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Old 05-22-13, 05:59 PM   #1
shrub100
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Default Warm air central heating - conversion

I live in a 3 storey terraced town house that used to have an old warm air central heating unit installed. This has subsequently been removed and replaced with a regular hot water central heating unit, however all of the old warm air ducting is still present in the house.

I was reading with some interest a post on this site regarding the reuse of warm air from the attic. With a 3 storey house, my attic gets extremely warm despite all the insulation, so I was thinking of reusing the old warm air central hearing ducts and vents to push warm air from the attic back into the house.

I also figured that I would also be able to have a second unit installed that worked in the opposite direction to remove hot air from rooms in the summer.

Does anyone have any experience converting such systems? I could imagine that the installation of a few fans, some air filters, ducts and non-return valves could be relatively cheap. As the ducting is all in place, I imagine I could quite easily take advantage of some savings in heating costs.

Jon

PS - I live in the UK. So summers and winters are never that severe.

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Old 05-23-13, 09:19 AM   #2
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Shrub,

First, welcome to the site.

Yes, you can "move" the hot air from rooms in summer to the attic to be vented, but where does the replacement air come from? The outside of course.

If the outside air is cooler, then why not just open a few windows on the third and first floors and let natural convection do the work?

The other alternative is to install an efficient AC unit that would use the existing ducting.

I have been in London in the summer and I found it damn hot! Actually quite humid, but there were days in the mid 30's (mid 90s F to us non metric folks). And absolutely NO wind.

I found it otter than many days here in central Oklahoma (just north of Texas).

Keep thinking on how to use these ducts!

Steve
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Old 05-23-13, 09:37 AM   #3
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Welcome to the site Jon! Its good to have you here.

I think the idea is worth a shot. I know I'd like to expand my hot attic air idea to use more of the heat that is collected up there. Some days my fans are going well into the night after I go to sleep. Your idea takes it to the next level. I'm looking forward to seeing how it works out.
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Old 05-26-13, 07:32 AM   #4
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You would need to have 2 temp sensors, one for the attic and one in the return air duct below to determine if there is enough heat capacity in the attic. A RESOL solar controller could do this and run the pump and fan motor (if there is one as some of the old systems were gravity circulation). It would have to be variable speed pumping to keep any deltaT high enough so as to not make the air feel too cold. It is doable. You could use an Arduino control if you are electronically handy.
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Old 05-27-13, 01:50 AM   #5
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Sounds like an idea with merit.
Are the ducts on the internal or external walls?
What about the vents, are they floor mounted or at ceiling height?
As I was reading your post I was imaging a solar chimney type system, although I'm not sure how that would work over 3 levels. For cooling it would be easier. Heating might be a challenge to get the heat down to the lowest level.
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Old 05-27-13, 06:18 AM   #6
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Unlike in the USA where, and i cannot understand the logic, many ducts are placed in the attic, I suspect the old ducts in the UK stay within the building envelope. If there can be a 10C difference between the air temp at the lowest level and that of the attic, he can transfer heat with just the 2 hydronic coils and a small pump. The piping would be 3/4" PEX or whatever is available. I think it could work but it depends on the attic temps.
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Old 05-29-13, 08:38 AM   #7
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Thanks for all the responses - it sounds like this could be an interesting experiment and that it could have some positive affects on my heating bills.

To answer some of the queries:
1 - The heating ducts are all found internally to the building.
2 - Vents are located in the floor of the ground and first floor, and in the ceiling of the second floor.
3 - The vents run in every room and the ducting is about 20 cm in diameter. Enough for a good push of air.
4 - Temperatures in my attic are typically at least 10 degrees higher than on the ground. floor. I do tend to lower the heating on the ground floor as it is not used as much. Heating the ground floor would be advantageous to me if it is cost effective.
5 - I dont think I will be using any kind of hydronic coils etc. I just want to stick to a basic air system similar to what the ducts were used of originally.

--------------

Overall I think this idea has some legs and would be an interesting experiment. I am about to renovate the property and was initially interested in whether to pull the ducting out or leave it in place. On the basis of this thread I will probably leave most of it in.

With regard to cooling of bedrooms. I have lived in town houses all my life. The top floor gets incredibly hot even with windows open. The only option is to have a fan to move the air around, but I only do this in extreme conditions. If I can adapt the ceiling vents to minimise the necessity of using the fan then this would be ideal.

Queries I still have are:
Can anyone recommend a decent fan that would be good for this type of set-up. The core requirement would be that it needs to be quiet, cheap to buy run. Once installed I do not want to hear the thing in the attic whilst I sleep :-)
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Old 05-29-13, 09:11 AM   #8
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My issue with not using coils is that the air in the attic may come with lots of dust and insulation if you intend to do it directly. Also, where air comes in, it must go out....somewhere....which means you are going to exhaust heated air to the exterior which defeats the purpose.

If you have ducts in the attic and they are uninsulated, and don't want to put hydronic coils in the system, perhaps there is enough ductwork which could have aluminum heat exchangers screwed to it to absorb the heat from the attic, then a differential controller, like the RESOL could measure the air temp in the attic and on the main floor and vary the fan speed to move the heat down while keeping the necessary dT. This would keep the air within the building envelope.

Just a thought...
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Old 05-31-13, 01:27 PM   #9
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I have cellulose insulation in my attic, and my attic heat fan doesn't have any issues with blowing dust into my house. I've been using it for two years now.

My thread:
http://ecorenovator.org/forum/solar-...eat-house.html
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Old 05-31-13, 03:12 PM   #10
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What if there has been an asbestos based insulation, like some of the the vermiculite products, in your attic? I would be a bit reluctant to do it. As fun as it is, I think long term, it would be better to have a barrier of some sort between the attic and rest of the house.

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