Space Heat Limiting, Draft and NG Pressure Drop Mod/Con Lochinvar NKC 150N Combi

Peregrine · January 5

hope you all had a great holidays.

the appliance is maintained and cleaned Meticulously once a year.

given the 3X Over size of the 150k BTU 10:1 turn down modulating appliance, space heat is Limited to 10% and the house has Never been cold. at that limit it runs for hours at a zero temp day. i didnt design the system.

will the fact that it runs at low fire for so long Damage the burner because the flame is too Close to the surface of the burner? Please comment.

gas pressure at "off" is 8.15 inches w/c, is 8 inches w/c at low fire (10%) and at 6.3 inches w/c at high fire. Please remember that the appliance runs at no more than 10%. that pressure drop at high fire is a New development. the burner and gas valve are 2 months new given combustion problems not solved by a new burner. i think the combustion problem might be recently solved given CO levels at 125ppm and O2 and CO2 levels within ranges at high fire. the gas regulator works in warmer weather as indicated by pressure drop does not go away. piping size is adequate because the pressure drop is a new problem. that pressure drop has Not been resolved. Please comment on the pressure drop .

Draft measured 2.5 feet from the bottom of a vertical stack is 0.1 at low fire and 0.13 at high fire. there are No specs available from the manufacturer and there is no mention of draft in the install or service manuals. from what i think i understand is that draft should be Negative numbers for modulating appliances. the pressure switch does not shut the boiler off indicating no blocked vents. vent size is 3"pvc and lengths are 15 feet long. as i think i understand poor draft can Damage the burner? Please comment on the positive draft.

please help.

LRCCBJ · January 5

A Lochinvar model number will be beneficial………….you don't have a "general" problem…………it is specific to the boiler and likely requires someone very familiar with that boiler to assist online.

Peregrine · January 5

NKC 150N. just added to headline sorry.

GroundUp · January 5

The pressure drop is due to either the regulator or the gas line, unless there is something boogering up the gas valve. Are you measuring the drop on the designated gas valve port or elsewhere? And yes, low fire all heating season will cause undue stress on the burner/HX but if it's being meticulously maintained as you say, it's of little consequence.

@LRCCBJ though it wasn't specifically stated, Lochinvar only makes one 150k NG combi boiler so it's an NKC-150N

Peregrine · January 5

regulator and gas line worked for 7 years; no pressure drop on modulating ramp. gas valve is new 3 months ago.

hot_rod · January 5

Gas regulators can fail at any point in time. Just because it worked for 7 years doesn't really matter. It's easy enough to check the regulators pressure? You should not have to mess with the regulators adjustment, it should stay at the factory setting. Is it your reg or does it belong to the fuel provider?

I'll ask the burner folks at AHR this year about continuous low fire, how it effects the burner. The boiler will be efficient when you expose a 150K heat exchanger to a 15,000 flame. You have a lot of surface area to condense on.

Peregrine · January 5

my next plan is to call the utility and ask them to check their regulator.

any feed back on the positive draft reading on a modulating boiler?

thanks Hot Rod

pedmec · January 5

I'm getting a little concerned with the question because if its a mod-con boiler its should be vented to the outside thru approved venting material. But your question of why its a positive draft is concerning because your implying that it should be negative. But that would be for atmospheric cat 1 boilers that would vent thru a chimney under a negative draft. A mod con is a forced draft appliance which has to operate under a positive draft to remove the flue gas products of combustion and you should never be in a chimney unless the chimney is just used as a chase.

Peregrine · January 5

it is vented to the outside through approved venting material and not in a chimney. and i just learned something that a modcon is a forced draft appliance and my draft reading is ok. i could'nt be happier.

thank you so much pedmec and have a great day

GGross · January 6

Do you have records of the gas pressure from previous years that you can compare to, or is it just a new development because there were no faults before? I'm assuming this is natural gas? have you added any gas fired appliances since the install? or replaced any other gas fired equipment?

Peregrine · January 6

the pressure drop 2 months ago was 0.5 inches w/c upon high fire from 8.25 to 7.75 in the summer. The pressure drop 2 weeks ago went to 6.3 inches w/c from 8.1 inches w/c and it is winter. And there has been no change to the house. I called the local utility to explore if it is the gas regulator. Would be great to get some input. Thank you

GGross · January 7

https://forum.heatinghelp.com/discussion/comment/1832497#Comment_1832497

Would seem like a regulator issue. What exactly did I say that you disagree with I was asking questions to try to help you lol?

Peregrine · January 7

i dont disagree with anything didnt mean to give you the impression i did. Grateful for your onterest

Space Heat Limiting, Draft and NG Pressure Drop Mod/Con Lochinvar NKC 150N Combi

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