Thursday, February 9, 2012

Experiencing an Energy Audit

Last week, I had an audit of our house's energy use done and I wanted to share a few impressions of the process.  Partly I hope to inspire a few readers to do the same, and partly I figure some of my readers know a lot more about this than me and can answer some of my questions.  The audit was performed by Jon Harrod of Snug Planet, a local energy efficiency firm here in the Ithaca area of upstate New York.

For background, our house is a Victorian farmhouse from either 1850 or 1870 (we heard both in the sales process) and has about 2100 sq ft of floor area.  It's stud construction and sits on a vented stone basement with a part dirt/part concrete floor which is always damp at best, and often with standing water after rain.  A first round of energy efficiency improvements in the 1980s had seen the walls insulated (probably with blown in cellulose), about six inches of cellulose blown into the attic, and fiberglass installed between the ground floor joists.  Most of the windows are the original single pane Victorian casements (and are obviously drafty) but some have been replaced with double-paned windows probably in the 1960s.

Since my family bought it early last year, we've done very little beyond some cosmetic things (refinish the floors, some paint) - we've mostly been focussed on just getting settled in.  The main energy-relevant thing we did right away was to replace the coal stove we inherited from the previous owners with a modern wood stove (Lopi Endeavour).  Wood is our primary form of heat, but the house also has electric heating which kicks in when it's colder, especially in the peripheral areas of the house where the heat from the wood stove tends not to reach as well.  I also put a dehumidifier in the basement since all the floor joists, plumbing etc were dripping water down there constantly - it was clear the basement was pretty much always at 100% relative humidity year round, and about the bottom 1/4-1/2" of the floor joists were rotten as a result.  I guess they could be a lot worse after 150 years of sitting over a damp basement. The house has no natural gas or propane fittings and we buy 100% renewable electricity.  We've spent $3800 on electricity on the bills from March 2011 through Feb 2012, and I estimate we'll have burnt about $600-$700 worth of wood to heat through the current (extremely mild) winter.  So it's costing $4500-$5000 worth of energy to run the house in the condition we inherited it (complete with a set of pristine circa 1980 appliances).

I paid $400 for the audit.  Depending on income level and state there may be rebates that cover part of the cost for many people but we didn't qualify in New York.  However, Snug Planet will rebate the audit cost from any actual corrective work we have them do.  In any case, I felt quite satisfied that I got my money's worth as Jon - obviously fairly expert in the subject - spent over three hours going over the house with me assessing all aspects of its performance, and then later provided me with a detailed written report with recommendations.

There are two main tools he used.  The first was a sensitive infrared imaging camera (something along the lines of this).  We walked around the house and examined all the interior walls.  The camera is sensitive enough that you can easily see the pattern of the studs where they thermally bridge the siding and the interior wall surface, transmitting more heat than the insulation in the cavities.  The camera also very clearly pointed out that a couple of cavities had been forgotten by the insulators when our house was originally done, and that insulation in the downstairs floor had settled so that the top 10% of the cavities or so was now unfilled.  While this would be correctable by blowing in more insulation, he thought the walls were not a very high priority given that they were mostly up to present standards.  To majorly improve them would require wrapping the exterior of the house in rigid foam (thus cutting transmission through the studs a lot) but this would be a big job involving moving all the windows, and residing the house.

Next we moved to the basement which Jon felt was a major source of the relatively poor thermal performance of the house.  We have noted that the ground floor surface is always cold.  Jon's view is that unenclosed fiberglass insulation over a drafty basement doesn't function very well, especially after a few decades of damage to it by animals etc have caused lots of gaps and places where the cold, wet basement air can directly access the underside of the flooring.  He wants to do the following:
  • Seal all exterior air entry into the basement with mortar/foam as appropriate and board up the windows/vents.
  • Cut channels in the floor to bring all inflowing liquid water to a sump pump at the lowest point in the basement (from where it would be pumped to the outside).
  • Cover all exposed dirt/concrete/stone floors and walls with a heavy plastic membrane to cut down the water intrusion into the basement air
  • Use either a dehumidifier or a heat pump water heater to keep the basement humidity down below 55%.
The heat pump water heater in particular sounds like a cool gizmo that I wasn't familiar with - though it's obvious that a heat pump should be able to heat water with significantly less energy input than the conventional electric water heater we have now.  But being able to dehumidify the basement at the same time, essentially for free, seems like a very neat trick.

I'm curious to know whether any readers have had similar basement sealing work done on a vented dirt basement or crawl space, and how it has held up?

Also, Jon (and his supplier Basement Systems) seem to believe that once the air sealing is done on the basement, then insulating the floor is not important.  I don't get this.  Newton's law of cooling says that the heat flow across a surface is given by A*(T2-T1)/r where A is the area, T2 and T1 are the inside and outside temperatures, and r is proportional to the R (insulation) value of the surface.  If a house is at 70F, the outside is at 30F, and the basement is at 50F then the temperature differential between the house and basement is half that between the house and outside.  However, if the walls are R12 and the uninsulated floor is R1, then there will be six times the heat loss through the floor (per unit area) as through the walls.  Am I missing something here?

After this, we moved up to the attic, which was where the biggest surprise was.  The first point was that the insulation is not up to modern standards.  After some compression, there's only about 5" there (estimated to provide R17-R21 insulation).  Jon wants to blow in more cellulose bringing this up to R49.

However, the most striking thing in the attic was we found that several upstairs interior walls are not sealed at the top.  So there is essentially very little preventing convection between the inside of the drywall in those walls and the unheated air in the well-vented attic.  This will obviously cause massive heat loss as a single layer of drywall is not much insulation at all.

The last stage of the audit was the blower door.  This is a large and powerful fan that fits into a special metal frame that stretches a plastic membrane over the back door of the house, except for the fan opening.  All windows and doors in the house are closed and the fan is turned on to depressurize the house (by a target of 50 Pascals).  This causes air to come howling in through every little opening and gap in the structure. Then we wandered around the house with the infrared camera looking to see where the intrusions were.

In the case of our house, the fan was barely able to maintain the desired 50 Pascals, indicating the house was very leaky.  This was not any one main thing but instead appeared to be the result of hundreds of individual issues great and small.  Air was pouring in
  • through a missing threshold under a door to an unheated side attic, 
  • through missing switch plates on upstairs walls that communicate with the attic, 
  • between loose window casements - mainly the nineteenth century ones
  • through the siding and then in gaps in the downstairs wood paneled ceilings
  • up from the basement through endless little chinks in the floor
  • through poorly weatherstripped entries to the basement, the attic, and the entry doors to the house
  • through the bathroom fans (which turned out to vent into the attic instead of the outside)
Overall the audit was a fascinating process and I learnt a lot.  In particular, it's certainly clear that while the 1980s work of insulating the walls, attic, and floor has done quite a lot of good, there's still a lot to do.  Some of it was always obvious (like the leaky windows) but much of it wasn't (like the lack of top seal on the upstairs interior walls).

A week or so after the audit I got the written report from Snug Planet.  It's very much organized as a series of proposals for further work to correct the worst problems, with rough estimates of payback time. Overall, they currently suggest doing about $17k worth of work - mostly focussed on the work in the attic and the basement.

It's worth noting immediately that New York State has this great sounding new program called On Bill Recovery for doing energy efficiency work.  The idea is that you finance the work at a low interest rate (currently 3%) and then repay the loan as a surcharge on your utility bill.  If all is well, the work results in more energy savings than the payments of the loan so your bill actually goes down, notwithstanding the surcharge.  So, having the work done essentially feels to the homeowner like it's free.

Obviously, the one question mark here is will the work actually have a sufficiently good payback time to more than offset the loan payments.  With $5k or so of annual energy costs, it doesn't sound crazy that $17k in improvements could more than pay for themselves over, say, ten or fifteen years.  Still, I'd like to be in a position to perform my own back-of-the-envelope calculation to verify that I believe in Snug Planet's payback estimates.  Although Jon struck me as a complete true-believer in energy efficiency who had got into this business because he wanted to do the right thing for the environment, situations in which the people estimating the viability of a project are also the ones who get the business always make me nervous.

So one last bleg - before I start scraping the rust off my physics PhD and come up with my own model for home energy loss, does anyone know of any good simple tools out there for doing this kind of analysis?  In particular, estimating the conductance losses looks straightforward to me but estimating the infiltration is not so straightforward.  I'm guessing if I knew the blower door flux required to maintain a 50Pa pressure differential, I could translate that into air changes per hour as a function of temperature and then use the heat capacity of air to get the heat loss.  However, I'm sure this stuff is all very well known so if someone can point me at resources to limit the reinvention of the wheel here, I'd be grateful.


Lucas Durand said...

Hi Stuart.
First of all, regarding energy modelling, much can be done simply by building a good spreadsheet - although this may require a learning curve and some research.

There are many deluxe modelling programs out there if you want to pay for them (Passivhaus Planning Package - PHPP for example), but here is a link to a decent free modelling program (HOT2000):

Also, here is a link to a fantastic website with a forum that regularily produces fast, professional and sage advice on exactly this type of thing:

I agree with your inspector that air-sealing work should take precedence over upgrading the insulation. This is because R value (thermal resistance) has little value if the air transport of heat energy bypasses the insulation (or passes through it by convection). It is important to also note that the air transport of moisture through the building envelope is a major durability issue.

Be careful though. If you air-seal your home and make it "tighter" while there is still a source of moisture indoors (damp crawlspace) you will trap that excess humidity in the house and it will do damage. The reason your house has survived so long, so far, without rotting is precisely because there is currently a large energy flux across the building envelope, ie: the excess heat loss is warming the framing some and helping to keep it dry.

I hope this helps some. And good for you for going this route.

Dan the Farmer said...

Rule of thumb: Divide the blower door CFM50 (cubic feet/min @ 50 Pa) by ten to get the equivalent leakage area in square inches. If your blower door number is 3000, you have 300 square inches of leakage.

However, translating the blower door number into a natural leakage number requires that you take climate, wind exposure, and building height into account. Lawrence Berkeley Lab worked these out, and auditors use the LBL number from a chart. A two story house in upstate NY with normal exposure has an LBL number of about 15. Divide the CFM50 by the LBL number to get CFMnatural.

Brian Johnson said...

Engineering toolbax has a rundown of home heat loss caculations

Build it solar has an online home heat loss calculator with a section for infiltration

Wikipedia has a good article on blower doors that has formulae for extracting air changes per hour from the blower door flow.

Source_Dweller said...

Hi Stuart, I'm an architect here in Ontario, and I had an audit done on my old frame house on stone foundation. My basement is dry however, and the gas furnace and water heater are in the basement, also it's used for storage.
Yours seems damp and unheated, which isn't good. Think weeping tile and sump pump.
As for air infiltration, it is nearly impossible to predict, but can be measured after the fact. Did your audit provide an ACH number? (Air Changes per Hour (at 50 pascals))Mine was an astonishing 15.6 ACH!
Really the only advice I should dispense is to consult a local architect experienced in vintage houses. Good luck with your home improvements,
R. Beckett

Stephen Smith said...

I think people can do more harm than good in an effort to make their old homes into modern homes.

By blowing in wall insulation...and worse by sealing the exterior and not the interior, you are trapping moisture vapor in your walls and wet cellulose is a poor insulator. Worse, it can conduct cold from your basement and foundation up through your walls. Even worse, it can rot your walls.

Personally, I would have sealed any air leaks in the walls and windows..added extra glass either via interior or exterior storm and called it quits. No it isn't going to be as efficient as a modern home, but you aren't living in a modern home.

His plan for the basement isn't a bad idea and you could see some savings. Personally, I'd pull all old insulation out, then have someone spray foam insulation over the underside and seal up any air leak sources that would move cold air up through you walls. Sump pump for drainage. Make sure you have interior dehumidifier to keep your floor from being too moist as the foam is going to act as a trap. I think this option would be cheaper, longer lasting, and offer the same degree of savings.

For your attic, I'd want all old insulation out or at least moved. Use foam to seal any gaps or areas where air can penetrate. Fix those vents and vent them outside through a proper vent that won't allow cold air to backflow.

Weatherstrip, rope caulk, those windows and doors. Add foam insulation to outlet and switch plates. Foam seal electric and plumbing entrances - they vent air and breed roaches.

Stephen Smith said...

Also, those fancy cameras and tests can be done for free if someone had the time and inclination. A windy day and a smoking incense stick will identify air leaks. Turn on your AC and you can find air leaks in your HVAC the same way. Get a flashlight and check out where your pipes and wire runs to. Put your hand on your floor. Is it cold?

John said...

Two comments:

1. You definitely need to insulate the floor joists. When we built our passive solar superinsulated house in the '80s we moved in as soon as the frame was done but before the interior was finished. There was insulation in the roof and walls but not the floor. We figured 'Hey, so the floor will be a little cold, how bad could it be?'

Pretty bad, as it turned out. We were pouring wood into our woodstove the first winter, and if the fire went out the interior temperature dropped like a stone. We got insulation into the floor the second winter and the house performed beautifully. You need to do the same. I am surprised the auditor did not catch this.

2. You are right to work on air infiltration, but if you do too good a job your woodstove won't work properly. It's draft depends on a ready supply of intake air (supplied at present by all the air leaks in your house). If you plug too many of those air leaks the stove won't be able to draw properly. The solution is an outside air intake for the woodstove. The auditor should have mentioned this too.

Good luck on your energy improvement efforts.

Stephen B. said...
This comment has been removed by the author.
Stephen B. said...

One last thing, I'm probably going to install a heat recovery ventilator too after I get the air leakage down.

But my situation is different as I'm reconstucting the house down to the studs.

porsena said...

Like Source_Dweller, I'm worried about the water in your basement. Living here on the NorthWet coast gives me a certain amateur respect for reducing humidity. Wood frame, low-rise apartment buildings in my city built to modern standards often need envelope replacement because the walls were constructed too air-tight (a problem with the building code). Water finds its way into the walls eventually and then into the inside of apartment units. Mold starts to grow on the studs and plates.

Sealing off the airflow in your basement without addressing the water ingress seems, to me, a recipe for encouraging mold. The two courses of action I'd consider would be to install perimeter drains around the house and to concrete the entire basement floor over a water barrier.

Stuart Staniford said...

Stephen Smith: "Also, those fancy cameras and tests can be done for free if someone had the time and inclination. "

I really don't think this is true except for a very small number of people who know a great deal about building performance. Sure - there's stuff that's obvious that you can figure out with elementary methods. But having gone through the audit, it's very obvious to me that the professional with the right tools did a vastly better job at identifying the issues than I would have done on my own in my present state of knowledge. (Not of course that I couldn't learn to do it, but there would have been a significant amount of effort required to understand the relevant issues in enough detail).

Stuart Staniford said...

I think I figured out (reading between the lines of a correspondent) why one might think underfloor insulation was not important in an air sealed basement. With the heat coming from above, and no infiltration to cause drafts within the basement air, the air will tend to stratify (warm air near the top of the basement will not change places with cooler air below) and thus there will be no convection. There won't be much conduction either since still air has an R value of around 5.5 per inch. Thus the loss downward will be constrained by how much can be radiated - and the net radiation between the floor and the rest of the basement won't be that much.

However, the duhumidifier could potentially stir up the air some.

Kweksma said...


closing the ventilation holes in the basement does not seem a good idea. Sealing the walls and floor with thick plastic will help reduce moist buildup. I did my basement, and the wet smell emidialty disapeared.
I insulated the sealing of the basement (the floor of the livingroom woth this product, which has an absurd low payback time of 3 years:

It's a dutch invention, basically alu-foil bags that create pockets of non-moving air, and radiating back heat because of the reflecting surface. My feat actually get warm when i let my feet sit in one place.

The insulation for a whole floor fits in a small box.

Very interesting article by the way!

made said...

To approach Passivhaus Standards you need 1.) low heat transmission trough opaque building components, 2.) high solar gains trough windows ( in a modern window the weak point is the frame and not the glass..)
3.) an airtight building, which in the end necessitates a controlled ventilation. The ventilation should be configured with heat recuperation, usually done with cross-flow heat exchangers. This is also important for your heat source, which needs combustion air.

The basement is usually outside of the airtight building "hull". So in a passiv haus insulation of the ground floor is important.
The damp basement is a sign of a high ground water level, wich can also be lowered by a well outside of the house. You could use the water of the well as a heat source for a heat pump...

made said...

The rotten ground floor joists are probably a result of warm air giving of condensate. Do the rotten parts correlate with leaks in the blower door test ?

Poul Andreasen said...

Love your blog, Stuart - keep posting.

Concerning humidity buildup when sealing off the building, I would suggest you consider a solar panel solution like SolarVenti
(, thereby reducing your dependence on electrical input.

The panels are affordable and easy to install. They produce dry, warm air that is fanned into the house (slightly pressurized), thereby replacing the existing, humid air, which escapes through the cracks that remain in the building after sealing it off (You might consider leaving some in strategic places :-).

The solution therefore doesn’t just remove moisture, but pushes fresh, warm air into the building. Systems have a capacity of 520-6500 cubic feet per hour (depending on solar and size). There is a valve for airflow regulation installed inside the house.

Panels can be roof mounted (pushing warm, dry air downwards) or wall mounted (pushing warm, dry air upwards). They also have special fittings for leading the air directly to basement level.


(In case you wonder: I am in no way connected with SolarVenti ...)

kjmclark said...

You might also consider blocking off part of the basement for a root cellar. It's not a bad way to get lots of free refrigeration in the winter. High humidity is a good thing for most root cellars. That may be part of the reason no one sealed up the basement before. Most old farmhouses used the basement for root cellaring in the winter.

Heading Out said...

One of my first posts at Bit Tooth was about a home energy audit and when we added on to our house we installed a wood-fired tile stove, underfloor heating and solar roll - but I also installed thermocouples and after monitoring these for a year discovered that I had put in way too much stuff (on the advice of a renewable energy contractor in the state) that would never pay for itself. We subsequently blanked off the underfloor effort (pipes in sand under a tile floor - a la hypocaust - ) since it took a huge effort to get that up to 60 deg F, using the tile stove. We now use the heat from the stove and the solar roll to preheat our water (gain of about 25 - 40 deg in mid MO). Long-term insulation was our first step, and sealing cracks, those smaller initial investments paid off, though I haven't got the numbers yet, I suspect that residing the house and changing the windows also made a big difference, since now we burn less wood to be comfortable.

Dan the Farmer said...

Oh but there's a lot of bad advice rolling in.

Concerning moisture venting: Vents won't help once moisture is in your cold attic and hits the dew point. You need to air seal and control moisture and keep water from getting into the attic in the first place. The same goes for walls.

Concerning root cellars: Root cellars should be cool and damp. Basements should be warm and dry. Put your root cellar somewhere else unless you want to rot out your house.

The heating boundary should be a continuous envelop where insulation and air sealing happen in the same surface. Insulate and air seal the basement walls if you don't want the pipes to freeze in the basement.

Stephen B. said...

Many thanks to Lucas for this hugely helpful and interesting house energy modeling program:

I spent several hours playing with it, using it to model my house as it is now and as I am planning to retrofit. The program only contains climate/weather data for Canadian locales, but since my house is a bike ride from Canada, I merely picked the closest city the program offered (Fredericton, NB)

One thing I learned is that my deep, uninsulated basement accounts for over 40 percent of my heat loss. Even when I go to the fancy closed-cell spray foam throughout the rest of the house, greatly cutting air infiltration and making most walls R 28 and the top ceiling/attic over R 60, it's the basement that is nearly half of the problem.

With the new windows, closed cell foam throughout, redone basement, and a heat recovery ventilator, I took oil consumption from over 700 gallons down to less than 100. The program also took furnace output for the design temperature from over 40K BTU down to less than 12K BTU, basically telling me I don't need a furnace any longer at all and some other, much smaller heat source will do.

In any case, I can't recommend people playing with this program or one like it, enough.

That all said, I deleted my other comment as it was just a mess to read.

Daniel Ridgeway said...

Why is there so much water in your basement? Are all your gutters and downspouts in working order? Does the soil around your house slope away from the foundation to a swale which carries run-off safely away from the building? These are relatively inexpensive fixes compared to a dehumidifier.

The best advice so far:

Seal the penatrations in the attic and floor before adding a ton of insulation,

Spay foam into any cavity that is accessable, e.g., joist cavities (including under the floor), stud cavities, etc.,

Use a sealed wood stove that has a duct for outside makeup air, and

install high performing, efficient windows and doors.

Thanks for a great blog

Wyoming said...


I live in a stone house with full basement built in about 1750. When I moved in I had all the problems you list and some others (you will find them after some time I bet).

From my experience with the wet basement (we would get up to 4 inches of water after hard rains). Get that sump pump in asap. This is very important. You just cannot fix many of the other problems until this is done. You will just trap water in the house unless the sump pump is getting rid of it. In our experience we did the sump pump as soon as we could and just that made a big difference in the comfort level in the house.

Then I would fix the air gap problems in the attic and get the attic insulation up to a much higher R factor. I assume that attic does have vents?

Both the sump pump and attic work are easy and you can do it your self and save about 2/3's of the money the contractor will want from you. Makes payback much faster.

Then work on the other air gaps around the house. Most of those are easy to fix as well. Do it yourself and you save a bunch again.

It is not that hard to fill the low spots in the walls and then fix the sheetrock (lathe or what you have).

Do each thing as you have time and see what the result is. I do not personally like to hire folks for this kind of work as it is well within the capabilities of any one. One learns a lot in the process and saves a lot of money.


Bruce Howlett said...

My late mother-in-law owned an old farmhouse not far from you in Ellis Hollow. She had almost the same set of problems -- wet basement, drafty windows, leaky attic. Combo of wood and electric heat.

First -- it may make you feel good that you are buying renewable energy but your electricity largely comes from the coal-fired plant on Lake Cayuga.

You really want to look at ROI. She did the best bang-for-the-buck items that some of the comments have suggested. She had the basement sealed and tile drained and then installed a second pellet stove there. No insulation in the ceiling so the basement stayed dry and the heat largely migrated upstairs. Very comfortable.

Added interior storm windows to preserve the historic look. Much cheaper than installing new windows.

Adding a second stove was a brute force method but very effective and provided much comfort. She loved her contractor but the day he showed up in a new F-150 that he said she paid for my mother-in-law ended the work.

Some comments have mentioned the needs of an old house. Be sure you aren't trading one set of problems for another. Older house have special needs.

kjmclark said...

"Concerning root cellars: Root cellars should be cool and damp. Basements should be warm and dry. Put your root cellar somewhere else unless you want to rot out your house."

Yes, root cellars should be cool and damp, but basements should *not* be warm and dry, so I guess I agree with the root cellar description and the "bad advice" bit.

Basements should only be warm if you plan to use them as living space and heat them. They shouldn't be "dry", though the joists shouldn't be wet, either. Ideally you want probably around 40% relative humidity around the joists. Less than that and they might start cracking.

These old houses were drafty in part because it helped to keep the relative humidity in a reasonable range for the building materials. That plan works as long as you're willing to dress warmly and don't mind a bit of cold. If you start sealing that up without watching the humidity problems you create, you will start rotting wood.

It doesn't take too much ingenuity to create a root cellar space in the existing basement, and seal that off from the rest of the space you're trying to dry up and seal off. And then you get the advantage of greenhouse gas free refrigeration in the winter, and don't have to contribute so much to carbon emissions from shipping food from distant places in the winter. It might even reduce the cost of the total project, because you don't need to seal up and drain the floor of the root cellar.

The bit of space we sealed off in our basement cost about $100 to construct, keeps about four fridges worth of our vegetables for the winter, and helps to keep our utility bills under $150 a month. I just wish we had more space to work with and an easier time keeping it humid.

And John makes a good point about the woodstove. Our Lopi had a knockout in the bottom for connecting an outside air intake. It also had threaded bolt holes in the bottom to attach it. I bought their kit, but couldn't figure out how it was supposed to work, so I just made my own. A small rectangular electrical box, bit of 1/2x1/2 angle iron, a tiny bit of bending 4" duct pipe, and metal duct tape and I had a nice replacement. I ran 4" duct through the basement to an outside wall, added a damper, and insulated the duct. Works great, though we almost never use the damper. I'd just skip it if I had it to do again.

Stuart Staniford said...

Brian Johnson - many thanks - those links are exactly what I needed.

Lucas - the Hot2000 exe looked promising but I'm strictly a Unix/Mac guy.