We recently hosted Max Reichlin on our Weekly Wednesday Free CEU webinar Series.

If you missed this session, want to rewatch it, or share it with a friend or colleague, you can now do so, as the recording is available below. In addition, Max answered some of the remaining Q&A below, and your question may have additional follow-up below.  

You can access the web based tool here

You can access the excel tool discussed here

Webinar Survey Revelaed: Participants learned a great deal from the session, particularly about using real-world utility data—rather than theoretical models—to perform energy-based load calculations for HVAC systems. Many found the Thermentor tool to be a valuable and accessible resource for simplifying this process, with repeated mentions of its usefulness, free availability, and ability to replace or supplement Manual J calculations. Key takeaways included understanding how to calculate heating loads from energy bills, how R-squared values help gauge data quality in regression analysis, and the value of top-down versus bottom-up methods. Attendees also appreciated learning where to find helpful tools like Thermentor and DegreeDays.net, and how actual energy usage enables more accurate, comfort-focused decisions about HVAC sizing and upgrades. Remaining questions and uncertainties centered on how to address variable heat loads, potential limitations of the method when estimating multiple variables, and whether this approach can be reliably used for broader energy modeling beyond heating loads. Overall, the training sparked curiosity and empowered attendees to explore these tools further.

### Questions and Answers

1. **Using previous electric bills to calculate and size PV systems?**  

   **Answer:** Energy-based loads are especially helpful for getting your head around the home’s existing energy use. Projecting new scenarios is a little more complex and depends on what’s being replaced. For predicting solar PV sizing, Clean Power Research has another product called WattPlan (www.wattplan.com) which applies much of the same data, but is focused on PV, EV.

2. **For the BTU calculation, don’t you need to subtract out the therms used for water heating and cooking?**  

   **Answer:** Yes. For an HDD type analysis like in the spreadsheet, you can assume that the summer constant load represents the water heating/cooking loads, which are largely constant throughout the year. Thermentor does the math differently, but the net result is the same – we assume that there are constant annual loads and remove those from the temperature dependent loads.

3. **What efficiency would you use for heat pumps? Assume a COP 2-3 but where is the best place to find that?**  

   **Answer:** For back of the napkin calculations, I usually use a COP of 3. For more granular estimates, you can use the HSPF/SEER of the units. It’s not perfect because the COP varies with temperature, but it will give you something to work with. Another good option is to use performance data from AHRI / NEEP if you have specific equipment in mind.

4. **Do you find that the swing months have lower efficiency because of more on/off losses?**  

   **Answer:** We’ve not observed that effect in our datasets, but I would expect it to appear most in single stage air conditioners/heat pumps and less in simple heating systems like gas furnaces.

5. **What is R squared?**  

   **Answer:** R² is a statistical measure of the correlation between two datasets. If R² is 1, the datasets are basically identical. If R² is 0, there’s no relationship between them. It’s not a perfect metric, but it helps to indicate if the data is likely valid.

6. **I’ve used this method before and it generates load estimates 2-3 tons less than other methods, like Manual J. Comments on these differences?**  

   **Answer:** We’ve seen similar results. Bottom-up methods are conservative, which is why ACCA recommends not overadjusting estimates. Our dataset from NEEA shows that these methods often overestimate heat loss.

7. **Is it wise to also consider refinements for anticipated change in HDD based on climate model predictions or increased cold-season thermostat settings as occupants age?**  

   **Answer:** Yes, the heating rate found through energy data can be extrapolated for anticipated changes in user heating needs. Adjustments can be made for expected changes in thermostat setpoints or design temperatures.

8. **What impact do you believe air leakage has on load calculations? Is it important to have a firm measurement of air leakage before proceeding?**  

   **Answer:** Air leakage affects both sensible and latent loads and depends on variables like wind speed and humidity. If a home is using excessive energy or reporting drafts, evaluating the envelope is crucial for comfort.

9. **Only see 17 states to choose from in the app. Will other states be added?**  

   **Answer:** We are adding almost all the missing states except Alaska this week.

10. **On heating type, it says Electric Furnace as a choice. Does that include heat pumps?**  

    **Answer:** No, we don’t currently support existing heat pumps, but we are looking into adding it soon.

11. **Does Central Air include heat pumps when that is added?**  

    **Answer:** Kind of? Air conditioners and heat pumps have similar cooling functions, but heating loads will be incorrect if using a heat pump primarily for heat. Caution is advised.

12. **What data was the R-value slide scale on the last slide associated with?**  

    **Answer:** The R-value in Thermentor reflects the overall thermal resistance of the home, including insulation and leaks. It’s based on the model’s physics and may exceed 10 in highly efficient homes.

13. **Would like to see a heat pump option on existing heat/cool, which would be helpful with replacing an existing heat pump.**  

    **Answer:** Thanks for the feedback! We’ll try to get existing heat pumps into the queue.

14. **Can you use a gas furnace if they have a boiler?**  

    **Answer:** Yes, that should be fine as long as you have an idea of the existing efficiency. If the boiler burns oil or propane, wait for support for delivered fuels.

15. **Will AI take over electrical load management in the future?**  

    **Answer:** It seems demand-side management is growing. I expect to see automated demand control for homeowners, but the specifics of underlying models are uncertain.

16. **Spreadsheet?**  

    **Answer:** Should be included in this follow-up.

17. **Demo did not change BTUH when Average vs Well Insulated was used. Why not?**  

    **Answer:** You probably didn’t click the “Calculate Loads” button again. You need to hit “Calculate” to see new results.

18. **Would the future of the Excel doc include using CDD similarly for cooling loads?**  

    **Answer:** Yes, CDD would have a similar approach, although AC’s/heat pumps are generally more efficient, making their energy signat harder to discern.

19. **Does Thermentor have a web API?**  

    **Answer:** Not yet, but we are looking into developing one and would love to hear your use case.

20. **When using Thermentor in coastal regions, which temp data should be used in the model?**  

    **Answer:** Thermentor currently uses dry bulb temperature. We plan to add improvements that assess solar loads, humidity, and wind speed biases.

21. **If doing new Geo Thermal HP, is it best to do separate Heat and Cool sub-systems due to humidity issues?**  

    **Answer:** Yes, it may be wise in any installation with significant heating and humidity loads during summer.

22. **Energy Collectives… Expect an Energy Synergy revolution?**  

    **Answer:** Ha. While change will be gradual, data is guiding our understanding of homes as interconnected systems rather than isolated boxes.