Refresher training on how to get max BTUs from your stove

[kinsmanstoves]

Lets look at the Harman P-68 for example. The stove has a rating of 68,000 max. BTUs. The average BTU for wood pellets is approx. 8,200 BTUs per pound. That would mean you take 68,000 / 8,200 = 8.29 pounds of pellets per hour to make that BTU. No remember your stove is not 100% efficient so you will lose heat out the venting. So if you are not burning over 8 pounds of pellets per hour you are not getting the max out of the stove. Let say you burn a bag a day, that is 1.6666 pounds per hour so other than efficiency loss you are only getting approx 13,666 BTUs per hour.

Eric

 

[DAKSY]

Something seems amiss here...
If you burn 8lbs an hour, 24 hours a day, then you will burn 192lbs a day.
divide that by 40 & you get 4.8 bags a day. Divide 4.8 into 50 bags (1 ton) =
10.41 days per ton. If you figure 150 heating days (Nov - Mar), you'll need just
about 15 tons of pellets to get the max heat out of your P68 for ONE winter.
Flame me if you like, but it almost seems pointless to burn pellets...

 

[Flammam]

Something seems amiss here...
If you burn 8lbs an hour, 24 hours a day, then you will burn 192lbs a day.
divide that by 40 & you get 4.8 bags a day. Divide 4.8 into 50 bags (1 ton) =
10.41 days per ton. If you figure 150 heating days (Nov - Mar), you'll need just
about 15 tons of pellets to get the max heat out of your P68 for ONE winter.
Flame me if you like, but it almost seems pointless to burn pellets...

No flame he is looking at MAX output. How hot do you think your house would be if the stove was at a constant 68k BTU's? I cant think of one time I have ever turned my Austroflamm to max, most of the time it runs between 1/4 to 3/8 max.

 

[kinsmanstoves]

Something seems amiss here...
If you burn 8lbs an hour, 24 hours a day, then you will burn 192lbs a day.
divide that by 40 & you get 4.8 bags a day. Divide 4.8 into 50 bags (1 ton) =
10.41 days per ton. If you figure 150 heating days (Nov - Mar), you'll need just
about 15 tons of pellets to get the max heat out of your P68 for ONE winter.
Flame me if you like, but it almost seems pointless to burn pellets...

NO flame needed. Just like a car motor, do you run it wide open all the time, nope. Refer to the last couple sentences. If you burn a bag a day.

Eric

 

[TheMightyMoe]

In my case, during peak heating season, I need that full 68k BTUs 45 minutes out of the hour, however, most the time I do not.

If I leave the feed rate @ 6 when it is 10* degrees outside, the stove turns on shortly, then turns off. Room will get hot FAST and cool slowly.

Feed rate @ 4 when it is 10* degrees outside, the stove cycles less. Room will heat evenly but take longer to reach set point. More comfortable.

Now this isn't a boiler, but efficiency wise, you are burning more effectively if you can modulate to meet a demand then to over shoot constantly.

In theory you get better heat transfer @ higher temperatures, but you will also be sending a lot more heat out of flue.

From an efficiency standpoint, you should be burning your stove to match heat loss of your home perfectly, but that is not realistic in the case of a pellet stove.

 

[kinsmanstoves]

I speak with almost all my customers almost once a year to ask questions about their stoves and how they run them. What seems to be the average is until it gets colder, 30 degrees they run on the thermostat. Once the temp drops they run on a manual setting with a constant burn. This does not work for everyone but does seem to be the average.

Eric

 

[lbcynya]

Maybe Eric meant to say "needing" instead of "getting" in the last sentance... In otherwords, you have a 68k BTU monster and only use 13k+ on a regular consistent basis. Just like a car, you only need horsepower when you want/need to go fast, otherwise you are only using a small percentage of the available capabilities... If you need 8 lbs of pellets per hour, you have way bigger problems than the cost of pellets alone...

 

[TheMightyMoe]

Exactly, by using stove temperature mode, and running constantly at a set temperature, in essence they are modulating to meet the demand of the house. (If the house does not over heat / under heat)

Comparatively, you would have to look at the cost of running 100% of the time @ precisely demand, vs cycling 50% of the time above demand (Thermostat + swing), and getting less wear on the equipment.

Rarely does my 68 burn full blast for long periods, it does modulate up to full burn though. It's hard for me to imagine needing a 68 in most places unless your home is extremely under-insulated / drafty / huge.

Now when it drops from 10* above to -40* or if I setback while I am at work, the stove will get quite the work out.

 

[subsailor]

I've been able to consistently find a sweet spot with my stove in room temp where the blower never shuts off and the stove will maintain temp within 2 tenths of a degree. Very comfortable running this way.

 

[jtakeman]

Pellets at 8200 BTU and feed at 8.29 p/h may give you a gross BTU input of 68K. But you will not get that from the stove. Actually output BTU's will be 75 to 85% of the 68K. So in all actuality you should expect something closer to 55K BTU's @ 80% effiency.

 

[kinsmanstoves]

Pellets at 8200 BTU and feed at 8.29 p/h may give you a gross BTU input of 68K. But you will not get that from the stove. Actually output BTU's will be 75 to 85% of the 68K. So in all actuality you should expect something closer to 55K BTU's @ 80% effiency.

You are correct, I never stated input vs. output. The man thing is the pellet and not all pellets are created equal.

Eric

 

[jtakeman]

You are correct, I never stated input vs. output. The man thing is the pellet and not all pellets are created equal.

Eric

Drop the input BTU of the pellet to 7800 BTU's and the exact same stove's net output drops.

7800 x 8.29 p/h = 64662 @ 80% = 51729 BTU's

Simply changing pellets can make a difference.

 

[kinsmanstoves]

Good pellets equal a good burn. That is one of the reasons I push for indoor and proper storage.

Eric

 

[harttj]

I don't think the average user understands that it takes more pellets to create more heat and how many lbs are required. I have a 175k btu input appliance but my load is only up to 60k max at worse conditions based on actual usage. Lots of corn or pellets during those periods of time. Also need to remember if you were not creating btus with pellets would be creating the same amount of btus with propain or oil or electricity, just at a higher cost.

 

[kinsmanstoves]

I don't think the average user understands that it takes more pellets to create more heat and how many lbs are required. I have a 175k btu input appliance but my load is only up to 60k max at worse conditions based on actual usage. Lots of corn or pellets during those periods of time. Also need to remember if you were not creating btus with pellets would be creating the same amount of btus with propain or oil or electricity, just at a higher cost.

A BTU is a BTU no mater what the fuel is.

you would need 21.34 pounds of pellet per HOUR to make 175,000 btu input. Now that is a lot.

Eric

 

[Eatonpcat]

This has been a public service announcement from "Eric Nye the BTU Guy"!!