Complimentary heat pulling from woodstove by fan; Broan vs Fantech vs Panasonic

Discussion in 'HVAC Heating & Cooling' started by annelisemcl, Jun 10, 2013.

  1. annelisemcl

    annelisemcl New Member

    Messages:
    12
    Location:
    Rose Valley, Pennsylvania
    Hello all & thanks in advance for any suggestions.

    I have a wood-burning woodstock soapstone stove that I am looking to pull at ceiling height heat into a nearby room when in operation in the cooler months. Essentially this will consist of a wall grated opening, insulated ductwork, some type of extraction fan, and a floor level register return.

    My gc recommended a Broan 270 CFM through the wall exhaust fan- I am concerned it will be very noisy as our stove is in our kitchen where the main part of our activities occur.

    In my research, I was considering a panasonic whisper quiet or a Fantech inline FG series. In speaking with Fantech, they recommended the FG4 inline. This is only 110-135 CFM (half the Broan) but the tech said I didn't want to much air exchange as it would cool down the heated air moving it.

    What are your thoughts, suggestions, and recommendations? Thanks. This will not be the sole source of heating. It will be complimentary to a Panasonic split being put into this adjoining addition space.

    Thanks,
    ann
    ______
  2. Dana

    Dana In the trades

    Messages:
    2,924
    Location:
    01609
    An exhaust fan would be g'dawful noisy- far noisier than a mini-split with it's blower on "high".

    Words like "...only 110-135 CFM ..." are a bit silly without knowing how much you actually need. As with anything, starting with the heat loss calculation of the room you're trying to heat, and which point you could hazard a reasonable guess as to the cfm requirements for moving the heat at some presumed temperature difference.

    Assuming there would be at least a 20F difference between the return air and the ceiling air (say 80-85F at the ceiling in the room with the wood stove, 60-65F at the floor of the colder room, every cfm (=60 cubic feet per hour) would deliver (0.18 x 60 x 20= ) 216 BTU/hr. So even a 50cfm whisper-quiet fan could deliver on the order of 11,000BTU/hr into the adjacent room- that's about 1/3 of the heat load of my whole house at 0F outdoor temp, and twice as much as the heat loss of the lossiest room in the house.

    Even a 20 cfm fan would probably do fine for a bigger room, a 10 cfm fan for something small. Setting it up with a thermostat at ceiling level to kick it on at say 85F, off at 75F would probably make sense, rather than running it at full power all the time.

    But lets' start with the heat loss calculation of the room you're trying to heat- how may square feet of window (and what U-factor or type of window), and how many square feet of exterior wall (and type/R-value), how many square feet of ceiling with nothing but cold attic above (and the R value in the attic)? What's under the floor in that space?

    The 99% outside design temp in your area is about +15F, and with the insulated wall/ceiling/floor R-values & surface areas, along with the window area and U-factors we can calculate roughly what it takes to keep it at whatever indoor temp you specify, then either design your ceiling-air loop to meet that using some educated guesses on ceiling & floor temps.

    Also, which model Panasonic mini-split? Odds are that even a 3/4 ton mini-split would be able to keep up just fine with the heat load of a room, and probably more cheaply than burning wood in 75% efficiency wood-stove (unless you're managing your own woodlot, and discounting your labor.)
  3. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,067
    Location:
    NW Ontario, Canada
    I supplement with wood heat and have an 8 inch 650 CFM in-line centrifugal blower down in my crawlspace. I built it into an enclosure to filter the air and muffle the sound and have it on a variable speed controller. It is louder than I can tolerate at times.

    I inquired with FanTech but they refuse to provide noise specs. Panasonic on the other hand does and I've been considering their FV-40NLF1 which is over 400 CFM.
    https://panasonic.ca/english/ventilationfans/whisperline_specs.asp
  4. annelisemcl

    annelisemcl New Member

    Messages:
    12
    Location:
    Rose Valley, Pennsylvania
    Thanks Dana & LLigetfa.

    The room is 19feet by 17feet with vaulted ceilings about 13 feet on center down to 8 feet exterior wall. 2 Exterior walls with a sliding glass door 6-0ft, by 6-8 ft .20 U-value, a casement window 2-4 by 3-6ft .20 U-Value, awning window 3-0 by 2-4ft .20 U-value and a velux non-opening skylight 2-6 by 4-0ft U-value of .45. The walls are SIPs with an r-23 value and the Roof are SIPS with an R-38 value- vaulted no attic. The floor is currently poured concrete on grade that sits ontop of crushed gravel, a vapor barrier, and 1inch sheets of white beaded sheets of insulation. Eventually I will be floating a bamboo floor over the concrete when it has had some time to dry out & cure.

    I haven't seen specs on the split system & it will either be a Sanyo or Panasonic (any negatives/ positives of either I am open to hearing). There will be a ceiling fan installed.

    LOL about the woodstove questions because in fact it is a high efficiency woodstove with a catalytic combuster to burn the gases a second time with the soapstone holding the heat long after the fire has burned down in the firebox and currently, I am splitting my own wood from a tree we had felled when we first moved to the property (beware of a girl with an ax!). BUT as I am the main fire builder/ tender in the house with 2 elementary aged children; a fire doesn't always get built. But when it does, much of the heat gets trapped in our kitchen to the point where we are opening the windows on cold winter days to cool off the room & this defeats the purpose of the woodstove. The existing part of the house is heated by 1950's cast iron radiators fired by a propane high efficiency Burnham boiler.

    In our old house we had an exhaust fan in the living room at ceiling height pulling the trapped warm air into our master bath & bedroom. Even with the fan having a control knob, when it was on high it was LOUD. I liked the idea I just don't want a loud fan. So in doing it again, I want to improve the concept. I like the idea of a thermostat setting at ceiling height. If I do this can I also have a wall switch to override the thermostat if I need to turn on or shut off the fan or reduce the speed?

    LLigetfa- is your current inline a Fantech? The one that is 650 cfm and too loud?

    Ahhh, Dana; on a somewhat different note. I wish you lived near to me in PA because I am sure your expertise would be able to help us balance our radiator system in our ranch house with the bedrooms with the thermostat in the master too warm if we want the remainder of the house comfortable and again too cold in the summer with the remainder of the house on the edge of stuffy hot.. If you know any recommended HVAC techs to do a heating & A/C evaluation- I would be very thankful for a name.

    Thanks again,
    ann
  5. Dana

    Dana In the trades

    Messages:
    2,924
    Location:
    01609
    The slab-R is on the skimpy side relative to the rest of it, but not too much. With framing fraction downrating of the R23/R38 and up-rating of EPS for ~40F center-foam temp it's hard to say exactly what the U-factors of the SIPs will be at +15F outdoor temps, but let's give it a WAG, eh?

    To hit R23 means you have 5.25" of R4.2/inch EPS inside the SIP for about R22, with the OSB skins adding the other ~R1. When it's +15F outside and 65F inside, the mid-EPS temp is about 40F, and it's average performance will be about R4.5/inch, for (5.25 x 4.5=) ~R23.5, add the R1 for the OSB and you're at ~R24.5. But something on the order of 10% of the surface area is thermally bridged by structural elements like top/bottom plates, window & door framing that runs about R1.2/inch for the most commonly used framing species. The 10% framing fraction reduces the average to about R19.5 nominal once the So the U-factor at your 99% outside design temp is about (1/R19.5=)U-0.051

    Similarly the roof SIPs have about 8.75" of foam, but have skylight/eave/ridge structures probably running about 7% of the total surface area reducing the average R to about R34, for a U-factor of (1/R34=) U- 0.029.

    You'll need to measure the actual surface areas of each to run the calculation- your description doesn't provide quite enough info for me to run it. But it's the same as what I'll show for your windows & doors:

    Assume an interior temp of 70F, exterior 15F, for a 55F temperature difference

    The slider has (6' x 6'8" =) 40 square feet, of U0.20, for a heat loss of (U0.20 x 55F x 40'=) 440 BTU/hr

    The casement has (2'4" x 3'6" ) 8.16 square feet of U0.20, for a heat loss of ( U0.20 x 55F x 8.16'=) 90 BTU/hr

    The awning has (3'0" x 2'4" =) 7 square feet of U0.20, for a heat loss of ( U0.20 x 55F x 7' =) 77 BTU/hr

    The skylight has (2'6' x 4'0" =) 10 square feet of U0.45, for a heat loss of ( U0.45 x 55F x 10'=) 248 BTU/hr

    Total window & door losses add up to (440 + 90 + 77 + 248= ) 855 BTU/hr.

    So, figure out the total roof area in that room (less the skylight), and use U0.029 x 55F x [area] to come up with the roof losses.

    Then figure out the total exterior wall area, and use U 0.051 x 55F x [area] to come up with wall losses.

    Ignore the losses out the slab- they'll be "in the noise" on the other errors.

    Add them all up, and that'll be about what to expect for the heat loss at design temp. In really crude guesstimations, assuming you have (19' + 17'= 36' of exterior wall that averages 11' in height, that's 396 square feet, less ~55 square feet of window & door leaves ~340' of U 0.0.51 wall, for:

    U0.051 x 55F x 340'= 954 BTU/hr

    Figure the relatively low angle roof is just a bit more than the 19' x 17' room dimensions for ~325' square feet. We'll ignore the skylight area, and figure the roof losses are about:

    U0.029 x 55F x 325'= 518 BTU/hr

    Add it all up, you're at a mere 2300 BTU/hr or so, thanks primarily to the triple-pane glazing performance. Add a 10% fudge factor for air infiltration etc, and you're still ballparking around 2500-2600BTU/hr.

    Assuming even a 10F delta-T on the air you're moving vs. the air returning, that's (0.18 x 10F=) 1.8 BTU per cubic foot of air. To meet a 2600 BTU/hr heat load that's 2600/1.8= ~1450 cubic feet per hour or (1450/60 minutes per hour=) ~25 cubic feet per minute.

    That's really all you'd ever need to heat that room.

    Oversizing woodstoves in tighter better than code homes is becoming a common problem, since it turns the room with the stove into a sauna unless it's a high thermal mass stove (like soabstone), and you build hot, but intermittent fires that are allowed to burn down to nearly nothing.

    Even the smallest mini-splits would heat & cool that room, so don't go any bigger than a 3/4 ton. A typical 3/4 ton mini-split would still have well over 10,000BTU/hr of heating capacity at +15F, but since they are modulating systems with between 3:1 and 5:1 turn-down ratios, it would still track the load. IIRC both Sanyo and Panasonic (Matsushita) use Fujitsu compressors & refrigerant valves in their mini-splits, but I don't have strong confidence in that recollection. They are both name-brand manufacturers with good reps, and the installer & local tech/parts support are the most critical aspects to pay attention to. A typical 3/4 ton Panasonic is rated ~14K in heating mode at +5F, with a pretty-good 10.5 HSPF (at 47F, full compressor & blower speed.) :

    http://s3.pexsupply.com/product_files/E9NKUA-submittal.pdf

    The older 3/4 ton Sanyos were something of a dog on heating efficiency (HSPF less than 8, barely legal), but I haven't seen a newer 3/4 ton from them.:

    http://www.sanyohvac.com/assets/documents/submittal/09KHS71_submittal.pdf

    Some of their bigger mini-splits test a lot better, but would be oversized beyond all reason, but there's no reason to go with anything that tests under HFPF 10 &/or SEER 18 for a single head mini-split heat pump these days. Mitsubishi, Fujitsu, and Daikin together hold down something like 3/4 the total US market, with Mistubishi being the sales leader, if not the efficiency or feature leader. The AOU/ASU 9RLS2 Fujitsu is probably the price/performance/distributor-service sweet spot for 3/4 ton mini-splits in many markets- with lots of installers familiar with the unit, excellent 12+ HSPF, and 27+ SEER. The hardware runs about $1500 from internet sources.

    Where and how you mount the compressor unit matters, since you do get hit with the occasional blizzard. Bracket mounting it on an exterior wall above the anticipated peak snowpack depth, protected by roof overhangs is best-practice. Don't count on eaves to protect fully- under the rake of the roof is better, or you could end up in a situation like this, despite 2' overhangs on the eaves:

    [​IMG]

    Most manufacturers have customized bracket mounting packages- but even if they don't, it's still possible to make up your own. This is what Fujitsu's bracket looks like:

    [​IMG]
  6. annelisemcl

    annelisemcl New Member

    Messages:
    12
    Location:
    Rose Valley, Pennsylvania
    OMG! Thanks for "the wag", Dana. My head is spinning from all your information and I will have to read it about 10 times to even remotely understand it BUT this way I am at least assured that I won't oversize our split unit and the idea to raise the compressor is brilliant because with my luck, next winter we'll get hit with a blizzard if we hadn't been told to raise this unit up prior. We moved into this new to us ranch with the intention of turning the existing garage into this addition and were hit with Hurricane Irene and watched 3 inches of water flood the garage almost up & into the doorway of the house. Almost 2 years later, a civil engineering plan and placement of a property water management system and demo of the old garage and construction is now occurring. I'll look into the other mini split manufacturers you mentioned. I try to buy made in the USA whenever possible to support our economy and USA workers, so this will be a consideration into my final decision.

    Again, thanks so much for contributing to this project through your expertise. I may not know much about all the aspects of building but thankfully I have a pretty good source on finding expert help such as yourself. Sometimes it isn't knowing the answers but rather knowing where to find the information.

    ann
  7. Dana

    Dana In the trades

    Messages:
    2,924
    Location:
    01609
    Oops! Order of magnitude math error:

    "Assuming even a 10F delta-T on the air you're moving vs. the air returning, that's (0.18 x 10F=) 1.8 BTU per cubic foot of air. To meet a 2600 BTU/hr heat load that's 2600/1.8= ~1450 cubic feet per hour or (1450/60 minutes per hour=) ~25 cubic feet per minute.


    Uh, make that 0.018 BTU/degree-foot, or 250 cfm (not 25 cfm) to carry the whole load, if you have only a 10F delta-T.

    But your actual delta-Ts are likely to be closer to 20F with the wood stove is stoked and it's +15F outside, making the Fantech FG-4 just about ideal. Running a 250cfm fan would be extreme overkill for the average (as opposed to the peak) wintertime heat load of that room.
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