By Poornima Gupta

SAN FRANCISCO, March 20 (Reuters) - An influential U.S. consumer watchdog is investigating online reports that Apple Inc's new iPad throws off an unusually large amount of heat and will publish its findings later on Tuesday.

Consumer Reports, which reviews everything from electronics to cars, noticed comments on online forums and on Apple's website about excessive heat from the new device, which went on sale Friday, and decided to look into the issue, a spokesman said.

The group will publish its findings on Tuesday after finishing a battery of tests, the spokesman added.

The third iteration of the iPad hit store shelves on Friday and about 3 million units moved in the first three days, a record first weekend for the tablet computer, launched in 2010.

Hundreds of comments posted on an Apple support website, here#17879177, centered on how the new iPad -- which sports a larger battery than its predecessor to power a sharper "retina" display screen and other bells and whistles -- could get uncomfortably warm.

"My new iPad ... definitely got significantly warm, almost too warm to hold warm, when running on LTE," rawwave commented on Friday. "Not even doing a lot of downloads (just browsing Twitter) but having the LTE radio on seemed to cause it to get noticeably hot."

An Apple spokeswoman said the iPad was "within our thermal specifications." The company's website lists the normal operating range for the new iPad as between 32 and 95 degrees Fahrenheit, or 0 to 35 degrees Celsius. It is designed to power down should that range be breached.

The company's shares were down 0.3 percent at $599.39 in afternoon trade.

The new iPad's battery is 70 percent bigger than the one in the previous version, said Kyle Wiens, chief executive of iFixit, a prominent Apple repair and parts supplier.

"It still has the same battery life," he said. "So it will run hotter."

The second-generation iPad 2 had a 25 watt-hour battery while the new iPad's battery has a capacity of 42.5 watt-hours, according to a tear-down analysis by iFixit.

Reviews have generally been good for a gadget that experts say falls short of being revolutionary, focusing on the iPad's ability to take advantage of faster 4G wireless technology as well as a sharper display.

On Friday, before comments about excessive heat began circulating online, Consumer Reports said in its preliminary review that the iPad was "shaping up as the best tablet yet."

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