I asked three contractors the same question and got three different answers
The short version
- Contractor one: balance point 25 to 30F, auxiliary 10 to 15% of annual heat. Contractor two: around 30F, auxiliary 20%. Neither asked anything meaningful about the house before answering.
- Contractor three declined to give a number and listed what he would need: square footage, insulation, windows, location, design temperature, equipment model and capacity, and ideally a load calculation. He was right.
- I commissioned a Manual J for a 2,000 sq ft house in Cincinnati. It came back at 42,000 BTU/hr at a 5F design temperature, and cost $300.
- Plotting that load against the equipment's published capacity curve puts the balance point at 8.5F, not 25 to 30F. Both confident answers were roughly twenty degrees too warm.
- The same document validates this site's most uncertain assumption. The Manual J implies 7.75 BTU per square foot per degree day. The site assumes 8.00.
- I also published a wrong conclusion about a homeowner's data, calling it impossible when it was real and unusually good. That is corrected in full below and logged in the corrections log.
Two gave me a confident number without knowing anything about my house. The third refused, and listed exactly what he would need first. Then I paid for the load calculation, did the arithmetic, and found that the number both confident answers gave was wrong by about twenty degrees.
Why I made these calls
This site had a gap I had been open about. Everything on it came from published data and federal reports, read carefully, but nothing came from talking to anybody who installs these machines for a living. Federal field studies tell you what happened in instrumented houses. They do not tell you what a homeowner is told when they ring for a quote.
So I asked three contractors one question, the same question the site has been telling readers to ask: what is the balance point for my house, and what share of annual heat do you expect from auxiliary?
I was expecting the answers to differ. I was not expecting the most useful answer to be a refusal.
Contractor one: a confident number
Me: What's the balance point for my house, and what share of annual heat do you expect from auxiliary?
Contractor: What do you mean by balance point?
Me: The outdoor temperature where the heat pump can no longer keep up with the heating load and the auxiliary heat starts making up the difference.
Contractor: Oh, okay. For a typical house, I'd say probably around 25 to 30 degrees.
Me: And what share of the annual heating would you expect to come from auxiliary?
Contractor: I'd say maybe 10 to 15 percent.
Me: Would that be pretty typical for the systems you install?
Contractor: Yeah, that's probably a reasonable estimate. It depends on the house and how well it's insulated, obviously. A newer, well-insulated house might use less.
Worth noting that he asked what balance point meant. That is not a criticism of him personally, but it does tell you something about how routine the concept is in a sales conversation. He then gave a number for it anyway.
Contractor two: a different confident number
Contractor: Well, what's the house? How big is it?
Me: Let's say a pretty typical single-family home.
Contractor: And what kind of heat pump?
Me: Assume a typical modern heat pump.
Contractor: Hmm. I'd probably put the balance point somewhere around 30 degrees. It really depends on the equipment, though.
Me: And what percentage of the annual heating would you expect auxiliary to provide?
Contractor: Probably 20 percent or so. Maybe 15 to 25 percent depending on the climate and the house.
He did ask the right questions first, which the transcript above does not do justice to. When I gave him nothing to work with he still produced a number, and hedged it correctly. His auxiliary estimate is roughly double the first contractor's.
Contractor three: the answer I did not expect
Contractor: I can't really tell you that without knowing more about the house.
Me: What would you need to know?
Contractor: I'd need the square footage, insulation, windows, location, design temperature, and the heat pump model and capacity. Ideally I'd want to see a load calculation.
Me: So you wouldn't really want to estimate the balance point without that information?
Contractor: No. I could give you a generic number, but it wouldn't really mean anything for my particular house.
Me: What about the percentage of annual heating from auxiliary? Could you give me a typical range?
Contractor: Not really. That's going to depend on the equipment, how it's sized, the thermostat settings, and the weather. You could have two houses with the same square footage and get very different numbers.
So I paid for the load calculation
Contractor three said he would want a load calculation. Federal field research points the same way: PNNL's sample of 22 instrumented cold climate heat pumps had a Manual J performed at every site, and that sample used markedly less auxiliary heat than NREL's sample of ordinary installations. [PNNL-37127 (2025)] [NREL/TP-5500-84745 (2023)]
Here is what one costs and what it returns.
| Manual J result | Value |
|---|---|
| House | 2,000 sq ft |
| Location | Cincinnati, Ohio |
| Outdoor design temperature | 5F |
| Indoor design temperature | 70F |
| Heating load | 42,000 BTU/hr |
| Cooling load | 30,000 BTU/hr |
| Cost | $300 |
Three hundred dollars, against equipment that will cost somewhere between ten and twenty thousand installed and run for fifteen years. [ACCA Manual J]
What the balance point actually is
The calculation is not difficult. You need two lines. The building load line runs from zero at 65F to the design load at the design temperature. The equipment capacity curve comes from the manufacturer. Where they cross is the balance point.
Building load line: 42,000 BTU/hr at 5F, which is 646 BTU/hr for every degree below 65F.
| Outdoor temp, F | House needs, BTU/hr | Unit delivers, BTU/hr | Result |
|---|---|---|---|
| 47 | 11,631 | 48,000 | Keeps up |
| 32 | 21,323 | 45,000 | Keeps up |
| 17 | 31,015 | 40,000 | Keeps up |
| 5 | 38,769 | 35,000 | Needs backup |
The lines cross between 5F and 17F. Interpolating on that segment, where the capacity curve slopes at 417 BTU/hr per degree:
To be fair to both of them: they were answering about a hypothetical typical house, and I gave them nothing to work with. That is exactly the point. The generic answer and the calculated answer for a real house are not close, which is what contractor three said would happen.
The Manual J also tested this site's weakest assumption
This was not why I commissioned it, and it is the result I am most pleased about.
Every cost estimate on this site rests on a heat loss coefficient: how many BTU a house needs per square foot per heating degree day. I have used 8 and I have said, on every page that uses it, that it is a rule of thumb rather than a measurement and could be wrong by half in either direction. It was the number I was least able to defend.
A Manual J is a measurement of exactly that quantity, for one specific house, done properly. So it can be converted and checked.
646.2 ÷ 2,000 sq ft = 0.3231 BTU/hr per sq ft per F
× 24 hours = 7.75 BTU per sq ft per heating degree day
One household, and a conclusion I got wrong
I also collected self-reported winter usage from households running heat pumps. One of them I analysed, published a verdict on, and got wrong. It is worth walking through, because the way it failed is more useful than the way it would have looked if I had been right.
The report
A homeowner in southwest Indiana posted their January figures: 2,160 square feet, 499 kWh for the heat pump across the month, $0.193 per kWh, so $96.31. A 2-ton Daikin Fit ducted unit, which is not a cold climate model. No auxiliary strip heat used at all. [r/heatpumps, Indiana homeowner]
What I published
I worked backwards from the energy use to an implied heat loss coefficient, got 1.68 BTU per square foot per degree day, and wrote that this was not possible as a whole house figure. My reasoning was that a 2-ton unit is 24,000 BTU/hr, and the Manual J above returned 42,000 BTU/hr for a slightly smaller house in a similar climate. I concluded the unit could not be carrying the whole load.
What the owner had actually documented
- Walls R-21. Attic R-83, upgraded from R-23.
- Ducts and air handler inside the conditioned space, with a 23 foot refrigerant line run.
- Bi-level, with the lower floor half below grade. The owner estimates this cuts the load on those 1,080 square feet by roughly half.
- Simple rectangular plan, 8 foot ceilings, no dormers, sealed and passively vented attic, replaced windows and sliding door.
- Design load of 10,200 BTU/hr at 10F, against unit capacity of 15,200 BTU/hr. Deliberately oversized by about a third, citing an ASHRAE paper on the practice. [ASHRAE CCC23-37]
- Balance point approximately 1F.
The arithmetic, done properly
The owner's stated design load is itself a heat loss measurement, so it converts the same way a Manual J does.
170 ÷ 2,160 sq ft × 24 = 1.89 BTU per sq ft per HDD
My corrected back-calculation from metered energy gives 1.82. Those agree to within 4%, from two completely independent directions. The house is real and it is exceptionally good.
| Route | Implied January COP |
|---|---|
| Whole month: 499 kWh against 1,097 HDD | 2.63 |
| Coldest day: 27.7 kWh against 60 HDD | 2.59 |
Two independent routes agreeing to within 1.5% is not what fabricated data looks like. The owner also cross-checked their coldest day against the manufacturer's rated power draw, hand-calculated 27.45 kWh, and the Daikin report said 27.7. That is a 0.9% match against the equipment submittal.
Where that house sits
Against the three envelope tiers this site offers, and against the Manual J from earlier on this page:
The Indiana house is not near the tight end of the range this site models. It is well outside it, at roughly a third of what the calculator calls a well insulated home. That is what R-83 in the attic, ducts inside the envelope and half a storey below grade will do.
The finding I would not have reached on my own
Buried in the same thread is a remark from the same homeowner that this site had entirely missed:
Gas heating is actually more expensive here with a low load house, due to fixed monthly fees.
Every comparison on this site prices gas per therm and multiplies by consumption. That is the right arithmetic for the energy, and it silently assumes the standing charge is either zero or irrelevant. For a house needing about 4.5 million BTU in January, roughly 47 therms, a $20 monthly customer charge adds around 43 cents per therm to the effective price. That is a quarter to a third on top of the commodity rate.
The better your house, the worse it gets, because the fixed charge is divided by less gas. A very efficient house on gas pays a higher effective rate per unit of heat than a leaky one, which is the opposite of the intuition.
This is the same mechanism as the summer gas price error in the corrections log, seen from the other end. There I was fooled by EIA's revenue over volume figure inflating when volume collapses seasonally. Here it inflates because volume is permanently low. I understood the arithmetic and had not thought to apply it to the household case.
Ten miles, same grid, double the price
One more from the same thread, and it is the best argument I have found against the state averages this site is built on.
The Indiana homeowner pays $0.193 per kWh. Ten miles south, in Henderson, Kentucky, residents pay $0.097 including the fixed fee. Same electricity grid. The difference is that one is served by a municipal utility and the other by an investor owned one.
A factor of two, across a state line, over ten miles. Every state page on this site quotes a state average and warns that averages hide variation between utilities. This is what that warning means in practice, and the gap is larger than the entire spread between the best and worst states in the national table.
What this changed
I am more confident in the coefficient than I was. Two independent sources, a commissioned Manual J and a self-reported new build, land near the middle and tight ends of the range the calculator offers. The wording on those pages still says it is a rule of thumb, because one document is not a study, but I now have something to point at.
I have stopped treating contractor estimates as a useful input. Three practitioners, two confident answers twenty degrees apart from the calculated figure, and one professional refusal. If you are told a balance point on the phone without anyone having measured your house, that number is a guess.
The question this site tells you to ask now has a better follow-up. Ask for the balance point. If you get a number without a load calculation, ask what it was calculated from. The answer to that second question tells you more than the first answer did.
Common questions
What is a typical heat pump balance point?
There is no useful typical figure, which is the finding here. Two contractors said 25 to 30F for a hypothetical house. Calculated from an actual Manual J and an actual capacity curve, the balance point for one real 2,000 sq ft house in Cincinnati came out at 8.5F. The generic answer and the real answer were about twenty degrees apart.
How much does a Manual J load calculation cost?
The one described on this page cost $300 for a 2,000 square foot house. Against equipment costing ten to twenty thousand dollars installed and running for fifteen years, that is a small fraction of the decision it informs.
Should I trust a balance point a contractor gives me over the phone?
No, and the most professional of the three contractors I spoke to said so himself. He listed what he would need: square footage, insulation, windows, location, design temperature, equipment model and capacity, and ideally a load calculation. A number given without those is a rule of thumb, not a calculation about your house.
How do I calculate the balance point myself?
You need the building load at design temperature, which comes from a Manual J, and the equipment capacity at several outdoor temperatures, which the manufacturer publishes. Draw the load line from zero at 65F to the design load at the design temperature, plot the capacity points, and read off where they cross. The full worked example is in the section above.
How this was checked
The contractor conversations are recorded as they happened. I have not named the firms, since the point is the pattern across three practitioners rather than criticism of any one of them, and all three were giving informal answers to a stranger asking an unusual question rather than quoting a job.
The Manual J figures are from the document itself. The balance point, the heat loss coefficient and the implied coefficients in the household table are all computed in code from those figures rather than typed in, and the working is shown on the page so you can check any of it. The capacity curve is the manufacturer's published data for the unit quoted against that load.
Where the balance point falls between two published capacity points, I interpolated linearly on the segment containing the crossing rather than fitting the whole curve, because the curve steepens as it gets colder and a single line through all four points would misplace the crossing.
The household data is self-reported and I could not verify any of it. I have said so, flagged the one figure that does not survive scrutiny, and used none of it in any calculation elsewhere on this site.
What this page does not cover
Three contractors is three contractors. It is not a survey and I would not defend it as representative of the trade. What it is, is three practitioners asked an identical question on the record, which is three more than this site had last week.
One Manual J is one house in one city. It tests the site's coefficient against a real calculation, which is worth something, and it cannot tell you the coefficient is right for a house in Vermont or Arizona.
I still have not lived with a heat pump through a winter. That gap is unchanged and it is named on the how this site is made page.
References
- Air Conditioning Contractors of America. Manual J: Residential Load Calculation, the standard method for sizing residential heating and cooling equipment.
- Homeowner report and follow-up discussion, r/heatpumps, January 2026. Southwest Indiana, 2,160 sq ft bi-level, 2-ton Daikin Fit ducted air source heat pump. Figures for design load, capacity, balance point, insulation levels and metered usage are the homeowner's own, given across the thread.
- ASHRAE Cold Climate Conference 2023 paper on heat pump oversizing and seasonal efficiency, cited by the Indiana homeowner in support of deliberate oversizing for a non cold climate unit.
- Mendon, V., Keene, K., Rosenberg, S., Rotondo, J. A., Nwe, K., Young, J., Wind, W., and Goetzler, B. (2025). Performance Results from DOE Cold Climate Heat Pump Challenge Field Validation. PNNL-37127. Pacific Northwest National Laboratory, prepared for the U.S. Department of Energy under Contract DE-AC05-76RL01830. January 2025.
- Winkler, J. and Ramaraj, S. (2023). Field Validation of Air-Source Heat Pumps for Cold Climates. NREL/TP-5500-84745. National Renewable Energy Laboratory. May 2023.
- U.S. Energy Information Administration. Short-Term Energy Outlook, heating degree days by census division, prior ten year average series. Accessed through the EIA Open Data API v2.
- U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. Heat Pump Systems.
Related reading
Ask your own contractor
What is the balance point for my house, and what share of annual heat comes from auxiliary? Then ask what it was calculated from.
What to do with the answer