Success: Passive Control of Radon in My Single-Family House

My House lies along the path of Missoula Floods erosion of land about 110,000 years ago, in a dramatic stage of erosion that formed The Columbia River Gorge,

https://en.wikipedia.org/wiki/Ice_Age_Floods_National_Geologic_Trail#/media/File:Wpdms_nasa_topo_missoula_floods.jpg

Concentrated glacial deposits are associated  with higher concentration of radon release from soil.

The Oregon Health Authority warns of high radon levels in homes of East Portland:

https://geo.maps.arcgis.com/apps/MapSeries/index.html?appid=f7691be8bc40430fa8480fc325287f7c

For too many years of my life, I was aware of radon levels persistently above ten picocuries per liter in my home. EPA recommends: Fix your home if your radon level is 4 picocuries per liter (pCi/L) or higher.

A Citizen's Guide to Radon - US EPA

I have at last achieved the needed fix, by novel means employing the natural drive of chimney effect. I think this is a really big deal. By my example, every home could be fixed with modest up-front cost and without any operating cost or degraded home value by zip  code or neighborhood. This must be good news, not bad, for all of us, including abatement contractors. 

(11/12/2012)

My quest for passive control of radon began with fitting two 4" warm air pipes sealed full-length, between my crawl space and my attic. There is excess space in a bathroom wet wall; put some of that to use. There will be significant chimney-effect drive of air flow when the pipe(s) are completed through-roof.

I expected to make this work someday, avoiding a radon pump if possible. How big is the needed pipe? Maybe 6" diameter?  The two 4" pipes equal one 6" pipe, and that much fits in the wall. If one is enough, the other might serve as an ample  wiring conduit between crawl space and attic. 

Minimize wet wall thickness above a tiled shelf. With an epoxied-on copper band, avoid reliance on caulk in sealing the new tub behind backer board and tile. Read more about the tub install in this blog post of October 2013: Insulate Exterior Wall of a Bathtub or Shower

For years then, the pipes did nothing, not connected through-roof and not collecting from the soil of the crawl space. House radon levels were unchanged.

(August 2019)

Dig this trench in the dry, hard dirt of my crawl space.

Hereafter I will own an over-abundance of these tubs. I disposed this many tubs of dirt, a carload, twice.

Use landscape cloth to separate collection ducting from the dirt.

The gravel fill is crushed quarter-minus.

At both bottom and top of 4" ducting, engage 4" warm air pipes with a spun-aluminum roof penetration adapter. In the crawl space the adapter flat face is upward. A wide circle of two-sided butyl tape bonds the adapter to the Americover Goldentouch 16 mm scrim-reinforced plastic sheeting, the central element of my conditioned crawlspace. On the roof, the adapter makes a better water barrier under an additional layer of shingles. A roof cap just blocks rainfall.

Here is another use of rope-form putty weatherstripping.

There has been a large binge of benefit from the clean ground cover for plumbing, wiring and heating of the grand kitchen remodel off in the far distance at left here. 

At lower right here, see the mending of strength of the 2x8@16" oc, 12-foot floor beams, where the beam centered under the bathtub was necessarily notched to accommodate drain plumbing. The mending is reported in blog post Strong Attic Floors .

At last, it makes sense to complete the roof penetration  of the radon ducting.

Here are several months of observations by the renters of my house. Please see this report and other album pages that support and go beyond, the content of this blog post:

Passive Radon Control, My House

Stack-effect drive is proven to be ample in summertime conditions with a path having very small flow resistence.. At engineeringtoolbox.com, find a calculator of natural draft, working whenever the outside temperature is less than temperature in the radon-suction stack, as occurring most of the time, through all seasons. In the calculator try a 6 meter closed-column height, and a temperature difference of 40 °C (-20 to +20°C)... Result: 0.4" wc.

A typical Fantech fan at noisy maximum power not-wanted, delivers 0.9" wc.

It is easy to see that natural drive should work

(April, 2021)

Work near the radon vent to add some ceiling LED lights in the living room.See that extensive flooring is an asset to ceiling access, not an obstacle.

More Furnace Plena and Flex Duct Quality Work

This story began with call to fix insulation in a crawl space, 2007 construction, 2x12@16"oc framing. Code required simply R30, or at minimum R19, to fill the framing. The proper requirement is that insulation shall be in full contact with with flooring. Well-placed insulation almost never "fills" the framing, and as such, must not rely on twining of framing bottom faces.

During the height-of Summer insulation repair, I found that the crawl space was noticeably cooled by leaks of conditioned air, mainly in a very restricted space over the furnace. Where I am not invested in cheap, flawed methods and am known for integrity and professional engineering experience with hydraulics and more, the customer trusted me, to fix the HVAC ducts in the crawl space. I would start over, in a further demonstration of highly efficient ducting that challenges common practice with crudely-hacked D-boxes and octopus ducting.


The story is drawn from this complete photo album:
Furnace Plena And Flex Duct Innovation Multnomah Village October 2014 

A sampling of photos and captions is posted to Picasa for public sharing.

https://picasaweb.google.com/108533770292578040917/MultnomahVillageBetterHVACFlexDucts 

Here are some of the photos and captions of the Picasa web album:

A 10” flex duct to a 90° elbow atop the warm-air D-box serves floor registers of the main floor. The elbow lower end is not sealed in any way and loses at least 20% of its flow to the crawl space. It was just too hard to reach. What could the installer do? Simply grab the elbow with a couple of straps, with no tab-ins.

The topside 10” elbow with its two loose straps and a sector of hacked sheet metal concealed but did not seal a badly-nipped D-box opening. No goop here. No tape.

Awful return at bottom. A plate closing the filter box couples with a 16” elbow. Most furnace noise is here. The jet from the 16” elbow has no space to adjust to the shape of the filter. The filter is misaligned with the furnace opening. Velocities far exceed that in developed flow of a 16” duct. More than half of the blower head is simply wasted, right here.

Imagine a better duct system with no D-boxes and with efficient furnace plena, instead.

Use turning vanes and development length in the lined plena. Insulate and seal all metal fittings with two coats of applied flexible grout, where most volume in the grout is insulative ceramic microballoons.

I believe in turning vanes. Here they are in the air-return plenum. Try to avoid air churning. It does expend energy.

Survey the completed crawl space. An intelligent return plenum with excellent filter, is prettier too.

It is still difficult to view the warm ducts attachment atop the furnace. Now, please be assured, they are leak-free and efficient.

Crawl space headroom is very much improved.

The found crawl space was barely navigable, with octopus supply ducts from a crude hub. All D-boxes are highly resistive to air flow and should be eliminated. No flow junction should be with full losses of velocity head in re-forming into sharp take-off ducts. Employ steady onward flow in well-formed wyes, or with chamfered lateral take-offs for a single register.









In Summer, 2016 This little crawl space portion of a finished basement, was somewhat- "conditioned." Excellent local business Terrafirma Foundation Systems , beautifully and usefully performed Cleanspace Crawl Space Encapsulation .It was well that my work with floor insulation and re-imagining heat ducts, was done first. This extended "furnace room," is still vented to outside, not circulating conditioned air.

Let My Conditioned Crawl Space, Inspire Yours

Here is my photo album for work so far:
My Conditioned Crawl Space 

A crawl space can become a cheerful, bright work space. Much was accomplished in less-pleasant conditions, including that visible PEX water line, run from the street, under the foundation and on throughout the house.  Hopefully I will never need to dig in the dirt again. Future tasks include revision of the entry hatch, air tight and insulated, foam panel insulation on foundation walls, batt insulation of the floor sheathing, and draw of exhaust from the house, via the crawl space. The ventilation  scheme is experimental, and will demand scientific monitoring.

Steel Ducts Heat Capacity, Forced Hot Air Heat

I am enjoying steadier, quieter heat, where I replaced the leaky old steel warm air ducts in my crawl space.

I don't want to remember found conditions in my crawl space, where an impassable 14" diameter trunk fed variously-wyed 6" ducts at mid height. Here is a less-traumatic view, ducts down this past Summer:

Here is the new trunk 10" by 20" by 10 ft, lined.

Here are views, with flex ducts attached.

The crawl space will be conditioned and warmer. I won't need precarious duct wrap, except at the floor boots. There is ruggedness, simplicity, and very assured sealing of ducts. All good, but I wonder, have I done even more good by taking away waste of heat in warming the old ducts in each furnace heat cycle?

Surely the internet will tell me. Google-search ""heat capacity of steel" steel heat ducts", and get;

1. PDF] 
   

   Fourier-based Calculations of Temperatures of Structural Steel

   www.serendipity.li/wot/temperatures_of_structural_steel.pdf

   File Format: PDF/Adobe Acrobat - Quick View
   Structural steel, when exposed to a uniform heat source at temperature T, will, in the absence of .... specific heat capacity of steel ..... AC and heating ducts, 4.

Modern Hydronic Heating: For Residential and Light Commercial ... - Page 127 - Google Books Result

books.google.com/books?isbn=1428335153

John Siegenthaler - 2011 - Technology & Engineering

by 1°F. The heat capacity of a material can be found by multiplying the specific ... theheat capacity of steel, which reflects both its specific heat and density, ... water can convey the same amount of heat as a 14- by 8-inch duct conveying air, ...

No, it is not a well-expressed topic. Nothing more relevant further down, within my limits of patience. The second hit is interesting in questioning acceptance of forced air heat and consequent badly-placed ducts, but not on-topic.

Here are my assumptions doing this afresh, by myself:

• Crawl space at 200-day heating season average of 50°F.
• Average air temperature within ducts in a cycle is 90°F.
• Wrapped ducts heat inertia is such that temperatures are followed 50%.
• The furnace cycles every half hour, 48 times per day.
• The total mass of ducts is 120 pounds.

The temperature change of the total mass of heat ducts is 10°F in each cycle.

The heat consumed in each furnace cycle is:

m * Cp * delta T

where m = 120 pounds mass

Specific Heat Capacity, Cp = 0.12 BTU/pound/°F

delta T = 10°F

BTU wasted in each cycle: 120 * 0.12 * 10 = 144 BTU

Times 48 cycles

Times 200 days

Result: 1,380,000 BTU per year

Times 0.00001 to convert to therms, is 13.8 therms.

Times $2 per therm is $28 per year.

I think this is low by a factor of two or more. The average cycle is perhaps by more than 10°F. I would believe 30°F is common for a well-ventilated crawl space in moderately cold climates.

I think the heat capacity issue outweighs savings in stopped leakage. Heated air doesn't cost much, with its tiny heat capacity.

Surely there are savings to justify the new ducts, beyond making them airtight and assuredly wrapped. I like the near-instant response, warm air out of ducts.

Google now finds this post, top of list. Bing is out to lunch.

At 10/1/2013, insert a test phrase, to see when it becomes detectable:

"heat up cool down HVAC steel duct mass energy used " I am at the top of search results of course. Little else that follows, is on topic. NREL, US DOE mentions the concern , but does not offer the math.

Please find more posts on this subject:
http://energyconservationhowto.blogspot.com/search/label/Heat%20Capacity%20of%20HVAC%20Ducts 

At 8/8/2017, add some content about coating of duct interior, with flexible grout, as means of reducing dynamic thermal mass. My flexible grout is half ceramic microballoons, as aggregate content. Tiny, hollow glass beads, must reduce surface thermal conductivity, and retard cyclical heat transfer.

This 3 1/4x14x48" steel duct and two register-mating elbows, weigh eleven pounds. I should of course do anything to avoid waste of heat in swung metal temperature.

























Two successive coats of flexible grout brushed on a wet surface by palm, go on quickly. I give up a total two hours of progress in the coating, mostly in wait of drying.

I can't claim how much energy this saves, but it must be worthwhile. Measured numbers would be achieved in a sponsor-worthy experiment at some University. Ducts with and without interior coating should have different outside surface temperature, with proportionality to heat loss.