UV filter for home central heating?

[DaveC426913]

TL;DR

Had a guy come and check my furnace because it had an error code. Recommended a UV filter. Good? No?

Had my central air system checked when it sortta wasn't working. I guess I hadn't replaced the filter.

Guy suggested I might want to get a UV filter accessory. He said it would "kill bugs and particulates". I know UV can kill the former, not sure how he thinks it's gonna murder the latter.

Now I'm finding out there's more than one type of UV filter: one for the air flow and one for the coil. He was suggesting we might get one for the air flow, but now we'll have to change the bulb regularly.

Yes, we have animals. Yes, I am allergic to them. Yes, this is the first house I've had with central air (had rads for 60 years).

We rent this furnace. Not sure yet what/if there's an additional monthly cost for the add-on, but I assume so.

Good idea or nah?

Paging @russ_watters

 

[russ_watters]

UV light does kill microbes. It doesn't work very well in forced-air HVAC because the air moves too fast for enough exposure. A lot of my clients looked into it during COVID but more fresh air and remote work both worked better to avoid infection.

If you're having issues with pet allergens/dander, what you need is filtration. Use good filters in your HVAC unit and consider an air purifier. Almost all of them are a scam, so either pick a big, ugly and cheap one or make one with 4 filters, a box fan and a bunch of duct tape. The only thing that really matters with an air purifier is airflow: more is better.

 

[Baluncore]

Laminar flow cabinets circulate air through filters. UV light is used to sterilise the filters, to prevent colonisation of the filters with pathogens.

 

[DaveC426913]

Laminar flow cabinets circulate air through filters. UV light is used to sterilise the filters, to prevent colonisation of the filters with pathogens.

Yes, this is as I understand it: two types - one for air flow, one for filter sterilization.

 

[256bits]

TL;DR: Had a guy come and check my furnace because it had an error code. Recommended a UV filter. Good? No?

We rent this furnace

Why would one need a UV light for a furnace??
Are there cooling coils for the summer in the ductwork??

 

[DaveC426913]

Why would one need a UV light for a furnace??
Are there cooling coils for the summer in the ductwork??

Central air heating/cooling unit.

 

[russ_watters]

Why would one need a UV light for a furnace??
Are there cooling coils for the summer in the ductwork??

Not sure of the exact thrust of the question, but it's forced-air over furnace coils(plates). If you're saying that since they are hot they are sterilizing, that's true. But yes, the same system will have an AC coil that sits on top for the summer. A high fraction of residential systems in the US are that configuration.

 

[DaveC426913]

Thanks. I think there's a lot of things we can do to keep up our air more effectively (and cheaper) than a UV filter in our airways.

 

[Averagesupernova]

As far as I knew the UV lights that are installed in residential air handlers kill anything that starts to grow on the air conditioning evaporator. Better filtering ahead of this will decrease the things that start to grow there by reducing the contaminants that reach the evaporator core. Most residential air handlers are not sealed up well enough to seal everything. So a super dandy good filter isn't helping as much as the folks selling them would have you believe.

 

[Rive]

He said it would "kill bugs and particulates". I know UV can kill the former, not sure how he thinks it's gonna murder the latter.

Supposedly kills pollen, breaks down lint, activates (mineral) particle surface so they gather/settle faster.
It's just that these are not supposed to pass the first filter... In this usage this smells much like snake oil for me...

Also, I'm not exactly sure that burnt stuff is better, safer. I would prefer to rely on the good old (mechanical) filters and clean, not sterilised air.

 

[DaveC426913]

Also, I'm not exactly sure that burnt stuff is better, safer.

As long as it been rendered non-volatile - or at least less volatile.

Burning is bad when it leaves behind molecules that can are chemically active and can then interact with one's body (eg. carbon monoxide). If they are given sufficient energy beforehand, those interactions should occur before reaching one's delicalte body parts, leaving only non-volatile byproducts.
At least, that's my rough understanding. (CO is not the best example of UV's efficacy, but I don;t have any others available.)

 

[Averagesupernova]

From the second hand experience I've had, the point of the UV radiating onto the innards of the air handler is to stop mold growth. Anything else can/should be handled by sealing up any leaks after the filter to prevent debris from being drawn in where the filter can't stop it.
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Keeping a stand alone dehumidifier running in the house can help as it lowers the amount of humidity that can cause excess condensation in the central air unit. Not only that, lowering the humidity can allow you to raise the setpoint of the thermostat of the air conditioner and still feel comfortable.

 

[DaveC426913]

Keeping a stand alone dehumidifier running in the house can help as it lowers the amount of humidity that can cause excess condensation in the central air unit. Not only that, lowering the humidity can allow you to raise the setpoint of the thermostat of the air conditioner and still feel comfortable.

Has a built-in dehumidifier that keeps the house bone dry.

I have a separate humidifier running in the bedroom so that my airways don't stick together and suffocate me in my sleep.

I don't really get it though, I bought a hygrometer for home use and it tells tell my humidity ranges between 40 and 50%, which is not bone dry.

 

[russ_watters]

As far as I knew the UV lights that are installed in residential air handlers kill anything that starts to grow on the air conditioning evaporator.

That's the marketing reason but it isn't a good one. There should be nothing growing on an evaporator coil because it should be dry except when the AC is running.

Most residential air handlers are not sealed up well enough to seal everything. So a super dandy good filter isn't helping as much as the folks selling them would have you believe.

Leakage affects efficiency when the system is running, but I'm not seeing how it would be a big issue for air quality. Sure, you might get 5% attic/crawl space air pulled in on the return side, but 95%+ of that air then goes through the filter (<5% leakage around the filter).

It also depends on what the air quality issue is that you're trying to solve. Dave mentioned pet dander, so that's something coming from inside the house, as opposed to an external allergen/microbe.

 

[russ_watters]

Anything else can/should be handled by sealing up any leaks after the filter to prevent debris from being drawn in where the filter can't stop it.

Note that usually the filter is on the return side of the air handling unit, so the only place particles can get in when the system is running is through the casing (which will be very well sealed) or through the filter housing (which isn't). The supply ductwork is positively pressurized so there's no leakage-in.

Keeping a stand alone dehumidifier running in the house can help as it lowers the amount of humidity that can cause excess condensation in the central air unit. Not only that, lowering the humidity can allow you to raise the setpoint of the thermostat of the air conditioner and still feel comfortable.

I wouldn't recommend that. The AC unit is designed to remove humidity from the space, so reducing that load is superfluous and wastes energy. And for comfort there's a sweet spot of 40-60% RH. Trying to go below that reduces comfort and wastes energy.

 

[Averagesupernova]

Russ I realize I'm discussing this with a HVAC engineer. As far as leakage after the filter goes, I've found plenty of cases where there are places where debris gets in. I realize where the filter is in an air handler.
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There should be nothing growing on an evaporator coil because it should be dry except when the AC is running.

Plenty of opportunity for mold to grow on the evaporator. If it's not very clean, mold can start. I have a family member who has health issues and is fighting this.
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I wouldn't recommend that. The AC unit is designed to remove humidity from the space, so reducing that load is superfluous and wastes energy. And for comfort there's a sweet spot of 40-60% RH. Trying to go below that reduces comfort and wastes energy.

Did you miss the part about raising the setpoint of the main thermostat? If the goal is lower humidity and the air conditioner can't get it low enough without feeling too cold I will run dehumidifiers. I have allergies to dust mites. You cannot keep a house clean enough to eliminate them. The solution is to keep the humidity low enough because they are unable to survive in low humidity. I'm told the only way they get moisture to survive is from the air. Get the humidity down to 35% and they can't survive. You do 'you' and I'll do 'me'.

 

[russ_watters]

Plenty of opportunity for mold to grow on the evaporator. If it's not very clean, mold can start. I have a family member who has health issues and is fighting this.

Fair enough. I've seen dirty coils, but haven't encountered mold. Admittedly my experience is mainly high-end commercial/industrial.

Did you miss the part about raising the setpoint of the main thermostat?

No, I was just letting it go: lowering the humidity below 45% or so isn't going to enable raising the temperature for most people because it's already below the typical comfort sweet spot for most people, which the AC unit already provides. Big caveat here in that you didn't say what temp you're shooting for.

If the goal is lower humidity and the air conditioner can't get it low enough without feeling too cold I will run dehumidifiers.

Too cool would different issue, but yes, in times/locations(basement, San Francisco) of cool but humid weather a dehumidifier would be the way to go.

I have allergies to dust mites. You cannot keep a house clean enough to eliminate them. The solution is to keep the humidity low enough because they are unable to survive in low humidity. I'm told the only way they get moisture to survive is from the air. Get the humidity down to 35% and they can't survive. You do 'you' and I'll do 'me'.

This is what research tells ASHRAE about RH levels vs IAQ challenges, but sure, we make our own choices:

 

[Averagesupernova]

Fair enough. I've seen dirty coils, but haven't encountered mold. Admittedly my experience is mainly high-end commercial/industrial.

It's actually my sister who had had some health issues. I've thought she's crazy about some of the things in her house that she can smell that the rest of us cannot. When her son lived at home he could never smell anything but she could. When he visits he cannot tell either. Her system is a heat pump. In winter the refrigeration process is opposite of course and when the coil in the air handler heats up it about drives her nuts. Luckily there are resistance heating coils down stream of the evaporator so she can turn the heat pump off and the air is warmed by the heating elements. In this system only the return air goes past the refrigeration coil. Now I've thought about this and wondered if it were a gas or oil furnace the evaporator coil might get hot enough through the winter to take care of some of the contaminants on it since the heat exchanger would be prior to the refrigeration coil concerning airflow in that type of furnace. House was new in 2015.
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Edit: She would also have a hard time without the dehumidifier in her house.