Solar system design for home radon fan remediation system (off-grid)

I use a radonaway RP145 fan. I have a few spare RP145 units as well. As far as I know there are no DC radon fans. I think converting the piping and the system over to a new unit would be out of the question at this point.

If using a larger inverter is generally a bad idea (I assume there is a good reason), then I can simply buy the 100W unit and the 2000W unit. I will test the 2000W unit and then keep it in a box, just in case I never need it. It would just be as simple as connecting it if I ever needed it. Optionally, I could also hook them both up side by side and have then both connected with circuit breakers. Then I could turn them on or off as needed. Then the unit could be there if needed, just by throwing the breaker for it.

I'm not sure how many days backup I would need since I hadn't thought of just running it off a UPS. I hadn't considered just running the fan off of a UPS because I was looking for a more permanent (solar) solution that I didn't have to worry about charging or messing with in the event that the house lost commercial power. I thought if I had a strong enough solar system I wouldn't have to worry about the fan any more besides changing the batteries out every few years.

If I run the fan off of a UPS type system as you suggest, I'd just need the float charger, the batteries, and the 100W inverter. That would buy me a few days of UPS if the grid went down but doesn't offer a long term type of solution. I do have a 9200W portable generator that I can connect to the house via a 40A cable. I have one of those mechanical lockouts in my breaker panel to switch over to generator from grid power to keep everything safe and the generator has a floating ground. I have about 30 gallons of gas on hand. I suppose I could hook the generator up to house in the event of an outage and use a few of my 6A chargers to get the batteries up to full charge but I'm thinking that would take a while.

While I do agree that it's a much cheaper solution, using generators and and having the radon fan on "UPS" sort of defeat what I'm trying to accomplish though, making the fan and power system self contained and not requiring any outside intervention, other than brushing the snow off the panels in winter. I'm also not thrilled at the ideal of using lead acid batteries since they off-gas hydrogen and I have a finished basement. If I were to go that route, I'd probably also buy one of those little honda generators and just run the fan (or UPS) off of the tiny generator 24/7 until the power came back.

When you ask about the fumes, I'm not sure if you mean radon fumes, exhaust fumes (from a generator), or hydrogen fumes from lead acid batteries. There is no way to seal off the basement area (it's a walk out basement that's finished) because of the HVAC system. It has intakes and exhausts in the basement plus radon sort of creeps wherever it wants when the fan is off. I have no way of reliably blocking off the upper sections of the house with any vapor barrier.

These are great ideas though, I appreciate them.

For the questions about the radon, remediation, and HVAC:

The house has 3 floors (basement, 1st and 2nd). Every room in the house has a supply and a return (except the bathrooms, there is no return in the bathrooms). The basement has 4 supplies and one return. The basement is finished. The basement cracks were "sealed up" when radon was discovered and a sub slab pump was installed. Most houses in PA have radon, some are higher, some are lower. There is nothing you can do other than install a fan, or ignore. We chose to install a fan. When the fan is running, the levels are 0.4 pCi/L in summer and 0.8 pCi/L in winter. If the sub slab fan is turned of, gets broken, or is without power for 24 hours, the basement levels will return to anywhere between 25 pCi/L or 50pCi/L.

Adding a passive pipe has no effect at this house, that's the first thing they try. If the passive pipes dont work, they cut them and then add a fan inline. Nothing can be added to the house at this point to change the dymanics of air flow, seal anything any differently, or change any designs of anything. I'm stuck with keeping the fan running. We have an electronic Radon detector on each floor and I monitor them every day. They also have an audible alarm when the level goes above 4.0 pCi/L (the action level recommended by the EPA).

Worst case, if we lose power (and we're home), it's possible to open all the windows and the sliding glass door in the basement. Since the HVAC wouldn't be running, theoretically we'd be fine. The way that works is, air must come into the basement and pressruize the slab enough so radon can't come in. You would think you'd want to suck the air OUT through the windows but that actually makes it worse. You want the outside air to creep in and pressurize things. This is obvlisluy unsafe for many reasons and not a good solution. It's not something I'm willing to test for 2 days though.

If I hook the generator up, it's appx 9000W and will literally run everything in my house, including the heating system in winter (natural gas and forced air) and the A/C in summertime. That also runs the radon fan. The problem is, this is not a 'long term' solution.

The goal of my project is not to keep the fan running until power returns. My goal is to have a solar/battery system that always keeps the fan running and is totally separate from the grid. For me, this is the best solution, one I should only have to check on once a week or so to make sure that I'm not in danger of killing my batteries. I really want to avoid running a UPS type of system that needs to constantly be checked/maintained and would die after a certain amount of days if not charged back up by generator.

The goal of this project is to find out how much overhead I need to build in to run a 75 Watt Radon fan and a 5W Radon detector 24/7/365. I'm guessing checking the batteries once a week and brushing snow off would be my two biggest maintenances.

If I need to buy 6 panels (100W or 150W each) then I'm willing to do that. If I need to buy 4 100Ah batteries, then I'm willing to do that. I'm thinking if buy 6 panels and run them in two rows of 3, that's two legs that top out at 75V open and the rows can be put in parallel. I'm not sure if that would be enough, I don't have any real world experience with solar so I don't know how to size it correctly. Whatever it takes so that I always have enough power to run the fan all of the time with as little intervention as possible, regardless of a few days of bad weather. I could always put some type of low voltage alarm on the system so that I have an indication that we've had too many days of bad weather to maintain without battery damage if needed. Then I could put a charger on it get the system back up to speed. The goal though would be not to have to worry about that.

Thanks for the write up Bill. I've read the post a few times and what I'm getting from this is that to meet the bare minimum of:

"1,800 WH * 1/0.52 off grid AC system eff * 1/2.62 hours of sun per day (Dec avg) = 1,321 Watt array "break even" Dec avg."

I would need at least thirteen 100 watt panels and seven or eight (12V) 100Ah batteries. If I wanted to make the system so that it never needed attention, regardless of bad weather, I'd need to roughly double that to twenty six panels 100W panels and fourteen to sixteen 100Ah batteries.

I think basically what you're telling me is that to meet the bare minimum, I'm looking at about $3300. If I want to make it maintenance free (no generator charging) and weatherproof (a run of shady weather), I'd need to spend about $7000. Also, I'll never make the investment back for the amount of electricity generated under any circumstance. Finally, In 3-7 years I'll have to replace the batteries, and in about 10 years I'll need to replace the charge controller and the inverter.

The fan is hard wired into the basement "lighting" breaker. I don't think I could get an accurate reading with my clamp meter. I have a kill-a-watt meter but I'd have to cut the wire that feeds the fan, put a plug on one end and an outlet on the other to read the consumption. It's entirely possible that the fan only uses 45 to 50 watts of energy, it depends what fan has to pull to get the correct sub slab vacuum. I tried to get them to put in the RP140 unit which only uses about 25W of electricity but they said they don't use that unit because it has a lower CFM and the wattage difference is "nominal" on people electric bill.

I suppose the first thing I have to do is figure out EXACTLY how much power the fan is using to figure out if it's going to be worth the investment or not.

At this point it would probably be cheaper just to buy the most gasoline efficient tiny honda generator made (perhaps 1000W) and figure out what's the best or cheapest way to make a UPS for the fan to run on off of grid power. But then I'm back to square one of manual intervention.

This is kind of bumming me out...

I am considering buying this generator: https://www.homedepot.com/p/Westinghouse-1-200-Watt-Gasoline-Powered-Portable-Inverter-Generator-iGen1200/301466638

It's comparable in wattage to the 1000W Honda, has the same noise rating (around 55dB), uses 0.8 gallons per 9 hours for the load I'd be running it at, and is about 1/2 the price. It also has higher ratings than the Honda on both the Home Depot and Amazon sites. That just may be because people like that it's cheaper though and really aren't comparing apples:apples...I have a Champion 9KW whole home generator so I doubt I'd buy a backup 1000W generator.

I have tried every fuel stabilizer and the one that I've found works best is PRI-G. That's what I use in all of my stored fuel. I always keep a minimum of 30 Gallons in cans. Propane is out because of the cold temps in PA, it doesn't flow when it's cold out and it's not my favorite thing to store. We have 3 of the BBQ grill size cans of it (one in our grill, one in our fire pit, one extra we keep to swap out when one gets empty).

What would you recommend then for the battery/charger/inverter/transfer switch setup? I'd want to use a 100W inverter. I'd want to use AGM batteries (they will always be sitting at roughly 60 degrees F). I'd want it to be a "2 day" system dedicated for just the Radon fan (75W worst case) and one Radon meter (5W). I'm not sure what charger to use, perhaps they make a charger that's both a quick charger and a float charger? It would always stay connected to grid power until the grid power drops. Then I'd have to move the charger over from grid to 1000W generator via an extension cord (most likely a 75 or 100 foot cord), or I supposed I could have something wired up in advance so I dont have to leave the door or window cracked open with a cord running through it. Ideally then, it would be best if there was some combination of equipment I could buy that would function as follows:

1. Radon fan (and Radon meter) is always connected to the 12V Inverter (I'd have to purchase a spare inverter so figuring on 2x of that unit)
2. Inverter is connected to 12V AGM battery bank (not sure how many batteries or what Ah)
3. AGM Charger (possibly quick charge and float charge) hooked up to both "grid" and "outlet for generator on outside of house" via some type of transfer switch that falls over to generator when generator is hooked up and doesn't back feed into house breaker (downstairs lighting breaker)

Or you were also suggesting a different setup that would always be running the fan from grid power but switches over to the inverter when the grid goes away so that the batteries aren't constantly being discharged/charged...

1. Radon fan (and Radon meter) is always connected to a transfer switch, that is then connected to both the inverter and to grid power
2. Inverter is connected to 12V AGM battery bank (not sure how many batteries or what Ah)
3. AGM Charger (possibly quick charge and float charge) hooked up to both "grid" and "outlet for generator on outside of house" via a second transfer switch that falls over to generator when generator is hooked up to the outside outlet and doesn't back feed into the house (downstairs lighting breaker)

So the inverter probably doesn't matter too much as long as it's 100W, but if you have a recommendation on the 12V AGM fast/float chargers (if that exists), 12V AGM batteries (both rating and total amount of batteries), or transfer switches (or a different combination of things that are combined into one unit), I'm interested to see what you'd recommend.

I've had bad experiences with Amazon warehouse items. I think a lot of times they're returns that Amazon just assumes are fine and stuffs back into a box. I have no way of knowing if the last person that had it started it up with no oil in it and sent it back because it "had scratches on it". I do appreciate you trying to help out with pricing though! This whole situation is a bit of a bummer.

No one has suggested being able to seal up the basement with anything for any amount of money, I was just hoping there was some new type of sealing that I hadn't heard of yet. I'd be happy to pay to get it fixed permanently instead of stacking up methods of remediation and ways to power them. These solutions of constantly running a fan and then powering the fan with batteries and solar power are all less than ideal.

For the area I live in, almost every house on the street is between 4 pCi/L and 8 pCi/L. Some houses are 25, some are 50, and some are as high as 200. It's just a roll of the dice. Some houses that pass retest later on and they are high because something cracked under the house. Some people don't care about it at all and don't bother retesting every year or so. I worry about it so I installed real time detectors in the house. They'd help to let me know if the fan unexpectedly failed. I'm just very paranoid about it. I realize if the SHTF one day, Radon probably won't matter anyway, but it's something I don't want my children getting sick from in the long term. Some people are of the opinion that we'll never lose power in our development because we've only lost power 2 times in 15 years. Once for 12 hours with Hurricane Sandy and once in the summer for 2 hours when a fuse feeding the development blew.

It's very hard to say what the problem is. The house has been like that since it was built. The only test I've done recently is to turn the radon fan off and see what happens. The problem with that test was, all the windows are closed but the HVAC is still running (draws in air from the outside via a pipe with the furnace which shouldn't matter too much) and the water heater runs intermittently (power vent model). The water heater (power vent) basically sucks air in the basement into it and blows it outside the house. This is a possible source of the problem. I'd assume that it puts a bit of a negative pressure inside the basement when it's venting. The radon fan must be strong enough to make up for it though.

The only other tests I could run would be to shut off the breaker for the whole house, which would simulate a power outage. Then I could see how fast the radon levels rise with no power, no fans, not extra air draw on anything. Then I could also run the same test, but with just one window open in the basement and all other windows in the house closed. Then I'd have to repeat the test in the summertime with one open window in the basement and multiple open windows on the top floor. I'd have to see what each test results in after 24 hours.

The only way I'd be able to do that would be to send my family on a vacation somewhere for a week without me. I doubt that would go over well.

I'm sure most people don't understand why this is bothering me so much but I'm just trying to figure out the best solution. I've talked about this with multiple people and I just get "open your windows, you'll be fine" or "don't worry about it, it won't make you sick for 20 or 30 years anyway".

That's correct, there is no safe level of Radon.

The furnace is operating correctly, it draws in a massive amount of air from outside. There is a fan that feeds the furnace combustion system and a second fan that moves air throughout the house. The 'fire' fan has both and intake and exhaust pipe with many safety features. It's made by a company called Heil and it's bundled as both furnace in winter and air conditioning (with outside unit) in the summer.

Similar to this model: https://www.homedepot.com/p/ROYALTON-44-000-BTU-95-AFUE-2-Stage-Downflow-Forced-Air-Natural-Gas-Furnace-with-Variable-Speed-Motor-95G2DF045BV12/307689738

The water heater is a goofy design but it's what most builders in PA use because it has a cheaper 'installation cost'. it pulls in air from the top of the water heater with a large fan and then pumps all of that air outside via a pvc pipe. All the combustion air is pulled into the unit from inside the room it's in.

Similar to this model: https://www.homedepot.com/p/Rheem-Performance-50-gal-Tall-6-Year-38-000-BTU-Ultra-Low-NOx-ULN-Natural-Gas-Power-Vent-Tank-Water-Heater-XG50T06PN38U0/300676632

There is a CO detector and explosive gas detector in the water heater room, the furnace room, and on each floor of our house (basement area/1st floor/2nd floor).