Chimney & fireplace
Fireplace Efficiency Calculator
Compares fireplace efficiency, where an open fireplace can be a net heat loss.
Result
Not all unbilled time is waste. Travel, restocking, training and warranty calls are necessary and will never be zero. The useful question is whether the share is drifting, not whether it reaches 100%.
Get a Free Business AuditHow the calculation works
Efficiency here is the share of the fuel's heat that reaches the room rather than leaving up the flue. The honest comparison across appliance types is wide. An open masonry fireplace delivers very little of the fuel's energy into the room and simultaneously draws heated household air up the chimney to feed the fire, which is why its net contribution can be negative over a heating season. A closed appliance, a stove or an insert, delivers a large share of it. Gas direct vent and electric sit differently again because of how their energy is supplied.
What moves the number
- Appliance type, which is the dominant factor by a wide margin.
- Whether the appliance is closed and sealed or open to the room.
- Where combustion air comes from, since drawing it from indoors loses heated air.
- Fuel cost per unit of delivered heat, which is the figure that matters to a bill.
Where this one goes wrong
An open fireplace burning while the heating is on can cost more than it contributes, because the fire needs air and takes it from the heated house, pulling cold air in elsewhere to replace it. That is why a roaring fire can leave the rest of the house colder. It does not make open fireplaces pointless, since the pleasure of one is the actual reason people have them, but it does make the energy argument for one honest. Comparing fuels needs to be done on cost per unit of delivered heat rather than on the price of a cord, a therm or a kilowatt hour, because those carry very different amounts of energy.
Before you quote
- Compare appliances on delivered heat, not on fuel unit price.
- Account for combustion air drawn from the heated space.
- Be honest that an open fireplace is for pleasure rather than heating.
Where the rules come from
Questions
About this calculator
Does an open fireplace actually heat a house?
Barely, and over a season it can be a net loss. Most of the heat leaves up the flue, and the fire draws heated household air with it, pulling cold air in elsewhere. That is why a room with a roaring fire can feel warm while the rest of the house gets colder.
How much more efficient is an insert or a stove?
Substantially, because it is a closed appliance that transfers heat into the room rather than losing it up an open flue, and it does not draw room air in the same way. Converting an open fireplace with an insert is the single largest efficiency gain available in this group.
How do I compare the cost of different fuels?
On cost per unit of delivered heat rather than on the price of a cord, a therm or a kilowatt hour, because those units carry very different amounts of energy, and the appliance efficiency then changes how much of it reaches the room. Comparing fuel prices directly is meaningless.
The formula
utilisation = billed hours / paid hours
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How to use this calculator
- Paid hours per day. Enter your own figure; the page starts at 8.
- Hours that reach an invoice. Enter your own figure; the page starts at 5.2.
- Number of technicians. Enter your own figure; the page starts at 3.
- Rate charged per hour ($). Enter your own figure; the page starts at $125.
- Cost per paid hour ($). Wage plus burden.
- Working days per month. Enter your own figure; the page starts at 22.
The result updates as you type, so you can try a figure, see what it does to billable share of the day, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Paid hours per day | 8 |
| Hours that reach an invoice | 5.2 |
| Number of technicians | 3 |
| Rate charged per hour | $125 |
| Cost per paid hour | $34 |
| Working days per month | 22 |
What comes out
| Result | Value |
|---|---|
| Billable share of the day main result | 65.0% |
| Unbilled hours per month | 185 |
| Revenue those hours would have carried | $23,100 |
| What the unbilled hours cost in wages | $6,283 |
65.0% of the paid day reaches an invoice. The rest is 185 hours a month, costing $6,283 in wages and carrying $23,100 of revenue that never happened.
How sensitive the answer is
Holding everything else steady and changing only rate charged per hour, this is what happens to billable share of the day. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Rate charged per hour ($) | Billable share of the day |
|---|---|
| $63 | 65.0% |
| $94 | 65.0% |
| $125 example above | 65.0% |
| $188 | 65.0% |
| $250 | 65.0% |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Paid hours per day
- A number, between 0 and 24, starting at 8.
- Hours that reach an invoice
- A number, between 0 and 24, starting at 5.2.
- Number of technicians
- A number, between 0 and 500, starting at 3.
- Rate charged per hour ($)
- A money amount, starting at $125.
- Cost per paid hour ($)
- Wage plus burden.
- Working days per month
- A number, between 0 and 31, starting at 22.
What the results tell you
| Result | What it is |
|---|---|
| Billable share of the day | The headline result. A percentage. |
| Unbilled hours per month | A number. |
| Revenue those hours would have carried | A money figure. |
| What the unbilled hours cost in wages | A money figure. |
Estimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.