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hotwater heat over coil in ducts?

| Posted in Energy, Heating & Insulation on February 6, 2002 04:45am

*
My 40-50 yr old furnace is gasping it’s last few breaths and I would like a new system, and am looking for advice/ experience. I am thinking of ripping out the old furnace and placing a coil in the ductwork, feeding hot water to the ductwork coil via a good large capicity electric water heater. All I should need then is a zone valve and a fan?

I am also thinking I may be able to lay the water heater horizontaly under the stairs to save space in my small abode, I think I had better talk this one over with the supplier!

My place is 20’x20′, 2 floors, insullated to r40 in the ceilings, r 20 walls,with vapour barried. The windows and doors are not up to standards but I plan on changing them soon. Any thoughts tor input folks?

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Replies

  1. David_Thomas | Feb 01, 2002 11:52pm | #1

    *
    Bake: Sounds like the insulation was retrofitted in (unless you installed a used furnace in a new house :-) ). I'd estimate your house needs 22,000 BTU/hour when it gets down to 0F outside. Aside: Why doesn't anyone post WHERE their house is located?

    So, yes,a 7000 watt electric HWH would work, just barely. But why do that?

    Just put electric heating elements in the ductwork. Four hair dryers would do it*. No piping needed, no space needed for the HWH, no pump.

    *I am JOKING there. Use elements designed for this purpose.

    But a more fundamental question is why heat with electricity instead of the NG/LPG/OIL you are using now? Electricity will cost 2 to 6 times as much.

    A gas-fired HWH would be a viable option. It would have to mounted upright and be properly vented. But the current furnace location is presumable more than big enough and has a more than large enough flue already. It would have enough additional capacity to provide domestic hot water as well (inspector willing), which would save you some space and/or regain you one storage closet.

    Can you mount an electric HWH on its side? Ask your inspector. If he/she says no, then you can't. Would there be problems with it? Sure. When you fill the heater with water, how do get all the air out? The upper side of the tank will never be purged of air so about 40% of its volume would be filled with air initially. That would compress from 14.7 PSIA to about 40-60 PSIG (=55 to 75 PSIA). While that would reduce it to 10% of the tank volume, compressed air has a LOT of energy in it. It makes a rupture in the HWH much more dangerous and it will take longer to purge the plumbing for any repairs or maintenance.

    Also, the two heating element of an electric HWH assume gravity points down. The upper one comes on first and only when it is happy does the lower one come on. Some of those elements (like the 7000 watt ones) go all the way across the tank. If any of the element is in air instead of water, it will burn out in seconds.

    As soon as you start thinking "outside the box" as you have been doing, you need either: 1) to be fairly proficienct at plumbing, electrical, engineering, and building codes or 2) hire someone who is. Barring that, better to examine the spectrum of standard options. They will be better supported and hold fewer surprises for the instaler and the homeowner. Good Luck, -David

    1. The_Tennis_Court_Builder_...on_t | Feb 02, 2002 12:49am | #2

      *sounds like a... parden my expression...a half baked...idea.near the stream,ajFinish baking with fuel and you will be fine. New furnace time.

      1. bake_ | Feb 02, 2002 01:23am | #3

        *David, good input, thanks and yes I did reinsulate the place. Location is Revelstoke, British Columbia.I am merely investigating what may be possible to do here and am a lisensed electrician with lots of time on controls, that part dosn't fool me, I have a lot of good trade related buddies (plumbers etc) that would be willing to lend a hand but like I said I am just investigating today. A chat with a plumbing wholesaler today confirmed what you have told me.AJ, personally don't see anything wrong with looking at the way things are done and seeing if they can be changed to make a more efficiant system. I always thought one of cavemans first invention was the furnace, there are a lot of reasons that I just don't like them. I had heard such systems were in use and hoped it would meet my requirements.

        1. David_Thomas | Feb 02, 2002 01:45am | #4

          *Bake: No disrespect intended and I'm glad to see that you're doing thorough research.Being in a modest sized house myself, I can understand the desire to reduce the space needed for utilities. For low installation cost, small space, and reasonable operating costs, it would hard to beat a standard or direct-vent hot water heater serving both space heating and domestic hot water needs.My plumbing supply house didn't have pre-fab fin tube in a circular cross section when I wanted to put some in an existing duct. So I plumbed two lengths of straight fin tube as a long, skinny U of fin tube and shoved it in the duct work. Worked fine. The air velocity over it gave several times the BTUs per linear foot as when fin tube is installed normally in a basboard with only passive convection going on. -David

          1. The_Tennis_Court_Builder_...on_t | Feb 02, 2002 01:58am | #5

            *What David said x 2.near the stream,ajI have an idea.. I am pulling out my electric resistance that is in my heat pump. I could sell it to you for $100. It will definitely heat your place as my place is 2000sqft. What do you pay for electricity? Here it is way more than using oil or even LP.

          2. teo_ | Feb 02, 2002 06:21pm | #6

            *American Hot Water heater company sells a HWH to forced air heating system. Saw it in the last brochure.

          3. bake_ | Feb 02, 2002 07:07pm | #7

            *I should have incuded the fact that my furnace is taking up a big hunk of interior realestate I want to reclaim to make my floor plan better suited to me. Part of my upgrades around here is going to include a 5'6" whirlpool tub that will need a better hwt anyways. Whatever system I install will have to change locations rendering the present chimney usless, which is why I thought of the system I described.My other options include building a "bumpout" outside and putting the new system in there. AJ; we are paying .0057 per kwh, Oil and propane are available to us but because our community is remote the prices are high, I cannot quote them at this time. I am sure the utilities here are enjoying their "captive audience"teo; I will investigate your lead, thanksbakeAJ; we are paying .o577 per kwh

          4. Brian_Smith | Feb 06, 2002 06:02am | #8

            *should go in the bump out. that's why you thought of it. conventional & your insurance company likes convention.BTW, why call it a HWH and not a WH? ;)brian

          5. bake_ | Feb 06, 2002 06:28am | #9

            *Guess I am used to seeing it that way on blueprints, old habbits die hard.

          6. Tim_Rice | Feb 06, 2002 03:44pm | #10

            *I'm used to seeing water heaters designated as DWH (domestic water heater) on drawings.Bake, a question or 2: Do you have AC? Is the location of the existing furnace near the exterior? Did you say where in the country and what fuel?What I'm getting at, is if you want to reclaim floor space, ever consider a packaged gas/electric (or just gas/oil/lp if you want no AC) unit sitting on grade next to the house? One different way to do it. If the ductwork is close and a suitable space is available, something else to consider.

          7. Alan_Kim | Feb 06, 2002 04:45pm | #11

            *You may want to look into Munchkin boilers - very small and slowly catching on with installers. Most feedbacks I've read have been very positive.I believe it is either gas or oil.It could probably mount in a bumpout to isolate it, and indirect domestic hotwater heating could be taken care of with a stainless steel heat exchanger plate. A hotwater coil loop could be installed in the ductwork for heating.Go to HeatingHelp.com (their forum.).It seems Canada should have more progressive and sensible products available for your needs.

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