<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-12-31</periodOfReport>

    <issuer>
        <issuerCik>0000105634</issuerCik>
        <issuerName>EMCOR GROUP INC</issuerName>
        <issuerTradingSymbol>EME</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001160599</rptOwnerCik>
            <rptOwnerName>MACINNIS FRANK T</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 MERRITT SEVEN</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NORWALK</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06851</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-12-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>G</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>26434</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>717867</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>26434</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Frank T. MacInnis 2012 GST Family Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2013-01-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>197254</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>35.90</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>520613</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>223688</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Frank T. MacInnis 2012 GST Family Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">On December 31, 2012 the reporting person transferred 26,434 shares of the common stock of EMCOR Group, Inc. (&quot;EMCOR&quot;) to the Frank T. MacInnis 2012 GST Family Trust (the &quot;Trust&quot;) for the benefit of the children and other descendants of the reporting person.</footnote>
        <footnote id="F2">On January 22, 2013 the reporting person transferred 197,254 shares of common stock of EMCOR Group, Inc. to the Trust in exchange for that part of the trust corpus that consisted of securities other than shares of EMCOR common stock and which trust corpus was equal in value to the 197,254 shares of EMCOR common stock, all as permitted by the terms of the Trust.  Inasmuch as the reporting person's spouse is trustee of the Trust and his immediate family members are beneficiaries of the Trust, the transferred shares are reported as indirectly held by the reporting person.  The reporting person disclaims beneficial ownership of the transferred shares, and the filing of this report is not an admission that the reporting person is the beneficial owner of such securities for purposes of Section 16 or for any other purpose.</footnote>
        <footnote id="F3">Includes shares issuable in respect of restricted stock units.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Frank T. MacInnis</signatureName>
        <signatureDate>2013-02-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2012-12-31
0000105634
EMCOR GROUP INC
EME
0001160599
MACINNIS FRANK T
301 MERRITT SEVEN
NORWALK
CT
06851
1
0
0
0
Common Stock
2012-12-31
5
G
0
26434
0
D
717867
D
Common Stock
26434
I
By Frank T. MacInnis 2012 GST Family Trust
Common Stock
2013-01-22
4
J
0
197254
35.90
D
520613
D
Common Stock
223688
I
By Frank T. MacInnis 2012 GST Family Trust
On December 31, 2012 the reporting person transferred 26,434 shares of the common stock of EMCOR Group, Inc. ("EMCOR") to the Frank T. MacInnis 2012 GST Family Trust (the "Trust") for the benefit of the children and other descendants of the reporting person.
On January 22, 2013 the reporting person transferred 197,254 shares of common stock of EMCOR Group, Inc. to the Trust in exchange for that part of the trust corpus that consisted of securities other than shares of EMCOR common stock and which trust corpus was equal in value to the 197,254 shares of EMCOR common stock, all as permitted by the terms of the Trust.  Inasmuch as the reporting person's spouse is trustee of the Trust and his immediate family members are beneficiaries of the Trust, the transferred shares are reported as indirectly held by the reporting person.  The reporting person disclaims beneficial ownership of the transferred shares, and the filing of this report is not an admission that the reporting person is the beneficial owner of such securities for purposes of Section 16 or for any other purpose.
Includes shares issuable in respect of restricted stock units.
Frank T. MacInnis
2013-02-12