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Electric Forced Air Furnace

Post in 'DIY and General non-hearth advice' started by chrisasst, Dec 31, 2012.

  1. chrisasst

    chrisasst Minister of Fire

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    Looking to install an electric forced air furnace. Any one have a good one they can recommend? I have one register in my living room that I can hook a duct up to. I have no other except that one. Any good books or videos on how to install one of these units? Unless I can find a cheap contractor or something.

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  2. FanMan

    FanMan Feeling the Heat

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    Is there even such a thing? I've never heard of an electric forced air furnace, why would you want such a thing? Electric heat is usually just baseboard heat or portable.
  3. Seasoned Oak

    Seasoned Oak Minister of Fire

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    An electric heat pump would qualify as an electric forced air furnace.
  4. brian89gp

    brian89gp Feeling the Heat

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    Most forced air furnaces will need more then one register unless the register was huge.

    What you need to search for is either a modular blower with a heat kit or a booster with a heat kit.
  5. chrisasst

    chrisasst Minister of Fire

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    Can someone heat a home with one or two heat pump being the sole source of heat. I dont know much about heat pumps. but they look interesting.
  6. woodgeek

    woodgeek Minister of Fire

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    The answer is yes. W/o ducts and in your climate, you would want mini-splits, and would likely need two to carry you. The 'trick' is getting the sizing right.....the cost is higher than a furnace and proportional to the BTU output, so you don't want to go too big. Do you know how much wood you burn in a season??

    If you are a wood burner the payback on the HP will be slower.....it might make sense to do 1 HP and cheap electric baseboard on the other end of the house. The 1 could carry your AC needs, heat you 100% during the shoulder seasons and help the rest of the time, including when you were burning wood.
  7. chrisasst

    chrisasst Minister of Fire

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    I have two pellet stoves right now. Those are our only heat source. We were looking to move in the summer, and either take the pellet stoves with us or sell them, and of course that means we need a source of heat in this house so we can sell it.
    I was looking at videos of the ductless mini splits last night. I would probably need at least two or maybe even three of those in my house if that was the only heat source that I had here.
  8. FanMan

    FanMan Feeling the Heat

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    Couple of propane heaters might be a better choice... nobody wants electric these days, and aren't heat pumps impractical (or at least less efficient) for colder climates?
  9. WhitePine

    WhitePine Feeling the Heat

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    Newer heat pumps can produce usable heat down into the teens.
  10. woodgeek

    woodgeek Minister of Fire

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    If you're moving, then you have to do something 'conventional' and cheap. Mini-splits are neither in that area. If there is no ductwork, then elecric baseboards can be cheap, if you can DIY install.
  11. FanMan

    FanMan Feeling the Heat

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    I didn't know that. I know they're much better than electric resistance heating at more moderate temperatures Do they use significantly less electricity than straight electric heating at those low temperatures?
  12. chrisasst

    chrisasst Minister of Fire

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    I was thinking that, but I would have to install several of them, unless I am not looking at the right ones.
  13. WhitePine

    WhitePine Feeling the Heat

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    Yes, they do these days. Heat pumps have a specification called the Coefficient Of Performance or COP. Any given heat pump model will list its range of COP at different temperatures, sometimes in the form of a chart. As the outside temperature drops, the COP declines. At some specific temperature it will be down to 1 or equal to electric resistance heat. Above that temperature, the heat pump will show an energy savings. As the outside temperature increases the COP will rise providing increasing efficiency over resistance heat.

    Rheem, the brand I am most familiar with, lists a COP range of approximately 2.2 to 2.8 at 15F for their top of the line products. In other words, their heat pumps are more than twice as efficient as straight electric heat even down at 15F.

    It should be noted that a single stage heat pump properly sized for cooling will not provide enough heat to heat the house by itself at low temperatures. Supplemental heat in some form will be required. However, it is practical to size a two stage heat pump for heating, since it can run on low when used for cooling. That is the setup we have. We heat three ways, passive solar when the sun is shining, wood stove or heat pump at other times. We prefer the wood stove, of course.
  14. woodgeek

    woodgeek Minister of Fire

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    Yes you would. There are also cheap wall mounted propane heaters out there....but I wouldn't want to buy a house heated with one or two of those.
  15. woodgeek

    woodgeek Minister of Fire

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    While I'm a big fan of HPs, and they can work well below freezing, nailing down a specific COP number (versus temp) is quite tricky. My 'conventional split ASHP', (looks like a central AC) is listed as COP=3.0 at 30°F by the manufacturer, but that does not include the blower, defrost or cycling losses. Installation matters a lot....my installer set the unit to defrost every 30 minutes of run time, during which it calls a 15 kW resistance heater 'for comfort'...the effect was to give me a COP closer to 1.5 at that temp! After some tinkering with the defrost control, I think I am at COP~2.3, at 30°F, but if I wasn't a tinkerer...I would be SOL.

    The nice thing about the minis is that they are better designed for cold (versus conventional systems that are designed for Atlanta). They use the same refrigerant as my unit, and have similar theoretical efficiency, but they get much closer to the theoretical value through a slew of good engineering details (and have less for stupid installers to mess up).

    Still, I agree that all modern units will have COP>1 down to 0°F or below.
  16. WhitePine

    WhitePine Feeling the Heat

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    Supposedly, the performance numbers given by HSPF include those other factors that COP doesn't consider, but I find that COP provides a simpler and more direct example of the differences, so I usually use it when I am trying to show that modern heat pumps can work well at low temps.

    Yeah, installation is critical and there are a lot of really bad installers out there. Our unit has demand defrost, which helps tremendously, but then again, it's top of the line and wasn't cheap. The first thing I did as soon as the door was bouncing of the installation crew's departing rear ends was to reprogram the smart thermostat to meet our requirements and most importantly, lock out the heat strips above 10F.
  17. Retired Guy

    Retired Guy Feeling the Heat

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    You can buy two $50 electric baseboard heaters that would provide nearly the same BTUs as the $2000 mr slim, 8500 vs. 9000 (rated). The baseboard heaters use 2500 watts. The heat pump uses 650 watts at 17 degrees f to produce 6700 BTUs. So the HP uses about 25% the electricity to produce 80% of the heat of resistance heaters.
  18. chrisasst

    chrisasst Minister of Fire

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    oh boy, My head is spinning now.. I guess I need to find a HVAC person in my area and see what my best option would be.
  19. woodgeek

    woodgeek Minister of Fire

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    COP is a temperature dependent quantity, and 'seasonally averaged COP' or SCOP will tell you your average heating cost over the season, but it clearly depends on your climate. HSPF is just SCOP*3.414 (BTU/Wh), so the HSPF you get in practice must depend on your climate too. In the specification for nominal HSPF, the climate used is Atlanta, GA. Where I am, SCOPs are typically ~15-20% lower than nominal HSPF/3.4. In the middle of NYS they might be 30% lower.
  20. WhitePine

    WhitePine Feeling the Heat

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    As I understand it, HSPF was designed as a means to compare heat pumps, not as a nationwide sizing guide. It is supposed to take into consideration things like defrost cycles, which it does by balancing heat output against total energy consumed.

    Any selection and installation should be done by someone who can run a Manual J properly, which leaves out a whole lot of people. Even better is a HEED calculation.

    http://www.energy-design-tools.aud.ucla.edu/heed/

    When I ran a HEED calculation on our house, I got a 2 ton cooling requirement. Our HVAC contractor said I was crazy. We ended up installing a 4 ton dual stage system that has a 50% first stage, mainly because of its comfort features and the ability to heat the house without any assistance from the grid strips. It turns out we can indeed cool the house with two tons. The system hardly ever runs stage 2 in the summertime.
  21. FanMan

    FanMan Feeling the Heat

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    Why? Or if you're talking about "vent free" (unvented) say no more; I wouldn't want to either.

    Last year, I just installed a 30 kBTU gas fireplace and two 7500 BTU direct vent gas wall heaters to replace my aging oil furnace, heating a 1500 SF house. So far so good down to 20°F or so, but we'll see how the rest of the winter goes.
  22. woodgeek

    woodgeek Minister of Fire

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    I'm just a snob about cheapo wall mounted (direct vent) heaters. They have their place (in a shop or garage) but not in my living room.

    Of course, probably better than the previous owner dropping a lot of coin for a heating system I don't want, and then rolling it into the price.
  23. FanMan

    FanMan Feeling the Heat

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    Well, in my living room I don't have the "cheapo" heaters (which aren't all that "cheapo at around $400 list, though I paid half that)... the living room has the 30,000 BTH gas fireplace.

    The little heaters don't look that bad in a bathroom or bedroom corner... certainly no worse than the inside heat exchanger of a mini-split. And they work when the power is out... we've had weeklong power outages twice in the last two years...

    [​IMG]
  24. chrisasst

    chrisasst Minister of Fire

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    What are these? Are these your primary heat source?
  25. woodgeek

    woodgeek Minister of Fire

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