You can always add a stand alone room 'air purifier'.

SR

through what does the hot air blow?
where is this unknown hot air deliver system located?

did the tech tell you what this set up is called?

best of luck.

The hot air blows throw some kind of ducts. Only the rooms sort of above the heating system use hot air, the ends of the house use steam radiators. The hot air output vents are in a couple bedrooms and a living room above the furnace. Everything is heated by an oil furnace in the basement. It's my parent's house so I wasn't the one to talk to the tech. (I wish I was).

I'll try to attach a pictures of a possible air intake vent.

I have seen something like this. The "furnace" was in the basement and it had ductwork going down to the exchanger and up and the ducts were huge. The ducts were angled up steeply across and up towards the vents. The air circulated pretty well but I bet the efficiency was horrible and the btu's were probably mind blowing cause the air that came out of the vents was almost like stepping on a floor furnace grate hot.

It sounds like your parents have a gravity furnace. They are not designed to have a filter. I would image a lot of dust has accumulated in the ducts over the years. A duct cleaning may help the dust problem.

Is it possible to add additional steam radiators and close up the vents?

The picture is of the intake. It is on top of a gigantic duct. The output are smaller wall gratings that look more normal...hot air kind of slowly wafts out.

Gravity furnace sounds about right. How would you do a duct cleaning? The fact the air intake is a floor never struck me as a good thing.

Would placing regular floor air purifiers above the air intake and in front of the ducts help?

Pictured below is the metal duct that the above grate is on top of.

This post was edited by edlincoln on Wed, Nov 13, 13 at 23:21

I think you are going to have to hire someone to clean the duct work. I usually don't recommend this for forced hot air furnaces, but it may be worthwhile with this type of system. It may require cutting a hole in the ductwork in the basement to in order to gain access. I would not waste time with the $59 duct cleaning offers. You want to find someone who has experience cleaning a gravity furnace system.

I have no experience with air purifiers. I assume they would help. It wouldn't hurt to try.

An expensive HEPA purifier might be less than effective for dust generally in the house? I don't know either. But if a little background noise is not a problem how about a box fan with a generic furnace filter on intake side?

lifting the grates and fitting inexpensive furnace filters beneath them? I don't think they would restrict the flow of gravity risen heat at all.

Overkill, but might be an idea on a smaller scale if you have a shopvac. I once lived in a three story train depot in Savannah, GA. Turn of the century. We were getting it reconditioned. After the first month the dust was getting to everyone badly.
I bought a Ridgid shop vac (i swear you can't kill those things), replaced the filter with a sturdy wire mesh colander, attached thirty ft of cheap 3" dryer vent hose to the exhaust. Put the hose out of any nearest window and plowed through the dust from top floor to bottom. Worked the charm. Of course, the "central heating" there was a ceiling hung gas furnace 12 ft above the first floor. No ductwork.

"I usually don't recommend this for forced hot air furnaces"

Sorry to hijack a little, but may I ask why? I was recently considering it.

This post was edited by svejkovat on Fri, Nov 22, 13 at 5:41

If the ducts are properly sealed then the filter should catch most of the dust entering through the return.

If the ducts are leaky and the house is old then there will be some amount of dust accumulation. Unfortunately most duct cleaning services don't do a very good job. They advertise a low price to attract business. A proper cleaning is a time consuming job which may require to open up holes in the duct work to get access. Most outfits don't do a very good job and in some cases cause more problems by scattering dust through the house during the "cleaning".

If the ducts have mold then you have to first correct the mold problem and then thoroughly clean the ducts.

Here is an article from the EPA.

Here is a link that might be useful: Should You Have the Air Ducts in Your Home Cleaned?

I would like to say that the situation seems a bit complex. I suggest that you go for a professional help regarding this. You would also like to consult the technician who visited your parents' house.

I would be more inclined to worry about humidity levels with a gravity hot air system and steam. both tend to dry air - especially a gravity hot air system with the high heat exchanger and air temps. look into a humidifier to help your fathers lung/ respiratory issues, this is likely far more significant than any household dust issue.

svejkovat: The Box Fan and generic furnace filter is actually a decent idea. Elegantly simple. Not sure I understand the "Shop Vac" idea. What would you be using it on?

mike_home: As it stands there is NO FILTER at all. The furnace man was quite clear on that. This old system is not designed to use filters. (I was told without a fan to force air a filter could obstruct air flow too much.) I doubt duct work is sealed at all.

berlin: Very possibly, actually. I know my Mom had humidity problems and used to use a humidifier in the bedroom. My Dad spends more time in the rest of the house. I'm always leery of them because if you don't clean them or change the filter (depending on the design) enough, they can breed mold. Maybe something I should consider again.
This was started because last winter my Dad (who is getting on in years) had a flu that sort of never completely went away until the end of the winter...he blamed it on dust, and sure enough it went away when the furnace was turned off in the Spring. The humidity issue would explain that equally well.

My comment about a filter catching most of the dust was in response to another poster. Sorry for participating in a post hijacking. I agree you cannot add a filter to your parent's system.

Low humidity in a house is not caused by type of furnace. The air does not care how the temperature was raised. Most of the humidity problem is caused by air leakages through windows and exterior doors.

Mike, in the real world it does. I understand the gross oversimplification that "high temp rise/high heat exchanger temps = low humidity" but high temp rise leads to a number of downstream effects that lead to lower relative humidity than an equivalent space with lower air temp rise and lower register temps. One of those downstream effects is, as you mentioned, increased outside air infiltration due to increased indoor air stratification and greater stack effect of the house itself.

I know this is an old thread, but as the owner of a house with a gravity furnace, I'd like to weigh in.

You cannot add a filter to a gravity furnace. The furnace does not create dust nor does it move it around much. The low air flows from a gravity furnace neither help or hurt a dust problem. Use a stand-alone air cleaner to filter dust.

Low humidity is best fixed by comprehensive air sealing. It is outdoor air infiltration that results in low humidity in the winter. A humidifier is not the ideal way to fix it.

Here is a link that might be useful: Stand-alone HEPA filter