Ductwork advice from wetheads

Tom Hopkins

One adult asthmatic (me) and one child. I've grown into the condition resently, myself (lucky me) so we're relatively new to coping as a family. At a minimum, any system that allows us to keep doors and windows closed during the various allergen explosions is going to be a boon.
Filtration schemes being equal, the high velocity systems seem most compelling because of higher CFM and lower humidity levels. I suppose the most important take away, as usual, is having confidence in the installer- a crackerjack tin job beats a poorly done high tech High Velocity install.
Thanks again to all- I'll repost any interesting findings.
Thanks,
Patrick

Tom Hopkins

best air ducts?

Hi all,
We're looking into augmenting our 1-pipe steam based HVAC system (which is currently just an "H" system) with air handling ductwork. Half the family has asthma, and we're looking for some relief through whole house air filtration. While not an immediate priority, we'd probably also look to get AC out of it, someday. All this means dealing with scorched air guys and DUCTWORK, that dirty, dusty stuff that is often no friend to asthmatics.
Before listening to the scorched air guys' dog and pony, any advice from you all (I'm guessing you've got lots of experience listing the cons of air-based heating) on maybe the best types of ductwork or installation or design methods when air quality is the number one priority?
Thanks,
Patrick North

Rich L.

High Velocity with HRV

In a retrofit such as you descrice Patrick a High Velocity small duct system can be a good fit to allow AC to be added with a minimum of intrusion and keep your steam. You could tie in a combo heat recovery ventilation unit with a built in HEPA filter for indoor air quality. Broan makes several models that do this.

Chap

and

I'd suggest checking into the Inverter mini-splits. Some have SEERs in the 20's with HSPFs higher than 10.5. No ductwork to harbor dust bunnies and bugs.

Tom Hopkins

Interesting. For what it’s worth, the “ease of retrofit” aspect of the mini-vent types is probably not very important. Given the layout and other renovation going on, fulls sized ductwork may be fine (and cheaper). Does make me wonder if less duct volume=less potential to harbor dust and crap, especially with the higher fan speeds. Makes sense, but lots of things make sense to me!
As for mini-splits, are they really as adept as ducted systems at air filtration? AC is a secondary concern.
Thanks as always for the great advice.
Patrick

David Sutton_6

Ductwork

Becareful Pat, you need a set CFM per room of surply AND return air this will decide what size ducts you need,

My goal is allway to have at least 10-20 % more return than surply, if you duckwork is not sized right you will have problems, Make sure you have a return in EACH room (except bathroom ;-) and kitchen )Your system will balance better and be much more comfortable.

David

John L

ductwork

It depends!! that great phrase that we crop up in postings from time to time. Reading from what you said, the numero uno proirity is air quality, then you have to consider what system you will use to provide this enhanced air quality. In this case hot/warm air is not a consideration as you have a boiler that is being retained. Therefore, before considering which sytem of delivery to use you have to select which method/system that will best fit you needs for air/cleaning/purification/quality. Then you can choose what method you want to deliver this air throughout the home. Again you will get lots of opinions here on the delivery system. getting to the air cleaner, you should look at ventilation systems, air purifiers and HEPA filtration. Do some research on these and what combinations you can use/want. With regard to the delivery system the 2 best known and used are hi-velocity and conventional ductwork.There are pros and cons to both systems. Hi-V has the advantage of being used in small spaces, however it's biggest advantage I believe is it's superior dehumidification potential, somewhere in the region of 30% better than low- v air handler. Dehumidification is an important issue when considering air quality. A Hi-V system typically has one return, although that can be modified, depending on the system. A Low-V air handler can have a variable speed blower allowing constant air flow and air cleaning/purification.
A Low-V, depending on the circumstances, usually has multiple returns.You can also have a high SEER with the A/C with a Low-V system, should you choose add A/C, which I don't why you would not as the air handler alredy has an evap coil, so you half there to A/C, regardless of which type of air handler used.
This will entail some research on your part, but at least you will be more informed on what is available to you to fit your particular needs.
An educated consumer is our best customer
John L
P.S.
Everyone has a dog and pony even the hydronic gods.

Tom Hopkins

Thanks!

Great info, as always. Thanks, guys.
Patrick

tim smith

air system for house, how big is house???

depending on size of house, style ie rambler, multi floor box and budget helps in deciding the type of system that would be best. The new VRF multi zone variable capacity units are quite nice but sometimes budget or space for the horizontal air handlers they make don't fit. If larger house, say over 3500sft, then the multi zones can cure alot of issues with getting ducts all over the place and also give better control. Ps, the multi zone I am talking about is the ducted models not mini splits. You can put good filtration on these units. If ducted, dont use flex duct on job or inner sound liner on duct as this tends to trap more dust & bugs than smooth metal. Definately add a heat recovery ventilator to system for fresh air to house, this will also help along with good filtration. If going with conventional unit, look at Carriers Infinity zone system with maybe their hepa filter bank setup they have. Make sure all ducts are duct sealed with brush on sealant. You will have a much cleaner system. Good luck

Mike T., Swampeast MO

I [suspect] that the type of filtration will matter more than the ductwork, but do utterly insist that ALL ductwork (including returns) be very well sealed. One good thing about high-velocity is that it's an inherently well sealed system as "typical" duct leakage would prevent the system from operating.

Are the asthmatics children, adults or both? Do you know their main triggers? I had fairly severe asthma as a child and my two main triggers were physical activity and changes in temperature when I went into an air-conditioned space on hot summer days. Pet dander, mold, pollen, etc. seemed to bring on other problems (e.g. runny eyes & nose), but not the asthma. Fortunately, like many, I outgrew the worst of the asthma with puberty and just had to learn to live with the allergy problems, which BTW with all of our rain this spring, are HORRIBLE this year.

You should NOT use air ionizers as these produce large amounts of ozone--a known irritant and trigger for many asthmatics. Some electrostatic units also produce rather large amounts of ozone--if the mfgr. publishes the ozone production it's probably because it's low; if they don't it's probably because it's high...

A combination of activated carbon, HEPA filtration and UV sterilization is [likely] the best for reducing most airborne asthma triggers without producing ozone. I know that portable air cleaners with this combination are easily available, but I have no idea if similar all-in-one units are available for centralized systems.

John Starcher_4

You should consider....

....the "Accuclean" air filter from American Standard.

Here's a web link: Accuclean!

Rich L.

Note

One note Patrick, High Velocity does not give you more CFM. It gives you higher velocity with a lower CFM than standard ducted systems. CFM for standard ducted systems is 400 CFM / ton. High velocity standard is 250 CFM / ton. That's how thay keep the small ducts with big throws of air without being noisey. Also how they achieve more efficient dehumidification - not moving the air across the evap coil as quickly.

Good luck whichever way you go, let us know how it works out! Rich L.

hvacfreak

I guess...

I guess I'm still a fan of old school , large 600 fpm sheet metal returns and 1.0 sp ( @ 100ft ) supply ducts....using complicated twisted transition drop - cheek multi-branch whatevers , lol.

Seriously...I have never seen any of these small duct systems ( high velocity ) that I could compare to a properly sized ( and correctly installed ) standard velocity system. Perhaps it's something that works well in northern states , I'm near Washington DC and I have no experience with one of these that the owner is happy with.

I know the complaints I get in commercial buildings with supply air at 900 - 1000 fpm...I would not have the nerve to try to get this in someones bedroom. However if someone lives happily with one of these systems or installs them with success , it is a beautiful thing.