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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-03-03</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001215543</rptOwnerCik>
            <rptOwnerName>MATZ R KEVIN</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 MERRITT SEVEN</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NORWALK</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06851</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP - Shared Services</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2005-03-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2337</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>40.97</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14345</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The common stock reported herein as acquired represents shares of common stock issuable in the future in respect of restricted stock units (&quot;RSUs&quot;) granted pursuant to the Company Executive Stock Plan which required the reporting person to accept a portion of his 2004 bonus in RSUs and permitted the reporting person to accept a portion of his 2004 bonus in RSUs.</footnote>
        <footnote id="F2">Includes shares issuable in respect of RSUs.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>R. Kevin Matz</signatureName>
        <signatureDate>2005-03-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2005-03-03
0000105634
EMCOR GROUP INC
EME
0001215543
MATZ R KEVIN
301 MERRITT SEVEN
NORWALK
CT
06851
0
1
0
0
SVP - Shared Services
Common Stock
2005-03-03
4
A
0
2337
40.97
D
14345
D
The common stock reported herein as acquired represents shares of common stock issuable in the future in respect of restricted stock units ("RSUs") granted pursuant to the Company Executive Stock Plan which required the reporting person to accept a portion of his 2004 bonus in RSUs and permitted the reporting person to accept a portion of his 2004 bonus in RSUs.
Includes shares issuable in respect of RSUs.
R. Kevin Matz
2005-03-04