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  1. #1

    Retrofiting heat strips / element in existing gas furnace

    I am not sure if it was even discussed in this shape and form but I was wondering how difficult would it be to customise existing natural gas furnace by adding electric heat element. So, in other words create a custom dual fuel heat system when you can switch from natural gas to electric depending on current energy prices or any other considerations. I realize that is is not a simple question but besides the following obvious, even to me (an armature) problems and issues.

    1. Finding the place in plenum for electric heat strips / element and properly mounting / installing them.
    2. Modifying or finding a new control board capable of firing either one of heat sources.
    3. Bringing 220 Volts 60-80 amps service to the existing natural gas furnace.
    4. Wiring independent thermostat controlling electric heat only

    Did I miss anything? I am sure I did and I am asking everybody how tough is the project? Did anybody accomplish anything similar to what I am describing? I understand that there is another solution, i.e. buying prepackaged electric furnace and incorporate it in existing ductwork, however it requires additional space which would be difficult to get in my case. I also wonder from the stand point of pure $$$'s consideration, which method is cheaper?

    TIA for your always constructive input.

    Merry Christams and Happy New Year to everybody.

  2. #2
    Join Date
    Apr 2009
    Location
    Central New Jersey
    Posts
    253
    What are your current electric and gas rates? What size and efficiency is the current furnance? How big is your house?

    Before you embark on this project, you should calculate what the price of two fuels need to be to make this cost effective. I can't imagine using heat strips can ever be cheaper than using natural gas, but perhaps in your part of the country it could happen.

  3. #3
    Thanks for your kind response. Let's forget the rates for the time being, I would like to understand the project complexity.

  4. #4
    Join Date
    Mar 2010
    Location
    Rochester, NY
    Posts
    471
    energy freak....
    What you are asking for is possible, you should call a professional and get a quote. They will have access to different elect. heating packages that will work and most importantly that are U.L. listed and installed according to the national electric code. If you "rig" something up it may be a hazard to you and you can't sell or rent your place until the elect. heat is removed or passes code.

  5. #5
    Dear Perfectionist, thanks for the advice. I do not think I'll be able to find the right person for what I'm planning to do and I painfully realize the challenges and safety issues involved.

    I'm trying to build a mock-up / prototype and there are several questions that I'm trying to answer. First and most important - locations of tubular duct elements (above A coil?, makes sense to me but maybe I am naive and dumb), secondly what type of control to employ as far as delivering gradually BTU's from the bank of heating elements..etc

  6. #6
    Join Date
    Dec 2010
    Location
    Down by the river
    Posts
    1,692
    so you are ''rigging up something''. We as Pro's frown upon that, cause it's when your house burns to the ground that the state makes up a new code, making it harder on us and costing you more in the future.

  7. #7
    Join Date
    Jun 2010
    Location
    Charlotte, NC
    Posts
    155
    It sounds like you want to ignore the fact that the only reason to do dual fuel when you have gas is to gain efficiency by taking advantage of a heat pump which heats more efficiently and economically than gas. Unlike the electrical resistance heat you want to use, which is much less economical.

    For some mysterious reason, you want to design and install a system where you have the option to use electric coil heat instead of gas, when it pretty much has no advantage. Perhaps you expect the NG supply to be interrupted when electricity won't be. An emergency backup system of sorts.

    One thing an electric furnace has already had engineered into it is insulation and fireproofing of the enclosure surrounding the elements. Yours won't have that, and doing that properly requires engineering design and testing.

    Another issue is getting the heat distributed where you need it. The most efficient way is to move the elements as close as possible to where the heat is wanted. Ideally in the enclosed space itself.

    For that, we have an invention already--an electric space heater. Installation is simple: you plug it into a wall socket.
    No duct losses. Thermal control is available by paying $10 more per unit to get a thermostat controlled model. Great zoning flexibility--each room can have its own set point! You can even move them from room to room. Total design and installation cost for 5 would be about $150 bucks. (sorry about mentioning pricing) You might also need a couple more 20 amp circuits if you are going to have them all on at the same time at full power, depending on how well the house is wired.

    Good luck on your invention of a more expensive, less efficient alternative to a space heater.

    But seriously, there are not many good reasons one would put coils in a duct system instead of just installing properly hard wired electric baseboard heat on independant circuits if one really wants electric resistance heating (other than that it provides work for electricians instead of HVAC pros.)

  8. #8
    Join Date
    Dec 2001
    Location
    Ocean Pines, MD
    Posts
    7,034
    Your trying to re-invent the wheel when it has already been determined that the square ones don't work.

  9. #9
    Join Date
    Feb 2004
    Location
    Pacific NW
    Posts
    571
    A few years back shen NG prices were peaking, son bought a house with a downflow gas furnace. Trade showed HP down to about 20 F was lower cost to run.
    Garage had 12 t ceiling, so was able to stack a totally independent air handler for HP on top of the NG furnace. Custom metalwork required. Custom switchover circuit needed, could not find (or figure out) how to make any commercial thermostat to work for both without modification or addition of another switch.

    So, it can be done, but you may have to search to find someone able to do it.

    Like others have said, resistance heat will never (in the eforeseeable future with NG from shale being developed) be lower operating cost than NG. If you want it for 'emergency heat', then a few space heaters are your solution..

  10. #10
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,909
    For electric resistance heat to save money, your electric rate would have to be pretty damn low - like 3 cents per kwh or less.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  11. #11
    Ok guys. I appreciate all responses and multiple lectures about comparative fuel cost and to tell you the truth, I can give those lectures myself. I never asked about that because I clearly understand the advantage of blue flame over resistance heat. That was never in doubt or question for that matter!

    I am also appreciative of all warnings regarding potential dangers of this project. I am well aware of them too. My questions were about design and potential bottlenecks of this retrofit / intellectual exercise (if you will) and if you guys do not have anything of substance to say besides quoting forum rules regarding liability issues and other general stuff, then thanks again and

    Merry Christmas / Happy New Year to all of you.

    PS. I never asked for blueprints, I only want to ascertain the project feasibility and /or complexity.

  12. #12
    Join Date
    Dec 2010
    Location
    Down by the river
    Posts
    1,692
    you shoulda been able to get all that out of what we posted.

  13. #13
    Join Date
    Dec 2009
    Location
    McCook NE
    Posts
    91
    Quote Originally Posted by junkhound View Post
    A few years back shen NG prices were peaking, son bought a house with a downflow gas furnace. Trade showed HP down to about 20 F was lower cost to run.
    Garage had 12 t ceiling, so was able to stack a totally independent air handler for HP on top of the NG furnace. Custom metalwork required. Custom switchover circuit needed, could not find (or figure out) how to make any commercial thermostat to work for both without modification or addition of another switch.

    So, it can be done, but you may have to search to find someone able to do it.

    Like others have said, resistance heat will never (in the eforeseeable future with NG from shale being developed) be lower operating cost than NG. If you want it for 'emergency heat', then a few space heaters are your solution..
    This is kinda what I was thinking regarding my dual fuel system handling defrost mode. It seems to me a heat strip would be better for defrost then my gas backup.

    The problem with me is I never know when I'm brain storming or brain farting. So I leave the fun stuff to the pros.

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