Tankless coil, indirect storage or electric water heater with side arm?

[muncybob]

We are looking very closely at an oil and wood boiler(Wood Gun).We won't have a heat storage tank for at least the first 2 seasons. One of the options is to receive the boiler with the coil for DHW. I realize that in the heating season a coil is not a major issue but during the summer I'm guessing if we rely on oil for hot water the coil is probably the most expensive way to go. It seems from an initail start up cost the electric water heater would be the cheapest. So, I guess I'm asking that if I were not to rely on wood in the summer for DHW should I not get the boiler with a coil and go electric or even indirect? Should I get the boiler's coil and also use the elctric or indirect?

I considered on demand units for hot water but electric units scare me with the deregulation soon and propane or natural gas are not an option. Solar also won't be feasable except possibly in the winter due to the shade from trees.

 

[ohbie1]

I'm not sure I understand the question, but if I do the following should make some sense:

One thing you will want to investigate is whether the DHW coil will produce HW quickly enough for your needs. For example: My oil boiler has a DHW coil, but it never kept up with our HW needs, so I wound up using the coil as a pre heater, which fed into a HW tank heater (propane for me). When that tank heater went, I switched to an "on demand" fed by the DHW coil. It used very little propane but produced unlimited HW.
If your coil will give you enough HW for your needs, I don't think running the OB to produce the HW could cost more than heating the water from scratch with electricity. (You said yourself you are afraid of it)
If the coil will not give you enough HW alone, you could use it as a pre heater into an electric HW heater (on demand or tank), or you could use a Boiler Mate (check it out online) which would probably be cheaper in the long run.
I'm sure others will have suggestions in addition to these.

 

[muncybob]

My current oil boiler coil meets most of our needs, not sure what the rate is. The wood boiler coil shows flow of 5 gpm and as long as that's hot constantly I'm sure it will be OK for us since we are a 2 person household now. But I'm wondering if I'll be farther ahead of the game by skipping the coil and use an electric hot water heater and it's source in the summer but use it along (no electric)with the heat from the boiler(side arm?) during the months I'll be using the boiler. This makes sense to me but I'm also intrigued by the indirect water heaters. I'm just not sure if using an indirect heater in the summer with a coil in the boiler using oil to heat the water makes sense? I can see where it makes sense using wood.

I guess in the long run I'm asking......if wood and electric are my only energy sources and I'm not going to use wood in the summer, what would be the most cost effective way to have hot water?

 

[Nofossil]

My current thinking is this: you want a DHW tank with a backup heat source, and you want to heat that tank with the wood boiler when possible. You'd also want to overheat it and use a mixing valve on the outlet so that the DHW tank lasts you longer when the wood boiler isn't producing heat.

The DHW tank could be an indirect with coil (like the SuperStor), and electric, gas, or whatever. I'd leave the DHW tank thermostat set for some relatively low temp - 115 to 120, for instance. That way, the backup heat source takes over automatically.

In order to heat the DHW with wood, you have three basic choices:

1) Sidearm

2) Use the internal coil if it's an indirect tank

3) Circulate water from the DHW through a coil in the wood boiler, either by thermosiphon or potable water circulator

I use an indirect tank and I have logic in my control system to open the DHW zone and heat the DHW to 160 degrees when the wood boiler is running. I have a writeup onthe evolution of my DHW solution here.

 

[Chris Hoskin]

use an indirect water heater (SuperStor, Boiler Mate, etc.). The most efficient way to use your oil boiler to heat DHW in the Summer. Because the indirect is set up like another zone, once you hook up heat storage you will be able heat the indirect from the stored heat too. If you have the space and budget, an indirect is hard to beat.

Chris

 

[Nofossil]

use an indirect water heater (SuperStor, Boiler Mate, etc.). The most efficient way to use your oil boiler to heat DHW in the Summer. Because the indirect is set up like another zone, once you hook up heat storage you will be able heat the indirect from the stored heat too. If you have the space and budget, an indirect is hard to beat.

Chris

I would tend to agree, but there's a consideration. If the oil boiler is firing up once or twice a day to heat the indirect tank in the summer, then it's heating the entire mass of the boiler each time, and that heat is wasted once the indirect tank is up to temp.

If DHW usage is low and/or there's another alternative heat source during the summer, it may actually be more efficient and much lower initial cost to use an electric DHW tank.

As I mentioned above, I have an indirect DHW tank and I agree with the virtues pertaining thereto. However, being a fanatic, I use my controller to scavenge the leftover oil boiler heat - first to overheat the DHW tank, then to heat the hot tub.

Here's a writeup.

 

[pybyr]

However, being a fanatic, I use my controller to scavenge the leftover oil boiler heat - first to overheat the DHW tank, then to heat the hot tub.

Here's a writeup.

At NoFo-ville, it sounds as if the motto is "No BTU Left Behind" - which is an excellent result to aim for

 

[MrEd]

use an indirect water heater (SuperStor, Boiler Mate, etc.). The most efficient way to use your oil boiler to heat DHW in the Summer. Because the indirect is set up like another zone, once you hook up heat storage you will be able heat the indirect from the stored heat too. If you have the space and budget, an indirect is hard to beat.

Chris

I would tend to agree, but there's a consideration. If the oil boiler is firing up once or twice a day to heat the indirect tank in the summer, then it's heating the entire mass of the boiler each time, and that heat is wasted once the indirect tank is up to temp.

If DHW usage is low and/or there's another alternative heat source during the summer, it may actually be more efficient and much lower initial cost to use an electric DHW tank.

As I mentioned above, I have an indirect DHW tank and I agree with the virtues pertaining thereto. However, being a fanatic, I use my controller to scavenge the leftover oil boiler heat - first to overheat the DHW tank, then to heat the hot tub.

Here's a writeup.

I like the idea of a sidearm to scavenge heat for the DHW electric tank during heating season - is it feasible to use a solar panel to feed the sidearm during the summer when you are not burning wood?

 

[Fred61]

We are looking very closely at an oil and wood boiler(Wood Gun).We won't have a heat storage tank for at least the first 2 seasons. One of the options is to receive the boiler with the coil for DHW. I realize that in the heating season a coil is not a major issue but during the summer I'm guessing if we rely on oil for hot water the coil is probably the most expensive way to go. It seems from an initail start up cost the electric water heater would be the cheapest. So, I guess I'm asking that if I were not to rely on wood in the summer for DHW should I not get the boiler with a coil and go electric or even indirect? Should I get the boiler's coil and also use the elctric or indirect?

I considered on demand units for hot water but electric units scare me with the deregulation soon and propane or natural gas are not an option. Solar also won't be feasable except possibly in the winter due to the shade from trees.

I once was the owner of a WOOD GUN 140 at my former residence and I can tell you that the coil will make hot water faster than you can use it. In fact, I used to use it to thaw a stubborn 12 foot long 10 inch culvert under my driveway that iced up a couple times each winter. I would just add a few splits to the firebox and run a hose out tied to a piece of rebar that I kept on hand specifically for that purpose. As for making hot water with the oil side, I felt it was very inefficient. With the losses attributed to the incomplete insulation of the vessel and other factors, I finally decided to go with a free standing hot water heater for the off season. Since the unit was within the confines of my living space this also made my home cooler. If I were to buy a WOOD GUN now, I would buy it without the oil burner and use a more efficient means of heating with oil if the need arises.

 

[muncybob]

I think we have decided on an electric tank type water heater. Have heard too many negatives on the electric tankless units. I had thought about a used electric since I've seen a few ads locally for them but isn't a used unit a bit of a risk as I cannot be sure of the interior condition?

 

[Wet1]

I bought mine used, $25 on CL. I just asked the sellers to give me the date of manufacture on the tank. The one I picked up for $25 was a 50 gallon unit and it was 3 years old. But yes, it's a crap shoot so don't pay much for it.

 

[SolarAndWood]

Has anyone looked at/purchased any of the tanks on kotly.com? http://kotly.com/index.php?currency=USD&cPath=30_141&sort=2a