View Post
    Our return is high on the wall with 3.3 metre ceilings, there is still a lot of dust that gets caught by the filter, if you want to minimise the fine dust that gets caught in the ducts I would install a filter.
    The location of the heater unit appears to be in the middle of a large open living area, you may get a lot of noise from the unit, ideally you place the unit over a utility area to help reduce noise.
    Some of the ducting looks like you may have close to 6 metres run in 6", also tee's in the middle of a 6" run, this may not provide much flow at the end of the run. I would use larger duct until closer to the registers and also step the duct down at the BTO's for the run to the master bedroom I would use 8" and step down to 6" closer to the registers and at the tee.

    Here is a copy of a design guide for Braemar systems the ducting and location principles should be the same.
    Hi droog, thanks for the feedback, and for that doc. Have had a quick scan and looks to be some very helpful info in there.

    Re. the location of the unit. I think it's about as isolated from living/sleeping areas as I can get it, while still making it accessible and having room for the ducts. Clearance in the roof space is the biggest issue. It's not a trussed roof and I've got struts and collars and hanging beams all over the place. I am hoping to be able to get it a bit further over the ensuite though.

    Thanks for the suggestion too for the duct for the master bedroom. I wasn't sure if those two runs of 6" at that length would cut it. So you think a longer run of 8" from the branch then a couple of shorter runs of 6" off the BTO to the registers?

    My wife wasn't too keen on the idea of not having a filter on the return, so your suggestion will make her happy

  10. #10
    Seasoned DIY droog's Avatar
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    Yes we had a single run of 6" over 6 meters to a single register, just could not get the flow needed, replaced the 6" run with 8" apart from the last metre or so, much better.
    Would probably be better to have your BTO branches at steps in the ducting, eg Have 12" to the BTO, with two 6" (for bed and bath) and 10" that feeds to the next BTO for two 6" to the end beds. Also the take off to the master and ensuite should not come off the 10" run to the living but at the step down from 12".

  11. #11
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    Had to read that a couple times droog to get it right in my head but it does make perfect sense to me now. Thanks again!

  12. #12
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    Hi
    I had ducted gas installed last year. My take home messages on duct design are

    - No need to heat the bathrooms. Use exhaust fan/heat lamps instead for the amount of time you are in there.
    - Have the outlet over the dining room, not the kitchen. If you are in the kitchen cooking up a storm, you don't need to cook also. A little cooler is better.
    - The return is fairly noisy sucking air through, particularly when fan is on high. Work out whether you want the noise in a living area/kitchen or near the bedrooms (do the kids care about noise when they sleep as much?)
    - The return in the roof is OK (no other option for me),but no good near an outlet, as it will suck the warm air straight back in. The passage by the laundry door looks a reasonable spot (centre of house), but the bedroom would need the door closed to heat properly. There's usually enough of a gap under the door to allow enough return without pressurising.
    - As mentioned, ducts as far into the edges of the room as you can. Incidentally, the installers fitted the duct to the register on the ground, then fed the duct up through the hole, snapping the register into place and connect up the duct on the T's - less crawling around!
    - Minimise duct length and maximise diameter as much as possible. Think more of using a T to split a line rather tapping into a central duct.
    -If all else fails, be a new customer and get a rep to come out and give you a quote and system design for you - if you know what I mean!

  13. #13
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    Ducted heating SUCKS!! Get hydronic heating. It may cost more to install, but in a log run, it will pay off, and the comfort is incomparable.

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    Hi. I was very involved with ducted heating some years back (retired). I am not familiar with the heating unit you mention. Is it not a weatherproof unit?. Can it go outside the house where the 300mm supply and return ducts can get under the house? Is there room under the floor generally? How high are the ceilings? Any heating system coming from the ceiling needs have enough air power to get the warm air to floor level. It will build up eventually and replace the cold air but there are always issues with stratification and owners continually complain of cold feet when sitting in living areas. It is not so much of a problem in bedrooms. I notice that you have not used 200mm duct anywhere. A 200mm duct could feed up to 3 x 150mm outlets ( depending on where they are) and a 250mm duct up 6. You should think about where you want most of the air to be directed as it will want to take the course of least resistance including at junctions. A "y" shape junction will give you fairly even air both sides, whereas a branch take off will send the air mainly straight on. Installers these days do not give this much consideration but it results in a much better system. In my opinion your plan directs too much air to the bedrooms. If you have to balance the system distribution with the balance flaps in the outlets, you could end up with an air noise problem. You also have one room with no outlet. More than one outlet in the main living areas gives a much better heat distribution. Also remember that if you put a filter in the return air, the grill size needs to allow for that and ease of cleaning. They can become clogged quickly. You can also utilise a "v" shaped filter which gives more surface area.
    cheers
    oldroofer

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