whole house generator in detached garage

[motorusti]

another 40hrs of no power this week (michigan).
I was working out of town, so talking my wife through starting up and wiring the rolling generator to power the furnace/fridges/freezers was not an option.

I would like to setup a whole house NG generator in the 2nd floor of my detached garage. I have NG and 220 1phase in the garage today (furnace/compressor/etc).

I am just starting to figure out the most feasible and cost effective way to do this.
1. I would like to put a 10kw +/- gen in the 2nd floor of the detached garage. it needs to be vented/exhausted.
2. it needs to be automatic, generator needs to fire up when the power is out. I think a load shedding transfer switch would be ideal, but I am not sure. in reality, only the bare minimum circuits need to powered (fridge/freezers/furnace)
3. house is 200amp panel, garage sub is a 60amp panel, i assume i would need to up that to 200amp to backfeed from the garage panel to the house?
4. i assume the transfer switch would be in the garage?

any constructive recommendations? I probably have plenty of time before the next major outage so I am not in a hurry to build a dodgy solution.

yes. i know this one is loaded with tons of code issues and reality.

 

[Want2race]

Most generators aren't rated for inside use. The reason being they need air in and out.

I recently looked very seriously at the whole house options. The Costco deal appeared to be the best at around $2500. Major problems for me would be the permitting and gas lines as well as the fact that reading online the reviews for 3600rpm generators was eh.

Depending on your state check out the solar city power wall. I am going to get one. Price was around $2k after rebates and I don't think I would add the solar panels to the house just yet.

Having those extra kw of power would keep my heat and essentials on for about 3 days. It would be a rationing effort but the permitting complexity is almost none and for me not running gas lines saves a good bit

 

[motorusti]

I already have gas in the garage for a furnace, so that is not would not be an issue in this case. solar is most likely not a great option..

 

[mm08822]

another 40hrs of no power this week (michigan).
I was working out of town, so talking my wife through starting up and wiring the rolling generator to power the furnace/fridges/freezers was not an option.

I would like to setup a whole house NG generator in the 2nd floor of my detached garage. I have NG and 220 1phase in the garage today (furnace/compressor/etc).

I am just starting to figure out the most feasible and cost effective way to do this.
1. I would like to put a 10kw +/- gen in the 2nd floor of the detached garage. it needs to be vented/exhausted.
2. it needs to be automatic, generator needs to fire up when the power is out. I think a load shedding transfer switch would be ideal, but I am not sure. in reality, only the bare minimum circuits need to powered (fridge/freezers/furnace)
3. house is 200amp panel, garage sub is a 60amp panel, i assume i would need to up that to 200amp to backfeed from the garage panel to the house?
4. i assume the transfer switch would be in the garage?

any constructive recommendations? I probably have plenty of time before the next major outage so I am not in a hurry to build a dodgy solution.

yes. i know this one is loaded with tons of code issues and reality.

I don't think you will ever find any ng gen rated for interior use.

If you want load shedding features it will have to be an automatic xfer sw with load shed circuity (control or power) or load shed modules in series with specific loads - elec oven, elec dryer, ac, etc.

At your proposed 10kw sizing, 60a feeder would be adequate. Would not need 200a. 10kw gens can struggle with startup inrush.

Your biggest problem with this entire concept is that the xfer switch needs to be in the house to disconnect from utility. So the gen needs to be next to the house so wiring is very short. You do not want 2 xfer switches!

How far is the house from garage?

You need the gas line very short - again next to house.

Just b/c you have a gas line to the garage does not mean it is sized for the entire device load to deliver required scfm's at minimum req'd pressure. (Even with a diversity factor calculated in.)

Since you are not in a hurry, I recommend you consider next to house with a whole house xfer switch, properly size generator (load calcs req'd), spec piping sizes, check ng meter/regulator thruput as these 2 items typically need to be upsized from 250 cfh to 425 cfh. Save your money, wait longer if needed, but do it right first time.

Otherwise you will have a "dodgy solution" that will cost a lot, do a little, be inconvenient and you may struggle for AHJ approvals.

 

[misurveyor]

Also in Michigan. Luckily we kept power at home the whole time.
I just built a pole barn about 130' from our house with the intent of setting a whole home generator next to it. We have LP behind the pole barn that it will run off of.
The biggest problem was the automatic transfer switch issue. Easiest way to solve this was to bury 2 sets of wire in the trench to the barn. 1 feeds the barn from the house. The other will feed the house from the generator. We could not come up with a safe or legal way to backfeed the house from the generator through the same service.
I have not yet installed the generator but plan on a 22kW Generac.

Sent from my SM-G900V using Tapatalk

 

[mm08822]

Also in Michigan. Luckily we kept power at home the whole time.
I just built a pole barn about 130' from our house with the intent of setting a whole home generator next to it. We have LP behind the pole barn that it will run off of.
The biggest problem was the automatic transfer switch issue. Easiest way to solve this was to bury 2 sets of wire in the trench to the barn. 1 feeds the barn from the house. The other will feed the house from the generator. We could not come up with a safe or legal way to backfeed the house from the generator through the same service.
I have not yet installed the generator but plan on a 22kW Generac.

Sent from my SM-G900V using Tapatalk

Your lpg line will be short so that is good.

However your generator line back to the house and 7 control wires have to be upsized for that total distance. What wire did you use for the generator (power and control) back to the house?

Try to mount your transfer switch inside next to the main panel - much better to keep xfer switch out of weather.

 

[wyliesdiesels]

mm08822 already answered the OPs questions so I will just backup what he said.

xfer switch MUST be near main service panel as it must switch the utility and generator power feeds. It CANNOT go in garage.

How long is the run between house and garage?

What size is the gas line in the garage? Its probably not big enough to support the large demand of a generator.

For these reasons, putting the generator in the garage is most likely not feasible.

If noise is the reasoning behind putting it in the garage, u could always build a sound attenuated generator shelter next to the house.

 

[motorusti]

the garage is 15' from the house, the electrical run would be about 30'
the NG is 3/4".

 

[mm08822]

the garage is 15' from the house, the electrical run would be about 30'
the NG is 3/4".

Well that's critical info. Every other thread on here garage is 100'+ from the house. Some talking 300+.

3/4" is barely enough for a 10kw gen alone for proper flow and pressure. Probably won't get by with that size with AHJ. AHJ is going to make you total all gas loads in garage and apply a diversity factor. DF = .67 to .75 is typical accepted number range.
Better off just adding another dedicated gas line from house to gen. 1" especially if load calcs require larger gen than 10kw.

Load calcs need to show 10kw can handle house and shed anything above. 10kw is still light. Startup inrush really taxes smaller units and the connected loads.

Still need xfer switch in/at house. For 30' of conduit, just run gen output in seperate conduit to xfer switch in house and forget existing feeder to garage.

Run gas and conduits in same trench.

 

[brewchief]

3/4" gas line will be marginal with the smallest standby units if it is more the 20-30 feet from the meter total.

Indoor generator can be done but it will not be cost effective, any generator rated for that type of use will likely be an industrial type unit, finding a unit rated to be on a wood floor may not be easy either, most indoor generators I've seen were on a concrete slab in a masonry building.

 

[mm08822]

3/4" gas line will be marginal with the smallest standby units if it is more the 20-30 feet from the meter total.

Indoor generator can be done but it will not be cost effective, any generator rated for that type of use will likely be an industrial type unit, finding a unit rated to be on a wood floor may not be easy either, most indoor generators I've seen were on a concrete slab in a masonry building.

Right, no one makes an indoor ng gen at a residential price point. 6 digit price tag is real easy to hit.

 

[matt_i]

I went thru the same thing when I thought I wanted a whole-house solution. I called up DTE and eventually talked to an engineer who limited my genset to 12kW due to the size of the incoming gas line. Not enough to run my choice of a 20kW to handle it all. Cost to upgrade line at time of initial construction? ~$500 range. Cost to upgrade line right now? ~$5500.

I had 3 days out outage, but just going to get a standard roll-around genset, mainly because I need 240vac for the well pump. I figure with all of this dead wood out of the way its going to be awhile.

 

[mm08822]

I can get a meter and regulator upsized from 250 to 425 cfh for nothing from gas co.

Replacing line/digging would be a different story.

 

[reader2580]

I have 2 PSI gas service and a 10 KW generator. The company who installed the gas line said they would use 1/2" line because of the high pressure gas.

 

[mm08822]

I have 2 PSI gas service and a 10 KW generator. The company who installed the gas line said they would use 1/2" line because of the high pressure gas.

Are you saying the output of the gas regulator before the meter is 2 psi or the input to the regulator is 2 psi?

 

[reader2580]

Are you saying the output of the gas regulator before the meter is 2 psi or the input to the regulator is 2 psi?

All I know is the meter says 2 PSI metering pressure. I thought there used to be a tag on the output that said 2 PSI, but no tag anymore.

The company that did the gas piping said they would use 1/2" to meet the 199,000 BTU requirement since the gas is 2 PSI.

 

[CNGsaves]

^ ^ You're lucky Reader2580 to have high-pressure 2 psi NG service.

Most residential NG service is around 1/2 psi . . . ie 7 to 10 inches WC. If that is the case for OP, then his 3/4" NG line for even 10 ft (ie due to large NG demand of genset) WILL be a problem as other GJer's have said.

OP probably should pursue 2 psi NG at meter from GasCo (also larger meter) and put regulators downstream to reduce pressure for specific NG appliances (ie furnace, hot water heater, etc). Then his 3/4" NG line to garage will be fine.

 

[mcmlvif100]

I would like to setup a whole house NG generator in the 2nd floor of my detached garage.

1. I would like to put a 10kw +/- gen in the 2nd floor of the detached garage. it needs to be vented/exhausted.

yes. i know this one is loaded with tons of code issues and reality.

I have a Generac 6250 whole house Guardian Series running on NG and am very happy with it. That said, I was surprised by how much heat it puts out when it's running. It is a LOT more heat than I would have expected. This might be an issue for your proposed installation. I probably shouldn't have been so surprised as this model has a 999 cc air cooled engine running at 3,600 RPM.

Will be interested in seeing how your final installation addresses the venting / exhausting.

 

[mm08822]

I have a Generac 6250 whole house Guardian Series running on NG and am very happy with it. That said, I was surprised by how much heat it puts out when it's running. It is a LOT more heat than I would have expected. This might be an issue for your proposed installation. I probably shouldn't have been so surprised as this model has a 999 cc air cooled engine running at 3,600 RPM.

Will be interested in seeing how your final installation addresses the venting / exhausting.

That generator has ~ 308,000BTUH input when outputting full load of 20 KW.

20KW =~69,000BTUH

So 239,000BTUH is lost in conversion - mostly heat! Be happy that is not your home furnace efficiency!

 

[mm08822]

^ ^ You're lucky Reader2580 to have high-pressure 2 psi NG service.

Most residential NG service is around 1/2 psi . . . ie 7 to 10 inches WC. If that is the case for OP, then his 3/4" NG line for even 10 ft (ie due to large NG demand of genset) WILL be a problem as other GJer's have said.

OP probably should pursue 2 psi NG at meter from GasCo (also larger meter) and put regulators downstream to reduce pressure for specific NG appliances (ie furnace, hot water heater, etc). Then his 3/4" NG line to garage will be fine.

Yup. 2 PSI is ~55"WC. So at 8-11x the standard operating pressures (5-7"WC), that is a game changer - if you can get it.

I have not ever seen that in residential where I am. Is it regional or by individual utility co preference?

 

[mcmlvif100]

any constructive recommendations? I probably have plenty of time before the next major outage so I am not in a hurry to build a dodgy solution.

yes. i know this one is loaded with tons of code issues and reality.

I don't think you will ever find any ng gen rated for interior use.

Since you are not in a hurry, I recommend you consider next to house with a whole house xfer switch, properly size generator (load calcs req'd), spec piping sizes, check ng meter/regulator thruput as these 2 items typically need to be upsized from 250 cfh to 425 cfh. Save your money, wait longer if needed, but do it right first time.

Otherwise you will have a "dodgy solution" that will cost a lot, do a little, be inconvenient and you may struggle for AHJ approvals.

Another related consideration -- will you be able to insure your property afterwards even if you overcome all of the technical issues associated with an indoor, second floor installation?

It was for this reason that I had both the electrical and gas connections done by highly recommended, licensed professionals. My whole house generator installation was pretty standard stuff, with it located close to both the gas meter and the main panel inside the house, and largely within my (or my friends) capabilities. Regardless, I wanted to be absolutely "clean" when it came to insurance for our house and property. That said, I did everything up to the actual connections, including setting the generator on a custom concrete pad.

Just a thought but maintaining property insurance is something worth considering before you finalize your plans.

 

[Dick in Wisconsin]

WOW! There is a a lot more to this than I would have ever expected.

I learned more than what I wanted to when I decided to put in-floor heat in the detached race shop with a NG boiler. I thought we were ready to hook the boiler up and heat the floor when the plumber said he called the gas company and they were doing something to the meter (either increasing the output pressure or increasing the size of the output orifice or both). Once that was done, the plumber ran a special copper line from the gas meter through the house to the line to the race shop.

I asked "why". Then the plumber explained something I had NEVER thought of ... was the gas meter and the gas line into and through the house sized big enough to handle the gas FWA furnace, gas water heater, gas stove/oven, gas dryer, and the gas boiler in the 1000sf race shop. The thought never entered my mind.

So OP ... is the gas line (1) into and through your house big enough for the gas appliances in your house and proposed generator and (2) is the gas line from the house to the garage/shop big enough to handle both the furnace in the garage/shop and the proposed generator?

Do you have a transfer switch now? How large is your pull around generator now? If you don't have a transfer switch now, why don't you:

1. Put a transfer switch in the house with a plug-in receptacle on the outside of the house above a small concrete pad for the generator to sit on.
2. Teach your wife to pull the generator to the pad, plug it in, fill it full of fuel, start the generator, let it warm up for five or ten minutes.
3. While she goes the main panel and turns off the breakers you've marked with blue tape (or whatever color you choose) which denote the circuits that you've calculated you don't need when running the generator after a power outage.
4. Then when the warm up time for the generator is over, she then flips the transfer switch and the house now has power to the necessary circuits to survive the power outage.

This could be further enhanced by marking ALL the breakers (blue for not needed in a power outage and red for needed in power outage), turning off all the breakers initially while the generator warms up, and then turning on the red breakers one by one with a five to ten second delay between each to allow for start-up loads to be spread out against the generator.

Sounds like you have a generator already ... why buy another? If you were home, how would you have hooked the generator into the electrical system? Through the dryer outlet? (Your friends on the GJF hope not!)

I understand that for many people, hooking up a generator to a house when the power is out can be a very daunting task ... but if your house is set up right, you provide clear, concise written instructions, and practice them once in a while ... just about anyone should be able to do it.

Noise ... it should be only a temporary situation. You and the neighbors should be able to live with it. If its a problem, put a bigger muffler on the generator.

Keep us posted as to how this works out.

 

[mm08822]

Another related consideration -- will you be able to insure your property afterwards even if you overcome all of the technical issues associated with an indoor, second floor installation?

It was for this reason that I had both the electrical and gas connections done by highly recommended, licensed professionals. My whole house generator installation was pretty standard stuff, with it located close to both the gas meter and the main panel inside the house, and largely within my (or my friends) capabilities. Regardless, I wanted to be absolutely "clean" when it came to insurance for our house and property. That said, I did everything up to the actual connections, including setting the generator on a custom concrete pad.

Just a thought but maintaining property insurance is something worth considering before you finalize your plans.

This where the permitting process provides a great level of CYA for homeowner or contractor involved in the installation....

Plan review/approval, properly executed permits/fees, and most importantly - inspection and sign off by AHJ(s).

I always take before, during and after pics as recommended advise from someone in the business for many years. He told me you will never know when some trivial pic (today) will save your a$$ (tomorrow)

 

[yeldogt]

The gas company can give you all the information .. some areas have high pressure main lines other have very low ... mine I think are .5psi (very low) The older the area the lower the pressure (that's what I was told) My service line and meter are huge -- it's a couple inch pipe from the street.

I have a 400k pool heater and all the normal gas appliances.

I just asked this of my propane guy and he said with full pressure to a regular at the generator all I need is 3/4 for a 20k unit.

 

[motorusti]

So OP ... is the gas line (1) into and through your house big enough for the gas appliances in your house and proposed generator and (2) is the gas line from the house to the garage/shop big enough to handle both the furnace in the garage/shop and the proposed generator?

IDK, probably. my neighbor is a 30 yr commercial HVAC pro and besides the inside generator, he is pretty confident that there would be plenty of gas at the right pressure to feed the generator.

I only run the furnace when I am working in the shop. during an outage, I probably wouldn't be working in the shop. so that's not an issue. only the gen would be running. we typically just hunker down when we are looking at extended power outages (portable generator just powers well pump, furnace and fridges/freezers).

the original thought was to find an affordable larger generator onan/etc and put it up in the 2nd floor of the garage that would power most of the house. typical extended outages here are few and far between (every couple years), but when they are long (4-5 days) they can be difficult. the latest outage was particularly difficult as I was working out of state and couldn't leave to setup my normal generator.

like i said I probably have all sorts of time before the next major outage.

it seems the best bet is just to setup a generac on a pad next to the house. this will probably cost 2x what I was planning, but is simple and solves the problem.

I learned a lot from this thread. tons of good info from lots of bright folks.
thanks!