A tale of two buildings...........

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Which one used 15 tons?


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heaterman

Minister of Fire
Oct 16, 2007
3,374
Falmouth, Michigan
I found this very interesting and bring it up because I saw a comment about someone building a new log home in another thread.....

I spoke with both of these people this week making my rounds and checking with customers to see how they did this winter.
Both buildings are heated with a radiant floor system and fired with identical Windhager pellet boilers.

Building 1: 80x80 pole barn construction, 6,400sq ft, new in 2008, 7-1/2" walls blown cellulose with 1/2 Tuff-R on the exterior, 16" cellulose in ceiling. 3" of foam under entire 6" slab with radiant floor heat. 3,200 sq ft of building has 16' ceilings, 3,200 sq ft with 9' ceilings. There are 12x14 overhead doors on the east and west walls of the tall part and 4 9x8 overhead door on the low part. 12 3x3 windows plus 4 standard sized entry doors. Entire building is maintained at 65* minimum with 1,600 sq ft kept closer to 70*. The building is used primarily as a workshop but the owner and his wife practically live out there rather than in their house because it is so comfortable.

Building 2: 38x44 two story full log home plus basement built in 2007, one side of which is full walk out with 2- 9x7 overhead doors plus entry door. (parks his vehicles in there) The logs are 12' machined full Swedish cope chinking. Lots of glass on the South exposure and two glass sliders to the west, only 5 4'x4' windows in the rest of the house. The basement slab is 4" and the main and upper level are thin slab gypcrete. Ceiling roof combination that is 12" thick, main floor has cathedral ceiling in half with bedrooms and a loft area on second level. If you figured the house as three distinct floors you would have just over 5,000 sq ft of space.

Both heating system are set up nearly the same with the Windhager supplying 160-170* water to the main manifold and then using a mixing device to lower water temp to the level required for the floor. One key difference is that the pole structure has weather responsive injection mixing, the log structure uses regular thermostatic mix valves which are manually set to a fixed temperature.


One of these structure was heated with 8 tons of pellets this winter, the other used 15 tons.
Bear in mind that the pole barn has roughly double the cubic feet of heated space
 
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Oops meant to cast my vote for the other building.

TS
 
Heaterman,

How many btus are these Windhagers delivering per pound of pellets? 15 tons has gotta be close to 200 MM btus/yr!!! . Not too far fetched to imagine a large log home needing something close to that though;sick. That's just wrong for new construction in 2007. Maybe not so bad for 1707 but there weren't many(ANY ?) 5000 sq ft log homes built back then and for good reason.

What is the design heat load of each building?

Noah
 
Heaterman,

How many btus are these Windhagers delivering per pound of pellets? 15 tons has gotta be close to 200 MM btus/yr!!! . Not too far fetched to imagine a large log home needing something close to that though;sick. That's just wrong for new construction in 2007. Maybe not so bad for 1707 but there weren't many(ANY ?) 5000 sq ft log homes built back then and for good reason.

What is the design heat load of each building?

Noah

I did a heat loss for the pole barn which came out to 121,000 iirc.
The rated output of these boilers is 88,000 btu
Did not do a calc for the log home.
 
I voted -how long you making us wait to see if we were right or not?

==c

Going to wait and let the suspense build.::P

Then I'm going to do a poll to see if you guys can guess the main reason why.:eek:
 
Heaterman,

How many btus are these Windhagers delivering per pound of pellets? 15 tons has gotta be close to 200 MM btus/yr!!! . Not too far fetched to imagine a large log home needing something close to that though;sick. That's just wrong for new construction in 2007. Maybe not so bad for 1707 but there weren't many(ANY ?) 5000 sq ft log homes built back then and for good reason.

What is the design heat load of each building?

Noah


Normally we see flue gas efficiency in the 84-87% range so figure around 7000-7100 per pound.
 
Another thing to consider is the total cubic feet of conditioned space in each building.

The pole barn is roughly 76,800
The log home is about 43,000
 
Going to wait and let the suspense build.::P

Then I'm going to do a poll to see if you guys can guess the main reason why.:eek:

I would guess air leaks are a bigger factor than insulating differences. Log homes have a bad rep for leaking air, so the air leakage may have a larger heat loss compared to the pole building. I would think the pole building would have a larger heat loss compared to the same building on an insulated foundation. They probably paid a lot of attention to this during construction, the wall to slab insulated transition.

You don't indicate, but the log home foundation is probably not insulated or poorly insulated. Radiant heat in the basement slab, is it wrapped and isolated on foam board? That would be the two biggest factors I would guess, air leaks and improper foundation insulating method for the basement radiant heat. Biggest factor for lower fuel consumption would be lower heat loss., not sq ft size.

Fixed mixing vs reset mixing would have an effect on mild days, fewer start stops and longer run times at a lower constant burn rate. That would be an interesting data point to gather, if you can track start stops over a years time. Could be a big number, double or more start stop cycles. Lower start stops would be a lot better for lower maintenance. Fuel savings should be some, but I don't know if I would guess huge fuel savings.
 
A blower door test would be really depressing for the home owner. And even if they could tighten up the house it would only be temporary.

I've certainly never heard of the log home that required mechanical ventilation.

I just hope these folks knew what they were getting into before they had the house built. I'm sure they are thrilled now to only have to pay around $3k/yr verses whatever they were paying to heat their house.

Noah
 
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my guess is that the the demand caused by the constant churning of max temp supply water to the trv;s and possibly a leaky structure and minimally insulated emitter pipes?
 
I've built a log home and have known people that have lived in them. Over time the logs shrink and allow more infiltration over the years. Some people are unaware that you need to provide a slip connection when attaching an interior wall perpendicular to the outside wall otherwise the logs will not be able to settle together.

Infiltration is always on the top of the list of heat loss offenders and is separated by a huge gap from the second on the list.
 
All good and valid thoughts here. Keep 'em coming.

I have a theory as to what is going on in the high use structure but have to find my way through a little math to back it up.
 
Which one did you vote for?
I didn't want to give it away............. LOG!

Wood is not a good insulator.......can you say thermal bridge with 1000 cubic inches of leakage + expansion and contraction + the entire wall is a thermal bridge, oh I said that already:rolleyes:

TS
 
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You got it Taylor.
The log home is a fuel bandit.:eek:

The factor that has me rubbing my chin on this one, along with the R-value and air infiltration of course, is the chimney.
I mentioned it to the owner when we installed the BioWin in October. He had a Horstman wood fired boiler the size of my F-250 connected to his system. The chimney of course was sized for that beast. It's a 12x12" flue.
We had to put 2 barometrics on the connector pipe to try to get the draft under control. Even after that the lowest we observed was -.06" which is at the upper end of the recommended range.
I'm sure during the winter when the wind was howling across the 80 acre field next to his house both of the regulators were slammed wide open and the draft was still off the charts.
I think his actual efficiency suffered and we were also exhausting a LOT of heated air from the house right straight up that stack. Have to confess I don't know how to put a number on that with any kind of accuracy given how variable draft conditions can be......but I am willing to bet that it was worth almost a bag of pellets a day for the whole heating season.:oops:!!!:oops:!!!:oops:

We told him that a liner would be in order to reduce the flue size but he declined to have it installed.:confused: Now he has a little better understanding of why it's important to have the entire system designed correctly. It's not just the boiler.
 
And I'll bet that there was no shortage of supply air to support those wide open barometrics.
 
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Exactly Fred. Even with that kind of volume going up the stack we saw no indication that the house was going negative.
 
I'm thinking that huge flue is like a giant Hoover sitting up there on top of the house sucking warm air out of it.

I also think that the variable speed injection on the pole barn vs the fixed set point mixers on the log home have more effect than is realized. Again, I don't know how to quantify that or measure it but I know the boiler in the pole barn modulates to a much greater extent than the one in the log home.

Couple those factors with the obvious R-value and air infiltration allowed by the construction and you have a recipe for doubling your fuel use.
I'd hate to think what it would cost to heat the log home with LP gas.
 
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II'd hate to think what it would cost to heat the log home with LP gas.

Very entertaining thread. Thanks.

I would hate to think about what it did cost to heat that home with pellets: 15 * ~$250 = ~$3750 !!!
And if your propane prices are similar to ours in NE, he would be looking at about 2.5 times as much in propane.
 
We are really fortunate to have several manufacturers within an 80 mile radius and that reallt holds down the price. His pellets cost him $185/ton delivered so even as bad as the consumption was his fuel cost was tolerable.
Compared to propane at $2.50+/gallon it was still fantastic.
 
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