Guide to a net zero home

Two years ago my partner and I became home owners and moved into our first (and hopefully last) home. As our plans to start a family get closer we want to prepare of home for little ones, in laws, future proofing, and maybe even save some money along the way (the jury is still out on this one).

What is net zero?

At the most basic level a net-zero home produces as much energy as it consumes, there is other official designations like "passive home" but for our purposes we are keeping it simple. In general the energy consumption of a home is composed of:
1. Space heating/cooling: furnace, fireplace, space heater, air conditioner, etc
2. Water heating: water heater, pool heater, hot tub, etc
3. General consumption: Appliances, devices, etc

The above are ordered by proportion energy consumption, 30-50% of a homes energy consumption tends to be space heating/cooling, 10-20% water heating, and the rest is general consumption. There is one significant omission which is personal vehicle energy consumption, if you drive alot this could be your largest energy consumption category but you also might not drive at all. I have chosen to ignore personal vehicle energy consumption because they vary so much from person to person.

How to reach net zero?

Our home is a modest size 3 bedroom 1960's bungalow and as you will read in this series it was far from modern standards of energy efficiency, in spite of this I was surprised with how affordable it was to take steps to reduce our cost of utilities and total energy consumption.

This guide will be largely drawing from my personal experience as the owner of a single family home in Ottawa Ontario but this will be quite transferable to most folks in similar climates and similar building codes. Im going to cover the 4 steps that I took to go from a mediocre bungalow to net zero energy consumption.

0. Do nothing

It might be really tempting to just immediately jump at the opportunity to start retrofitting and there may be an argument for doing this in some cases but I highly encourage to just do nothing first. If your just moving into a new home just live in it for a bit to record a baseline to reference against, every change you make should have an expected impact on your energy consumption and a baseline allows you to know if you are hitting your predictions. If you start adding insulation or replacing equipment you need a reference so you know if your calculations were incorrect, the installer exaggerated the benefits of certain equipment, or maybe you incorrectly performed the retrofit and need to fix something.

If you really want to retrofit now you might consider installing a smart thermostat or an energy monitor to allow collection of more detailed information about your homes heating and cooling requirements or other energy needs, this will be very helpful later.

1. Keeping in the energy your consuming

The highest value retrofits start with air sealing and insulating, this is because:

1. It can be accomplished with low cost readily available materials
2. It can be done piecemeal
3. It generally doesn't require any certification so it can be easily DIY'd

In addition to being more accessible its vital to perform this step first as it will have compounding effects to subsequent retrofits like reducing the size of heating/cooling equipment your home needs and depending on the system you have can actually result in higher efficiency as they are more efficient when they are operating below maximum capacity.

ACH50

One of the most significant quantitative metrics for keeping a comfortable home is ACH (air changes per hour) often measured as "ACH50" or "air changes per hour at 50 pascals". An ACH50 of 3 is considered "tight", higher then that will likely be when you start noticing drafts around the home and significant temperature gradients.

We were planning significant retrofits so we hired a local company to perform an energy audit on our home, if you aren't willing to make that investment you can check your local library to see if you can rent a thermal camera and look around your home for hot/cold spots where the thermal envelope of your home might be compromised, this could be around light fixtures, electrical receptacles, baseboards, window trim, weatherstripping, etc.

Our 1960's bungalow had an ACH of ~4.3, this is not horrible but definitely room for improvement. Using this information we purchased several tubes of interior caulking and sealed all our interior baseboards, receptacles, window trim, recessed light fixtures. The result lowered our ACH50 to 3.1 which basically eliminated the drafts we experiencing in areas of the home and will likely save us far more then the $50 in caulking.

Design load

This metric represents the amount of energy your home requires to maintain a temperature at a given design temperature; the more energy you can keep in, the lower the design load. The most effective way to reduce your design load is improving the insulation of your home and slowing the energy transfer in/out of your home.

We got a design heating load from our energy audit but there are plenty of load calculators online that can help you ballpark your design heating load and how retrofits might impact that.

Our initial design heating load was ~14.5 kw or approximately 50,000 BTUs, using the load calculator listed above we were able to estimate that increasing our attic insulation from ~R30->R60 would make the largest impact to our design load reducing it nearly 20%. This DIY retrofit took 1 day and cost ~$1,500, in the year following the retrofit our natural gas consumption went down approximately 15% which is inline with our expectation.

Other retrofits that can reduce your design load include updating exterior wall insulation, higher efficiency windows, or insulating currently uninsulated areas (ie basements or crawlspaces). There are also cost effective alternatives like "window shrink and seal" for older windows and doors or weatherstripping doorways into uninsulated spaces.

2. Efficiently use the energy you consuming

Once you take care of all the more accessible retrofits you can start looking at what equipment would best suit your home, the most significant areas to reach net zero is:

1. Space heating equipment: Furnace, boiler, baseboard heaters, heatpump.
2. Water heater: Tank/Tankless Water heater
3. High energy appliances: Clothes dryer, stove/bbq, fireplace

I won't explain every possible option but if your goal is net zero the options for retrofits here quickly narrow, for space heating you likely want to move to a cold climate heat pump, for water heating you want an electric / hybrid electric water heater, and for appliances you want a ventless clothes dryer, induction stove, and to eliminate any natural gas appliances.

Space heating: Here is a great video from Technology Connections explaining what heatpumps are but the main feature is they don't create heat but rather move it this means they achieve over 100% efficiency which is better then any fossil fuel heating solution. If you followed step 1 you know your design load and so you can start collecting quotes from installers to see what equipment they recommend for you, if you have a forced air system it will likely be trivial to switch to a heatpump but if you have radiant heating or particularly small ducts you may be best served moving to a mini-split heatpump system.

Water heating: Same as space heating you want to go with the highest efficiency equipment, electric water heaters are more efficent then any fossil fuel water heaters and hybrid-electric uses a heatpump to get even more efficiency. If you have a tank water heater then the retrofit off of natural gas is simple but if you have a tankless water heater and don't have space for a tank then it may be more involved. Tankless electric options exist but require significant amperage which many peoples breaker panel may not allow without a service upgrade, if possible its best to move to a tank water heater for maximum efficiency.

Clothes Dryer: Apologies if Im repeating myself but ventless dryers leverage heatpumps to more efficiently dry your clothes, in addition to this they don't vent air outside which means your not exhausting your conditioned air out of the house and creating negative pressure indoors. This reduces the energy needed to dry your clothes, reduces the demand on your furnace to maintain your homes temperature, and ventless dryers are less harsh on your clothes.

Induction stove: Gas stoves are notoriously wasteful, on average they only transmit ~30-40% of the energy from the combustion of natural gas into the pan/pot on the stove top, resistive electric stoves are around 70%, and induction is the winner at 85%. Among other things the key benefit from an energy efficiency perspective is that you are not heating up your house with waste heat from the stove just to use more electricity to run the AC and cool it back down, this is less of a problem in the winter months where you are going to be using energy to heat your home anyways but remember if you have a heatpump you will be heating your home at greater than 100% efficiency.

Upgrading our equipment

Do not rush to replace perfectly good functioning equipment, the whole point of moving to net zero is sustainability and throwing away perfectly good equipment is antithetical to that goal, that being said you should make sure you approach these purchase decisions holistically and imagine how these systems work together to improve your homes overall energy consumption.

When we moved into our home it had a 60,000 BTU forced air natural gas furnace from 2008 (14 years old), a ~85% efficient conventionally vented natural gas water heater from 2014 (8 years old), and a side discharge AC unit with an 8 SEER rating from 1991 (30 years old). We also have a 10 year old vented dryer and a 8 year old electric stove/oven.

Our goal was eventually to electrify our home and get off natural gas, at this time we really didn't have any intention to replace everything or even consider installing solar but wanted to reduce our carbon footprint and minimize our dependency on fossil fuels. We didn't intend on making the retrofits so soon but once our furnace failed the first time we started collecting quotes on heatpumps, because of the air sealing / insulation improvements we had reduced our heating design load such that we only needed a 36,000 BTU heatpump (rather then the 40,000-50,000 BTUs our energy audit indicated we needed previously).

We also asked the folks performing the HVAC install to swap out our natural gas water tank at the same time with the cheapest 50 gallon electric water heater. To install the new cold climate heatpump, air handler, and electric water heater was $13,919 and reduced our energy consumption by ~30%, this means the cost of the new equipment (which was among the best quotes) was 9x the cost of air sealing + attic insulation it reduced our energy consumption by a fraction of that amount, this means that even if you have very old equipment air sealing/insulation is likely many time more effective at reducing your energy consumption compare to upgrading your equiptment.

3. Sustainably produce the energy you consume

Once you improve the thermal efficiency of your home and electrify your various equipment / appliances to higher efficiency ones you can assess if it makes sense to invest in a energy generation system like rooftop solar. Im currently working on an article about the practicality of our rooftop solar and how to perform the break event calculations but still need to collect more data.

At this point we are almost 2 years into retrofits and stoked with the results from previous steps, if we compound the energy efficiencies made that is approximately a 40% reduction in overall energy from ~21MWh (combined natural gas and electricity) to ~13MWh of electricity from the relatively clean Ontario power grid. Approximately a ~90% reduction in carbon footprint!

We absolutely could have stopped here and honestly most people in similar situation probably should, if you have a clean-ish power grid, relatively low energy needs, and live in a lesser sunny city it doesn't make much sense to install rooftop solar but if you want to directly contribute to more sustainable energy in your area and reduce your exposure to energy markets then paying the premium for rooftop solar might make sense.

This process was the most extensive, it involved multiple visits from our local utility company, several back-and-forths with the installer for documents to setup net-metering, and multiple ESA inspections to make sure everything was installed correctly but we are happy to report the system is working and our solar array is projected to produce a little more then 100% of our home energy requirement for the year for the foreseeable future!

Conclusion

I know alot of people might be asking "so whats ROI? When do you the break even?!" and I am working on a series of articles to work through that cause I think people are not considering all the factors when they are making significant long term capital investments like buying a furnace/water heater/appliance but thats not quite ready. For now what I can say is we have spent alot of time and alot of money to get our home to net zero but I think its going to be worth it, I want to recognize the privilege and if you want to make similar changes to your home but maybe don't have the funds I would recommend checking out some of the other articles on the site regarding how you might be able to improve your saving and investing strategy.

Additional resources

NRCan Keep the heat in: This is a great resource which walks you through in great detail the steps to make the retrofits I mention above. I used it frequently in my journey.

Technology Connections: Seriously watch all this guys videos they are great, there are several on heatpumps and proper HVAC sizing

Heatpumps Subreddit: There are tons of folks here from different climates and regions that are sharing their experiences with different equiptment

Heatpump cost calculator: If your specifically concerned about saving money I made this calculator to see how much you might save switching to a heatpump