What is the size of the main breaker in your current service panel? That would be one piece of information to determine generator size. The electricians will need to understand how the smart board allows to Bosch to start up with less current. If they don't have that information they can't factor it into their calculations.

It's a 200 Amp panel. We currently have a subpanel with disconnect that allows me to run my 4400W portable generator (for septic and well pumps, refrigerator and freezer and one outlet). I'll open up the geothermal anel to see if there's a brand/model on the soft start...

FWIW, here's what my owner's manual says about a similar sized Water Furnace unit.

Optional IntelliStart® (compressor Soft Starter) shall be factory installed for use in applications that require low starting amps, reduced compressor start-up noise, off-grid, and improved start-up behavior. IntelliStart shall reduce normal starting current by 60% on 208/60/1 units

What I would do if this were my house would be to connect a ‘True-RMS’ recording clamp-on ammeter to the electrical entrance to measure the whole house usage using the 1ms peak, 100ms peak and average ranges to see what you record after turning the main power ‘OFF’ for an hour or more to get a series of true ‘baselines’ of what you’re actually drawing on startup. You might even have an electrician install a ‘data logger’ to record this information so that you at least know where you’re starting from with some kind of certainty and useful known data to present to the generator consultant. Data logger inductive probes can also be installed on specific circuits as well for deeper analysis.

The more you approach this from a Professional Engineering point of view the better your outcome is likely to be.

IMPO

SR

Found it... It's an Eltwin Sure Start #SS1B16-32SN... https://www.eltwin.com/download/18.671e02ea177c956976b852/1624020462526/Datasheet_SureStart_single_phase_low.pdf

"Start current reduction of 60-70% of LRA."

Assuming a voltage drop of 15% (should I assume this?) during start-up and LRA drops to 70% of nominal (from the Sure Start)... 20.294kW ?

Is this math correct?

So adding a little bit of safety factor I'd need a 22kW generator?

Others have said this would be overkill. Is that correct?

Because I don't fully understand the important factors in this decision... Back to my original questions... What size generator would we need to comfortable run our home with everything considered? Should we leave anything out of the backup circuits?

That's the plan... let let the contractors size the system. I'm just looking to have an idea for what's needed so I can ask appropriate questions if their numbers don't seem reasonable,

Your highest priority is your 5 ton geothermal system to start up when powered by generator when you are not home. When you are home, you would like your refrigeration to operate and lighting so you have to sit in the dark. I don't recall what type of hot water heating you have. I would think in a long power outage you want to be able to take a hot shower.

Whatever size you are given, ask the person to show you have the size is calculated. You should also ask if they have ever installed a generator that powered a 5 ton AC or heat pump. Don't be surprised if the you get different sizes. Fsq4cw had the best suggestion about monitoring the start up conditions of your geothermal system. You don't know the actual current draw and what voltage drop the geothermal will tolerate until you actually measure it. The geothermal manufacturer may be of some help in this area.

"I'm just looking to have an idea for what's needed so I can ask appropriate questions if their numbers don't seem reasonable,"

In that case you'll be substituting your "expertise" or that of anonymous houzzers for the expertise of folks who sell generators as part of their day job. Tell them what you need to keep running in the event of an outage and ensure a performance clause in your purchase agreement that guarantees what they specify will meet the performance requirement.

Have the contract you’re going to sign, endorsed/signed/stamped by the company’s Professional Electrical Engineer before signing.

Read all the small print very carefully before signing - Front and back !

IMPO

SR

We purchase and install a couple of emergency generators each year in new homes we build. Emergency generator dealers in my area don't employ professional engineers on staff and don't consult with them when sizing a generator. Sizing an emergency generator is not rocket science, but homeowners are better served by relying on the dealer's expertise than their own unless they're power engineers.

The basic problem is the generator dealer can't rely on the specification sheets provided by geothermal equipment manufacturer and the easy start device to determine how much current and voltage is needed instantaneously at start up under all temperature conditions. The best advice I can give is to find a dealer who has done similar installations. Talk to at least two dealers and compare how they approach solving the problem.

The 1st contractor will be here tomorrow... Thanks to all!!

"Emergency generator dealers in my area don't employ professional engineers on staff and don't consult with them when sizing a generator."

I think this is the usual case for this kind of work.

The comment CR Homes was responding to was from a Canadian who, as everyone else, is a most welcome and appreciated participant here but who often doesn't realize that requirements and practices he assumes to be the same in another country as they are where he lives, are frequently different Things should be expected to change when a border is crossed. Any border.

Yes, I understand. In any event, there are no PE supported electricians in our area that I'm aware of. I'd have to go at least on hour away and greatly increase my cost. I'll stick with the locals having a professional approach and strong references.

In my experience - the cost of the generator itself doesn't vary greatly until you go up a "class". I'd go bigger than you think you need if you want the true feedom to live "normally" during an outage. I.e. cook dinner and run your blow dryer, etc.

Re: Elmer - Yet Again

Thank you for allowing me to post here. I was awaiting your invitation with bated breath on this site for years till you arrived.

What you fail to understand is that HVAC is an integrated industry on both sides of the 49th. Training is attended by people on both sides of the border - this is mentioned and discussed all the time at seminars and courses where necessary. Americans train Americans and Canadians; Canadians train Americans and Canadians - All together!

There is not much HVAC hardware (it’s more likely to be on the software side of things) that’s made or patented specifically for Canada as it’s a much smaller market. There’s not a whole lot of daylight between the 2-countries as far as HVAC is concerned. I get that building, construction, electrical and safety codes are different. They also vary regionally within either country.

The laws of physics don’t change just because you’ve crossed a border. That goes for pumps, power, pressure, pipes, plastics, fluids and the laws of thermodynamics.

Your contention is based on ignorance and is condescending.

IMPO

SR

Sorry, no. I was pointing out what appeared to be misinformed assumptions related to the contractor business faced by a potential customer, having nothing to do with anything technical.

Your follow on suggests you misunderstood the issue and my comment. You said "Have the contract you’re going to sign, endorsed/signed/stamped by the company’s Professional Electrical Engineer before signing."

Whole house generator installs are usually done by electrical contractors, many who focus on doing residential repair and remodel, sometimes building too. Such little mom and pop businesses would not employee an engineer. Further, the PE license for engineers is common for engineers who do third party project or consulting work. An in-house engineer at a large contractor doing large jobs (well beyond the scale of providing and installing a whole house generator) wouldn't be likely to have a PE license. I believe sizing, providing appropriate equipment and connection services, and getting a permit are all within the boundaries of what licensed electrical contractors may do on their own. If that's not the case, I will welcome someone with knowledge of practices in the US to correct me and in which case, I myself would be guilty of being misinformed.

In my rural area the electricians are as described by Mr. Fudd. ;)

The electricians review the layout in the home, and seem to develop their plan, then review it with the local Generac sales engineers who seem to provide the 'professional/knowledge base' needed to ensure the 'design' is appropriate for each installation. Not being directly involved in the process I am inferring that from conversations with the electricians.

Re: Re Modeling

“The electricians review the layout in the home, and seem to develop their plan, then review it with the local Generac sales engineers who seem to provide the 'professional/knowledge base' needed to ensure the 'design' is appropriate for each installation.”

You seem to have resolved your own issues!

If Generac representatives are “Sales Engineers” they should be Professional (electrical) Engineers (otherwise they should just be called sales representatives). That being the case, everything should be perfect - providing the electrician properly installs what is specified on the contract to the local code.

End of story - Happy Ending!

IMPO

SR

Re: Elmer

“Your follow on suggests you misunderstood the issue and my comment. You said "Have the contract you’re going to sign, endorsed/signed/stamped by the company’s Professional Electrical Engineer before signing.”

There was no misunderstanding on my part and if the OP’s last post is correct that the ‘Sales Engineer’ is in fact an engineer, then he, they, it or whatever just have to put ‘PE’ after their name and signature on the contract and that would likely stand up in court in the event of a legal conflict.

Your comment also carried the implication that as a Canadian, I should stay out of American issues.

IMPO

SR

New info but they're doubtless a double check to confirm the contractor's work to match structure requirements and equipment size. Expensive to return and replace equipment affixed to a concrete pad if it turns out to be too small, for example.

Companies who manufacture and sell technical products of a bigger than a breadbox variety, or that perform technical tasks, have in-house engineers to coordinate with potential customer personnel, to facilitate the sales. I worked with many companies in such businesses, some whose average individual customer sales were large (tens of millions of dollars). The technical resources I knew of were called Sales Tech Support, Sales Support Engineers, or even Pre-Sales Tech Support. At the companies I knew all had Engineering degrees, they weren't techs. "Sales Engineers" is close enough. They were in-house employees, some of whom I knew personally. I knew none to have had state licenses. Maybe it's different in Canada.

Your advice was to have the contract signed/stamped by a Professional Engineer. Which again, for those who don't know, is a title for a person with a state license to practice engineering for compensation as an advisor or consultant. Which isn't what sales support engineers do. What if the sales tech support person isn't licensed? In-house engineers don't require state licenses in the US and only infrequently have one,

Again, I agree with Mr. Fudd. I am a mechanical engineer and worked my entire career never having needed or earned a PE certification. Application Engineer could be another applicable title for this person. I would be very surprised if the Generac representative had a PE. The explanation for the difference of thoughts in this discussion could be as simple as the difference in custom for the way such things are done in the US vs Canada.

Re: Re Modeling

I don’t think you have anything to worry about, with your education, life experience and Generac guidance I have little doubt that but that you will choose the right generator.

Why you felt the need to post here beats me…

IMPO

SR

"Why you felt the need to post here beats me…"

He did so to inquire info of others for info that might help his pursuit of a solution for his issue. I think quoted comment applies much more to your "contributions" here and in the first thread, than it does to Mr/Ms re model.

As a mechanical engineer I ran projects of all sizes, working with folks from many specialties. I'm no electrical engineer and know my limitations. Having opinions of others is always helpful in being able to see things from a new perspective (even if their thoughts are ultimately discounted). I find Houzz especially interesting because you get thoughts from professionals and lay-people alike.

Re modeling, you're my kind of person. Take this as a tongue in cheek comment - I've spent my adult life in an area that someone out hunting for engineers would describe as a "target-rich environment"- Silicon Valley. "Knowing one's own limitations" doesn't seem to be an attitude that's as prevalent among engineers here as it is among the general population. Among many, it's often absent.

Aware this is an old threat but what size generator did you get for the geothermal?

Answered my own question: For our system which has a 5 ton Geo and soft start a generator would need to be able to handle a peak of 10,580 watts to start the system. This means starting from an off condition not the typical running condition where it kicks on to keep the room at a set temp. It has running watts of about 4600 watts when heating and 3700 when cooling. However if the AUX Heat kicks in the running watts can increase to about 10,000 watts. So in a power outage I'd feel more comfortable with a 20 kw generator to be able to run other house circuits.