Pre heating hot water with stove advice needed

[agz124]

Hi,

My Quad 4300 is located in the middle of our open floor plan 1950's cape on the first floor. It has plenty of heating potential and I have even set up a duct system in the ceiling near the stove to get heat into one of the upstairs bedrooms with an in-line duct fan and thermostat (works perfectly). Of course, I am not too good at sitting still so now I want to pre heat (just a little bit) my domestic hot water before it enters my electric hot water heater. The hot water heater is in the basement, almost directly below my stove (about 12 feet away).

My idea is to take about 50' of 1/2" copper and mount it on the brick behind my stove. There is about 2" of the clearance between the back of the stove and the brick and the air temp back there is about 120F most of the time. The water would travel through the 50' copper coil and then enter the hot water heater. I am well aware of danger of steam but there is an expansion tank downline and the temp behind the stove is not that hot. My concern is: will I cut down on the rate of flow significantly? Also, would I be better off mounting an old cast iron radiator behind the stove and using that instead of copper? My guess is that an old radiator will never offer clean water no matter how long I flush it out.

Any advice is greatly appreciated.

 

[BrotherBart]

I am leaving this post here for contributions but you really should post in the Boiler Room and get some feedback. Those guys know all about heating water and not sending the water heater up through the roof.

 

[begreen]

I would think you'd get better results attaching the tubing directly to the stove back, but this will require safety systems perhaps including an additional expansion tank and relief valve above the stove. Have you looked at John Gulland's design?

http://www.gulland.ca/homenergy/stove.htm

 

[soupy1957]

My wife and I were (this goes back to the mid-80's) looking for a house in a neighboring town. One of the houses shown to us, was owned by a retired Mechanical Engineer, who was by that time, living in a Convalescent Home. In his house were a variety of Engineering marvels.

One of these "marvels" was a big copper tank in the basement, (about the size of an oversized Argon Gas tank, like what you'd see associated with Welding equipment), sitting next to the hot water heater.

The concept (and an apparently successful one, at that), was simple, and yet effective. He had his outside water from the town, piped into that copper tank, and then had a pipe from that, to his hot water heater. It, in effect, pre-warmed the outside water to room temperature, so as to allow the hot water heater to run on shorter cycles, since it didn't have to work as hard to heat the water which was already at room temp.

Simple, and creative.

-Soupy1957

P.S.: If this were a Mechanical Engineering Forum, I'd tell you of some of the OTHER things he had designed in that house, that would amaze you as they amazed me!!

 

[NH_Wood]

I've been considering a version of this to preheat water: http://www.motherearthnews.com/do-it-yourself/woodstove-water-heating.aspx

I'm waited to see how the stove can heat my home though (I'm on year 1) before pulling out BTU's for hot water. If I do it, I don't want to drill anything into the stove - the back of my stove sits about 6 inches from the brick back wall. I'd like to use small vertical bars as support for the bottom of the coil system, and then 2 small horizontal bars that can offer pressure from the brick wall to the back of the stove. If I can get this running, I'd like to tie it into a used electric hot water heater, and then have this tied into my oil burner. But, no idea how hot I can get the water AND how many BTU's it will take from the stove. One thing I like is that it is using radiant heat from the outside of the box, rather than stealing heat from the inside of the box - I'm assuming less risk of lowering the combustion temps too much and creating more creosote. I'd love to be able to maximize the energy from the stove and get some preheated water, but not at the expense of a much colder house. Anyone have any thoughts on how much this would take away from the heat to the house - when the circulator pumps is running vs. not running? Cheers!

 

[agz124]

Thanks for the info, but I am not willing to mess with the stove in anyway and I certainly do not want to worry about steam (pressure). The idea of a tank in the basement is a good one as it is totally safe, the problem is my basement is really cold as the furnace never runs In the 70's my uncle stripped all the insulation off an old water heater and set it next to his oil fired furnace, he called it a "tempering tank" as it would warm up the water before entering his real water heater.

Thanks

 

[NH_Wood]

Thanks for the info, but I am not willing to mess with the stove in anyway and I certainly do not want to worry about steam (pressure). The idea of a tank in the basement is a good one as it is totally safe, the problem is my basement is really cold as the furnace never runs In the 70's my uncle stripped all the insulation off an old water heater and set it next to his oil fired furnace, he called it a "tempering tank" as it would warm up the water before entering his real water heater.

Thanks

Okay - one thought for your idea might be even more copper tubing. if you have a large space in back of the stove, can you go with an even longer loop of copper coil? I think the link i posted above was a 60' coil and seemed to fit in a small space. Could you get a whole lot more copper for a whole lot more surface area? Cheers!