Is heat Loss Linear?

Alrighty you engineer types... is heat loss linear? In other words, if my heat loss is 50K BTU per hour at temps 0 degrees outside and 70 degrees inside... and NO BTU per hour heat loss at temps 70 degrees outside and inside, can I graph these two 'points'... draw a straight line between them and predict with some measure of accuracy the heat loss I can expect when the temps outside are 30 degrees and inside 70 degrees, when temps are 45 degrees outside and 70 degrees inside.

Why you may ask? I HAVE A NEED TO KNOW! Just kidding - I'm attempting to gauge if I need to go ahead with a purchase of an AHS or buy a cheaper used unit (savings of maybe $ 4K if purchasing a used unit) like a keystoker or an EFM 350/520. I'm guessing that I will not see the return in spending the extra on the limousine of coal boilers if the heat loss in my home is not great enough. I also want to factor in the ease of use. I'm hearing that the AHS - if buying the thermocouple in the ash grate 'system' - is nearly automatic and takes little tuning... VERY easy to run and maintain. I don't hear that kind of claim from anything else. Could someone set me straight on this misconception if indeed it is a misconception? I'm currently a wood/oil burner. I'd like to have an automatic ash removal system that I'm working on in theory only at this point, an overhead bin that at the flip of a switch my hopper is filled - so that the operation is as smooth as can be designed.

I need to say that I am the optimist of all optimists! Often I need to be shot down from the third hemisphere from which I spout many of my ideas... to stay in touch with reality - my wife is gifted in this regard (this is a compliment fellas)! Any help would be much appreciated. I need to make a decision here in a couple of weeks. I actually am kicking myself for not buying that EFM 350 that sold just a bit ago on the forum.

Thanks AGAIN fellas - for everything.

Pret

Yes and no

You cannot plot a linear heat loss curve on ODR alone

but you can come closer if you use degree day measurement

Well I was wrong again and I will edit. - Heat loss is a function of the transmission rate of the material and the difference in temperature from one side to the other.

Double that temperature difference, and you double the heat loss.

But degree day measurement can better predict load demand and fuel use and my head was there when I responded last time - Sorry for the goof!

Pret, Hi. I'm sort of new to this coal business but what I have figured out is pretty solid. Basic physics seems to suggest that heat transfer rates increase as temperature difference increases. More heat loss when its colder outside. That's as far as I care to venture about that. There boiler issue is all a matter of a point of view. The AHS Is indeed more efficient. 87% I think. An EFM520 is 80%. 7% more efficient looks real good on paper. If you burn, say, 5tons of coal per year, Which I've heard is avereage, 7% of 10,000 lbs is 700 lbs. Quite alot of coal. If your coal cost $200 per ton that would equate to a savings of $70.00. If you are justifying a cadillac of coal boilers for an additional $4000, it would take 59 years to recoup the additional return of your investment. Of course, those numbers could be tilted quite far either way. Major coal usage or extremely high priced coal will change the equation significantly. My point is , it all depends on how you look at it. It truly seems to me hard to chose which boilers to get because they are all good in their own way. I haven't read a post yet about a boiler owner that said "Do not buy one of these" They are all great units. Have fun deciding. It's part of the coal burnin process. Scott

At the most basic level, yes, heat loss is a linear function of the difference of the temperature inside vs outside multiplied by a constant which represents your house's thermal conductance. However, in practice this method of predicting heat loss is only a very rough estimate and only useful if dealing with day, week, or monthly averages using heating degree days. For instantaneous predictions things like sunlight (angle of incidence, intensity, and where it is hitting the house), cloud cover, wind, rain, humidity, snow, etc. can all wreck (often times severely) a perfectly good estimate based on the ideal, linear heat loss calculation.

If you're wanting to figure out what BTU rating a heating appliance needs to have for your needs there are books and worksheets available to guide you through the calculations. Yanche (or maybe is was LsFarm or WNY) has posted them previously, you should do a search for his name and maybe "heat loss calculation", "boiler sizing", "boiler rating", or other such things. Could also PM him for the links. Lastly, you could contact a local boiler dealer or HVAC contractor to have them do this measuring and calculation for you. This last option may be a good way to go if this is the first water based heating system installation in the house and/or you aren't particularly adept at plumbing work.

Hey Pret, why not consider a used AA? It is the same as the AHS except for the grate movement system is a little more middle ages and the auger kinda sounds like a cement truck. Another option is the eshland boilers, basically the same as an AHS with a few monor exceptions. I bought one with a hopper and auger feed for $1,750 this season and it is in great shape.

Paul gave you some good ideas about sizing, and Yanche has the forms if you can't find the post you could PM him. As Scott said boiler efficiency is not the only consideration, if you find a good used unit for a decent price and parts are available, the payback for the more efficient unit stretches out into the double digits. IMO, used is better, but then I'm a junk collector.

hey Mattaus... is it for sale $$$$? :,)

Actually I'm keeping the Eshland but I will have an AA 130 completely refurbished and ready to go later in the summer, PM me when you are ready.

Hi pret,, I would say that if you can find a good used EFM ,Gentlman Janitor, Van Wert , Keystoker, Harman, AA or AHS, buy it.. The EFM like the AA requires a coal bin/hopper near the boiler,, The AHS has the big 'funnel' hopper.. the Keystoker and Harman have a rectangular hopper attached to the boiler.

ALL the units are good units.. the Keystoker and Harman use a bed type stoker, the EFM, VW,and GJ use an underfeed stoker/firepot. The AHS/AA sort of a top-feed firepot. [which you know].

I don't think you can go wrong with any of them,, and even if you get one,, and later decide to change to another, the changing of the plumbing isn't that tough, as long as you plan ahead for a potential change-of-boiler.

Have you decided to incorporate a chimney in your new home? Have you finalized the plans??

Greg L.

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I figured at it's most basic element, heat loss is linear... I'm looking for the worst-case scenario. I'm assuming that the wind, in theory, increases the temp differential to something akin to the wind - chill vs. inside temp. Angle of incidence would be a cool problem - the home will be facing southwest... so I believe the sun in the summer will be more over the house and shinning on our porch, but in the winter, we should get the sun on the back of our house... shinning in the windows. I'm not exactly sure the direction the house will be facing... but a quick mental eval leaves me to believe that it's facing southwest. EITHER way... I'm excited!

pvolcko wrote:If you're wanting to figure out what BTU rating a heating appliance needs to have for your needs there are books and worksheets available to guide you through the calculations. Yanche (or maybe is was LsFarm or WNY) has posted them previously, you should do a search for his name and maybe "heat loss calculation", "boiler sizing", "boiler rating", or other such things. Could also PM him for the links. Lastly, you could contact a local boiler dealer or HVAC contractor to have them do this measuring and calculation for you. This last option may be a good way to go if this is the first water based heating system installation in the house and/or you aren't particularly adept at plumbing work.

See my post on a new topic "BTU Heating Calculations, Manual J" BTU Heating Calculations, Manual J

PM Yanche for the links to the workbook so you can figure out that worse case scenario and know what the max rating of your boiler needs to be. Be excited, but be smart and do the necessary homework and planning before buying anything.

Another method is to look at your existing boiler/furnace and see what the BTU rating is. If it was installed by a professional heating contractor that contracts for the fuel company you can almost bet that it's oversized. Most houses that require 100k BTU's based on the average coldest days will get a 120k btu unit installed, it's the way they all do it to prevent a service call on an extremely cold day (and it sells more fuel). The EFM 520 is very easy to set up and tune. You set it to the chart in the instruction sheet and then just fine tune it to the coal you are using. Once set that's it, if you are like most people you'll never touch it again. We talk about it on here for hours but in reality it's simple,

Yanche to the rescue: http://www.nepadigital.com/bb/about4104.html#p37473

Hey Mattaus... I tried PM 'n you... not sure it worked. It's listed in my outbox... not listed as being sent. Could you let me know if you received it? Thanks.

Pret

Hi Pret, yes the way an outgoing PM works is that it will show in your out box until I read it, then it will be gone. If you delete it before it is read then the recipient will not be able to open it.

Anyway, I read your PM, will reply tonight when I get a chance with some details and answer to your questions. Plus my ideas on your science project... er um... I mean boiler installation plans.