Fuel Consumption with brand new Lochinvar Noble Combi Unit

Smith19 · February 8

Hello Everyone -
since April I have been living in a new construction standalone apartment in Massachusetts. It was finished in 2022 and is insulated like crazy; the walls, attic, and floors are packed with foam. The heat is a single hydronic baseboard zone running off of a Lochinvar Noble combi boiler, which burns Propane. The propane tank is 100 gallons.

Aside from the boiler, the gas range/oven in the kitchen is the only other appliances that burns propane. This is my first time heating with propane, and my first winter in the place, and I've totally run clean out of propane twice. I'm amazed at how much this boiler is consuming. I am filling the tank every three weeks and it's just too expensive. A few questions:

Do these boilers have issues with their burners? I've seen them installed everywhere and have heard only good things. This unit has also locked out four times this winter for a variety of reasons: low water pressure, not enough oxygen, low gas pressure, and return water temp. being too high.

I can't imagine that I'm really using this much propane in such a small, well insulated space. There is a chance that the unit is meant to burn gas but was never converted to propane. I say this because the landlord told me that the stove wasn't converted to burn propane, and I've noticed.

Jamie Hall · February 8

You really need to get a technician in there who knows and understands Lochinvar boilers to ensure that it was properly set up for propane and that ll the combustion adjustments were checked -- with instruments -- and adjusted to be correct.

Sounds to me as though if that were done -- and i have my doubts -- it wasn't done right.

If you are responsible for the fuel, you may be able to bypass your landlord. Maybe not.

pedmec · February 8

Should be green sticker from lochinvar indicating it was changed to propane. when you swap the natural gas venturi to a propane venturi you're supposed to put the sticker on the front cover. my experience when you run with propane on a natural gas venturi it will rumble. Only had this situation once

hot_rod · February 8

Typically they only fill tanks to 80%, so you need to go by the meter reading that they leave to get an actual consumption

Smith19 · February 8

hot_rod said:
Typically they only fill tanks to 80%, so you need to go by the meter reading that they leave to get an actual consumption

I did notice this. They filled mine to 70% and charged for 80%, but confirmed an order of 100 gallons. Which I paid for. I've heard that the 80% rule really only applies during warmer months and is hyperbolized in the winter.

yellowdog · February 8

More than likely you have a 120 gallon propane tank, not 100 gallon. An 80% fill on a 120 is 100 gallons. How big is the apartment? What temperature do you keep the apartment? Do you do a lot of cooking? Do you use a lot of hot water? The fact that you 've had so many issues with the boiler already leads me to think it may also be grossly oversized or not set up to run such a small load. Your usage is 5 gallons a day for heat, hot water and cooking if you are truly emptying the tank every 3 weeks. That seems like it is a little high, but not grossly high consumption.

kcopp · February 8

How much baseboard is in the home and how many sq feet? What is the operating temperature? Does it have the outdoor sensor connected?
Was a heatloss done to start with?

Smith19 · February 8

yellowdog said:
More than likely you have a 120 gallon propane tank, not 100 gallon. An 80% fill on a 120 is 100 gallons. How big is the apartment? What temperature do you keep the apartment? Do you do a lot of cooking? Do you use a lot of hot water? The fact that you 've had so many issues with the boiler already leads me to think it may also be grossly oversized or not set up to run such a small load. Your usage is 5 gallons a day for heat, hot water and cooking if you are truly emptying the tank every 3 weeks. That seems like it is a little high, but not grossly high consumption.

The plaque on the tank seems to note 120 gallons - you are correct. As mentioned, the apartment is little north of 500 square feet. I do most of my own cooking and know that gas ovens are not terribly efficient. (I have no idea why they're so popular around here, most new builds seem to have them).

Since the apartment is only 520 or so square feet, I am fairly certain that the boiler is oversized. How can that be addressed? The landlord's plumber friend installed it and he doesn't want it touched by anyone else.

Smith19 · February 8

kcopp said:
How much baseboard is in the home and how many sq feet? What is the operating temperature? Does it have the outdoor sensor connected?
Was a heatloss done to start with?

I have 34.5 linear feet of convector as mentioned in a 520 square foot (approx) apartment. Aquastat set at 145. Since I wasn't around when it was installed, I have no clue if they did a heat loss, which seems very standard to do. There is no outdoor reset.

pecmsg · February 8

Smith19 said:

Since the apartment is only 520 or so square feet, I am fairly certain that the boiler is oversized. How can that be addressed? The landlord's plumber friend installed it and he doesn't want it touched by anyone else.

Not much you can do about it.

Ask the landlord if it's OK to bring someone else in but he can say NO!

Hot_water_fan · February 8

Combis often end up massively oversized for heating, which is what’s happened here. You can ask for a lower set point to get more condensing. An outdoor reset would also accomplish the same thing but wouldn’t be free. There are some other settings which deal with short cycling if they’ll let you change those.

GroundUp · February 8

Your emitter is only capable of putting out about 13,000 BTU so if the boiler is anything but a 110k, it's short cycling with every call for heat. It's grossly oversized for the heating regardless, but if it's a 150k or 199k it's short cycling which beats the heck out of the boiler and the efficiency. The model number inside the right side panel will designate whether or not it was an LP unit from the factory (for example, NKC-110L would be LP or NKC-110N would be NG) and if it was NG, there should be a red sticker somewhere on the unit stating that it was converted to LP gas. I'd be pretty skeptical of this particular boiler running at all on propane if it was set up for NG. With that said, your hot water usage plays a huge role here. One 10 minute shower per day at 110 degrees may very well take half a gallon by itself, plus whatever other usage you've got. Either way, some homework needs to be done here to figure out which unit you actually have and whether or not there was a combustion analysis completed

Smith19 · February 8

Hot_water_fan said:
Combis often end up massively oversized for heating, which is what’s happened here. You can ask for a lower set point to get more condensing. An outdoor reset would also accomplish the same thing but wouldn’t be free. There are some other settings which deal with short cycling if they’ll let you change those.

Wouldn't a lower set point just result in convectors not heating up as much? That has already been an issue as it is, it can take ages for the place to warm up to the thermostat set point in the morning.

kcopp · February 8

Something does not add up. You say there is tons of spray foam but you also say it takes forever to heat up....
Are you doing a large set back at night?
I would get the outdoor sensor installed and make some adjustments. The sensor should have been installed from the start.

Hot_water_fan · February 8

Wouldn't a lower set point just result in convectors not heating up as much? That has already been an issue as it is, it can take ages for the place to warm up to the thermostat set point in the morning.

Depends on how it's operated. A steep setback with undersized baseboard with obstructed airflow? It'll take some time. How long is "ages" and what's the setback?

But in general, the hotter the water the higher your bill. Around 120F is where you want your return temps.

GGross · February 8

Just some quick figuring. 34.5 feet of baseboard at 1 GPM with 140 average water temp gives you 11,040 btu/hr, that would give you 21 btu per square foot, a standard guesstimate for a decently insulated structure, on the coldest day of the year is 20 btu per square foot (that is only a guess!) and that is normally higher than what is needed, and is definitely higher that what is needed the rest of the year except the coldest day of the year. I am thinking that you have something else going on here, whether it be a lack of insulation, maybe some cabinet only baseboard sections, low or no flow (which would make the excess fuel usage even more questionable) very high ceilings with tons of glass, or that boiler is heating another space as well.

Smith19 · February 9

GGross said:
Just some quick figuring. 34.5 feet of baseboard at 1 GPM with 140 average water temp gives you 11,040 btu/hr, that would give you 21 btu per square foot, a standard guesstimate for a decently insulated structure, on the coldest day of the year is 20 btu per square foot (that is only a guess!) and that is normally higher than what is needed, and is definitely higher that what is needed the rest of the year except the coldest day of the year. I am thinking that you have something else going on here, whether it be a lack of insulation, maybe some cabinet only baseboard sections, low or no flow (which would make the excess fuel usage even more questionable) very high ceilings with tons of glass, or that boiler is heating another space as well.

All ceilings are 7' 8", no sections of baseboard are obstructed. I have been told that everything is packed with spray foam, and I've seen it in the attic - but I do live over the garage so it's hard to say. The boiler is only heating my space.

Smith19 · February 9

GroundUp said:
Your emitter is only capable of putting out about 13,000 BTU so if the boiler is anything but a 110k, it's short cycling with every call for heat. It's grossly oversized for the heating regardless, but if it's a 150k or 199k it's short cycling which beats the heck out of the boiler and the efficiency. The model number inside the right side panel will designate whether or not it was an LP unit from the factory (for example, NKC-110L would be LP or NKC-110N would be NG) and if it was NG, there should be a red sticker somewhere on the unit stating that it was converted to LP gas. I'd be pretty skeptical of this particular boiler running at all on propane if it was set up for NG. With that said, your hot water usage plays a huge role here. One 10 minute shower per day at 110 degrees may very well take half a gallon by itself, plus whatever other usage you've got. Either way, some homework needs to be done here to figure out which unit you actually have and whether or not there was a combustion analysis completed

I doubt proper setup was done with this unit. And the landlord simply will not allow it to be looked at, which screws me on the fuel bill. He says a friend of his - who's a plumber and the town plumbing inspector - installed it, so he has total confidence. In terms of showers, the mixing valve has to be cranked all the way hot to get hot enough water, another clue of how the boiler may be cycling.

jimna01 · February 9

I will let the heating experts comment on the heat demand and boiler issues but if the range is properly converted to propane it is not responsible for your gas usage unless you are using the oven for hours a day. I own a six burner gas cooktop which has three burners way more powerful than the apartment stoves (a 13.000, 19,000 and 22,000 BTU burners). I cook a lot including hi temp wok cooking and meat searing. I burn about 35 gallons of propane per year. and the cooktop is the only gas appliance Mine is dual fuel which means the oven is electric.

Jamie Hall · February 9

Smith19 said:

GroundUp said:
I doubt proper setup was done with this unit. And the landlord simply will not allow it to be looked at, which screws me on the fuel bill. He says a friend of his - who's a plumber and the town plumbing inspector - installed it, so he has total confidence. In terms of showers, the mixing valve has to be cranked all the way hot to get hot enough water, another clue of how the boiler may be cycling.

That kind of thing should be (and, in fact is) illegal. Not much you can do about it.

hot_rod · February 9

Has someone enabled all the settings to make the boiler better fit your situation? I would clamp down the SH setting to limit the boiler to 15 K or so.

GroundUp · February 9

If you need to crank the mixing valve, the DHW temp simply needs to be turned up in the boiler control. It takes 5 seconds to do. I will ask again, what model is this boiler?

Smith19 · February 10

GroundUp said:
If you need to crank the mixing valve, the DHW temp simply needs to be turned up in the boiler control. It takes 5 seconds to do. I will ask again, what model is this boiler?

Tenant isn't allowed to touch any of that stuff, so unless a tech comes, the cover is staying on.

The convectors will get warm, but never hot.

GroundUp · February 10

So what's the reason for the post if you aren't going to do anything about it? We can't help you if you won't help yourself.

pedmec · February 11

you sure your not heating other apartments with your boiler? you said stand alone so you have just one house? a 500 sq ft house?

Smith19 · February 14

pedmec said:
you sure your not heating other apartments with your boiler? you said stand alone so you have just one house? a 500 sq ft house?

The apartment is over an unheated garage, and unless there's a pipe trench to another building, I'm not heating anything else.

GGross · February 14

Are you able to take a few pictures of the installation? wide framed so we can see as much as possible

EBEBRATT-Ed · February 14

Over a garage is always an issue. Most garage doors leak air like crazy

pecmsg · February 14

EBEBRATT-Ed said:

Over a garage is always an issue. Most garage doors leak air like crazy

The floor between the apartment and garage must be spray foamed.

MaxMercy · February 15

Smith19 said:

since April I have been living in a new construction standalone apartment in Massachusetts. It was finished in 2022 and is insulated like crazy; the walls, attic, and floors are packed with foam.

Do you know the square footage?

Smith19 said:
I'm amazed at how much this boiler is consuming. I am filling the tank every three weeks and it's just too expensive.

Propane has about 40 percent less BTU per gallon than heating oil if that's what you are comparing it to, so expect to use 40 percent more propane than oil.

Jamie Hall · February 15

Propane in New England is almost always more expensive than oil -- sometimes a LOT more expensive.

Smith19 · February 16

GGross said:
Are you able to take a few pictures of the installation? wide framed so we can see as much as possible

Yes - I can get these tomorrow.

Smith19 · February 16

pecmsg said:

EBEBRATT-Ed said:

Over a garage is always an issue. Most garage doors leak air like crazy

The floor between the apartment and garage must be spray foamed.

Floor box is 12" TJI PACKED with foam.

Smith19 · February 28

Everyone, here is the system. Filled propane tank yesterday but was locked out today, this time on low water pressure again. System was installed by the former town plumbing inspector, but seeing his work, my confidence is low. As the readout says, there is no outside reset, and I don't think this unit is setup for propane.

hot_rod · February 28

you need to have a gas pressure gauge connected as it fires and runs.

It comes with a LP conversion kit, was it installed?

Combustion analyzer used, where is the readout?

That gas flex could be an issue also. I prefer the 3/4” size

GGross · February 28

If it is continually locking out on low water pressure, and the fill valve is then refilling the unit, the installer must come back and find the leaks and repair them. Let your landlord know that the leak, and then refilling of this unit will turn a 20 year appliance into a 5-10 year appliance, and that is disregarding the obvious possibility of water damage if the leak is severe and concealed, and ignoring the loss of comfort due to the boiler locking out, as well as the safety hazard of an appliance being left to knowingly run all the way to a low water condition.

GroundUp · February 28

hot_rod said:
you need to have a gas pressure gauge connected as it fires and runs.

It comes with a LP conversion kit, was it installed?

Combustion analyzer used, where is the readout?

That gas flex could be an issue also. I prefer the 3/4” size

The Noble does NOT come with an LP conversion kit.

GroundUp · February 28

For the 3rd time, what model is this boiler? What EXACTLY does the lockout message say? There are several different "low water" derivatives so without the exact message, nobody can help you. Likewise, without the model number, nobody can help you.

hot_rod · February 29

Any parts like this lying around? Also there is a sticker to apply when the unit has been converted to LP.

Does the manufacturers tag indicate LP or propane? It may have shipped as LP ready.

You need to know if it is LP converted, or you may damage components.

Smith19 · February 29

I will ask the landlord if I can remove the cover and get the serial number.

I'm confused about the green LP sticker. If it's missing, it likely hasn't been converted? Is this boiler offered with the option of an LP conversion or not?

pedmec · February 29

the orange sticker on the side is the sticker indicating this model is using propane. sorry i thought it was green.

Fuel Consumption with brand new Lochinvar Noble Combi Unit

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