This post is a part of the Manitou Hills Project series.
It is a bit tricky to build an energy budget for an off grid home. It requires much more planning than with a typical home, as one has to figure out all of the details in advance. At the beginning of the planning process, I made a list of all of the electricity that we could expect to use, and then followed that up with trying to make sure that all purchase decisions would fit into that energy budget. As I mentioned in a past post, the one significant mistake we made was to have a heating system that required electricity to run - it wouldn't be much for a typical house, but is tough for an off grid house in the winter.
It is currently much more expensive to generate energy off the grid than to buy grid power, so one has to be very careful to make everything as efficient as possible. If we were connected to the local utility, Hydro-Quebec, our electricity rates would be less than $.10/kWh, some of the cheapest power available anywhere in the world. However, with our backwoods location, generating our own power was the only viable option. When I estimate the cost and expected lifetime of all of our solar panels, electronics, batteries, backup generator, etc., our power cost will end up being much closer to $1/kWh, at least 10 times the cost of grid power. This means that economizing and conserving is the only way to keep the total cost of power reasonable.
Below I have attached a fairly accurate version of our energy budget updated to account for our first full year of use of our home. At all times we run a refrigerator, an HRV, the solar electronics, and a few other electronics that make up our internet and security systems. In the winter, the boiler also runs nearly every day to keep the house heated. On top of that, we have pretty bare bones usage of power as compared to a typical home, and I've done my best to reduce the vampire loads down to almost nothing.
Our total electricity usage for the past year was a bit less 1500 kWh, which makes an average of roughly 4 kWh/day. Our 1500 kWh of electricity usage is
dwarfed by the typical household in Canada, which uses an average of 11,900 kWh (32.6 kWh/day). While our place is extremely efficient, I
must make clear that one of the reasons our usage is so low is that
we are only in the house a bit less than half of the time, as work
and other responsibilities call us into the city far more often than I
would like. If one factors in the power that we use in our rental in the
city, we still are below average, but not by all that much. We are striving to reduce our energy consumption, especially of non-renewable energy, but it is a task that takes time to accomplish.
One other disclaimer to make is that our electricity usage still makes up significantly less than half of our total energy use. The technology is simply not yet available (at any sort of reasonable price) to heat a house through a cold, gray, and snowy Canadian winter with solar power alone. Propane and/or wood are an absolute necessity to be able to stay warm out in the countryside. With the fast dropping prices of solar, batteries, as well as improved building envelopes and heating technologies like air to air heat pumps, this may become a possibility a decade or two down the road, but the time is not yet ripe.
Tuesday, 24 November 2015
Thursday, 12 November 2015
Generating power off the grid
This post is a part of the Manitou Hills Project series.
For better or worse, the property that my wife and I fell in love with was over a mile back down a private road, and our few other neighbors have summer-only cabins. There are no services of any kind that come down our road, no phone, no cable, no fiberoptics, and of course, no power lines. The neighbors heat with wood when needed, and handle cooking and a small amount of power generation with propane. I looked briefly into bringing power lines back to our site, but an off grid solution became the obvious choice when I realized that the price would greatly exceed $100,000 just to put in the power poles. I already had quite an interest in sustainable energy and solar power, so this provided just the impetus that I needed to pursue an off grid home.
I'll list the vital statistics of our system first, and then say a bit about how the system has worked so far, as well as the updates that have already been implemented.
Our electricity generating system:
Photovoltaic panels: 12 Solarworld 235 watt panels (2820W in total)
Additional panels (fall of 2015): 12 Jinko 250 watt panels (3000W total)
Batteries: 8 Deka Deep cycle solar batteries, lead acid AGM 12V 265 Ah (a nominal 25 kWh storage)
Backup generator: Generac Ecogen, 6 kW
Electronics:
How the pieces fit together
Any electrical grid starts with power generation, and ours is no different. The majority of the time, all of our electricity needs are supplied by solar panels. However, there are times when the panels can't produce enough power (at night and on cloudy days) when it is needed. Generally the batteries serve the role of storing enough energy to get us through a couple of days without much sun. When the battery charge gets too low, the backup propane generator turns on, sending power into the house via an alternator to be used both to power the house and recharge the batteries.
The electronics provide for energy transformations and communications. The charge controller takes high voltage power coming from the solar panels, and steps it down so that just the right amount and voltage (a bit over 48V DC) of power is passed on to the other systems. Most of this power is dumped straight into the batteries, which chemically store that electricity for later use. When power is needed for loads in the house, that 48V power coming from the batteries and charge controller is drawn into the inverter, which converts the power into the normal household power found in any home, 120V alternating current, which goes out through a standard breaker panel to the house. The inverter is actually an inverter/charger, so in addition to taking DC power from the batteries and solar panels out to the house, it can also convert AC power from the generator (or for others' setups, the power grid) into DC power to charge the batteries. The Automatic Generator Starter is able to start the generator whenever the battery voltage falls below a certain level, ensuring that the batteries are never discharged too deeply. Finally the Combox provides an interface for controlling all of the other devices, as well as being able to connect to the internet, which I use to check the system remotely and send regular system status updates by email to myself.
Solar panel orientation
There is a simple rule of thumb that I learned from our solar installer when we were discussing our system setup, with the best orientation for stationary panels being due south, with an angle equal to one's latitude on Earth. This maximizes the annual output of power from a given solar panel. We are at 45° north, so we ought to set our panels at the same angle to the ground. For our original panels, we were able to get this orientation, due south and at a 45° angle.
Through our first winter, I realized that there are some nuances to an off grid system in the northcountry that aren't captured by that rule of thumb. There are two main problems with following this rule. The first is snow. It turns out that panels set at 45° don't shed snow as well as I'd hoped. The snow will clear after a day or so of sunny weather, but while the snow is still there, no power is produced. Clearing them manually works fine, but we are not always there to do it. The second problem is that an off grid home is not in the business of producing the maximum total power over the year, it is about always having enough power available to keep the house running. Our summer power loads are extremely low, as no heating is needed, days are long and so little lighting is needed, and we are outside much more often. In the winter, when there is already less sun, our electricity needs are actually much higher.
These two problems have a shared solution, to set solar panels at a much steeper angle. This allows snow to shed off very easily, and squares the panels much better to the low angled winter sun. Of course it is possible to get around this problem with such things as seasonably adjustable solar panels, or the significantly more complicated sun tracking systems, but the simplicity (and reduced cost) of fixed panels is quite attractive. I would go so far as to say that if one is going to have stationary panels in the northern US or Canada on an off grid home, that orienting them for the winter is the best path to follow.
In our first two winters, we were overly reliant on our (poorly functioning) generator through the winter, and so earlier this fall, we added just such an upgrade, an additional solar array set at an angle of 65° from the ground. These should greatly reduce the amount of run-time that will be needed from the generator in future winters. As you can see from the picture below, the new panels also are turned a bit to the south-west, which is intentional. There is a better clearing in the trees toward the west, and so the new panels are turned a bit so that they will be receiving direct sun for a greater portion of the day.
Power generation through the year
Finally, I've attached the power production estimate that my solar installer created for me prior to installing the system. While a few details changed after these estimates were made, there is an incredible wealth of data here about our local solar resource, expected consumption of power at our home, the efficiencies of the various components of an off grid power system, and more. For any readers who may actually be considering building an off grid system, this is the sort of nitty gritty details that you will need to consider.
For better or worse, the property that my wife and I fell in love with was over a mile back down a private road, and our few other neighbors have summer-only cabins. There are no services of any kind that come down our road, no phone, no cable, no fiberoptics, and of course, no power lines. The neighbors heat with wood when needed, and handle cooking and a small amount of power generation with propane. I looked briefly into bringing power lines back to our site, but an off grid solution became the obvious choice when I realized that the price would greatly exceed $100,000 just to put in the power poles. I already had quite an interest in sustainable energy and solar power, so this provided just the impetus that I needed to pursue an off grid home.
I'll list the vital statistics of our system first, and then say a bit about how the system has worked so far, as well as the updates that have already been implemented.
Our electricity generating system:
Photovoltaic panels: 12 Solarworld 235 watt panels (2820W in total)
Additional panels (fall of 2015): 12 Jinko 250 watt panels (3000W total)
Batteries: 8 Deka Deep cycle solar batteries, lead acid AGM 12V 265 Ah (a nominal 25 kWh storage)
Backup generator: Generac Ecogen, 6 kW
Electronics:
- Schneider MPPT 80 600 Charge Controller
- Schneider Conext SW 4048 Inverter/Charger
- Schneider Combox
- Schneider Automatic Generator Starter
How the pieces fit together
Any electrical grid starts with power generation, and ours is no different. The majority of the time, all of our electricity needs are supplied by solar panels. However, there are times when the panels can't produce enough power (at night and on cloudy days) when it is needed. Generally the batteries serve the role of storing enough energy to get us through a couple of days without much sun. When the battery charge gets too low, the backup propane generator turns on, sending power into the house via an alternator to be used both to power the house and recharge the batteries.
The electronics provide for energy transformations and communications. The charge controller takes high voltage power coming from the solar panels, and steps it down so that just the right amount and voltage (a bit over 48V DC) of power is passed on to the other systems. Most of this power is dumped straight into the batteries, which chemically store that electricity for later use. When power is needed for loads in the house, that 48V power coming from the batteries and charge controller is drawn into the inverter, which converts the power into the normal household power found in any home, 120V alternating current, which goes out through a standard breaker panel to the house. The inverter is actually an inverter/charger, so in addition to taking DC power from the batteries and solar panels out to the house, it can also convert AC power from the generator (or for others' setups, the power grid) into DC power to charge the batteries. The Automatic Generator Starter is able to start the generator whenever the battery voltage falls below a certain level, ensuring that the batteries are never discharged too deeply. Finally the Combox provides an interface for controlling all of the other devices, as well as being able to connect to the internet, which I use to check the system remotely and send regular system status updates by email to myself.
Solar panel orientation
There is a simple rule of thumb that I learned from our solar installer when we were discussing our system setup, with the best orientation for stationary panels being due south, with an angle equal to one's latitude on Earth. This maximizes the annual output of power from a given solar panel. We are at 45° north, so we ought to set our panels at the same angle to the ground. For our original panels, we were able to get this orientation, due south and at a 45° angle.
Through our first winter, I realized that there are some nuances to an off grid system in the northcountry that aren't captured by that rule of thumb. There are two main problems with following this rule. The first is snow. It turns out that panels set at 45° don't shed snow as well as I'd hoped. The snow will clear after a day or so of sunny weather, but while the snow is still there, no power is produced. Clearing them manually works fine, but we are not always there to do it. The second problem is that an off grid home is not in the business of producing the maximum total power over the year, it is about always having enough power available to keep the house running. Our summer power loads are extremely low, as no heating is needed, days are long and so little lighting is needed, and we are outside much more often. In the winter, when there is already less sun, our electricity needs are actually much higher.
These two problems have a shared solution, to set solar panels at a much steeper angle. This allows snow to shed off very easily, and squares the panels much better to the low angled winter sun. Of course it is possible to get around this problem with such things as seasonably adjustable solar panels, or the significantly more complicated sun tracking systems, but the simplicity (and reduced cost) of fixed panels is quite attractive. I would go so far as to say that if one is going to have stationary panels in the northern US or Canada on an off grid home, that orienting them for the winter is the best path to follow.
In our first two winters, we were overly reliant on our (poorly functioning) generator through the winter, and so earlier this fall, we added just such an upgrade, an additional solar array set at an angle of 65° from the ground. These should greatly reduce the amount of run-time that will be needed from the generator in future winters. As you can see from the picture below, the new panels also are turned a bit to the south-west, which is intentional. There is a better clearing in the trees toward the west, and so the new panels are turned a bit so that they will be receiving direct sun for a greater portion of the day.
Power generation through the year
Finally, I've attached the power production estimate that my solar installer created for me prior to installing the system. While a few details changed after these estimates were made, there is an incredible wealth of data here about our local solar resource, expected consumption of power at our home, the efficiencies of the various components of an off grid power system, and more. For any readers who may actually be considering building an off grid system, this is the sort of nitty gritty details that you will need to consider.
Thursday, 5 November 2015
Heating systems for our home - and some lessons learned
Being a newcomer to living off of the grid, I did not make the best initial choice for our heating system. In order to help others to not make the same mistakes, I'll both lay out what we did and how it was problematic, as well as how we went about fixing the problems for the future.
What we installed initially
We installed a hydronic heating system powered by a propane fired boiler (a Trinity LX150). The system has a heated concrete floor in the lower level with four zones (one for each bedroom and one for the bathroom), and two hydronic baseboard registers in the upstairs. This system provides amazingly warm and comfy floors in the bedrooms when we run the heating system. Some people with heated floors don't get to have the warm foot experience that often with high efficiency homes, but this has not been the case for us. As the house is used primarily as a weekend retreat in the winter, we turn up the heat considerably when we first arrive. We have to wear warm sweaters when we first get in the door, but then have a full day where the floor is toasty warm.
The secondary heating system, and the one that I enjoy using much more, is a free standing wood stove, a Jotul F3CB to be precise. It is a relatively small (42,000 btu) high efficiency stove out of Norway, but it is more than sufficient for our well-insulated home. The stove is located in the open concept upstairs, and in just a few hours it can take the 1000 square foot high ceiling space from sweater temperatures to shorts weather.
We have only one full winter of usage to measure our consumption of propane and wood, so it is difficult to draw big conclusions from it, but the usage was about what was expected. In the 12 months up to November of 2015, we burned 400 gallons of propane across all uses, primarily for heating the house, but also for domestic hot water, the backup generator, and a propane range in the kitchen. My best guess is that 75% of that, perhaps 300 gallons of propane, went to space heating. For the wood stove, we burned just a bit less than a cord of wood last winter, and had a fire in the stove during at least part of the day during most every day that we were there last winter.
The problems associated with the first effort
The big problem with our heating system was that it was relatively complex and brittle. We aren't there all the time to run the wood stove, meaning that the boiler system really needed to carry the load. The problem with this is that the system requires a constant, and quite significant, supply of electricity at the time of year when it is most difficult to generate power from the PV system. Running full power, the heating system requires approximately 400W for the boiler and circulation pumps, meaning that if it runs for 10 hours per day (which can happen on the coldest days of winter), the heating system alone needs 4 kWh/day, which is almost the full amount of our target daily electricity budget. The other problem is that the hydronic system is sensitive to freezing, which occurred during last winter (our first full winter). We lost power last winter and had a few frozen water pipes, as well as a break in one of the hydronic heating lines. There was glycol in the mix as an antifreeze, but apparently the installer did not put enough. It did take a very serious set of combined circumstances to bring down the house, consisting of it being the coldest week of the year when we were away for a week visiting family at Christmas, with several snowy days covering the solar panels and preventing power generation, and the final straw of the backup generator breaking down.
Steps taken to make the house resilient going forward.
So we have no desire to repeat the emergency situation that we found ourselves in for a good chunk of last winter, and have taken quite a number of steps in service of making our home more resilient in the face of future mechanical problems. I plan to discuss some of these steps more thoroughly in a future post, so I'll just highlight briefly here those that aren't heat related. What did we do?
-Set the house to send daily emailed status reports giving conditions of the solar system, including power generated, power used, generator run time, battery temperature. These daily reminders tell me how the system is functioning, and I know that if I fail to receive one, that there is a problem with either the power or internet systems.
-Increase the amount of solar panels. During the first winter, the generator was needed relatively frequently over a 6 month period from the fall through the spring, and it was far too often for my taste. Therefore, we doubled the capacity of the solar system.
Finally, we added a new backup heat source that would not be dependent on either our being there every day or electricity. We did this by using an older, simpler technology - a direct vent propane wall heater. These have been used for many years in garages, workshops, cabins in the woods, as well as in quite a number of off grid homes. If I had done more research about off grid heating, or if I had had better advice, I may have decided to handle all of our heating needs with a couple of these heaters from the beginning. The biggest advantage of these units is that they require no electricity at all to function. They have a pilot light and a milli-volt thermopile thermostat, which uses a temperature gradient to produce the small amount of current needed for the thermostat, and they rely on convection to circulate air past the heating elements. We have installed one to provide for some of the base load of heating, as well as to ensure that the house would never freeze again regardless of any issues with the electrical system.
How to size this new heater? I relied on the boiler company to help make this decision with the original heating system, but this new installation was a much more hands on endeavor for me. We have the good fortune of having a good energy model of our house, needed for the LEED certification (to be discussed in a future post). This shows an estimate of 33,200,000 BTUs of heat needed per year for the whole house, which is about a 70% reduction over a similar sized house built only to code. Heaters are generally rated as per the BTUs/hour that they produce. To get a first approximation of our heating needs, we take the heating load for the year, divide by 100 days to account for the heaviest part of the heating season, divide by 24 hours in a day to account for a heater running full time, which gives:
$$\frac{33,200,000 \ BTU}{1 \ year}*\frac{1 \ year}{100 \ days}*\frac{1 \ day}{24 \ hours}=13,800 \ BTU/hr$$
This calculation would be assuming that we heat the entire house to 70 degrees (20 degrees Celsius) with just the wall unit for the entire winter. In actuality, we will keep a lower set-point, and this unit will instead keep just a local area of the house at about 65 to 70 degrees, while allowing the rest of the house to be cooler when we aren't there, and continuing to be heated by the hydronic system. This calculation is just an estimate of the average heating load, so this amount of heat wouldn't be able to keep up with heating the whole house on the coldest days of winter. We selected the Empire DV215 heater, a 15,000 BTU unit, which sits in the central bedroom, radiating heat out to the rest of the lower level. We shall see in the coming winter how the upgraded heating system works out.
Update March 11, 2016.
Winter is now on the run, and I can report that the wall heater was an amazing success in terms of reliability and reducing the use of electricity with our heating. The heater was able to carry essentially all of the heating load for the house during the weekdays when we were often in the city. The heater was placed in the kids' bedroom, and set to around 68 degrees. Upon our arrival after a few days away, the adjacent rooms were always 60 degrees or warmer, and the upstairs was always warmer than 50 degrees. From a starting point like this it was quite easy to turn up the boiler, start a fire in the woodstove, and be down to shirtsleeves within no more than 2 hours.
One other new (more like forgotten and found again) fact is that our energy evaluation also included a calculation of peak heating loads for the home and boiler system, which actually end up matching quite closely to the calculation I did above. The HERS calculation of peak heating load for our house is 23,400 BTU/hour, which including the caveats that I mention above, is relatively close. This 23,400 number is the amount of heat that would be needed to keep up on the coldest days of the year, not the typical winter day that I tried to estimate for. This peak load calculation also showed our actual boiler specification, with a max heat output of 136,000 BTU. This is nearly 6 times our maximum heating load and is majorly overkill, but I have heard time and again that heating and cooling contractors usually overbuild these systems, and our house does require a much smaller heating load than the standard home.
What we installed initially
We installed a hydronic heating system powered by a propane fired boiler (a Trinity LX150). The system has a heated concrete floor in the lower level with four zones (one for each bedroom and one for the bathroom), and two hydronic baseboard registers in the upstairs. This system provides amazingly warm and comfy floors in the bedrooms when we run the heating system. Some people with heated floors don't get to have the warm foot experience that often with high efficiency homes, but this has not been the case for us. As the house is used primarily as a weekend retreat in the winter, we turn up the heat considerably when we first arrive. We have to wear warm sweaters when we first get in the door, but then have a full day where the floor is toasty warm.
The secondary heating system, and the one that I enjoy using much more, is a free standing wood stove, a Jotul F3CB to be precise. It is a relatively small (42,000 btu) high efficiency stove out of Norway, but it is more than sufficient for our well-insulated home. The stove is located in the open concept upstairs, and in just a few hours it can take the 1000 square foot high ceiling space from sweater temperatures to shorts weather.
We have only one full winter of usage to measure our consumption of propane and wood, so it is difficult to draw big conclusions from it, but the usage was about what was expected. In the 12 months up to November of 2015, we burned 400 gallons of propane across all uses, primarily for heating the house, but also for domestic hot water, the backup generator, and a propane range in the kitchen. My best guess is that 75% of that, perhaps 300 gallons of propane, went to space heating. For the wood stove, we burned just a bit less than a cord of wood last winter, and had a fire in the stove during at least part of the day during most every day that we were there last winter.
The problems associated with the first effort
The big problem with our heating system was that it was relatively complex and brittle. We aren't there all the time to run the wood stove, meaning that the boiler system really needed to carry the load. The problem with this is that the system requires a constant, and quite significant, supply of electricity at the time of year when it is most difficult to generate power from the PV system. Running full power, the heating system requires approximately 400W for the boiler and circulation pumps, meaning that if it runs for 10 hours per day (which can happen on the coldest days of winter), the heating system alone needs 4 kWh/day, which is almost the full amount of our target daily electricity budget. The other problem is that the hydronic system is sensitive to freezing, which occurred during last winter (our first full winter). We lost power last winter and had a few frozen water pipes, as well as a break in one of the hydronic heating lines. There was glycol in the mix as an antifreeze, but apparently the installer did not put enough. It did take a very serious set of combined circumstances to bring down the house, consisting of it being the coldest week of the year when we were away for a week visiting family at Christmas, with several snowy days covering the solar panels and preventing power generation, and the final straw of the backup generator breaking down.
Steps taken to make the house resilient going forward.
So we have no desire to repeat the emergency situation that we found ourselves in for a good chunk of last winter, and have taken quite a number of steps in service of making our home more resilient in the face of future mechanical problems. I plan to discuss some of these steps more thoroughly in a future post, so I'll just highlight briefly here those that aren't heat related. What did we do?
-Set the house to send daily emailed status reports giving conditions of the solar system, including power generated, power used, generator run time, battery temperature. These daily reminders tell me how the system is functioning, and I know that if I fail to receive one, that there is a problem with either the power or internet systems.
-Increase the amount of solar panels. During the first winter, the generator was needed relatively frequently over a 6 month period from the fall through the spring, and it was far too often for my taste. Therefore, we doubled the capacity of the solar system.
Finally, we added a new backup heat source that would not be dependent on either our being there every day or electricity. We did this by using an older, simpler technology - a direct vent propane wall heater. These have been used for many years in garages, workshops, cabins in the woods, as well as in quite a number of off grid homes. If I had done more research about off grid heating, or if I had had better advice, I may have decided to handle all of our heating needs with a couple of these heaters from the beginning. The biggest advantage of these units is that they require no electricity at all to function. They have a pilot light and a milli-volt thermopile thermostat, which uses a temperature gradient to produce the small amount of current needed for the thermostat, and they rely on convection to circulate air past the heating elements. We have installed one to provide for some of the base load of heating, as well as to ensure that the house would never freeze again regardless of any issues with the electrical system.
How to size this new heater? I relied on the boiler company to help make this decision with the original heating system, but this new installation was a much more hands on endeavor for me. We have the good fortune of having a good energy model of our house, needed for the LEED certification (to be discussed in a future post). This shows an estimate of 33,200,000 BTUs of heat needed per year for the whole house, which is about a 70% reduction over a similar sized house built only to code. Heaters are generally rated as per the BTUs/hour that they produce. To get a first approximation of our heating needs, we take the heating load for the year, divide by 100 days to account for the heaviest part of the heating season, divide by 24 hours in a day to account for a heater running full time, which gives:
$$\frac{33,200,000 \ BTU}{1 \ year}*\frac{1 \ year}{100 \ days}*\frac{1 \ day}{24 \ hours}=13,800 \ BTU/hr$$
This calculation would be assuming that we heat the entire house to 70 degrees (20 degrees Celsius) with just the wall unit for the entire winter. In actuality, we will keep a lower set-point, and this unit will instead keep just a local area of the house at about 65 to 70 degrees, while allowing the rest of the house to be cooler when we aren't there, and continuing to be heated by the hydronic system. This calculation is just an estimate of the average heating load, so this amount of heat wouldn't be able to keep up with heating the whole house on the coldest days of winter. We selected the Empire DV215 heater, a 15,000 BTU unit, which sits in the central bedroom, radiating heat out to the rest of the lower level. We shall see in the coming winter how the upgraded heating system works out.
Update March 11, 2016.
Winter is now on the run, and I can report that the wall heater was an amazing success in terms of reliability and reducing the use of electricity with our heating. The heater was able to carry essentially all of the heating load for the house during the weekdays when we were often in the city. The heater was placed in the kids' bedroom, and set to around 68 degrees. Upon our arrival after a few days away, the adjacent rooms were always 60 degrees or warmer, and the upstairs was always warmer than 50 degrees. From a starting point like this it was quite easy to turn up the boiler, start a fire in the woodstove, and be down to shirtsleeves within no more than 2 hours.
One other new (more like forgotten and found again) fact is that our energy evaluation also included a calculation of peak heating loads for the home and boiler system, which actually end up matching quite closely to the calculation I did above. The HERS calculation of peak heating load for our house is 23,400 BTU/hour, which including the caveats that I mention above, is relatively close. This 23,400 number is the amount of heat that would be needed to keep up on the coldest days of the year, not the typical winter day that I tried to estimate for. This peak load calculation also showed our actual boiler specification, with a max heat output of 136,000 BTU. This is nearly 6 times our maximum heating load and is majorly overkill, but I have heard time and again that heating and cooling contractors usually overbuild these systems, and our house does require a much smaller heating load than the standard home.
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