Moldy smell from previously dormant radiators

trynakeepitwarm

Long time reader, first post. I saw a previous question about a moldy smell inside a building with radiators that were turned off for years and then made functional again. The respondent theorized it could be from mold that grew when the radiators had been turned off, but didn't specify where the mold was or how to fix it.

Is the mold inside the radiators or outside of them (e.g. on top or behind them)?

I have the same exact issue: I moved into an apartment that had its radiators turned off for years. I finally replaced the steam valves and air vents on two radiators this year, and there's a really bad mold smell coming from them. It only smells bad when the steam circulates and the radiators function. I'm not sure if I just need to paint the outside of those two radiators to encapsulate and prevent off-gassing from layers of built-up hair/dust/etc (let alone lead paint flaking off them, etc.), or if I somehow need to clean inside the radiators?

I don't see any mold outside the radiators, just dust and very old/crusty paint. An elderly couple lived in the unit before me, and pretty much everything but the radiators has had a through clean. I'm hesitant to clean the outside of the radiators too much, since there is almost definitely lead paint on them.

For what it's worth, there was also definitely some nasty kind of water built up inside the radiators, since they dripped a couple of drops bit when I took off the broken old air vents and replaced them with a new one (it was rust-colored, and smelled a little…organic). I was a little bit surprised they dripped drops from the air vents, since the air vents had been painted completely shut for years and the air vent is half way up the radiator vertically.

If the mold is inside, how would one even clean out the inside of the radiators? They weigh hundreds of pounds are connected to the steam pipes that run throughout the building. Is there any way to clean inside my radiators without disconnecting them?

Also, since they're connected to the whole steam system, wouldn't they be spreading any mold and smell inside them to other units down the steam line? Is there a way to "flush" or clean the whole inside of a steam heat system's pipes and all radiators in the building without causing any flooding or issues of any kind from radiators in other units? I am on the building's board and can initiate this type of maintenance, if necessary and appropriate.

Our building is 100 years old and no one on the board knows anything really about how the heat works except for me, and I'm only now beginning to learn out of necessity.

Thanks in advance for any insight.

Danny Scully

Steam systems are open to the atmosphere. Even if mold developed (which I doubt), the beauty of steam would have killed it. The best way to eliminate odor would be to skim the boiler. Do you have access to the boiler? If so, post pictures.

trynakeepitwarm

Thanks for the quick reply. That makes sense about steam being a disinfectant—I'd assumed the same, which is why I was puzzled about the source of (and a good fix for) the smell. It's surprisingly powerful and fills the whole apartment when the radiators come on. I thought I'd have seen more definitive information about this elsewhere on the forum, since I'd assume this type of smell may be a common issue with steam systems, but I couldn't find any. In your opinion, is the mold possibility from the other post not accurate, then?

Just in case, I plan to turn off the two suspect radiators, thoroughly clean the (substantial) dust between their sections, and repaint the exteriors and between the sections to eliminate any possible smell coming from the radiators' surfaces when they get hot. The previous tenants lived here for decades, and there's a thick layer of dust deep inside the radiator, perhaps with hair or other organic matter mixed into it. Since microorganisms can survive in dark, moist, or high pressure locations (e.g. around geysers), I also had wondered if mold or bacteria could grow in dormant radiators, and then get forced out/aerisolized through the air valves when they became functional again. The air valve was fully sealed shut (painted over) and the steam could only partially (though not fully) circulate into the radiator, keeping a third of its sections cold, a third of it lukewarm, and a third of it pretty warm but nowhere close to hot. I figured those moderate internal radiator temps and the presence of moisture could have caused mildew or mold to grow inside the radiator, since the hot steam was prevented from circulating as normal inside it for several years (which I assumed would more likely have killed any mold or mildew).

Last year, I repacked the steam valves on two radiators following Richard Trethewey's instructions (https://www.youtube.com/watch?v=y0VQOZqiw7U&t=100s) and kept them fully turned off because the apartment was too hot even with the radiators fully off. Before this heating season, I got a Runwise smart thermostat installed on our boiler (it uses wireless temperature sensors in a few apartments to accurately gauge and smoothly control the building's average internal temperature). It has been very effective and all units are down 2-4 degrees of excess heat day and night. As a result of this, my unit was no longer overheated, and I installed new air vents on the two non-functional radiators and turned them back on again for the first time in years. That’s when the smell began. Of note, there are two other vertical steam pipes in the apartment that have had functional air valves all along and have never emitted any odors, so it seems possibly specific to the large radiator in particular (detectable though much less so from the smaller radiator). I tried enclosing the new steam valves on the radiators with a MERV-18 filter, just to see if it might be a smell coming from the steam valve or from the surface of the radiators when they heated, but it didn’t help, possibly due to steam pressure pushing the smell through the filter.

I have access to the boiler and can post photos soon as I get home. What exactly would be helpful to have photos of? I could try to get photos inside the boiler with its cover off, or of the steam pipes around it, etc. Here’s all the basic info I know about the system, for context:

• Boiler is 34-year-old Weil-McLain LGB Version 2 natural gas (Exact model: LGB-10), 1.1M BTU
• Rebuilt in 2006 due to a section leak
• Subsequently, the inside of part of the boiler rusted, and the burners in two sections corroded
• Tech recommends boiler replacement next summer due to overall boiler condition and uneven burner output (larger yellow flames on the two corroded burner sections on one side, smaller pure blue flames on the other)

A different tech suggested that the boiler’s "dirty" water from the open flame area inside the boiler might cause organic smells in the steam at apartments. Does this sound plausible?

Regarding skimming: What’s a safe approach given this rusted boiler and the old pipes/radiators? I’m concerned about causing any damage with harsh chemicals or chemicals getting into apartments through steam coming from the air vents (there are young children in some units and elderly folks with chronic diseases in other units, who would all be sensitive to harsh chemicals that ended up vaporized or mixed with steam and in the apartment's indoor air).

For next year, when we replace the boiler, the current one is rated at 80% efficiency, but a technician suggested it's closer to 40-60% with our setup. Do you think it's actually that inefficient, or is it closer to the rated 80%?

I’m also considering transitioning to a higher-efficiency (95%+) boiler, which could lower fuel costs, but I’ve heard installation is more expensive than a standard 80% model. Can you provide a ballpark cost for installing a standard-efficiency 1M BTU boiler versus a 95%+ model, including labor? I’m trying to estimate how many years of gas savings it would take to make up the difference in upfront costs.

Apologies if any of this is off base, going off some conflicting information and my (limited, though growing) knowledge of how these systems are designed and actually function. Many thanks for your advise.

Danny Scully

That’s a lot to unpack there @trynakeepitwarm 🤣. I think (although admittedly could be wrong) that you’re not smelling mold. Steam radiators can emit odors if the water content is dirty. This would be even more likely if the rad has been turned off for years. What I was looking for with pictures is a skim tapping. I wouldn’t suggest using any chemicals. Skimming does not have to be done with chemicals. Finally, we don’t discuss pricing here (nor would a ballpark be possible without being onsite), but a conversion would involve a complete system piping overhaul, not simply changing the boiler. You can accomplish a lot more than you think at a much lower price point with simple upgrades to the existing steam system. To start, skim the boiler.

trynakeepitwarm

Right! Makes sense about the skimming. Great to hear re: chemicals - I’ve seen various things before about skimming using TSP, etc. that seemed caustic, and appreciate that it can be done with gentle or no chemicals. Attached are photos (a few angles on the controls). How does skimming work with this WM LGB-10 model?

Understood no cost discussion thanks for the info. Is all repiping needed to upgrade to a new 95%+ model in the boiler room, or would any repiping be needed throughout the building? The new models seem nice - very compact footprint, quiet, seem to burn cleanly and efficiently.

The Runwise thermostat alone is projected to save 25-30% on fuel from previous years (from no longer overheating the building). Would be curious what other efficiency upgrades along with a new traditional 80% boiler would be recommended. Thanks again.

Jamie Hall

That's a pretty decent install. If the boiler is running well and not leaking — keep it.

You mention 95%. Nope. That's only available on "mod/con" boilers for water heat — not steam. Steam, however, should run around 85%, and that one will if properly adjusted. Changing to hot water would be a HUGE mistake.

The best bang for your buck is going to be tightening up the building. See my comment on windows…