Archive for July, 2012

Radon test results

We ordered a radon test kit from the New York State Department of Health last month. The kit is small canister of charcoal that you open and place in the test area for several days. We let it sit for 4 days in our basement, then sent it off to the testing lab. The results came back about a week later.

For reference, the EPA defines the safe limit of radon gas at less than 4 picocuries per liter of air (pCi/L). Our result was 38.6 pCi/L, almost 10 times the limit, ouch!

We had been somewhat slow to get the basement tested for radon because we spent a great deal of time and care sealing everything in the basement. Our blower door test confirmed that we had done a good job overall. So we assumed we would have no problems with radon.

Unfortunately, the radon is getting in, and because the house is so tight, it’s not getting back out.

Thankfully, we installed vent piping under the slab and sub-slab insulation when we built the house. We capped it off at the surface hoping we wouldn’t have to use it.

How sub-slab radon mitigation systems work

A vent pipe installed below the slab and vented to the outside depressurizes the area below the slab. Radon gas will take the easiest route to the outside.  Our vent pipe runs the full perimeter of the inside of the footing under both the slab and 6″ of XPS insulation (R-30).

The EPA recommends running the vent pipe up the center of the house to the outside because the warmth of the house creates a stack effect, inducing a natural draft in the pipe without using mechanical ventilation. Unfortunately this method also cools the house in the winter, something we hoped to avoid.

So rather than run the vent through the house, we ran our exit vent pipe through the footing to the outside of the foundation wall and capped it at surface level. We figured if/when we determined we had a radon problem, we would extend the vent pipe up outside the house, through the soffit, into the attic, connect to an inline fan and exit through the roof.

The fan will use energy continuously but at least it won’t be cooling the house in the process. The installation cost will be minimal since we did most of the hard work when we poured the foundation.

In hindsight, we should have found a way to integrate the vent into an outer wall where it could still be insulated from the interior space. Running the vent up the outside of the house will take some work to make it not look like a strange pipe on the side of the house. We’re going to try to disguise it as a gutter. We’ll have more info on the details and photos as we start work next month.

For more information on radon in the home, read this EPA guide, A Citizen’s Guide to Radon.

June performance

June seemed to be in line with past year averages at least temperature-wise. (1 heating degree day less than the 10 year average, 52% less HDD than May, 8% more sun). We turned on the air conditioning for a couple of hours on three particularly hot and humid days. We’ve also started building a barn this month so that is starting to show up in our energy usage. This partially resulted in 5% higher energy usage in June. We used 0.36 kWh for space heating and 2.76 kWh for cooling. Our daily average usage was up 9% from May. We generated a 614 kWh surplus this month, our forth surplus month in a row and highest yet.

All values in kWh (except HDD) Jan 20121 Feb 20122 Mar 20126 Apr 20127 May 20127 Jun 20127
Solar PV generation 369 597 860 925 867 939
Usage 873 666 515 378 309 325
Net usage or (generation) 504 69 (345) (538) (558) (614)
Average daily usage 28.2 23.0 16.6 12.9 10.0 10.8
HDD (base temp 68F)3,4 1,2125 1,045 704 617 298 144
1 January values based on meter reads.
2 February values based on TED data.
3 Heating Degree Days (a measure of how many outside degrees in a day it is below a target inside temperature)
4 Calculated from our HOBO outdoor weather monitor hourly data, unless otherwise noted.
5 January HDD data downloaded from, Station ID: KALB (Albany International Airport).
6 March values based on meter reads. (TED died March 1st, eMonitor installed March 16, 2012)
7 Values based on eMonitor data.

Our ‘thermal comfort index’ is still quite high. The house generally maintains a cool temperature throughout the day without much window opening and closing. The evenings have been cool enough to lower the temperature of the house to stay comfortable for most of the day. This month was the first time we’ve used the air conditioning component of our ASHP. The unit is located on the first floor and definitely cools the first floor down very quickly. The upstairs did not cool down as quickly, although we have yet to run the air conditioner more than a few hours at a time. I suspect it will require more run time to cool off the upstairs. I’m sure we’ll find out in the next couple of months. Our ceiling fans make a huge impact on comfort.

June was also our first year anniversary for connecting the solar PV system to the grid, which means the electric company owes us a credit! But of course you have to pull some teeth to find someone to talk to about making sure the credit shows up on our account. I’m curious to find out what 3.65 MWh are worth at the ‘avoided rate’. I’m guessing a few cents a kWh, which would add up to roughly $100. We pay roughly $200/yr for connection fees. We’d have to get about 6 cents a kWh to get a credit of that size.

May was our third full month of circuit level data monitoring. All the data is available at You can now view solar, usage, net usage, temperatures and HDD for all of February and circuit-level data for 16 days in March and the full months of April through June.

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