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ideas, questions, need imput on SHW and heating water with wood
By LanceA0, Section Water Posted on Mon Oct 05, 2009 at 09:15:54 AM MST
looking for imput.

im going to be adding a wood furnace(basement) to my existing furnace and get rid of my wood burner(main floor). problem i have is i have a gas hot water heater and it is using the chimney i plan on using for the wood furnace. so i will have to come up with a new way to get hot water. i want to add a tube to heat my dimestic hot water in my wood furnace for the cold months. then make a drain back SHW heater to heat it in the summer months. i want them to be the same system only with shut off valves to eliminate one or the other depending on the season.
my idea is (need imput) to make a 4'x4'x8' holding take in my basement and instead of using coiled up pex submerge a 40gal elec hot water tank (not powered of course, just for water storage vs. coiled pex) in the holding tank and use that as my hot water tank. then cycle either the SHW or hot water from my wood burner around it. then as back up buy a electric tankless water heater. but a small one($200), not a whole house one($800)
will submerging a whole 40 gal hot water tank in water be ok?
the system will be like this one http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm
only instead of the pex in the holding tank im using a 40 Gal hot water tank and im also going to use my wood furnace to heat the water in the winter months. please tell me what you think.

ideas, questions, need imput on SHW and heating water with wood | 14 comments (14 topical)

Re: need imput on SHW and heating water with wood (3.00 / 0) (#1)
by scottsAI on Mon Oct 05, 2009 at 05:39:10 PM MST

LanceA0,
Could you give us a drawing? Not sure why you want to use a tank vs coil?
Have fun,
Scott.

Re: ideas, questions, need imput on SHW and heat.. (3.00 / 0) (#2)
by GaryGary on Mon Oct 05, 2009 at 06:35:10 PM MST

Hi,
I think a tank embedded in the big tank would work OK thermally -- its what Alan did on this project:
http://www.builditsolar.com/Projects/SpaceHeating/AlanTank.htm

But, from a life point of view, I wonder how long a regular hot water tank will last when submerged in hot water?

Your 40 gallon tank if filled with air would have about 330 lbs of buoyancy, so you would need to make sure it stayed full of water.

I guess I'm also wondering why not just use the big pipe coil?
Your heat storage is the water in the big tank, and you can add heat to it using either the wood heat source, or the solar heat source (or even both at the same time) -- I think?

If you are doing space heating as well as domestic water heating, you can take the hot water directly out of the big tank, circulate it around the radiant floor or radiator or whatever, and back to the big tank.

Home Power carried an article a while back about a home that used a large tank with several heat inputs (including solar and wood), and several heat ouputs (domestic hot water and space heating).

Gary
Gary gary@BuildItSolar.com www.BuildItSolar.com

holding tank (3.00 / 0) (#3)
by 12AX7 on Mon Oct 05, 2009 at 07:34:03 PM MST

You may want to check my numbers.. and with that said..
4x4x8=128 (cubic feet) and depends on whose numbers you use 1 cubic foot of water = 64.4lbs (another site said it's 62.3lbs)
So, 128x64.4= 8243.2lbs or 257.6lbs per sq/ft That's a lot of weight. Make sure your floor is up to it!

Heating water in a wood stove can be tricky!

Mark
ax7

Re: subject too long (3.00 / 0) (#4)
by frackers on Tue Oct 06, 2009 at 03:04:32 AM MST

I looked at using a water booster on the log burner to top up the hot water in the winter but by the time I'd put the indirect coil in the hot water tank and allowed for the venting in case of boiling I was much better off (and cheaper) just adding an extra 50% of solar tubes to the SWH.

The solar heater I'm using can run potable water through the heat exchanger manifold so the tank is way cheaper. I am having to uprate the HW tank to a stainless one as the existing enamel (also called a glass lined) tank is only rated to 80 deg C.

BTW - the tank runs at mains pressure so no header tank (just a pressure release valve or two).

It all gets installed next week :-)
Robin - Down Under (or are you Up Over)

Re: subject too long (3.00 / 0) (#5)
by LanceA0 on Tue Oct 06, 2009 at 09:16:34 PM MST

thanks for the imput everyone. i greatly appreciate it. im a rookie with big dreams, crazy ideas, limited money, and a busy schedule. im a DIY guy whos not afraid to get my hand dirty trying to learn something.

SCOTTSAI- i wanted to use the tank because i have a 40gal elec hotwater tank handy. and i want to have a large amout of hot water on tap, thats why i was thinking tank vs coil. i will try and draw up my idea soon.

GARYGARY- the tanks will be plumbed just like my existing hot water tank so there shouldnt be any air in the system. hot water goes out and is replaced with cold well water in.

how many gallons r in 200' of 3/4" pex? im looking to use this system as my only form(could be in dream land)of hot water. so the more hot water i have on tap the better.

the big tank would only be used for hot water. i have a forced air furnace that suplies heat to my house, and i will have the wood furnace added on.

12AX7- thanks for the calculations. i doubt my 1925 basement concrete would be able to hold the weight. so i will have to do coils in a smaller tank or something else..

FRACKERS- my only concern with going all solar is the fact that im in michigan and there are weeks(right now) that are overcast and not much strong sun. if i had the wood furnace making hot water too that would heat my hot water for almost 5 months out of the year. solar should handle the rest.

also the system would have to be a drain back system seeing as we have freezing temps here.

[ Parent ]

Re: subject too long (3.00 / 0) (#6)
by GaryGary on Wed Oct 07, 2009 at 08:36:24 AM MST

Hi,
You will have to check on the actual ID of 3/4 PEX, but if its actually 3/4 inch, then:

Volume = (200ft)(0.75^2*0.785 in^2)(12 in/ft)(1 gal/231 in^3) =4.6 gallons

If your concrete sits on dirt, I think that its like OK for the tank loading. The weight per sqft of the tank is about the same as you walking around on the concrete, and as long as there is dirt under it so that all the concrete has to do is pass the tank load through to the dirt, it should be fine. Both of my tanks sit on dirt with rigid foam board insulation between the tank and dirt -- even the rigid foam board holds up to 4 ft of water OK.

I think I would try to get some kind of line on whether that tank is going to last very long when immersed in hot water -- my gut (with no data) says it won't, and it would be a shame to put all the work into to building it that way, and them have it start leaking in 6 months -- not to mention the 6 inches of water in your basement :)

Gary
Gary gary@BuildItSolar.com www.BuildItSolar.com
[ Parent ]

revised idea (3.00 / 0) (#7)
by LanceA0 on Fri Oct 30, 2009 at 09:10:42 PM MST

well i came up with a new idea utilizing my existing water heater, and not using a water-to-water storage tank. please give me your imput.

here is the drawing
http://s2.photobucket.com/albums/y39/LanceA0/house/?action=view&current=hotwater.jpg

[ Parent ]

Re: revised idea (3.00 / 0) (#8)
by LanceA0 on Sat Oct 31, 2009 at 06:24:35 AM MST

also i will have a pressure release valve on each hot water tank for safety and i wil also add a mixing valve so my hot water isnt to hot.

[ Parent ]

Re: revised idea (3.00 / 0) (#9)
by GaryGary on Wed Nov 04, 2009 at 06:21:23 PM MST

Hi Lance,

One important safety thing. You show two valves that can be used to shutoff the flow to the coil in the wood furnace. You must have a pressure/temperature relief value on the furnace side of those valves. Not having the relief valve on the furnace side of these shutoff valves is exactly how some homes have been blown up.

Otherwise, the only problem I see is that it will be difficult to provide freeze protection for the collector? This kind of system in which water to be heated is pumped directly through the collector is usually limited to climates that don't get freezing weather.

Gary
Gary gary@BuildItSolar.com www.BuildItSolar.com
[ Parent ]

Re: revised idea (3.00 / 0) (#10)
by LanceA0 on Mon Nov 09, 2009 at 04:04:12 PM MST

thanks gary for the imput. i was thinking that a pressure relief should go there for safety too.

as for the collector that will be used only in the summer/warmer months. thats why there is a set of valves and a drain so when it gets cold it can be shut down for the season, and the wood burner will start heating the water.

now that i got the plumbing loop figured out, anyone have any ideas on how to control the pump so it doesnt have to run constantly?

[ Parent ]

Re: revised idea (3.00 / 0) (#11)
by ghurd on Tue Nov 10, 2009 at 05:10:37 AM MST

It will not need a pump if you set it up to thermosiphon.
A friend is running a pumpless system like you show, without the solar, and only one 40 gallon storage tank.
I could try to get a couple photos in a day or 2, if anyone has interest.
G-

[ Parent ]

Re: revised idea (3.00 / 0) (#12)
by LanceA0 on Tue Nov 10, 2009 at 07:47:22 PM MST

yes im always interested in pictures, and other people's set ups.

[ Parent ]

Re: revised idea (3.00 / 0) (#13)
by ghurd on Wed Nov 11, 2009 at 05:36:25 AM MST

Should be tonight.
Added a copper pipe loop in a coal stove so the coal water heater wouldn't need run in winter.
The coal water heater (no pump),
http://ghurd.info/images/Amish/waterheater.jpg

[ Parent ]

Re: revised idea (3.00 / 0) (#14)
by ghurd on Thu Nov 12, 2009 at 06:37:34 PM MST

Hey Lance, Sorry for the delay.

A bit of background:
They run the small coal water heater in warm weather.
The coal stove runs in cold weather. It is the only domestic heat. The silvery tin looking duct stuff around the stove increases air flow and makes the home more evenly heated. That silly thing really get the air moving!

Need that Magic Part thing. Bleeder? Proper name escapes me now. Long day.
Without it, pretty much it ain't gonna work very reliably.

Need lots of safety valves.

Need lots of valves to switch between 'furnace' and the summer 'water heater'.

Need valves with removable handles so grandchildren don't shut off something that causes a serious issue. Again.

Need a plan to take care of the T&P valve, because it WILL Pop-Off a few times before you get the logistics worked out. Hence the CU pipe on the floor going to the floor drain.

Need lots of safety valves.

Pay attention to how level everything is.

I don't show all of them, but Need lots of safety valves.

This area like to use NG water heaters as storage tanks because they have more water ports. I don't quite get it, but thats what they use.

This particular system puts a pipe on the chimney on the NG water heater and gravity feeds warm air to the bathroom. It is removed for summer and the water heater's chimney is stuffed with a few handfuls of fiberglass insulation.
(all my idea, BTW. It may be the only one like that) :)
I REALLY hate cold showers.

Need lots of safety valves. In case I didn't mention that before.
At least 4 T&P valves in this thing. Maybe 6.
It is that serious!

Not sure how organized the pics will show (it says there are 11 though I can only find 10), but they are here,

http://s701.photobucket.com/albums/ww20/ghurd1/Pumpless%20Water%20Heater/

G-

[ Parent ]

ideas, questions, need imput on SHW and heating water with wood | 14 comments (14 topical)

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