Hi,
I am remodelling an old house with 100A electrical service. It’s a small 2br, 2ba house which was already upgraded once for the electrical and has grounded service with romex wires in most places.
The house never had central AC, which I will be adding and has natural gas service, so as of now, the only large circuit is a 30 amp for the dryer.
6 slots (out of 20) are still available in the breaker box.
Adding the central AC will require another 30A breaker.
My question is about the water heater. I tore out the old gas heater, and due to the layout of the house, there is just no good place to put the new one in. The crawspace under the house is maybe 3ft at the highest point. Inside, the only feasible location is to build a closet in the kitchen.
I was wondering if an electrical water heater would work without upgrading the service, but that would be another 30A breaker. The three items: water heater, central AC, and dryer would take up 90 of the 100 available amps, and it’s very likely all three would be running at the same time.
I will be having an electrician do the work, but I’m in the demo / framing stage now and want to plan for where the water heater will go. Electric models are available in smaller sizes (lo boys) and without the requirement for venting, would give me more flexibility on the placement.
Adding up the circuits in any box normally exceeds the service amperage, but I was wondering what is the formula for that?
Thanks!
Jon
Replies
Though normally I'd argue against, this is one case where you might want to consider a tankless gas heater.
Otherwise, you almost certainly need to increase the service to 150 or 200A. But this is not a outrageous thing to do.
(It's normal for the sum of the breakers in the box to exceed the service size, but having 90 of 100A on those there loads is too much.)
Thanks Dan,
I did consider a tankless unit, and it might work. I would have to run exhaust duct if I got a gas model which would limit the placement of it. I don't know the regulations about installing them in crawlspaces. I already have a gas furnace down there and it could tie into the same flue.
Jon
If the flue for the gas furnace is sized correctly, you CANNOT add anbother combustion unit to the same flue. It could not carry the exhaust gasses from both at the same time and you would be spilling dangerous CO emissions into the house, possibly killing somebody
Direct vent water heater
We have used a version of a conventional water heater that uses a fan to exhaust the combustion gases out a PVC pipe.
The unit is designed with a solenoid switch that will only allow the gas burner to ignite if the fan turns on.
Most of the time it vents out the side of the house, but it can be configured to exit through the roof.
Don't know how short a unit is available to fit in a crawl space, but could be a possibility.
Terry
I'm not an electrician, but
here's a link that explains, in general terms how to calculate a residential load requirement http://www.ehow.com/how_4867984_calculate-power-supply-requirements.html
As the article above points out, you don't include the full load of large appliances. Although they may all be "running" at teh same time, they are very unlikely to be drawing the maximum current at the same time.
You mention that you will have an electrician do the work and this would be a good time to have him take a look at the service and confirm that it's sufficient.
You can actually design to run at 100% of the computed service capacity (80% is only for continuous loads) but it is still a good idea to have some growing room.
When I upgraded my old electrical panel, I ran my whole house off a 40amp main feed for about a month... that included computers, laser printer, coffee maker, microwave, 2 fridges, electric oven, and furnace. No trips.
Of course, you drilled holes through the main breakers and installed bolts, so that doesn't count.
As stated by gfretwell, extra capacity is always nice--
so if you decide to up-grade, price the difference between 150 and 200 amp. It's probably not that much difference and would allow for serious future expansion.
If you have overhead service the difference between 150 and 200 is negligable. They will both use the same panel and the breaker is the same price. The only difference is the SE down the side of the house. New overhead drops from the utility are usually going to be 200a rated if it is a twisted triplex. Don't be concerned that it looks like 2ga aluminum. They work with a different rule book than the rest of the world. (NESC). YMMV about the utility cost for the cutover. When I did mine, it was free but that was a while ago. "Free" is harder to come by these days. That is just a phone call tho.
Thanks for all the great advice. I do want to upgrade because the existing service enters the house by tying off at the overhang rafter, then goes into a hole in the sidewall between the main roof and the porch roof, and continues through the attic of the main house, then out the back sidewall of the main house and down through the low pitch roof of the back porch to a meter, which once was exterior on the back porch, but now has been closed in. The attached image shows the service entrance.
As you can see, a mast for the entrance wire would need to be towards the front of the house because the big oak tree would prevent spanning a wire to a mast at the rear, close to where the meter currently is (the meter is electronically read now, so being inside the structure does not matter). When I had an electrician look at it last year, he said he would put the breaker panel in the hallway in the middle of the house, but I would rather keep it in the back where it is now. That being said, could the wire come into the house in the front section, then run through the crawlspace and up to the panel in the rear? The electrician said they can't run them through attics anymore, but I would imagine crawlspaces have to be traversed. As I understand, it just cannot go across wall studs, it has to come straight up from the crawlspace into the panel.
The second image shows you where the current meter is on the once exterior porch that is now being closed in.
Thanks!
Jon
Not quite sure why the sparky said you can't run the wire through the attic.
Basically you can have the service entrance some distance from the breaker panel, so long as there's a disconnect (on the outside) at the service entrance and a few other details. Best to keep the distance as short as possible, but I don't know that there's any specific limit.
There is no specific language about how far you can go inside before the service disconnect but this is what is says
"The service disconnecting means shall be installed at a readily accessible location either outside of a building or structure or inside nearest the point of entrance of the service conductors"
Nearest point is usually considered, "right on the other side of the wall" or some short distance like 4 or 5 feet. It is certainly not up and over, across the attic.
The OP probably needs an outside disconnect, right at the meter and then an SER feeder (4 wire) over to the main panel if it is on the other side of the house. The disconnect will probably cost as much as the panel.