Recirulating heat

ViksB

I am not entirely sure where the best place to post this question is, but I thought I would start here and I can always get pointed else where.
We are thinking about getting an extension built which will contain a high vaulted type ceiling and in this room we are hoping to put a wood pellet boiler which should heat the room and do our central heating replacing and hopefully benefit from any RHI's However given the high ceiling in this room I was wondering if it would be worth adding a duct system. Ideally I would like to take the hot air which will rise to the ceiling and move back down to the floor. I thought that a air duct could be inserted in the ceiling and ducting fed down the walls to another duct on the floor. Would natural convection then do the rest of would a fan need to be placed in the ducting. I assume that the fan would need to be in the ceiling taking heat out of the room into the ducting so that it can feed back in.
Is there anything better? would the system work? Would I need a thermostat on the fan to turn it on.
Any advice much appreciated!!
Viks

zeupater

ViksB wrote: »

I am not entirely sure where the best place to post this question is, but I thought I would start here and I can always get pointed else where.
We are thinking about getting an extension built which will contain a high vaulted type ceiling and in this room we are hoping to put a wood pellet boiler which should heat the room and do our central heating replacing and hopefully benefit from any RHI's However given the high ceiling in this room I was wondering if it would be worth adding a duct system. Ideally I would like to take the hot air which will rise to the ceiling and move back down to the floor. I thought that a air duct could be inserted in the ceiling and ducting fed down the walls to another duct on the floor. Would natural convection then do the rest of would a fan need to be placed in the ducting. I assume that the fan would need to be in the ceiling taking heat out of the room into the ducting so that it can feed back in.
Is there anything better? would the system work? Would I need a thermostat on the fan to turn it on.
Any advice much appreciated!!
Viks

Hi

This is similar to something I thought about a number of years ago. We have GCH & a log burner and tend to leave most of our internal doors open, which used to result in the upstairs becoming uncomfortably warm when both were being used, so I considered a similar solution to the one you are pondering. Eventually it dawned on me that the problem wasn't the recirculation of the heat, it was the delivery of too much heat to specific areas (ie upstairs) ... the solution was simply to fit TRVs upstairs.

As described, your situation would benefit from being able to make use of the inevitable higher temperatures at height. Yes this could be done by ducting air from high to low, but it would need to be a powered system, probably using a in-line fan somewhere along the run of the hidden duct, however, it's possible to achieve what you need in other ways. What you are attempting to do is destroy warm air's natural tendancy to stratify (warm air at the top/cold dense air at the bottom), so all you need to do is stir the air a little, which can be done with either a ceiling fan or a standard fan blowing upwards ... we have a HEPA air filtration/ionizing unit which achieves this as a by-process quite well.

Another simple option is to have a thermo-electric fan on the top of the stove .... heat from the stove is converted to electricity and powers a fan which will stir the air .... whether you think they're well designed or simply ugly is pretty subjective, but they certainly do become a catalyst for conversation when you have visitors ....

Depending on the layout relative to the rest of the property it could be possible to simply install some passive ducting to circulate warm high air into the upstairs of the main building. I'm a great believer in circulating the heat around our house ... this is possibly because our log-burner would likely cook anything in the lounge if it's been running for a few days and warmed up the thermal mass in which case the heat needs to be dumped somewhere, either into the house, or out of the window .... I choose the house option ...

HTH
Z

Ben84

If you're right at the start of the design and planning stage, there's probably bigger opportunities to save energy and money available than using a wood pellet stove. You'll have site constraints I'm sure, but you may be able to use passive solar design? Also, with sufficient insulation - which is best installed during building, spaces can need very little heating at all. Anyway, in this kind of situation I would be exploring the best options to avoid the need to pump in large amounts of heat during the winter to sustain the indoor temperature, as that is becoming an old fashioned solution really.

ViksB

I haven't seen the thermo electric fans, I think they are pretty cool, certainly a talking point and something to consider. We had ruled out ceiling fans as we just don't like the look of them. We are still thinking about the ducting with a fan in it. Does anyone have any idea of the required throughput for this to work, I assume it would be related to the volume of the room? Would a normal 4 inch bathroom extractor fan work or does it need to be more specialised?

The new parts of the house are being designed with as much insulation as possible. I would love a passive house but that is simply impossible for this building, we are hoping the new part of the house will need little heating, but the old part of the house will still need lots, despite the improvements we are putting in at the same time.
We are still looking at various websites to see if there are any other ideas we can incorporate.
Thanks for the answers so far.

zeupater

ViksB wrote: »

I haven't seen the thermo electric fans, I think they are pretty cool, certainly a talking point and something to consider. We had ruled out ceiling fans as we just don't like the look of them. We are still thinking about the ducting with a fan in it. Does anyone have any idea of the required throughput for this to work, I assume it would be related to the volume of the room? Would a normal 4 inch bathroom extractor fan work or does it need to be more specialised?

The new parts of the house are being designed with as much insulation as possible. I would love a passive house but that is simply impossible for this building, we are hoping the new part of the house will need little heating, but the old part of the house will still need lots, despite the improvements we are putting in at the same time.
We are still looking at various websites to see if there are any other ideas we can incorporate.
Thanks for the answers so far.

Hi

As you're not looking at extracting the air but really stirring in order to prevent stratification I'd guess that there's no real industry guidance to reference (but will be happy to be proved wrong).

When I looked at it I was considering a solution with a couple of high pressure 'in-line' ducted fans which were capable of producing the higher duct pressures which the duct lengths required .... you would likely have shorter runs but the issue revolves around the volume of air which you want to move. Considering that you are talking about a vaulted ceiling I'd guess that you'd want to move the heat from the top third of the volume of the room about 3 times an hour, so you could start by looking at a fan unit which was capable of moving the same volume as the room contains per hour ... just a guess based on what I planned to do.

The fan units I looked at were pretty expensive compared to standard extractor fans, I'm pretty sure that they would be around £200+ each now, but they will likely get a lot more hours of use than a normal timed bathroom fan ...

HTH
Z