Box Stove to Base Heater Conversion Adventure

Is that 2.5 rule supposed to apply to all coal stoves ?

If so, it's way off from mine. For the coldest days (below zero ) it uses about 15% more and that's about as safely higher I can go without having the stop top glowing cherry red.

If I tried to burn even 2 times more, the stove would melt.

Paul

Sunny Boy wrote:Is that 2.5 rule supposed to apply to all coal stoves ?

If so, it's way off from mine. For the coldest days (below zero ) it uses about 15% more and that's about as safely higher I can go without having the stop top glowing cherry red.

If I tried to burn even 2 times more, the stove would melt.

Paul

It is merely an empirical observation, but back when I ran the "Rule of 2.5" thread it got a lot of positive affirmation, with only a single dissenter.

lsayre wrote:

KingCoal wrote:i was just trying to hunt up that period of weather on W.U. and didn't find it. where did you find the coldest day last season for 46550 ?

thanks,
steve

I know that Indiana often gets noticeably colder than Ohio, so I totally guessed at it. Our coldest day last year here had a mean temperature of -6.5, so I guessed that you probably hit -10 for the mean on or about that day. You may have even been colder than that.

i went and did more digging and found 70 HDD's for a couple days in Jan. last heat season so I guess that makes max use .857 #'s per HDD ?

interesting stuff.

Are you near Goshen, IN, and does its temperature profile pretty much fit your location?

I see where Goshen recorded 70 HDD's on January 7th and then again on January 28th of 2014. If you burned 60 lbs. on both of those days then you are (or rather, were, for your original stove configuration) at 0.857 lbs. burned per HDD for the coldest days of the year, just as you have calculated.

This is what you should track from here forward vs. your coal consumption. You are on the right track now.

Perhaps one of the things that this exercise will prove is that baseburners offer more efficiency than hand fired box stoves on low to moderate HDD days, if nothing else. I still contend that this benefit may to some unknown degree be directly dependent upon their lower overall draft characteristics.

Another thing that may come out of all of this is that it may reveal that hand fired stoves do not perform directly in conformance with HDD's on a day to day basis nearly as reliably as do stokers that are regulated by the homes thermostat(s). This would also perhaps explain why hand fired stoves do not conform as well (if even at all) to the "Rule of 2.5".

Larry,

you may have hit on something here. as little as I know about stokers, they are virtually isolated from any but operator set influences.

stokers have a combustion blower to create and hold the amount of primary air at a near perfect level for combustion of a set metered feed of coal prescribed by the thermostat(s). and it seems most operators prefer Baro. control of the chimney to help perfect this isolation.

hand feds on the other hand are natural draft supplied and heavily influenced by wind. this can of course be managed to a greater or lesser degree with dampers but since the wind isn't constant or steady at any one rate even this is imperfect. you also have the batch feed and fire progress cycle in the hand fed that is diff.

then there's the whole issue of house stack effect that a stoker doesn't have to contend with.

there are stoker boilers, stoker hot air distribution, stoker radiant w/ stove body fans etc. etc. and we seem to be comparing with just the base burner classification.

i think we have an apples / oranges situation on our hands and from my experience i'm afraid the 2.5 rule and #'s per HDD aren't going to give across the board comparisons.

The 2.5 rule is no where close for my kitchen range.

Which while it's firebox design is not as efficient as a round pot base heater's, it is more like a base heater in indirect mode with the long internal passages to slow flue gases, and much more surface area in proportion to that fire pot size to extract heat.

Paul

KingCoal wrote:i think we have an apples / oranges situation on our hands and from my experience i'm afraid the 2.5 rule and #'s per HDD aren't going to give across the board comparisons.

I think a comparison with last years total degree days and coal burned to this years should give a good figure. That is assuming a similar start and stop time and similar indoor temperature.

Let's look at Steve's regional HDD's for the 2013-2014 heating season.

From October through April his region racked up 6,071 HDD's. From October through April there are 212 days.

Average daily HDD's = 6,071/212 = 28.64

Coldest single days HDD's -= 70

70/28.64 = 2.444

For Steve's regional area last heating season it took 2.444 more BTU's to heat a home on the coldest day of the year vs. the average day of the heating season. That's pretty close to hitting the Rule of 2.5 directly on the head. It also applies science to the Rule of 2.5, lending it more credence than when I had formerly assumed it to be purely empirical.

hmmmm,

see next post, thanks.
steve

as I look back at this I have to admit that i'm still confused.

i can see that there are 2.444 more HDD's on the coldest day than the average day but I don't see how that can mean it took 2.444 more BTU's to heat the house on the colder day than the average day.

did it really take 2.444 times as much BTU's to heat the home on the colder day ? because the usage was more like 1.666 per hr. on the average day and 2.5 on the coldest.

???

KingCoal wrote:as I look back at this I have to admit that i'm still confused.

i can see that there are 2.444 more HDD's on the coldest day than the average day but I don't see how that can mean it took 2.444 more BTU's to heat the house on the colder day than the average day.

did it really take 2.444 times as much BTU's to heat the home on the colder day ? because the usage was more like 1.666 per hr. on the average day and 2.5 on the coldest.

???

If you were heating the home with a furnace or a boiler driven off of T-Stats the answer would be "yes", the Rule of 2.5 works. And also "yes" HDD's work. BTU's are linear to HDD's. That is why when your utility company sends you an estimated heating bill in the winter for NG or Electricity they include HDD's in their formula for computing the estimated bill (adding them to your baseline).

I went through our all electric days data and determined that my formula for the heat component of our electricity demand back then was:

3.45 x HDD's = Heat KWH's (whereas presently I'm at somewhere around 1.35 x HDD's = lbs of coal)

Looking at this past January where we had 1,428 HDD's here, this translates to:

3.45 x 1,428 = 4,927 KWH of electricity. Add ~420 KWH for the baseline stuff, and an additional ~270 KWH for the HWT, and my electricity consumption for last January would have been roughly 5,617 KWH if we had not replaced both the homes heat BTU and its DHW BTU needs with coal. I believe it was about 540 KWH actual for us last January.

lsayre wrote:I still contend that this benefit may to some unknown degree be directly dependent upon their lower overall draft characteristics.

Air in volume = air out volume, pressure dictates volume thru the combustion air opening. More combustion air makes the fire burn hotter. Air in volume = a combination of negative pressure in the fire box + the size of the opening for combustion air to come thru.

You can have a stronger draft with a smaller combustion air opening that will equal the volume of air flow thru a stove with a weaker draft and a bigger combustion air opening. I don't believe draft pressure strength has a bearing on efficiency with an air tight stove. A loose stove then, yes.

Lee: If a stove that is drafting at a manometer measured 0.03" burns only as much coal as an identical stove in an essentially identical setting that is otherwise drafting 0.06" (or more) then why bother with installing and maintaining barometric and/or manual dampers at all?

lsayre wrote:Lee: If a stove that is drafting at a manometer measured 0.03" burns only as much coal as an identical stove in an essentially identical setting that is otherwise drafting 0.06" (or more) then why bother with installing and maintaining barometric and/or manual dampers at all?

Just to keep pressure steady.

Lightning wrote:

lsayre wrote:Lee: If a stove that is drafting at a manometer measured 0.03" burns only as much coal as an identical stove in an essentially identical setting that is otherwise drafting 0.06" (or more) then why bother with installing and maintaining barometric and/or manual dampers at all?

Just to keep pressure steady.

To what end?