Category: Uncategorized

A: Yes, when in cooling mode. In New England the only time we need dehumidification is in the summer when the heat pumps are operating in cooling mode, but in Seattle where is it cool and humid you might still need a dehumidifier in winter, although some heat pumps (my Bosch ones for instance) will temporarily go into cooling mode even in winter time if they need to to reduce the humidity.

A: The noise level inside our house has dropped considerably with the new heat pumps. Outside the house you cannot hear the Bosch units at 50’ away and the Mitsubishi units are even quieter.

A: If you are using utility electricity at around 23c/kWh then heating with heat pumps will about increase your heating bill about 150% if you had previously been heating with natural gas. This fact never seems to get mentioned by either heat pump installers or heat pump advocates. Even if you are heating with heating oil, your bill will increase about 25% by switching to a heat pump on utility electricity.  The key to cutting your bills AND carbon emissions is to generate cheap solar electricity from your roof. Doing this will cut your heating bill (if you are on natural gas) by about 10% and if you are on heating oil it will cut it about 50%. In either case your heating will now have a zero-carbon footprint. You do not need a new heat pump. You need solar panels.

A: It is easy to calculate the carbon emissions of your house, just follow this link:

https://greenzerocarbonhome.com/2018/07/what-is-the-carbon-footprint-of-natural-gas-heating-oil-propane-and-coal/embed/#?secret=b6xtBilxJD

Q1: The price of elec makes it uneconomical to go heat pump w/o solar. 

A1. Yes but it is very economical with solar and most houses can generate electricity at 5-10c/kWh (even with some shade on the roof). With a COP of 2.5 (the average in NE for ducted and ductless combined, my Bosch ducted system is about 3.0) the breakeven electricity price at which solar is cheaper than heating with natural gas (not an option in Sherborn) is 12.5c/kWh so most people can save money with a heat pump and solar even if they are on natural gas. With heating oil the breakeven at COP 2.5 is 20c/kWh which almost any roof can do. If your roof is in total shade or is slate or you think solar is ugly then you can buy 100% solar electricity made in MA for about 20c/kWh. This means that using a heat pump can cut your carbon footprint to zero at same cost as heating with heating oil. This won’t save you any money but it will cut your carbon footprint to zero and you will not have solar panels on your roof.

Q2. Despite what was discussed last night if the client thinks solar is ugly…it’s ugly. 

A2. Yes.. See above.

Q3. Geothermal is not feasible forcing the client to continue maintaining the existing system. 

A3. Agreed, geothermal rarely makes financial sense unless you can get the wells drilled for cheap. I am currently investigating if this is feasible on an existing well on our rental property in Dover. I will keep you posted.

Q4. Many ducted AC systems are in the attic outside the envelope. 

A4. Yes but if the sloped sides of the roof are insulated you have brought it inside. Fiberglass is dirt cheap and you can install it yourself or get an installer which MassSave may pay for.

Q5. Window incentives are only available when replacing single pane. 

A5. Yes. This is why I only recommend adding triple-glazed windows when the existing windows fail. Then the incremental cost of the new triple glazed over the cost of new double glazed usually pays for itself in a few years. This is how we did it on our house and clients of mine have done it this way too and they are very happy with the results. Not just lower bills and carbon footprint but fewer cold spots in the house.

Q6. Based on my experience and our discussions a Mass/Save audit is iffy at best.

A6. I agree I have had several done and some were next to useless. That is a government program and suffers from those usual ills. I use it only as a gateway to get the 0% heat loan. This is one of the reasons I think coaches can be so powerful, there is a real shortage of high-quality independent advice.

Q7. It is not possible to power a boiler with a heat pump unless the house is 100% radiant. 

A7. I am genuinely not sure about this. I have not done it myself so I have no direct experience. Manufacturers claim it can be done, but I am wary of their claims. I am about to install an ASHP to power a radiant system. However, I do not see having an existing forced hot water system as a big obstacle. Heat pumps do not replace boilers and radiators. They replaced AC units. At least that is my approach. I have never recommended to a client to take out their existing heating system, forced hot air or forced hot water. If the house has ductwork for AC already then that can be reused for heating. I always recommend leaving the boiler and radiators in place anyway as a back up for when the heat pumps can’t keep the house warm on their own (which is about 20 days a year on our house and our rental house). I am going to be replacing ancient AC units with heat pumps at the rental property and am going to get quotes for using both the radiators and the ducts for distribution. So watch this space! If the house does not have ductwork for AC then it can sometimes be added at reasonable cost from the basement to the first floor and from the attic to the top floor. If none of that works then mini-splits can make sense. We added mini-splits to the other rental house and they work fine for both heating and cooling, though they were about twice the cost of the ducted system at our home.

The integrated energy/financial model I use I built myself. There are lots of software packages out there for calculating the energy performance of buildings but the reviews of them are terrible. They have a very poor track record of predicting the real-world energy performance of any particular house. See this review I wrote:

Zero-Energy Ready Home (ZERH) and Home Energy Rating System (HERS) 

The Department of Energy offers its Zero Energy Ready Home (ZERH) program but it is more aimed at certifying builders rather than buildings. Hence, just like the PassiveHaus and LEED programs it is focused on new construction, not how to go zero on your existing home. The ZERH program relies heavily on EnergyStar standards for appliances and windows and the HERS (Home Energy Rating System) for performance. HERS is focused on energy use relative to a benchmark house (i.e., how your home compares to a model house of the same floor area)  rather than minimizing energy or spending. A HERS rating is only available on new houses, not for existing ones. A review of the HERS rating system in Home Energy magazine found that,  in practice, “there was no clear relationship between the rating score of an individual home and actual energy cost.” Hmmm.

My model began with simple curiosity. I began with just correlating (drawing a line graph) the actual energy (heating fuel plus electricity) that was used every day in my home (I have two years worth of daily data) and the average outside temperature. The r-squared (statistical correlation) of these models (there were 5 of them – one built each time I added one of the fab four) was over 80%. This is a very high correlation for a model that left out known influencers of energy demand like solar heat gain and drafts. Nevertheless, despite these obvious weaknesses, the outside temperature was by far the biggest driver of energy use and hence energy bills. This was an “ahha” moment.

In a separate “ahha” moment I realized that the u-value for windows was not just an arbitrary scale (unlike say a HERS rating) but actually was the rate of energy flow across the window. Since I could approximate the R-values of all my walls, attic and basement, (and the u-value is 1/R value) I could build a mathematical model of how the energy flowed out of my house. Basic physics requires that over any period longer than a few hours, the energy flowing into a house must equal the energy flowing out. This allowed me to build a predictive model of how the energy flows into and out of a house. Since I know the energy flowing in (the combined energy in the electricity plus that burned as heating fuel) I could anchor the model to reality before we even got started. Hence, the inaccuracies in my model are going to be in allocating where the energy flows out (e.g., I might over overestimate the energy flowing out through the walls and underestimate the energy flowing out through the attic) but the overall amount of energy lost must be correct because energy cannot be created or destroyed, the energy lost by your house must be equal to the energy you put in. Put another way, if you cut off the electricity and turned off the heating, your house would eventually reach the outside temperature.

As far as I know, all the other software modeling packages out there start with modeling the thermal envelope of the house. They then model the heating inputs and then hope that they have got it right. One of the most respected models out there is Rem/RATE. I have repeatedly asked the owners of this software for data on how accurate it is in real-world situations. They have never answered my questions. The most that they were willing to say is that “it meets the standards”, but could not even tell me what the standards were. There is almost no published data on the performance of Rem/RATE software. The only data that I have been able to find is the following chart from 2009:

How Accurate Is REM/Rate as an Energy Modeling Tool?

Although the average prediction of the model (which is not plotted on the graph, the straight line is what at 100% r-squared would look like – clearly the model is no where near 100% r-squared, and they never publish this most basic statistic) it is obvious that there is enormous error in the predictions for one house vs another. In some cases the error is equal to the mean value! We use models to predict the heating or cooling load for one individual house, not the average of thousands of homes. Hence, I really doubt the value of Rem/RATE for helping homeowners cut their bills and carbon footprints. The HERS rating systems (which is reviewed negatively in the Home Energy magazine article that I quote above) is built on the Rem/RATE software.  I, and Home Energy magazine, are not the only one with these concerns, see this quote below from the same article:

“Of course, modeling older homes and heating, water heating, lights, and appliance loads is a different matter, and the divergence between modeled and actual energy consumption may be quite different. According to Blasnik, “I know from experience that many energy modeling tools—REM included—often do a poor job of modeling heating loads in older, leaky, poorly-insulated homes.”

 And yet, cutting energy use on “older, leaky, poorly-insulated homes” is exactly the problem we need to overcome! 

So I built my own model, and it not only predicted my actual annual heating bills to within 10% of the actual bills (the most current model is accurate to 5%) but it has proven itself in practice with all of my consulting clients. It has enabled me to make predictions of the real-world impact on both the energy use and the financial bills for actual changes to that home like adding insulation or adding triple-glazed windows. This is why I do not use any off-the-shelf energy modeling software. They simply have a poor track record of predicting real-world energy and financial performance on houses such as those most people live in. 

If you use one of these software packages please let me know how you get on. I welcome any feedback that I can use to improve the model.

A: We work hard to minimize the carbon footprint we create from all sources not just our home and swimming pool, both of which have zero carbon footprints. Any carbon footprint from air travel, selling paperback versions of Zero Carbon Home and selling the T-shirt  is offset with audited, verified-incremental, carbon offsets that we buy from Cool Effect. 

We are big recyclers. We buy only organic food in the first place. We throw out almost nothing. Any edible waste goes to our chickens. The chickens fertilize our garden making our fruit and vegetable gardens very productive. We have done a taste test of our tomatoes compared to the most expensive, local and organic tomatoes from Whole Foods Market and ours tasted far better. The same was true for our peaches, it was literally no comparison. The chickens give us eggs and meat. So, we eat very well. We are not even close to being self-sufficient and do not aspire to being so. But we do love the taste of asparagus in April, rhubarb in May, tomatoes and peas in June, cherries in July, peaches in August, just about everything in September, apples in October, pears even into November and fresh eggs year-round. Last October, I succeeded in transplanting peppers and tomatoes in pots to be grown indoors (growing under LED grow lights powered by my solar panels) and we were eating them up until Christmas. Anything the chickens won’t eat (onions and citrus for instance) gets composted as do all our used paper tissues. Almost everything else such as paper, glass, metal and plastic gets recycled and we trash only about a single 50-liter (13-gallon) kitchen waste bag each week.

I bought a Tesla this year, which I charge from my solar panels which means it costs 2c per mile compared to my old SUV which cost 15c per mile on gasoline. The Tesla, when charged by solar panels, has a zero-carbon footprint. This covers most of our local travel, but we still have two gasoline-powered cars. When they die they will be replaced with EV’s too. My wife recently drove the 400 miles to New York City and back in the Tesla. It cost $8. the Greyhound costs $26, and it emits pollution and CO2 every mile of the way. 

When we buy things, we buy almost always local and sustainable. For examples:

• For clothing we only buy organic, mostly cotton and almost all grown and sewn in the U.S.
• For food we buy only organic and usually U.S.-grown only though we do make a few exceptions for some rather excellent Swiss cheese and Italian balsamic vinegar. I used to drink mostly French wine but now drink mostly Californian organic wines. We have visited farms that provide many of our favorite foods like tomatoes grown at Longwind Farm in Vermont, cheese made at Gray Barn Farm on Martha’s Vineyard, and blueberries grown at D’Ottavio’s farm in New Jersey.
• For construction products (wood, paints, door hardware and light fixtures) and furniture almost everything we buy is made in the U.S. including many made in New England. We buy a lot of construction products because we are renovating, or have renovated, three properties. The wood that will become the flooring in the extension that we are currently building on our house will come from trees that fell down on our land. We had these trees sawn into “1 by” dimensional lumber, and they are currently drying out. Recently we received the first batch of wide pine boards that will become flooring in our extension.
• For cars, our Tesla was made in the U.S., the first American-built car we have ever bought. Before this, we bought only BMW and Mercedes.
• We buy almost no gasoline or heating oil and we buy zero electricity as everything is powered by U.S. sunshine. The heating oil we do buy is BioHeat30 which is 30% vegetable oil.
• For air travel, when we do travel by air (which we have not done so far this year, but not by choice) we offset the journey with carbon offsets. Any remaining purchases of gasoline, heating oil and electricity are zeroed out with certified incremental carbon offsets each year as Christmas presents from me to the other family members.

Q: I just replaced my natural gas furnace so I don’t want to do heat pumps. Does it still make sense to do the other 3. If so, in which order?

A: Yes it does. Insulation (and draft sealing), and triple-glazed windows (either replacing the whole window if the window is rotten or adding window inserts if the window is in good shape) will cut your energy bills not matter what the source of heat is. I suggest doing insulation and draft sealing first because they have the highest return on investment and often pay for themselves in a few months. Windows take longer to pay for themselves. The incremental cost of triple-glazed windows over the cost of double-glazed windows will pay for itself on our house in about 6 years. The cost of window inserts pays for itself in about 5 years – see chapter 3 in Zero Carbon Home for details. After that, I would do enough solar to offset your entire electric bill. If you are thinking of getting an electric vehicle or two then add on about 3,000kWh a year for each car. In most places this would be about an additional 3kW of solar panels or about 8 additional panels. This will get you about 12,000 miles per car at around 2c per mile. A gasoline car doing 30 mpg costs about 10c per mile. An average roof in MA can generate 3,000kWh per year from a 3kW array which will cost you about $8,000 before subsidies and about $3,000 after the federal and MA subsidies. 

Q: Does HITS apply to new construction?

A: The HITS recipe makes it fairly easy to make money by cutting your carbon footprint dramatically on existing houses. It is far easier to do the same on a new house. This is because it costs very little more to install 6” cavity walls and fill them with insulation than it does to install 4” cavity walls. If the sheathing (plywood) outside layer is made from structurally-insulated panels (which are boards made of an insulating layer like a 2” ISO board glued to a plywood structural layer which is painted in the factory to have a water-proof and vapor-proof layer on the outside which then has the seams between the panels taped and sealed on site) you can prevent water penetration, prevent vapor penetration, prevent drafts, gain rigidity and increase insulation in a single installation. This takes far less labor time to install than it does to install each component separately. Adding triple-glazed low-E windows costs only a few % more than double-glazed windows. 

Hence, it costs very little extra to build new a house with an excellent thermal envelope that will dramatically cut the carbon footprint and heating bills than it does to build a standard house. 

Since the heating and cooling loads in a well-insulated house are far lower than in a code-built house, the house probably needs smaller heat pumps to heat and cool the house, which saves money compared to a standard house. 

If the house is designed to have one side facing south with no shade, then the roof can generate all the electricity needed to cut the carbon footprint and energy bills to zero.

Estimates of the additional cost to build a zero-carbon house above that of a standard (“code-built”) vary from 0% to about 5% without the solar panels and 5-10% with the solar panels.

The moderator on our call built his own house with 10” thick walls. He heats it entirely with a single air-sourced heat pump, even in the depths of winter in St. Louis. He powers the entire house with solar panels on his roof. He pays no utility bills. 

While I have not built one of my own, I think the ROI on newly built zero carbon, zero bills houses can be excellent.

Q1. There was a question during the most recent webinar and I missed your response.  The question was what do you think of SIP’s (structurally integrated panels) – what are your thoughts about SIP’s?
Q2. BTW, I was just watching a Fine Home Building webinar entitled “Principles of Residential Ventilation,” most of it over my head, but the core message was that ERV’s (energy recovery ventilators) are the bee’s knees.  Do you have any thoughts on ERV’s (sort of outside your wheelhouse, I know)?  The sub-messages are moisture management & indoor air quality). 

A 1. I think SIPs are great, but they are only one of many ways to get insulation and structure. Walls have to perform a lot of functions in addition to holding the roof up. They must block rain, block wind, block cold/heat and block moisture that is in the air as vapor or humidity. The latter is because humidity/vapor becomes liquid water (condensation or dew) when the temperature drops. You do not want liquid water in a wall – it will lead to mold, rot and likely asthma for the family. This is not theoretical. A house in our town was condemned by the board of health after the owner was taken to the ER with asthma that was caused by mold ultimately caused by vapor condensing inside the walls that did not evaporate. See my other answers on the topic of condensation. Mold and rot, caused by condensation, are probably the most insidious problems in housing today.

Blocking rain and wind are fairly easy, this is what siding is supposed to do. However, shiplap (overlapped) siding and shingles do a great job of blocking rain and a fairly poor job of blocking wind. This is why, today, most builders install an air-tight membrane under the siding. Products like Tyvek house wrap allow humidity to pass through from the inside but block both water and wind. For Tyvek to be effective as a wind barrier the Tyvek sheets need to sealed by having their seams taped from the outside. This allows a wall to dry to the outside when it gets condensation inside it. This is exactly the same idea as in a GoreTex jacket – the fabric prevents rain from getting in but still allows humidity created by sweating to escape to the outside. Condensation in walls (and inside jackets when exercising) is inevitable but mold is not inevitable – you just need to allow that condensation to evaporate. This is the job of a vapor-permeable membrane like Tyvek. Or GoreTex. Some very high-end custom builders will now install vapor tight membranes on both the inside and the outside of the wall, which keep the interior of the wall completely free of condensation because vapor cannot even enter the wall and hence cannot condense. These membranes still allow vapor to travel from the inside to the outside (just like Tyvek or GoreTex) so, if the inside of the wall gets wet for some reason other than condensation (like a water leak) it can still dry out. This is best practice in wall construction today and is so far beyond code that most builders will not be familiar with it.

And I have said nothing so far about insulation. Best practice is to have some insulation outside the air blocking layer (e.g., outside the Tyvek layer) to prevent (or reduce) thermal bridging which is where heat leaks out through less-well insulated parts of the wall like the studs – wood is a poor insulator compared to the air trapped in insulation like foam or fiberglass. Then have even more insulation in the cavities of a wood-framed wall. This would normally be the 4” cavity created by the 2”x4” wood studs (the upright planks of wood that hold up the roof). This cavity is normally filled with insulation like spray foam, fiberglass or dense-packed cellulose. When you combine this outer layer of insulation with the cavity insulation, plus the membranes to block wind and rain, plus the siding (which blocks most of the wind and rain), plus the painted drywall on the inside you have the perfect wall. 

This “perfect wall” is more difficult to build than making a wall from SIPs, but SIPs at least get you insulation and structure. Some SIPs come with the outer surface painted with a waterproof and windproof paint with the joints sealed with tape on site. This makes a very good, but probably not quite the best, wall at a reasonable cost. At the end of the day, SIP or no SIP, your wall must must block rain, block wind, block cold/heat and block moisture. Oh, and hold the roof up. How you get there is less important than that you get there.

A2: I hope this answers your first question, but it is also a lead into to the answer to your second question. When you have a very tight building envelope, (that is, less than about one air-change-per-hour at 50 Pascals, know as 1ACH50. A pascal is a unit of pressure similar to pounds per square inch. Fifty Pascals is about the pressure of a 20 mile-an-hour wind) the air leakage into the house will not be enough to evaporate all the condensation that inevitably happens in walls. You are effectively living inside a Ziplock bag. This is sometimes what happens in PassiveHouses because PH certification requires less than 0.6 ACH50 per hour. Hence, with tight building envelopes, you need great walls that can dry effectively – see above. To make a great house that is low cost to run, low carbon footprint and healthy to live in, all these separate parts (walls, windows, ventilation, insulation etc) all need to work together. You can’t fix one without fixing the others. 

So to provide the fresh air you need when you have a tight building envelope, you need ventilation. Heat recovery ventilators (HRVs) bring air into the house through a pipe rather than through gaps and cracks in the walls. The air that comes through this pipe is warmed up with the air that is leaving the house. This gives you fresh air without losing all the heat. If you have a very tight building envelope a ventilator is not really an option, you need to have it. An HRV is better than just an air pipe. I have never installed an HRV because retrofits are almost impossible to get to 1 ACH50 and my consulting work so far has been entirely on retrofits. So neither I, nor my clients, have ever needed an HRV. So, I think that HRVs make good energy sense and you really need one if you are going to have a very tight building envelope. Whether they are cost-effective is another matter and I do not know the answer to that. I would definitely ask the installer how much energy and money they will save you and then calculate the payback period. Payback periods on heat pumps, insulation, triple-glazed windows and solar panels range from  about 1 to 9 years. When I did some back of the envelope calculations on the amount of money I might save with a HRV I found that I could generate the energy I need at less money with extra solar panels than I could save by installing an HRV.