Domestic Hot Water Pre-heat using a wood furnace

[TdiDave]

i figured i would start this thread to get some input and share my experiences with a domestic hot water pre-heat system using my wood furnace.

I tried a coil inside the firebox and found that it cooled the fire box down way to much and didn't do a good job of heating the water. So now i have install them in the hot air jacket and it is working very well. It thermo syphons most of the time but i do have a circulation pump and a dump zone kick space heater if the water gets to hot.

 

[Marshy]

Are you using this as primary heat for domestic hot water or to suplement your normal domestic hot water heater? (Edit: I see your title says pre-heat, oops)
Is your holding tank elevated compared to your stove?
How far from your stove is the tank?
You have a circ pump but you say is thermo syphons most of the time; do you have the pump vlaved out to allow it to syphon like this (I assume it wont work without removing the non running pump from the flow path)? Why/when do you use the circ pump then?
How does this intie with the rest of your system?

I have a huge interest in this and the thermo-coil. My ideal situation is to have an indirect hot water tank in which I can hook my base board boiler up to it and allow the normal circ pumps to take heat out of the indirect tank and send it to my zones or to heat my domestic water (might have to limit the flow though if more than one zone wants heat..). This way the thermo coil and water will be a stand alone mini loop that holds about 40 gal of water storage and can provide it to the normal boiler system...

 

[Gavman]

Iv'e been thinking of something along the same lines with my wood stove, might make it a project for this coming fall, basically get a coil made of either copper or stainless steel that will "sit" on top of my wood stove and using hot waters natural inclination to rise have it feed a storage tank without pumps.
I plan to gat some steel or heavy plate cut (maybe 2" thick) that will sit on top of the coil so sandwich it on top of the stove and heat it from both top and bottom.

The top plate can be cut to math the exact size of the stove and look factory haha. but I will make it look good.
Anyways this way I don't have to cut, drill or modify my stove in any way so as not to void insurance etc...

And it just happens that I have a closet that can hold the tank just behind my stove...

I did run this idea by a local WETT inspector last year and he saw no issue with it that he could mention (from the stoves perspective anyways)

I would like to circulate the water around the house in an infloor heat system so super hot water is not necessary...

Great thread....

 

[UpOnTheHill]

i figured i would start this thread to get some input and share my experiences with a domestic hot water pre-heat system using my wood furnace.

I tried a coil inside the firebox and found that it cooled the fire box down way to much and didn't do a good job of heating the water. So now i have install them in the hot air jacket and it is working very well. It thermo syphons most of the time but i do have a circulation pump and a dump zone kick space heater if the water gets to hot.

Nice preheat coil. That will save you some dollars. Was it pre-made or did you use a mandrel or something else? Anything that bumps that water up a few degrees will definitely help in the wallet. Have you measured the delta T when the stove is up to temp? I assume your incoming water is about 55 degrees (ground temperature), what is the leaving water temp before going into your water heater?

 

[Marshy]

Saving money might be a stretch, I assume he bought those coils from Thermocoil and they want about $300 just for the large one on top. Add anothe bill or more for the one on the side and your looking at about maybe 5-6 bills with the rest of the copper piping/fittings valves and if you had to buy a circ pump (maybe a tank)...

I have an oil boiler on my hosue that heats my baseboard and domestic hot water. I try to minimize its use to just domestic hot water and I still burn over 200 gals a year. Assuming fuel oil at $3.5 per gallon at 200 gallons the payback (3.5x200=$700) might take more than 3-4 years as a supplement system depending how much load it satisfies. That payback becomes shorter if you can make it meet more of your needs... Still seems reasonable in the long run, but ultimately IMO you need to have some idea of how much payback your investment has to justify doing it.

I think if your going to stay outside the firebox I'd recommend copper. If your looking to keep it cheap then use anything your can get your hands on, maybe black iron pipe.

Not trying to discourage anyone from doing the same thing but what do you think the payback on your setup is?

How much heating do you think it suppliments (estimate)?

How is your loop set up, is this you only hot water tank in the system and are you cycling your potable water through the coils and returning it to the tank?

 

[NSMaple1]

Saving money might be a stretch, I assume he bought those coils from Thermocoil and they want about $300 just for the large one on top. Add anothe bill or more for the one on the side and your looking at about maybe 5-6 bills with the rest of the copper piping/fittings valves and if you had to buy a circ pump (maybe a tank)...

I have an oil boiler on my hosue that heats my baseboard and domestic hot water. I try to minimize its use to just domestic hot water and I still burn over 200 gals a year. Assuming fuel oil at $3.5 per gallon at 200 gallons the payback (3.5x200=$700) might take more than 3-4 years as a supplement system depending how much load it satisfies. That payback becomes shorter if you can make it meet more of your needs... Still seems reasonable in the long run, but ultimately IMO you need to have some idea of how much payback your investment has to justify doing it.

I think if your going to stay outside the firebox I'd recommend copper. If your looking to keep it cheap then use anything your can get your hands on, maybe black iron pipe.

Not trying to discourage anyone from doing the same thing but what do you think the payback on your setup is?

How much heating do you think it suppliments (estimate)?

How is your loop set up, is this you only hot water tank in the system and are you cycling your potable water through the coils and returning it to the tank?

If you put in a new electric hot water heater & stopped heating DHW with oil all together, you would recover your cost for that new heater in a year.

One also would not want to use black iron pipe in a DHW application.

 

[hupte]

I agree the black pipe is for gas. it has certain anti corrosive properties for gas but it becomes more corrosive when used with water. the same is true for galvanized pipe. you want to use it for water not for gas. you don't want to use galvanized pipe inside the burn chamber though. it will burn off the galvanized coating and the smoke it gives off is toxic.

 

[NSMaple1]

I agree the black pipe is for gas. it has certain anti corrosive properties for gas but it becomes more corrosive when used with water. the same is true for galvanized pipe. you want to use it for water not for gas. you don't want to use galvanized pipe inside the burn chamber though. it will burn off the galvanized coating and the smoke it gives off is toxic.

I wouldn't use galvanized for DHW either. Just copper or pex. Or stainless, of course.

Black pipe is perfectly OK using with water, in a closed (pressurized) boiler situation, not exposed to DHW. I actually wouldn't use galvanized anywhere.

 

[Marshy]

I guess I left an incomplete thought when I wrote that. I would not suggest using it if you are running your domestic water through it, only in a closed loop to heat a tank with a heat exchanger like an indirect hot water tank for DHW side. That way the heating loop is a closed loop and does not mix with your DHW...

 

[TdiDave]

I had a coal stoker stove for several years and had the ss coils installed inside the stove directly above the fire.
I now have replaced the coal stove with the wood furnace. The coal stove made much more hot water than the current setup hence the need for the circulation pump and a "dump" zone to prevent water boil. The current setup so have has never got the water over 140f it does thermo siphon thru the non running pump. I so have a strap on thermal switch for the pump that is adjustable.

The tank is directly beside the stove slightly higher than the bottom of the coil. It is just a gut-less water heater that is plumbed in line with my existing electric hot water heater in another room.

The temps show are after 2 showers so it about drained this tank of hot water it will take it over night to recover back to about 120 on the inlet side (bottom).

 

[Marshy]

Well, I just bit the bullet and bought one of these...

http://www.geappliances.com/heat-pump-hot-water-heater/

It has a built in heat pump that keeps the tank hot and depending the mode you put it in, you can make it provide all of the heating to the tank. Depending on your usage/demand it might not keep up but I think it will suit my needs very well. Plus, it will be down in my basement near the woodstove and should see 80*F ambient air. The GE rep said all the issues have been resolved with the heat pump evaporator coils rusting out due to galvanic corrosion so that is no longer an issue. Im glad I called them and spoke with them about it because all the bad reviews online were really making me second guess the purchase.

I might still use my old indirect hot water tank as a preheat for DHW or as a heat source to my base board system. The goal would be to keep my garage above 32*F, not necessarly heat a living space... My biggest goal is to get away from having to use fuel oil! Anyone want to buy a fuel oil tank? I have 3 and have neve been able to afford to fill one lol.

I decided to prove the wife that I'm a responsible adult and bought this vs the snowmobile I was eyeing. Jury is still out on the adult part...

 

[zogger]

Well, I just bit the bullet and bought one of these...

http://www.geappliances.com/heat-pump-hot-water-heater/

It has a built in heat pump that keeps the tank hot and depending the mode you put it in, you can make it provide all of the heating to the tank. Depending on your usage/demand it might not keep up but I think it will suit my needs very well. Plus, it will be down in my basement near the woodstove and should see 80*F ambient air. The GE rep said all the issues have been resolved with the heat pump evaporator coils rusting out due to galvanic corrosion so that is no longer an issue. Im glad I called them and spoke with them about it because all the bad reviews online were really making me second guess the purchase.

I might still use my old indirect hot water tank as a preheat for DHW or as a heat source to my base board system. The goal would be to keep my garage above 32*F, not necessarly heat a living space... My biggest goal is to get away from having to use fuel oil! Anyone want to buy a fuel oil tank? I have 3 and have neve been able to afford to fill one lol.

I decided to prove the wife that I'm a responsible adult and bought this vs the snowmobile I was eyeing. Jury is still out on the adult part...

Oil tank would be useful for the bulk tank for a small diesel home genny. Or other equipment of course.

I just looked on ebay, they have some under a thousand bucks now, brand new. No idea on quality or anything, but they are there..

 

[Marshy]

Oil tank would be useful for the bulk tank for a small diesel home genny. Or other equipment of course.

I just looked on ebay, they have some under a thousand bucks now, brand new. No idea on quality or anything, but they are there..

I will end up keeping them all, I will need one for fuel when I get a tractor in the future. Who ever thought they needed 3 tanks in the house was quite optimistic, or oil was dirt cheap 18 years ago...
As far as the heat pump DHW heater, GE seemed to really step up and improve on the product with the most recent model. It's "proudly designed, engineered, and assembled in our Louisville, KY manufacturing facility. It is the first step in GE's commitment to invest $1 billion and create more than 1,300 new jobs in the U.S."

And they have made the necessary changes to the heat pump system that had premature failures in the previous model that was 100% China made! Kudos to GE, even if parts still come from China at least they will have Americans putting it together and tossing out poor quality parts instead of just installing them...

 

[stihly dan]

When did they start with the new model?

 

[Marshy]

When did they start with the new model?

Not exactly sure, from what I could find GE announced the opening of the KY facility in Feb of 2012. I cannot find a straight forward product history to answer your question... If really care to know I'm sure you can get that info if you call GE and asked them...

The second generation model is the GEH50DEEDS(R or C; R=Red, C=Charcoal). The first generation that they had the problems with was GEH50DNSRSA.

Here is a link to a PDF in which the Northern Energy Efficiency Alliance (NEEA) conducted an assessment of the product in September 2012. I did not have the chance to read it yet but will do so. I am interested if this was an independent assessment or if there is an affiliation with GE and NEEA. If there is an affiliation, I would expect NEEA to identify that in their report...

https://www.google.com/url?sa=t&rct...H-7oB4&usg=AFQjCNFxbJQ5jyK_oTfs5GUUVyuDfBbZZg

Hey, Sorry for hyjacking this thread man, I see there is another therad about Heat Pump DHW tanks here...
http://www.arboristsite.com/community/threads/heat-pump-water-heater.244836/

Im going to curb my discussion about it here and decided to start me own thead here...

http://www.arboristsite.com/community/threads/heat-pump-water-heaters-ge-geospring.253591/

 

[VW Splitter]

I have a Englander wood stove that I modified to heat my domestic hot water. Started by building a 1 1/2" thick chamber on the right side. The stove is about 2' tall by 2'deep. So the chamber is about 2'x2' 1 1/2". Inside the chamber is a 60' coil of 1/2" copper tubing with the ends stubbed out the bottom. The tubing is piped into the crawl space and into a 50 gal low boy water heater that I use as a storage tank. The 50 gal low boy could be turned on with the flip of a breaker if it was ever needed but I use it just for a storage tank. There is a thermostat on the wall behind the stove that turns on a circulating pump that circulates the water thru the copper coil and thru the tank. It draws the water from the bottom of the tank, where the coolest water is , and dumps it into the top. When we use hot water it draws it off the top of the storage tank, where the hottest water is and runs it thru a BIG whole house Electric instant hot water heater that is set on 130 degrees. So we always get 130 degree hot water no matter what the temp is in the storage tank. Even in the summer with no fire in the stove and no preheated water. The instant hot pulls 80 amps when drawing cold water thru it and around 20 amps with 90 degree water going thru it. With just me and the wife at home now, the water in the storage tank will stay between 95 and 130 degrees, depending on when the last shower was taken and how hot the stove is running. The hottest I have ever had it was 169 degrees, must have been going dirty without a shower. If the water coming out of the bottom of the storage tank is above 110 degrees, we can turn off the BIG instant hot and just use the hot water that the stove is making. I have a small control panel mounted on the floor near the stove where I can flip a switch and turn the instant hot off or on, also has 2 temp gauges to monitor the temp of the water going in and coming out of the stove, and a pressure gauge to monitor water pressure. Thats about it. It works like a charm. I enjoy beating the power co out of the money.

 

[Marshy]

How easy was it to bend the coper tube and how did you do it? I was thinking of using something larder than 1/2" but it might be too difficult to bend.

 

[VW Splitter]

I used 1/2 ", I think it is called soft drawn copper. Came in a 60' coil. I did very little bending. It pretty much fit in the box I had made right out of the box it came in. It was very easy to bend and shape. I just bent it with my hands, being careful not to crimp it.