Prosecution Insights
Last updated: April 19, 2026
Application No. 18/695,109

BURNER VESSEL AND FLUID HEATER

Final Rejection §103
Filed
Mar 25, 2024
Examiner
PAIK, SANG YEOP
Art Unit
3761
Tech Center
3700 — Mechanical Engineering & Manufacturing
Assignee
Digital Heat Limited
OA Round
6 (Final)
65%
Grant Probability
Favorable
7-8
OA Rounds
3y 9m
To Grant
82%
With Interview

Examiner Intelligence

Grants 65% — above average
65%
Career Allow Rate
907 granted / 1386 resolved
-4.6% vs TC avg
Strong +16% interview lift
Without
With
+16.5%
Interview Lift
resolved cases with interview
Typical timeline
3y 9m
Avg Prosecution
48 currently pending
Career history
1434
Total Applications
across all art units

Statute-Specific Performance

§101
0.1%
-39.9% vs TC avg
§103
57.6%
+17.6% vs TC avg
§102
17.6%
-22.4% vs TC avg
§112
17.4%
-22.6% vs TC avg
Black line = Tech Center average estimate • Based on career data from 1386 resolved cases

Office Action

§103
DETAILED ACTION Notice of Pre-AIA or AIA Status The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA . Claim Rejections - 35 USC § 103 In the event the determination of the status of the application as subject to AIA 35 U.S.C. 102 and 103 (or as subject to pre-AIA 35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis (i.e., changing from AIA to pre-AIA ) for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status. The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action: A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made. Claim(s) 34-36, 39, 41, 43-49, 51 and 53-58 is/are rejected under 35 U.S.C. 103 as being unpatentable over Palm et al (US 3,885,125) in view of McGraw (US 5,960,157). With respect to claims 34 and 54, Palm shows a burner vessel claimed including a vessel housing containing a combustible fuel burner (23) arranged to burn combustible fuel for heating fluid in one or more fluid circuits, a first cold fluid inlet (14), a first hot fluid outlet (15), a first fluid duct (defined by an inner shell 12 and an outer shell 13) extending between the first cold fluid inlet and the first hot fluid outlet, and a flue (27) arranged to convey waste combustion gas from the vessel wherein the combustible fuel burner is arranged to heat fluid in the first fluid duct (also, see Figure 1). Palm in another embodiment discloses that one or more electric heating elements (44) can be arranged in the fluid duct for directly heating the fluid as illustrated in Figure 7, but Palm does not show that one or more electric heating is used in combination with the combustible fuel burner for heating the fluid wherein one or more electric heating elements are able to provide heat in isolation to supply the demand without burning combustible fuel and that the heating elements are powered by a DC power supply via a controller as further recited in claim 54. McGraw discloses it is known to provide a hybrid electric-combustible fuel fluid heater including a combustible fuel burner (38) and an electric heating element (62) for heating fluid in a water tank (22) wherein the electric heating element directly heats the fluid as the heating element is immersed in the water tank (22; also, see Figure 1), and McGraw further teaches that only the electric heating element can be selected without selecting the combustible fuel burner to meet the desired fluid/water temperature (column 3, lines 38-46) and that the electric heating element can be powered by a battery (70) which is known to be DC power supply. McGraw further shows a controller (26) to control an amount of heating applied by the combustible fuel burner and by the electric heating element via a processor (28; also see column 7, lines 37-43). In view of McGraw, it would have been obvious to one of ordinary skill in the art to adapt Palm with one or more electric heating elements (44) that can be used for heating fluid in the fluid duct along with the combustible fuel burner which allows the user to select either the combustible gas burner or the electric heating elements in isolation with each other to predictably generate heat for heating fluid in the fluid duct, with the electric heating element to be in direct contact with the fluid as taught by McGraw along with the combustion heating, which allows operating either the electric heating element or the combustible fuel burner for cost saving purposes that depends on cost of operations. With respect to claims 35, 43 and 44, Palm discloses a plurality of fins (26) as a heat exchanger body that transfers heat from burnt fuel to the fluid and that surrounds a combustion zone (also, see Figure 3). With respect to claim 36, Palm discloses the duct comprising at least one duct wall (inner or outer shell) through which heat is transferred from the burnt fuel to one or more fluid circuits (e.g., external heating system; column 3, lines 45-47). With respect to claim 39, Palm shows a plurality of distinct electric heating elements in the duct as illustrated in Figures 5-7. With respect to claim 41, Palm shows the electric heating element (44) that is located in the duct, and optionally spaced from the burnt fuel heat exchanger. With respect to claims 45 and 46, Palm shows a housing with a cover or a multi-layer cover having at least one skin layer (outer layer) with one insulant layer (19) as illustrated in Figure 1 and 3. With respect to claims 47-49 and 58, Palm shows the fluid duct (defined by an inner and outer shell/wall 12/13/18) that is provided as a channel defined or located entirely within the heat exchanger or a sealed pipe through a space or channel that is entirely within the heat exchanger that is between the wall and the cover as illustrated in Figures 1 and 3 forming a U shape (as shown by the walls 13/18), and Palm shows the electric heating element located within the fluid duct or the channel (Figure 7). With respect to claim 51, Palm discloses the vessel housing containing at least one baffle (shown by a fin 26 that can restrain a flow of the heated gas/air) that would divert the heated air/gas which would increase thermal communication between the heated air and the duct wall. With respect to claims 53 and 55-57, McGraw discloses for the electric heating element that can be powered by a DC power supply (70) or an AC power supply shown 120 VAC (36) wherein the controller (26) is arranged to control the supply of power to the electric heating element from the DC power or AC power supply, and McGraw further discloses the controller to control the amount of heating supplied to the fluid based on a fluid temperature measured by a fluid temperature sensor (24) wherein it would have been obvious to adapt Palm with the controller to further control an amount of heating supplied by increasing or decreasing the fuel or power delivered respectively to the fuel burner or electric heating element to predictably meet the desired fluid temperature demanded or desired by the user. Claim(s) 50 is/are rejected under 35 U.S.C. 103 as being unpatentable over Palm in view of McGraw as applied to claims 34-36, 39, 41, 43-49, 51 and 53-58 above, and further in view of Obst et al (US 2012/0315024). Palm in view of McGraw shows the burner vessel claimed except for the electric heating element in a spiraled wire element. Obst shows it is known to provide an electric heating element for heating fluid wherein the electric heating element is in metal sheath formed of a spiral shaped wire element. In view of Obst, it would have been obvious to one of ordinary skill in the art to adapt Palm, as modified by McGraw, with the heating element in a metal sheathed element that is formed of a spiraled element as an alternative heating element structure that can also effectively heat the fluid as known in the art. Claim(s) 52 is/are rejected under 35 U.S.C. 103 as being unpatentable over Palm in view of McGraw as applied to claims 34-36, 39, 41, 43-49, 51 and 53-58 above, and further in view of Deivasigamani et al (US 2011/0041781). Palm in view of McGraw shows the burner vessel claimed except for the burnt vessel arranged to heat water in a first and second independent water circuits including a radiant heating and portable water heating. Deivasigamani shows it is known to provide a fluid heated vessel that provides heated fluid to one or more fluid circuits including a radiant heating and a potable water heating as a first water circuit and as a second water circuit, respectively. Also, see para 0143. In view of Deivasigamani, it would have been obvious to one of ordinary skill in the art to adapt Palm, as modified by McGraw, with one or more water circuit including providing heating water to a radiator circuit or providing portable water heating, or any other water circuits where heated water would be predictably used to deliver heat as demanded or desired by the user. Response to Arguments Applicant's arguments filed 2/27/2026 have been fully considered but they are not persuasive. With regard to Palm, Applicant argues that Palm discloses two distinct embodiments which disclose for an electric embodiment that displaces combustion heating rather than supplementing it, and furthermore it would require Palm to have two separate annular vessels and would not require a single fluid duct to be used for both types of heaters. Applicant further argues that it would not have been obvious to combine with teachings of McGraw since McGraw does not suggest a duct-type burner vessel integrating electric resistance heating elements into a combustion annular duct heat exchanger as claimed. It is noted that McGraw is applied to teach using both an electrical heating and a combustion heater for heating fluid which allows a user to either select one form of heating over the other, or in combination as stated in the ground of rejection. As McGraw teaches for such hybrid heating heater arrangement, one of ordinary skill in the art would also be motivated to combine the electric heating and the combustion heating wherein the combination would have allowed employing the electric heating that can be in direct contact with fluid as taught by McGraw which enables a user to select different heating source when desired, which can depend on cost of operations as known in the art, wherein employing an electrical heating element in to the combustion heating shown in Palm would not destroy its intended use nor would require two annular vessels as argued by Applicant. It is also noted that McGraw is not applied to a duct-type burner but for the combined use of an electric heating and combustion heating in tandem. Conclusion THIS ACTION IS MADE FINAL. Applicant is reminded of the extension of time policy as set forth in 37 CFR 1.136(a). A shortened statutory period for reply to this final action is set to expire THREE MONTHS from the mailing date of this action. In the event a first reply is filed within TWO MONTHS of the mailing date of this final action and the advisory action is not mailed until after the end of the THREE-MONTH shortened statutory period, then the shortened statutory period will expire on the date the advisory action is mailed, and any nonprovisional extension fee (37 CFR 1.17(a)) pursuant to 37 CFR 1.136(a) will be calculated from the mailing date of the advisory action. In no event, however, will the statutory period for reply expire later than SIX MONTHS from the mailing date of this final action. Any inquiry concerning this communication or earlier communications from the examiner should be directed to SANG Y PAIK whose telephone number is (571)272-4783. The examiner can normally be reached 9:00-5:30; M-F. Examiner interviews are available via telephone, in-person, and video conferencing using a USPTO supplied web-based collaboration tool. To schedule an interview, applicant is encouraged to use the USPTO Automated Interview Request (AIR) at http://www.uspto.gov/interviewpractice. If attempts to reach the examiner by telephone are unsuccessful, the examiner’s supervisor, Helena Kosanovic can be reached at 571-272-9059. The fax phone number for the organization where this application or proceeding is assigned is 571-273-8300. Information regarding the status of published or unpublished applications may be obtained from Patent Center. Unpublished application information in Patent Center is available to registered users. To file and manage patent submissions in Patent Center, visit: https://patentcenter.uspto.gov. Visit https://www.uspto.gov/patents/apply/patent-center for more information about Patent Center and https://www.uspto.gov/patents/docx for information about filing in DOCX format. For additional questions, contact the Electronic Business Center (EBC) at 866-217-9197 (toll-free). If you would like assistance from a USPTO Customer Service Representative, call 800-786-9199 (IN USA OR CANADA) or 571-272-1000. /SANG Y PAIK/Primary Examiner, Art Unit 3761
Read full office action

Prosecution Timeline

Mar 25, 2024
Application Filed
Sep 03, 2024
Non-Final Rejection — §103
Dec 01, 2024
Response Filed
Dec 19, 2024
Final Rejection — §103
Mar 19, 2025
Response after Non-Final Action
Apr 08, 2025
Request for Continued Examination
Apr 10, 2025
Response after Non-Final Action
May 27, 2025
Non-Final Rejection — §103
Jul 30, 2025
Response Filed
Aug 25, 2025
Final Rejection — §103
Oct 11, 2025
Interview Requested
Oct 21, 2025
Examiner Interview Summary
Oct 31, 2025
Response after Non-Final Action
Nov 28, 2025
Request for Continued Examination
Dec 01, 2025
Response after Non-Final Action
Dec 30, 2025
Non-Final Rejection — §103
Feb 27, 2026
Response Filed
Mar 13, 2026
Final Rejection — §103 (current)

Precedent Cases

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Study what changed to get past this examiner. Based on 5 most recent grants.

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Prosecution Projections

7-8
Expected OA Rounds
65%
Grant Probability
82%
With Interview (+16.5%)
3y 9m
Median Time to Grant
High
PTA Risk
Based on 1386 resolved cases by this examiner. Grant probability derived from career allow rate.

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