Generator power question

[dkpbxman]

I'm adding up all my essential power needs in order to get the right sized generator and from what I understand I need to keep a running total of the 'running' and 'surge' power requirements of the various fixtures or systems. Then, when I'm done listing all the needed draws, in both categories, add the two sums together in order to get the final number.
When allowing for the necessary 'surge' power needed, couldn't I just allow for the largest draw since that will take care of any lesser number?

also

I have an indirect hook-up between my 40 gal. SuperStor hot water storage tank (16 years old) and my Weil-Mclain 68 oil-fired boiler. About how much power should I allow for heating the water?

Thank you for your help,

[HayZee518]

the hot water heater will run at a constant draw. as the water heats up it doesn't reduce its output. same with the boiler. it's on or off. a refrigerator starts at a higher current then levels off as its running. lighting is pure resistance.

[Speedy Petey]

Originally Posted by dkpbxman

I have an indirect hook-up between my 40 gal. SuperStor hot water storage tank (16 years old) and my Weil-Mclain 68 oil-fired boiler. About how much power should I allow for heating the water?

The water is heated off the boiler. Simply allowing for the boiler is all that's needed. The load doesn't change because the water tank call the boiler. It's just one more circulator or zone valve running. Neither of those two is any noticeable draw.


As far as startup loads, figuring for the largest load is fine as long as only that load is starting. What if there is a 50% load on the genny and a large motor load, such as an A/C, comes on? Your startup figure just went out the window.

[dkpbxman]

I want to be able to take care of myself but I'm not 'survivalist' about it. Just want to take care of heat, hot water, my fridge, my computer, a microwave and a few lights. I know I'm exaggerating but sometimes it seems that the juice goes out every time it rains.

[Speedy Petey]

Since you water is heated off the boiler you are in much better shape than if you had an electric unit.

What you describe can be run off a decent 5500 watt unit. Go larger if you want more cushion for other loads.

How will you be transferring the load? If you intend on using a whole house transfer switch or main breaker interlock, I'd definitely recommend a larger unit. Something 6500 watts and up. it gets too easy to forget that you are on a genny if everything can be run.

[dkpbxman]

I was thinking of 6500 watts with a transfer switch but just for my education; why would you recommend a unit larger than 5500?

[Speedy Petey]

This:

It gets too easy to forget that you are on a genny if everything can be run.

If you get complacent and run too much the genny breaker will trip leaving you dark and unhappy for a short while.

[driz]

You end up needing more than you think if you are just going to do business as usual on a limited basis. What you need is at least a 5500 watt unit which is pretty much standard. Yes they are expensive and don't get a cheap Coleman or you will come to hate it. Decent ones are about a thousand nowdays but you can find them for sale hardly used where ever there has recently been a large scale disaster. Insurance companies tend to gather them up as well after such events and sell them.
You get into trouble when the well kicks on at the same time as your boiler's oil gun. Both have a pretty big start up surge and if they happen together it can cause you to have a brown out condition. That may or may not do anything but it can fuse motors which happened to me and cause all sorts of additional damage. If you are taking a shower its a good precaution to shut off the boiler while you are doing it and turn it on later. Of course if you get a big enough one you don't need to do that but those units are around 2500 bucks. For the usual emergency use its better to just watch what you are running at the same time. I think Generac has a listing of approximate surge ratings for various items you can refer to. Its good to print the stuff out and keep it handy as some of those small appliances like the humble coffee pot are real energy eaters while in use. Sears sells nice ones, generac I think, Makita are nice and of course Honda is the Cadillac of em on the consumer end. Onan is overkill for most of us.