I agree with Mike. Have you tried shutting it down (turn gas supply off before it enter's boiler and/or at storage tank) ,airing basement out to see if odor persists? There are other odors that can easily be mistaken for propane. There are also ways to harbor propane odor. Propane is actually odorless so an odorant is added to help warn of leaks.

The odorant is easily separated from gas then deposited on/in something else where it can remain strong for a very long period. For instance,if an old drip leg were remved and left in basement during a plumbing rework,it can smell for years. Same hold's true if residue from drip leg is spilled on floor,odor will linger indefinitely.

Thanks for the responses! Yes I am sure it is that model, I took a picture of the plate. I just read online that it does have an LP conversion kit. I do have CO detectors throughout the house but I don't know if their is one in the mechanical room. I can definitely install one.

It has been this way for 4 years and it has always bothered me, but the gas company + the plumber / heating specialist who installed it didn't find any issues. So not being a professional myself, I took them at their word.

I don't think there were leaks from years ago as the house was oil heat before I converted, and everything was new that I had installed.

Good point about the odorant. The gas company told me the same thing years ago. The smell in the mechanical area is worse when the propane tanks outside are low, which is when the odorant coming through is in a higher concentration. So that leads to me believe the smell isn't an old one, but a current leak / issue since the severity of the smell changes from time to time.

Since they couldn't find any leaks in the line, and the lines were pressure-tested when everything was installed. I was wondering if there could be something else inside the boiler that could cause that smell. Mike's mention of incomplete combustion is kind of what I was thinking about, when wondering if there could be an issue inside the boiler. Maybe they didn't install the conversion kit properly or something.

Besides the obvious odor, is there any test that you know of that could prove the issue is incomplete combustion?

Re: incomplete combustion. Even if that were the case,the fumes are extracted along with normal biproducts of combustion,,,,,,,,,,,,,,,,,,,,,,,if boiler is properly vented. If flue gas is backdrafting,a CO detector should alarm. Let us know after a detector has been installed near boiler.

This could be very dangerous. Can you get someone competent (not the installer) to look at it asap?

Check that the gas valve was converted and adjusted properly by the installing co. Often the furnaces and boiler may come in natural gas set up and installing company must install a propane kit.

The contractor said they definitely installed the propane conversion kit. They said if they didn't do that, I'd have flames shooting out of the bottom of the boiler.

I did put a CO detector in the boiler room and it has been there for 4 days or so. There hasn't been any issues with that.

I waited in the boiler room today when the heat kicked on. I definitely only smell propane when it fires up and is running, so it seems to me like it might be incomplete combustion? My contractor spoke with a rep from the supply house today, and he said that I probably don't have enough combustible air in that room, and I may need a fan in a can. Does that make sense? I am worried that if I am not burning all the propane that is being used, I am wasting propane into the air and increasing my fuel costs.

Here are my dimensions: Boiler room = 6'6" x 14' x 7'6". If I do need a fan in a can (make up air), could I instead just cut a hole / vent into the garage (which is on the other side of the wall from the boiler room)? I know there are calculations used to figure this out and maybe an HVAC tech here could tell me. Here are the 1-car garage dimensions = 22' x 11'5" x 7'.

Any info / insights are appreciated. Thanks!

Does the boiler room have a door, and do you keep it closed? I am skeptical about the lack of combustion air, but I am not an expert about propane fired boilers. If is lack of air then so you detect any smell if you keep the boiler room door open?

Are you able to see the flame when the boiler is running? If so the color may give an indication if the air and fuel mixture is set correctly.

Not familiar with that particular boiler, but I'm sure they only leak tested the exterior connections. Depending on the configuration of the internal burners, you could conceivably have a leak prior to the burner which doesn't combust. Soapy water is a very basic leak test - if you can smell the odorant, you have a leak and they should be able to detect it with a sniffer.

@ Mike - yes the boiler room does have a door and I keep it closed all of the time. I could try keeping the door open for a few days and see if the smell stays the same. Yes I can see some light from the flames on the floor under the boiler but I haven't gotten down on the ground to really look at the color. What color is ideal and what color is not good?

@sktn77a - Is a sniffer some sort of electronic leak detection device? If so, who would have that, the propane company?

Yes, the propane company should have a sniffer. And they should have skilled technicians that are familiar with your boiler. Next time you call them ask them to send someone out who is trained to diagnose leaks (I take it the propane company sold you the boiler)?

The flame should be blue. Some yellow at the tips is OK. I would not trust anyone employed by the propane company to diagnose your furnace. You need to hire a skill HVAC contractor. One that knows how to use a combustion analyzer would be appropriate in my opinion.

Okay, thanks. I will have to make some calls. It does look like the flames are almost completely blue. My plumber sold and installed my boiler. He does gas and oil boiler installs and maintenance.

My plumber found out that I need a fan in a can, or makeup air for the space I have it in. Apparently based on the 90,000 BTU input, I need 750 square feet of combustion air. The room this unit is located in, is only 91 square feet. I am told that without enough combustion air, not all of the propane is burning when the unit fires up, so that is why the room smells when the unit turns on, and I must also be wasting a decent amount of propane while the unit is in use.

I have a standard cape cod house and the boiler is in the basement in a center room under the stairs. I have a garage on one side and a finished area on the other (about the size of a 1-car garage). I probably have about 750 square feet on the entire lower level (finished space + boiler room + garage). One other thought I had is that I could cut in a vent from the boiler room to the finished area, and another one from the boiler room to the garage, and that might give me enough combustion air?

Any thoughts or insights into this would be great, thanks!

Only insight I have is as before, if you're still calling the same person, stop, he's incompetent. Adequate makeup air is an INSTALL step and consideration, not something done after the fact. Oops, forgot that. He botched the install. Want him to keep working on it? I wouldn't.

I have to agree with Elmer about your plumber's lack of knowledge. He installed a 90K BTU propane appliance in a 9 X 10 room which has no air intake! Now he says you need a 25 X 30 room so you don't get incomplete combustion. Did the laws of thermodynamics change since he did the installation?

Have you run the boiler with door open to the boiler room? Did you notice any difference? If I were you I would remove the door so no one is tempted to close it.

I am not expert in this area, but if there was incomplete combustion then I think you would have a high level of carbon monoxide. Did you install a detector yet? What were the readings?

Even though I first suggested it, I am not convinced this is an incomplete combustion problem. It could be some leakage of propane when the boiler fires up. Propane is heavier than air and it sits on floor inside your boiler room. You need to hire someone who knows what they are doing.

I wouldn't have him install the makeup air, I asked him to ask a contact at the supply company what we needed to do. I will call a new person to do the makeup air.

Yes I did leave the door open and the smell was a little better, but I am not sure if it was because of better combustion or just because the same smell could dissipate in a larger area. I smelled a little bit of that propane gas smell in the finished basement (with the door open) so I am not convinced either way yet.

Yes I have a CO detector in that finished basement, and always have had one there, but I installed another one in the boiler room about 4 feet away from the boiler. It has been there since your initial reply on this thread and has never gone off, and the screen reads "0" the whole time.

I appreciate all the insight and will reach out to a different professional to come in with new eyes and diagnose exactly what is going on. You guys have been very helpful. Thanks!