Heat loss calculations vs coal usage

Here's a conundrum.

I ran my heat loss calcuation based on what I know about my house and came up with between 28-38k per. Small footprint, blown in cellulose to the ceilings and walls, brick first story with single panes and storm windows. However, if I look at my usage last year, back out the loss due to efficiency and the loss due to DHW, I end up around 55-60k (85% eff., 13milbtu for DHW, 4.5tons total leaves 78.8k btus for heating). The only way I can get the calculator to give me those kinds of numbers is to decrease the R value of the windows (which may not be 2, they may be 1.5) or increase the amount of air changes per hour.

When it snows, I have almost no snow melt on the roof on the north side of the house, and it takes bright sun to melt the snow on the south. I figure that's a good indication that I'm not losing a lot of heat through the roof, but other than the windows I can't figure out where it might be going.

Add that I'm too cheap to pay for an audit atm and you have a lot of unanswered questions about heat loss and coal usage....

Best bet is to review the calculations, perhaps even use a different source (there are several available on line) and start over with new numbers. Don't forget the loss in the basement due to no insulation.
Based on what I saw of your house the number you came up with seems low, of course I'm no expert, just a jack of all trades!

Matthaus wrote:Best bet is to review the calculations, perhaps even use a different source (there are several available on line) and start over with new numbers. Don't forget the loss in the basement due to no insulation.
Based on what I saw of your house the number you came up with seems low, of course I'm no expert, just a jack of all trades!

I'll lose heat in the basement even if I'm not heating the space?

Heat travels from high to low. If the basement is not heated, the heat loss from the house is to the basement, then from the basement to the outside. Temperature will equalize based on the two heat losses. If you know what the basement temperature hovers at on a design day, then you can use that temperature as the temperature difference in the calculation from the basement to the outside.

Keep in mind, infiltration is the biggest number and the hardest to define accurately. It is also the biggest number in the heat loss calculation. Air changes can run from .5 ACH of an extremely tight house to 2 ach to an older loose house.

Figuring domestic hot water load is accurately is no easy task either. Incomming water temperature varies with what the previous season was like. The water is coldest in March/April.

It is one thing to figure a peak load for design sizing, but it takes complex energy modeling to figure out exact fuel consumption.

Combustion efficiency also varies in reality. A steady state peak efficiency of 85% is not realistic over the year.

Buy an over sized stove and don't worry. Your main threat is recirculated air, read the EPA site. Super insulated shut down homes are a menace. Of course, there is a step up from my c rappy Victorian leak box but don't go crazy.

kstills wrote:The only way I can get the calculator to give me those kinds of numbers is to decrease the R value of the windows (which may not be 2, they may be 1.5) or increase the amount of air changes per hour.

steamup wrote:Keep in mind, infiltration is the biggest number and the hardest to define accurately. It is also the biggest number in the heat loss calculation. Air changes can run from .5 ACH of an extremely tight house to 2 ach to an older loose house.

Bingo. Reducing infiltration is the #1 one thing most people can do to reduce the heating load of the house. I have been through that exercise in two different houses, and it is amazing how much some weatherstripping & caulk can pay you back. Don't go nuts and make the place airtight, but go after the "low hanging fruit" like gaps around the sill, cracked/missing glaze around old windows, etc.

As for the amount of coal burned vs. the average heat load. There will always be some questions about "where it all went". Timer cycles, temperature overshoots after heat calls, DHW load...none of that is easy to quantify. You can give yourself a headache trying to figure it out with a calculator.

Adjust the stoker to your needs, keep it in good tune, and clean the boiler as needed...in-between those things relax and enjoy the economical heat.

Define the age of the house. If you have blown in insulation, was it a retrofit? I am betting it was and that would indicated you have an older home. The problem is Blown in settles and isn't perfect for coverage.

An older house is also a good candidate for weather sealing. For a few dollars in caulk, weatherstripping and canned spray foam, you can seal things up enough to make a huge difference. I have lived for 20 years in the house I am in now and still find opportunity to insulate and leak stop.

You said small footprint but didn't define square footage that you live in. 78k btuh output sizing would not be out of line for an older 1500 square foot house.

steamup wrote:Define the age of the house. If you have blown in insulation, was it a retrofit? I am betting it was and that would indicated you have an older home. The problem is Blown in settles and isn't perfect for coverage.

An older house is also a good candidate for weather sealing. For a few dollars in caulk, weatherstripping and canned spray foam, you can seal things up enough to make a huge difference. I have lived for 20 years in the house I am in now and still find opportunity to insulate and leak stop.

You said small footprint but didn't define square footage that you live in. 78k btuh output sizing would not be out of line for an older 1500 square foot house.

The house is 83 years old, and is ~1400ft2. The insulation was blown in and I have no idea when.

In my calculation, I didn't factor in the basement. I'm somewhat confident that my infiltration numbers are not terribly bad, as the snow does not melt ever on the north side of the roof during cold days. So it does not appear that I'm losing a lot of heat out the attic. And in reviewing infiltration problems, most folks concentrated on large footprint gaps, not the small ones found around the windows and doors.

However, I have a serious discrepency between my calculated numbers and my real world usage (I know, I'm saving money, but this has become an obsession) so I'm looking for the area of the house that contributing the most to the heat loss. And my guess, based on the replies here, would be the basement.

If I put fiberglass bats in the floor joists, and my loss is not due to infiltration but to heat transfer from top to bottom, that should decrease that factor by quite a bit, no? Or would it be best to insulate the walls?

Building heat loss and heat gain calculation methodology can be very complex and especially difficult when you want an accurate answer. What method or software are you using? The more complex and accurate ones are based on the A/C Contractors of America methods, i.e. Manual J. I've posted on this forum about it. Do a search and compare your method, and the losses you chose to ignore in making your calculations.

The assumption of 85% coal burning efficiency might be misleading. Efficiency levels like that are generally achieved only when the boiler is firing. Boilers also idle, and at idle they are far less efficient. And if they idle long enough efficiency can drop off to about 25% during very extended idle periods (such as if you run all summer). It might be best to assume about 63% overall system efficiency during the heating season. That figure serves me well.

On top of that, don't assume the "dry basis" BTU figure of about 13,250 BTU's per pound for anthracite, as only testing labs can dry it out well enough to get that many BTU's from it. Assume about 6% moisture, and about 12,450 "real world" BTU's per pound as a consequence.

Putting it all together:

63% of 12,450 BTU's ~= 7,850 BTU's per pound as a fair "real world" output yield.

See if that brings your actual coal usage and your theoretical heat loss calculations closer in line.

If you come from a world of previously heating with electricity, that means 1 lb. of anthracite yields approximately the BTU output equivalent of 2.3 KWH of electricity.
If you come from a world of heating oil that means 1 ton of coal yields approximately the BTU output equivalent of 142 gallons of #2 heating oil (@80% eff. for the oil).

i agree that idling effiencies kinda suck but then again, im still right on track for the old, 180 gals of no 2 = 1 ton. might be slightly less during idling times and shoulder seasons, but i think once old man winter gets here i think that estimate will become more true.

331camaro wrote:180 gals of no 2 = 1 ton. might be slightly less during idling times and shoulder seasons, but i think once old man winter gets here i think that estimate will become more true.

That is the ratio I observed for my house and my dad's after installing EFM's.

Many older heating oil furnaces and boilers are down in the 60% efficiency range. Only very modern ones can claim that they get into the 80's. A few condensing models claim efficiencies in the 90% + range.

At 70% efficiency for oil the equivalence would be 1 ton to 161 gallons of heating oil.
At 65% efficiency for oil the equivalence would be 1 ton to 174 gallons of heating oil.
At 60% efficiency for oil the equivalence would be 1 ton to 189 gallons of heating oil.

Again, this would be for overall system efficiency, and I would assume that for oil there is a somewhat similar case as for coal, in that the output efficiency rating of any oil burning appliance is most likely to be a best case efficiency achieved in a lab setting, and not a real world end user total system efficiency.

my oil boiler is a newer dunkirk (2002), claims 86% effiencent.