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Which is more efficient a P38+ or a P61 ? Which is more efficient a big stove or a little stove ?

Post in 'The Pellet Mill - Pellet and Multifuel Stoves' started by lawlopez, Sep 27, 2008.

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  1. lawlopez

    lawlopez New Member

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    Which is more efficient a P38+ or a P61 ?
    Which is more efficient a big stove or a little stove ?

    I'd like to buy a P38+ ; many people have told me
    it is to small with our 2200 sq ft house.

    But we are a tight house with stress skip panels.
    Our 75K btu oil heater supplies domestic hot water
    and heat.

    And the P38 is actually 43,000 btus.

    So I'm thinking it is a wash.

    But if the P61 is more efficient I might as well go in that direction.

    Does anyone know or have experience with this ?
    Thank you kindly.
    Larry'

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  2. Hanko

    Hanko Minister of Fire

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    the P-38 had two engines and was very effective because of the fact it had a center cannon in its nose. the P61, what the hell is a P61? you mean P51 dont you? Good high altitude fighter. Escorted the B17's. Could kick the zero's ass
  3. cmonSTART

    cmonSTART Minister of Fire

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  4. SteveT

    SteveT Feeling the Heat

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    I don't know the answer but I'll take a shot...

    I can't imagine that the efficiency will vary to any measurable degree between these two stoves. Same manufacturer, therefore the same technology. If there is a difference it should be minimal and not part of the buy decision.

    If you read enough threads you'll find people who either wished they bought a bigger stove or traded up to get the bigger stove. I don't recall seeing any complaints about too large. So if budget and other considerations allow for the larger stove that is probably the better choice.
  5. lawlopez

    lawlopez New Member

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  6. lawlopez

    lawlopez New Member

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    Hearthstone Clydesdale:

    very good observation.

    Larry
  7. bungalobob

    bungalobob Feeling the Heat

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    Bigger is always better. I am getting the P68, it may not fly but it is supposed to pump out the BTU's. My house is around 2000 sq ft. May not heat the entire home, but at least I won't be wishing I bought the bigger unit.
  8. lawlopez

    lawlopez New Member

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    Good luck on your P68.
  9. lawlopez

    lawlopez New Member

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    My house is heated by a 75,000 btu oil furnace and also runs domestic hot water.
    My theory is that the 43,000 of the Harman would require very little of it to take care of heating the house.
    Something like 22,000 btus.

    Also running the oil system might distrubute heat better just when it is coldest.

    Of course I want a P68 but I am buying used and don't have much choice.
  10. lawlopez

    lawlopez New Member

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    But what about the original question, which I have completely forgotten about.
    Is a larger stove more efficient ?
  11. slink

    slink New Member

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    SAme manufacture but not quite same tech. The P61 has the room sensor technology and will measure the temp in the room and only burn the minimum required to mantain temp. The P38 is either manual adjust or wall thermostat. The t stat is not as efficient due to the lag time of the need to heat. Higher temp swings causes more fuel to get back to up to temp. The low burn rate is basicly the same for each stove so the P61 is a better value in my opinion.
  12. lawlopez

    lawlopez New Member

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    Thank you for that information.
    I forgot it entirely.

    Good.
  13. mkmh

    mkmh New Member

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    I would say that the efficiency is going to be pretty similar with those two stoves. However, i've read that many stoves run at their peak efficiency when they are set near the midpoint. I'm not convinced either stove would heat your whole place 100%, but if you're well insulated, and your layout is right you might be ok.

    If you can afford the larger stove I would go with it. The P61 gives you a huge temperature range to work with, which is pretty big plus. I really don't think efficiency will be much of a consideration between those two stoves.
  14. webbie

    webbie Seasoned Moderator Staff Member

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    My guess would be that most pellet stoves would burn better at a mid point or slightly upper point in their range - which means bigger is not better. But that is a guess.

    I think the excess air could lower the efficiency at lower burn rates.

    Maybe Corie can tell us if this has even a bit of truth to it....in general, of course.
  15. MCPO

    MCPO Minister of Fire

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    If you can actually distribute the extra amount of heat the larger stove is capable of putting out then I`d say get that one but I`d hate to be sitting in that same room if you can`t .
    And if you can`t utilize the extra heat what`s the sense of opting for it? Sometimes 2 small stoves is a better option.
  16. lawlopez

    lawlopez New Member

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    We can distribute it. It is a saltbox.
    Cathedral ceiling in bedroom and center hall.
    The wood stove is under the bedroom.
    It flows up, heat the bedroom floor and then goes up the center hall.
    The big fan up there pushes it down.
    The bedroom has a fan also.

    The big wood stove has twice been able to get the center hall fan to turn.
    Of course we were roaring the stove at the time.

    In addition I could turn on the blowers used in the hot air system to distribute the heat.
  17. webbie

    webbie Seasoned Moderator Staff Member

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    Well, then, the correct answer is that if you can use big heat, then a bigger stove is a good choice.

    Just remember that a pellet stove gets heat from....Pellets. That means to create more heat requires that many more pellets, no two ways about it.
  18. lawlopez

    lawlopez New Member

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    "That means to create more heat requires that many more pellets"

    The table below is based on published feed rates in the user manual.
    It shows on a per stove basis what the feed rate translates into btus and
    pounds per day and 40$ bags today.
    The btu range uses 8,000 btu per pound.
    The feed rate for the P38 seems surprising to me.

    So it should be clear that most will be able to burn more pellets than you would want to burn.
    So a larger stove can handle the peak demands.
    But anecdotally people might run 2 bags a day
    This is 27,000 btu per day.
    I'm thinking most of that is at night.
    say 2/3 at night and 1/3 during the day.
    18,000 btu during the day and 36,000 during the night.

    What is interesting is that we only have 10,000 btu headroom for the P38.
    We have 26,000 btu for the P61.
    When we run out of headroom the ice age starts.
    Is this a big problem ? I'm not sure. We could let the house
    temperature sink or let the oil burner come online.

    P38 .75 to 5.75 / hour, 8 to 138 #/day 6000 to 46000 btu .45 to 3.45 bags/day
    Accentra .75 to 5.00 / hour, 18 to 120 #/day 6000 to 40000 btu .45 to 3 bags/day
    Advance .75 to 6.00 / hour, 18 to 144 #/day 6000 to 48000 btu .45 to 3.6 bags/day
    XXV .75 to 5.75 / hour, 18 to 138 #/day 6000 to 46000 btu .45 to 3.45 bags/day
    P61 .75 to 7.75 / hour, 18 to 186 #/day 6000 to 62000 btu .45 to 4.65 bags/day
    P68 1.00 to 8.00 / hour, 24 to 192 #/day 8000 to 64000 btu .6 to 4.8 bags/day
  19. slink

    slink New Member

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    Your house will need a certain amount of btu to heat regaurdless of where it comes from. Assuming the effeciencies are equal(within a few percentage points) it doesn't mean you will burn more fuel if you have a larger stove.
  20. mkmh

    mkmh New Member

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    Yeah, I can confirm that when I have my P61 cranked up on high it blasts through a bag of pellets in no time. So as Craig points out, if you intend to make use of the high end you're going to want to buy a LOT of pellets. My P61 is big time oversized for the area I have it in. Consequently, it very seldom goes above the mid-point. I could have easily gone with the P38, but this was a 2nd hand special and the price and timing could not be beat.

    You may very well be better off with the P38, as long as your fine with burning some oil this winter. Pretty big price diff between the two, right?
  21. lawlopez

    lawlopez New Member

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    I was thinking that a larger stove might be more efficient.
    You paid more, better sheet metal to make it work better.
    ***
    I realized I had no handle on how much oil we burn.
    So I dug up 4 years of oil bills.
    We are running 900 gallons a year.
    Assumnig 100 gallons for domestic hot water & 8000 btu per pound
    we will need: 6.7 tons of pellets.

    If I assume half of that is in 3 months I come out to 25,000 btu per hour.
    2 bags a day is 27,000 btu per hour.

    So this al fits in.

    Where does it get me ?

    You need the bigger heater for the head room to take care of the really cold nights.

    Thanks all for all the help.
    Larry
  22. lawlopez

    lawlopez New Member

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    *** You may very well be better off with the P38, as long as your fine with burning some oil this winter. Pretty big price diff between the two, right?

    I'm looking for used only.
    Prices are all over the place.
    An XXV went for $2000 last week !!!

    Larry
  23. lawlopez

    lawlopez New Member

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    We have decided top get a 1 year old P61.

    thanks again.
    Larry
  24. mkmh

    mkmh New Member

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    Good for you, I think you'll be happy with it. The P61 is a good stove and i've found it to be pretty easy to work on. My stove needed some attention when I bought it, but (with the help of this forum) I was able to whip it into shape pretty quickly. Parts are readily available, and you may even get the balance of the warrantee, if the dealer is able to help you with the transfer.
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