High ceiling, pellet stove on lower level… will a ceiling fan help with stratification?
I looked at a two-story house today that has a high ceiling in the foyer, living room, and stairway area, with bedrooms arranged off of a mezzanine upstairs. There is a large pellet stove downstairs in the living room that is being used as the sole source of heat. The owner commented that the upstairs areas get about 10 degrees hotter than the downstairs, and asked if a ceiling fan installed upstairs might help circulate warm air back down and keep temperatures more even.
I’m not sure I’ve ever noticed anything definitive on this anywhere. Does anyone have sources that discuss this? In this case, it would be quite easy for an electrician to go up into the attic and wire up a ceiling fan in a fairly central location at the highest point of the ceiling.
I did talk to him about how air leakage is probably a contributing factor, and that part (probably the first part) of his strategy should be to have air-sealing done.
Appreciate your thoughts.
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David,
I'll be interested in the answers too. I remember some discussion about to fans not being useful in a well sealed house, but I still have a similar question to you: In a large, completely air-sealed room with a single heat source, how much stratification still occurs and why?
I imagine the correct answer is either none or very little, but it seems that there are probably external factors that come into play. In any case, this is an average house I looked at, and leakage (which I did not measure) is probably in the 4-6 ACH50 range, with the potential to knock it down to 2 or 3 depending on the level of heroics that could be tolerated. He's always going to have some stratification. It occurs to me that a lot of the heat coming from the stove seems to be in the form of very hot air moved by a fan, which probably doesn't help. By comparison, the woodstove in our living room creates virtually no perceptible air movements... it just radiates like a miniature sun.
I looked at a different house a few weeks ago with no fewer than three separate owner-invented systems for moving warm air. There was a sun porch with a couple of fans (one was thermostatically controlled) intended to move hot air from the porch into the house. There was a set of ducts with a fan intended to move hot air from the area directly above/in front of a fireplace, into a downstairs bedroom. And, there was a set of passive air channels running into the wall behind a woodstove intended to move heat upstairs. I doubt any of these do much if any good--more likely they use some electricity, risk moving combustion byproducts into sleeping areas, and make noise.
A ceiling fan will definitely keep the temperatures more even, but not necessarily make the occupants more comfortable, due to the wind chill effects.
Intense point source heat sources contribute to stratification- due to the extremely high temperature of the rising air films next to the point source (200-300F, in the case of a pellet stove) relative to the average temperature in the room. That buoyant column of air induces a strong convection current and mixes with the room air as it rises, but it's still going to be quite a bit warmer at the ceiling than at the floor. The stratification is quite a bit higher than say, a radiant floor delivering the same heat rate.
David,
With a single point source of heat, you won't get even temperatures from room to room, even in a very well-sealed, highly insulated house. In a leaky house like the one you describe, with 4 to 6 ach50, temperature variations from room to room will be even more extreme than in a well-sealed house.
I don't think that a ceiling fan installed above the wood stove will do much to change the temperatures of the second-floor bedrooms. Attempts to even out the temperatures between rooms with fans rarely work (mostly because people underestimate the air flow rates required for temperature equalization).
Improving the situation in the house you describe requires air sealing work or the installation of a different type of heating system. If the upstairs rooms are overheating, the homeowners could try shutting the doors of the upstairs rooms. That should help.
About 30 years ago, I visited in winter a Vermont A-frame cabin heated primarily by a stove. This is essentially the "large room with a single heat source" Malcolm asked about, but without the benefits of "completely air-sealed". At the apex of the A was mounted a shielded fan unit about the size and shape of a #10 tin can. Without the fan, the stratification was extreme: chilly at ground level outside the radiant range of the stove, and uncomfortably hot in the sleeping loft above. With the fan, things were a great deal more comfortable.
Please forgive me that after 30 years and a single brief visit I cannot provide more quantitative data.
Added in edit: Please note that the cabin interior was essentially all open space, especially the 2nd floor/loft.
Speaking from experience it'll help for the area right under the ceiling fan but it'll get chilly as soon as the heat turns off.
It'll also depends on how high the fan is. In my area Zone3A (Atlanta) these homes usually have the ceiling fan extend down to ~ 9-10 ft above the floor on the first level.