HVAC-based radon mitigation?

Our basement short term radon test told us to do a long term test. The long term test told us to call someone. The tech from that place is working up a quote for the "standard" approach of sort of creating a low-pressure area under the slab and venting it outside.

However, he also mentioned that some combination of HEPA/electrostatic filter on the HVAC system, with the fan run low when not actively heating/cooling, and possibly some sort of air exchange system, could also be effective, but that they leave that approach to the HVAC folks. Our radon numbers are not much above the limit, so we're far from a worst-case scenario, and I'm intrigued by both A) not poking a hole in our foundation and B) improving house air quality in general.

Anybody have any experience or expertise?

I called my favorite local HVAC place, but unfortunately they recently curtailed their Oregon operations and are only doing Washington. They recommended another place, and I've put in an inquiry, but hey, it's an arcane piece of information! I have to ask GRM!

I've never heard of the HVAC system before. 

I have the slab system on my house and it works very well - basically a 4" hole in the slab, attach pvc pipe to the hole and route through a wall to a full-time fan outside that evacuates the under slab radon and pumps it out a pvc chimney outside.  Cost me $1500 ten years ago, has worked fine ever since, our monitor (in the least ventilated part of the house, a basement workshop) never goes above 1.1, maximum permissible is 4.0.

I also have the standard slab-sucker and it also cost $1500 a few years ago and has worked fine since then. Ours is plumbed into the sump pit, which has a sealed enclosure over it to maintain the vacuum.

I'm not up on radon abatement, but I'm assuming that they are utilizing the HVAC system to A) positively pressurize the house a bit to prevent infiltration, and B) increase the number of air changes and introduce some additional fresh air makeup.

I bet you could put in an ERV (energy recovering ventilator) and get below the limit along with improving air quality. How big is your house? If you put this in a central location:

https://www.amazon.com/Panasonic-FV-04VE1-WhisperComfortTM-Ventilation-Patent-Pending/dp/B000XJNZ1Y

it would provide a steady stream of clean (non-radon-containing) outside air that's had some of the heat or cold removed from it by equalizing with the inside air it's exhausting. It ceiling mounts, and is low profile and unobtrusive looking. The only holes you would have to cut would be in the outside walls of your house for the dual 4" vents. (One inlet, one outlet.) Just that might be enough but running your hvac fan on low would also circulate the "clean" air throughout the house.

I have not used this ERV but have considered it for my house. It could use some fresh air, especially in the basement due to a dirt floored crawl space.

Slab sucker worked amazingly well for mom and dad's place.  Their tests showed >25 whatevers and now they have <2 whatevers.

Their house was built in the late 60s, so they have the advantage of 4" of gravel under the slab.  My house was built in 1900, so it probably started as a dirt basement and someone poured the slab right over it.  Slab suckers wouldn't work for me.... although mine hasn't been tested so I have no idea if I even need it.

The slab sucker would absolutely do the job. We're only at 5.2, so not far above the permissible 4.0. Really more a matter of finding out whether we should consider the other approach in order to do some additional good while we're at it.

As noted, the basic approach is cheap and reliable enough that it's a no-brainer unless the HVAC setup is reasonable and comes with meaningful air quality improvements without too much of an energy hit on swapping out some of the heated/cooled air.

dculberson, that's an interesting one. One of the issues of doing the HVAC thing is that it's really our basement that's the concern. It's not normally really conditioned, so we'd have to add inlets and outlets to the current HVAC system, which would bump the work the system was doing, and while I don't know how much overhead it has, it wasn't sized with that in mind. Something that just swaps out the basement air, and does some temp equalization while it's at it, might be pretty cool. OTOH, if we just do that in the basement, we're not gaining any filtering/fresh air in the rest of the house...

Actually, I should probably have mentioned that aspect, and it will quite possibly kibosh the HVAC approach; adding the entire basement to the HVAC system is a doozy. We don't spend much time there, and certainly don't plan to finish it. I'm actually just finally getting back around to finishing a wall to create a woodshop portion, but since we're about to move and start renting this place out, even the woodshop isn't really going to be usable room, though we certainly want it to be a healthy place for the renters if they spend time down there.

I installed a slab sucker system myself for ~$300 in materials about 2 years ago. Its not rocket science. There are a few websites that will explain everything. I think I used www.indoor-air-health-advisor.com for info and I also purchased my fan there too. I was able to seal off an unused sump pit and suck from there. Ran 4" pvc up from basement through the garage and out the roof. Fan is in the attic. Went from 24.2 pCi/L to 1.1 pCi/L. 

If you're that close to being ok, and it sounds like the basement is unfinished, try sealing all around the perimeter where the slab meets the walls, putting a seal on any floor drains and doing anything else like that to try and keep the gas from getting in. Also, make sure the furnace and any other burning appliances have proper makeup air plumbed to them and that there's a fresh air intake somewhere to make up for exhaust fans in the kitchen and bathroom.

How do they draw radon out of a home that has the water table just below the floor (i.e. a sump that always has a bit of water in it)?

Woody said:

How do they draw radon out of a home that has the water table just below the floor (i.e. a sump that always has a bit of water in it)?

You can seal the sump hole with the sump pump still inside (they make special covers you can buy or just do it yourself with plexiglass) then suck the radon from the sealed sump hole. Google "radon sump cover" or similar to see how it's done.

Woody said:

How do they draw radon out of a home that has the water table just below the floor (i.e. a sump that always has a bit of water in it)?

I have this problem but no sump. Guess I need to add one

As we near Halloween I decided to bring this Radon Based Thread back from DEAD! 

Radon test on my new house came back with an average below 4pci/l, but occasionally spiking to around 7pci/l. I'm going to get a digital detector (AirThings Wave Plus) to track levels around the house. My main worry is higher levels places where my kiddo spends most of her time. 

Neighbors across the street added an abatment system because there was getting as high as the 40's. 

How are abatement systems installed when you want to target certain areas of the slab? 

In reply to pheller :

I don't see why you'd target a specific area. I suspect it's a bit like trying to buy 1/4 of a $1 slice of pizza for 98 cents. Or maybe $1.04; it sounds harder not to apply the solution to the whole slab. Since it's all contiguous, the pump is set up at any point on the perimeter of the house and does the whole slab. Don't forget that being good to kiddo means keeping her caretakers in good shape for as long as possible.