What Clients say about Zero Carbon® Consulting Services and Client Case Studies

What Clients Say about Zero Carbon® Consulting Services:

“Working with David Green was an absolute pleasure, he guided me through the process with his experience in lowering my energy expenses and my overall carbon footprint.” DS, Long Island, NY.

“I wholeheartedly endorse David Green as a home energy consultant. He used his expertise in energy efficiency to focus on cost-effective solutions. As a result of following his suggestions, my house has significantly reduced energy consumption along with improvement in the overall comfort of my home.” – LA, Westwood, MA.

“I couldn’t have done it without you!” “Read his book!” – KA, Arlington, MA.

“we found your report to be very helpful indeed!” – ML, Needham, MA

Zero Carbon ® Client Case Studies

Case Study 1: 1,000sf single story home in NY state.

The first client of David Green’s Zero Carbon® consulting practice, David Sguazzin, has cut the carbon footprint of his modest home on Long Island, NY by approximately 4 tons of carbon dioxide per year and is saving over $1,100 per year on heating and electric bills. David Sguazzin is earning a 46% return on his investments in insulation, air sealing and triple-glazed windows. The triple-glazed windows were made by David Sguazzin and fitted to the inside of his existing single-pane windows using a technique pioneered by David Green on his own home. 

Before engaging Zero Carbon® LLC, the approximately 1,000 square foot, single-story house’s heating and electric bills were about $3,500 per year. Today, they are about $2,400 per year saving David Sguazzin $1,100 per year.  The total investment was about $1,300 in materials. The fee paid to Zero Carbon® LLC was 1x the annual savings on the bills or $1,100. The 46% return on investment includes the fee.

“Working with David Green was an absolute pleasure, he guided me through the process with his experience in lowering my energy expenses and my overall carbon footprint.” Said David Sguazzin.

David Green said, “If every household in the U.S. did what David Sguazzin has done, the US would more than reach its goals under the Paris Climate Treaty. And it could do it within a year. Every household would be better off by over $1,000 a year. Each year, every year and forever. This would be a $300 billion dollar economic stimulus to the U.S. economy every year. Using the standard rate of 8.34 jobs per million dollars of construction spending, this would create 2.5 million new jobs every year, just what we need to pull us out of this recession.”

If you live in Massachusetts, MassSave would have paid for almost all of David’s insulation program and would have installed the insulation for him.

On David Green’s own home, the return on investment in a more comprehensive program of energy reduction, heat pumps and solar panels that cut the house’s carbon footprint and utility bills to zero, was 15%. 

David Green’s “fab four” recipe for making money by cutting your carbon footprint has now been proven on houses ranging from 1,000 square feet to 14,000 square feet and from 1810 colonial farmhouses to brand new construction.

Case Study 2: 1,300sf, 1934, colonial-style home with limited solar potential in MA

Despite being a vintage home that did not allow for adding wall or basement insulation, and without changing any windows, this house’s bills and carbon emissions were both cut in half.

The house is in Arlington, MA with 5,600 heating degree days.

The program consisted of:

  1. Insulation was added in the attic, some air sealing was done in the attic (but neither insulation nor air sealing was done in the basement), 
  2. Air sourced heat pumps were added
  3. A fairly small solar array was added to the roof (which has considerable shade from nearby trees)
  4. The natural gas furnace was retained
  5. A wood-burning stove was added for both ambience and heating

Here are the details:

Congratulations are in order! You have cut your carbon emissions by 56% and your bills by 32%. The cut in the bills is despite the price of natural gas being 32% higher than it was when I measured your house back in 2019 and electricity having gone up 13% since 2019. Natural gas will soon have doubled in price from 2019 and electricity will soon be 50% more expensive so you have insulated yourself from those increases as well. You are also not funding Putin’s war in Ukraine.

In the year before I worked on your house your total bills were:
$2,632 for gas, $830 for electricity
$3,462 total
In the last 12 months they were:
$1,033 for gas, $722 for electricity net of solar, $600 for wood
$2,355 total

Your total carbon emissions before the “fab four” were 11.4 tons per year and after they were 5.8 tons, for a cut of 56%.

So I saved you $1,107 per year so that is what you owe me. This is 32% cut in your bills. And this is with the prices for both natural gas and electricity having gone up considerably since I started work on your house. If I recalculate your “before” costs at today’s prices for gas and electricity your “before” bills were $4,207, so you can think of your savings as having been more like $1,851 or a 44% cut compared to the recalculated costs before the Fab Four. So roughly roughly you can say you cut your carbon emissions in half and cut your bills in half too. I assumed you were using electricity from the grid at the average ISO NE emissions per kWh rather than the zero emissions from the “green” electricity you buy because you pay extra for that.

And here is the report that this homeowner wrote on her house for the Town of Arlington MA which has a sustainability initiative:

Case Study 3: 1,200 sf single story house in MA.

The program consisted of insulation, draft sealing and replacing two windows that were leaking water with modern triple-pane windows. Neither solar panel nor heat pumps were added.

I have analyzed the bills you sent me and roughly it looks like this:

Total annual spend on energy before: $2,612

Total annual spend on energy after: $2,699

So it looks like I saved you nothing! However your total energy use (heating oil plus electricity) was:

Before: 31,540kWh

After: 20,017kWh

This is a saving of about 36%. This is due to the insulation and air sealing. 

The reason I did not save you any money is because the cost of both heating oil and electricity skyrocketed after Russia’s invasion of Ukraine, which is not something I had anticipated! Heating oil was up 56% and electricity was up 59%. If I re-price your “before” heating and electricity bills to today’s prices then they would have been about $4,100. On this basis I saved you $1,400. However, the contract is clear that you only owe me what I actually saved you which is nothing. So you owe me nothing. 

It is because of all the difficulties I have had with calculating actual savings that I no longer charge clients on this “what I save you” basis. Today I charge by the hour and typical projects cost between $1,000 and $1,500. So if you feel my work was good for you then please pay me what you think was reasonable for the work I did. But by the contract you owe me nothing.

It was a pleasure working with you LA and helping you to cut your bills and carbon footprint. I suspect that you house is now much quieter and much cozier to live in with all that wall insulation and new triple-pane windows.

“I wholeheartedly endorse David Green as a home energy consultant. He used his expertise in energy efficiency to focus on cost-effective solutions. As a result of following his suggestions, my house has significantly reduced energy consumption along with improvement in the overall comfort of my home.” – LA, Westwood, MA.

Case Study 4: Small two-floor house with workshop in basement on electric heating.

Note that this case study was not actually a client of mine. However, he worked out a program that was very similar to what I would have recommended for him and he gave me permission to share it. You can download his report here:


On March 29, 2022 our daughter Zahava bought an all-electric house built in 1973. The first thing she did was to sign up for community solar, so that right away she eliminated the carbon footprint of the house.

However, the house has baseboard electric heat. It was using so much electricity that it required two 200-amp breaker boxes – one for the electric baseboard heaters and a second one for everything else.

When my wife Lonnie and I realized that our daughter’s dream house was an energy hog, we set to work making changes to make it more energy-efficient, and reduce monthly electric bills that could have exceeded $1,000 in winter.

We succeeded in reducing the electricity consumpQon of the house by more than half, as shown in the final slide.


This is what the breaker boxes look like.

The one on the leR supports the baseboard electric heaters.

The one on the right supports everything else – the hot water heater, the laundry, the refrigerator, the drinking water well, the lights, the electric outlets, etc.


We clearly labeled all the circuit breakers, which helped us gain a beSer understanding of what was using the most electricity in the house.

The old electric baseboard heaters were the major issue, but the water heater, the clothes dryer and the well pump were also heavy users of electricity.

Clear labels on the circuits also helped us communicate with electricians and other contractors.


When Zahava bought the house, the old refrigerator in the kitchen didn’t have a freezer, so there was a second old refrigerator with a freezer in the basement. That was both inconvenient and wasteful of energy.

We replaced the two old, inefficient refrigerators with one new, energy- efficient refrigerator. That cut the electricity used for refrigeraQon by at least half.


Next, we replaced the old laundry. We got an LG ventless heat pump dryer, which runs about 35oF cooler than a typical dryer and does not blow heat out a vent to the outdoors. It uses about 1/3 as much energy as a convenQonal clothes dryer.

The heat pump dryer dries the clothes by dehumidificaQon rather than heat.

Note the capped vent above the dryer in the photo. Rather than going outside via a vent as heated water vapor, water extracted from damp clothes goes down the same drain that the washing machine uses.

Only about 2% of U.S. homes have ventless heat pump dryers, but they are popular in Europe.


The walk-out basement studio had twelve 4-foot fluorescent light bulbs.

We hired an electrician to remove the ballasts and replace the fluorescent bulbs with LED bulbs that use half as much electricity. LED lights are bright, turn on instantly and last at least 10 years.

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We replaced the old 80-gallon water heater with a new 50-gallon heat pump water heater that uses much less electricity.

The new water heater extracts heat from the ambient air and transfers it to the water in the tank. Warm air from the adjacent studio enters the uQlity closet through a vent near the air intake of the water heater, and then the chilled exhaust air from the heat pump water heater goes back into the studio via a duct.

In summer, the chilled exhaust air keeps the studio cool.


Zahava is a poSer, so we installed an electric kiln in the studio. To save energy, we opted for 3” insulaQon in the kiln walls instead of the standard 2.5”. We were pleasantly surprised to find that firing the kiln to over 2,000o for 10 hours only uses less than $20 worth of electricity.

She only fires the kiln about six or eight Qmes a year. When she does, she turns up the thermostat on the heat pump water heater to capture some of the heat thrown off by the kiln and store it in the water heater.


The house has twenty-eight 50-year-old windows, which results in heat loss.

We got an esQmate to replace all the old windows with new, beSer- insulated windows. The price of $34,000 was a non-starter.

So we figured out a way to install inner storm windows made of 1/4” plexiglass, which is one-fiRh as heat-conducQve as glass and adds another insulaQng layer of dead air in the windows. Rather than hiring a handyman, Lonnie and I installed them ourselves, a few at a Qme, over the summer.

The cost of the materials and tools for all 28 inner storm windows was approximately $3,000. It took us an average of two to three hours to install each window.


First, we aSached a frame made of vinyl to the window using screws.

Then we affixed a 1⁄2” wide strip of self-adhesive white felt weather stripping to the vinyl frame.

Then we screwed the clear plexiglass to the vinyl frame, sandwiching the white felt weather stripping between the vinyl frame and the plexiglass.

We made the holes in the plexiglass slightly larger than the screw shaRs, so that the plexiglass can expand and contract with changes in temperature.


The inner storm windows are crystal clear and barely noQceable. Note the baseboard electric heaters.


Halfway through the window project, we changed the design to facilitate quick removal of the plexiglass panes.

We aSached the plexiglass to the vinyl frames using swivel tabs instead of screws.


With the swivel tab design, one can easily remove the plexiglass in less than 30 seconds.


5/16” white swivel tabs can be purchased at Amazon.


The plexiglass inner storm windows reduce heat loss across the windows. We got an inexpensive ($15) infra-red thermometer and measured the temperature of the windows.

The air temperature outdoors was 30o. The temperature indoors was 67o.

The surfaces of the walls were 64o. The surfaces of the plexiglass inner storm windows was 60o.

We temporarily took the plexiglass off one of the windows, and measured the inside surface of the glass at 52o.


We got a free energy assessment from Mass Save, which recommended more insulaQon and weather stripping.

We hired a company to add cellulose insulaQon in the alc and weather stripping on the doors.

Mass Save paid more than 75% of the cost.


The cellulose insulaQon in the alc is now about 17” deep.


We also got cellulose injected above the garage ceiling.

They had to drill these holes to inject the cellulose into the ceiling. When they were done, they plugged up the holes.

Again, Mass Save paid over 75% of the cost.


ARer smoothing over the holes in the ceiling with Spackle, Lonnie and I painted it.


We applied spray foam insulaQon on the inside walls of the uQlity room to prevent heat loss to the garage.


We got four heat pumps installed in August. Each one has a compressor outdoors and a wall unit indoors. Each has its own remote temperature control, so for example the master bedroom can be kept comfortable at night without using addiQonal energy to heat or cool the rest of the house.

The four units combined can provide 45,000 BTUs. That is enough for the whole

house, which has 2,200 square feet. When the temperature dropped to 14oF below zero in February, the heat pumps kept the house comfortably warm. We kept the electric baseboard heaters in case of emergency.

We got six quotes ranging from $20,600 to $31,000. We chose the low bidder, who did a very good job for us. We got a $10,000 rebate from Mass Save, and we paid the $10,600 balance with a 7-year, zero-interest Mass Save HEAT loan through a local credit union. The average monthly savings on the electric bills are much more than the monthly loan payment of $126.

The heat pumps came with a 12-year warranty from the manufacturer. According to EnergySage, heat pumps typically last around 10 to 15 years, but some experts claim a well-maintained heat pump can last as long as 20 to 25 years – about a generaQon!


Each of the four heat pump compressors drives one wall unit, which is more energy-efficient than having mulQple wall units driven by a single compressor.

The heat pump compressor and wall unit in the studio keep the studio warm, and also provide warm air for the heat pump water heater in the adjacent uQlity room.

The heat pumps were put to the test in early February when temperatures dropped to minus 14oF. The house remained comfortably warm through the cold snap.

Following is an excerpt from a February 8, 2023 Boston Globe arQcle.

As temperatures began to fall on Friday, the Globe asked heat pump users via Twi<er and an online survey to report how their pumps performed as the worst of the cold hit. More than 450 responded, and most said their pumps kept their living spaces as warm as they wanted. That was parCcularly true in Massachuse<s, where temperatures fell below zero but not to the extreme depths they hit farther north. And the best experiences were reported by people who had installed heat pumps intended for cold climates and whose homes were well-insulated.

In parts of New Hampshire and Maine, where temperatures plunged beyond 20 degrees below zero, a number of homeowners said their heat pumps couldn’t keep up, allowing indoor temperatures to fall into the low 60s or high 50s. Several who had that happen said their pumps were able to bring inside temperatures back up quickly aOer the sun rose and outside temperatures climbed back to 0 and above.



We replaced the old well pump and motor, which were 50 years old. Instead of repeatedly turning on and off, the new well conQnuously provides constant water pressure, which conserves energy.

Note the wood pile in the lower leR, which relates to the next slide.


This short-tailed weasel popped its head out of the wood pile while we were replacing the well.

Climate change is negaQvely affecQng wildlife populaQons around the world.


Monthly KWHs

Zahava purchased the house on March 29, 2022.

Over the 12 months prior to purchasing the house, it used a total of 20,520 KWHs. Over the 12 months after purchasing of the house, it used a total of 9,320 KWHs – less than half as much.

This reduction in electricity usage is especially significant because electricity rates increased from 27.9¢ per KWH in December 2022 to 35.1¢ per KWH in January 2023. At 35.1¢ per KWH, the reduction of 11,200 KWHs translates to an annual savings of $3,930.

The total cost of all the energy saving improvements was approximately $28,000 after rebates.

Annual savings of $3,930 represents approximately 14% return on investment. (Note that the house now has air condiConing, thanks to the reversible heat pumps.)

Energy saved by adding heat pumps

You can read more about the “fab four” by visiting www.greenzerocarbonhome.com where you can watch a 45-minute webinar, download the slides used in the webinar and download written Q&A from prior webinars, all for free.

David Green can be contacted at davidlcgreen@gmail.com

The mark Zero Carbon® is a trademark of Zero Carbon® LLC registered with the United States Patent and Trademark Office with numbers 5,730,207 and 5,944,678. Use without the written permission of Zero Carbon® LLC may be a violation of law. In addition, the trademark has been recorded with the U.S. Customs and Border Patrol to prevent the importation of articles bearing unlicensed versions of the trademark. For permission requests contact: email David Green

The books, website (including blog posts), website downloads, webinars and other form of communication (including the author’s answers to people’s questions in any form, written or oral) refer to the author’s opinions and experience with energy efficiency improvements, investing, tax, finance and regulations but neither the author, nor Zero Carbon® LLC is giving investment, tax, financial or legal advice, nor offering any warranty or guarantee of results.

Copyright © 2020 to 2023 David Green.  All rights reserved. No part of this publication, electronic or printed, may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the publisher, except in the case of brief quotations embodied in critical reviews and certain other noncommercial uses permitted by copyright law. All commercial use is prohibited. All photographs and illustrations are copyright © David Green, unless otherwise credited.