Cost Effective DHW?

[kshultz]

Hi There,

My wood boiler will be in soon and I am already thinking of a storage system for the DHW. My problem is that it seems to be too much bother, too expensive, and too long of a payback. Does any one have some ideas on a way that I can start planning a low cost storage system. I currently have a 50 gal. Top Performer storage tank now, which is pretty efficient at holding hot water, but with a storage system I am thinking I can really extend my wood burning season from early Fall thru Spring. I do have plenty of room in my basement. Suggestions any one?

 

[chuck172]

I'm in the same boat as you. The boiler is coming next week, no storage. I'm hoping Tarm comes out with pressurized storage soon. That's the rumor anyway. In the mean-time I have a plan. I have a good woodstove on my main level which I'll be burning in warmer weather and burn the Tarm solo40 on the colder days and nights. Hopefully Ill be getting plenty of hot water. The way I understand it, with experience, I can control the heat by varying the amount of wood I load.

 

[Eric Johnson]

Getting DHW out of a gasifier (or any other boiler) is not very expensive or complicated, if you're doing it during the regular heating season. You can put a coil in a boiler like a Tarm, or build your own sidearm hx to heat the water in your existing water heater. But trying to do only DHW in the summer without adequate storage (800-1,000 gallons) is, as kshultz suggests, not worth the effort. There's no point in firing up the boiler if all you're going to do is heat 50 gallons of water up to 180 degrees. There's no place to put the rest of the heat produced.

I wouldn't get too worked up about storage at this point. You can run your boilers alright without it when it turns cold, giving you the luxury of time to figure out what you want and what you can afford.

 

[kshultz]

Thank you, I will not get too worked up over it yet. My new wood boiler is going to be plumbed "in Line" with my existing oil fired boiler (on stand by with a lower set point), my current DHW is on it's own zone so when I'm burning wood in the winter everything should be a seamless process. I figured I could use the first heating system to really get to know the abilities & limits of my new wood boiler, then go from there. I track all my oil usage now, and will continue to do so after the wood sytem is up & running. After that I guess I'll amek the decision on what exactly to do. Hell in the summer the oil boiler water temp can be turned down & maybe completely turned off from 9-5 when no one is at home. That is probably the cheapest way to conserve! Thank You, Kevin

 

[WoodNotOil]

I am currently using my oil boiler with coil for summer DHW. I turn it down to 150* and have plenty of hot water for showers, etc. If someone wants a really full hot bath though, I have to turn it up. I am adding storage as we speak so I will no longer need any oil. I waited three years to add the storage and found this forum while looking for storage designs. Read all the posts here on storage and you should be able to find an option that will work for you in the future. Good Luck!

 

[Nofossil]

I'm pretty happy with my setup I use a 40 gallon SuperStor indirect DHW tank. This has a finned coil inside so that you can plumb it as a zone on your boiler. I also do a few other tricks to extend the useful life of a DHW tank. I've got a writeup here.

If you've poked around this forum, you've probably seen that I'm also not a fan of series (in line) plumbing. It probably is the simpler approach in some cases, but I suspect that you're paying a price in terms of reduced efficiency and slower system responsiveness.

 

[WoodNotOil]

Nofossil - I have seen a lot of these discussions about using the series (in line) versus not here and elsewhere. I would love to see a study on it if one has been done. I understand why people think efficiency is lost by keeping the other boiler hot, but I have seen no one willing to put a number on it. With a well insulated boiler and good heat siphoning control some of that is probably mitigated.

As far as system responsiveness goes, I would think in line would be better. When the oil backup is needed, the boiler is already almost at temp. Whereas in the other case it has to heat from stone cold. Also, some have suggested that keeping the oil boiler hot at all times could extend it's life expectancy. I am not sure what to make of the debate. I wish there was some concrete evidence to base this on instead of peoples personal preferences and assumptions. For now I am stuck with in line wondering how much efficiency is being lost.

 

[Nofossil]

Nofossil - I have seen a lot of these discussions about using the series (in line) versus not here and elsewhere. I would love to see a study on it if one has been done. I understand why people think efficiency is lost by keeping the other boiler hot, but I have seen no one willing to put a number on it. With a well insulated boiler and good heat siphoning control some of that is probably mitigated.

As far as system responsiveness goes, I would think in line would be better. When the oil backup is needed, the boiler is already almost at temp. Whereas in the other case it has to heat from stone cold. Also, some have suggested that keeping the oil boiler hot at all times could extend it's life expectancy. I am not sure what to make of the debate. I wish there was some concrete evidence to base this on instead of peoples personal preferences and assumptions. For now I am stuck with in line wondering how much efficiency is being lost.

That's a fair question. I suppose you could calculate the amount of energy that it takes to heat the water and cast iron in the boiler, and make some assumption about how much of that is lost up the chimney versus into the boiler room. That amount is what you lose every heat cycle.

In my case, both boilers are cold for months every year, so I don't worry about that aspect. In fact, my oil boiler is cold for all but about 20 hours out of the year.

The responsiveness I'm thinking about is the case where both boilers are cold and the house or DHW needs heat. In a series installation, you have to heat both boilers before you get any useful heat into the house. In my burn pattern, this happens almost every day.

I don't think that series is inherently evil, but I think it's less efficient and effective in most cases.

 

[WoodNotOil]

nofossil - thanks for the response. I see what you mean. With an indirect DHW tank as a separate zone I can see the efficiency loss. Most series installs are due to the DHW coil in the oil boiler. In that case the boiler acts a bit like the tank and maybe efficiency evens out. The indirect DHW tank must lose at least as much heat as the boiler. Efficiency would need to be estimated case by case I guess.

 

[Nofossil]

nofossil - thanks for the response. I see what you mean. With an indirect DHW tank as a separate zone I can see the efficiency loss. Most series installs are due to the DHW coil in the oil boiler. In that case the boiler acts a bit like the tank and maybe efficiency evens out. The indirect DHW tank must lose at least as much heat as the boiler. Efficiency would need to be estimated case by case I guess.

Indirect tanks lose much less than a boiler, as they're much better insulated. Mine loses about 1/2 degree per hour. I really think they're the best bet with the possible exception of a tankless heater.

 

[kshultz]

Thanks guys,
All your ideas & input are well appreciated. I think I'm going to stay the course on whatg I've planned. Although I never gave it too much thought on the efficiency loss when piping in line systems. I guess I will be keeping my oil boiler hot all the time. As for the DHW, my 40 Top Performer same as a SuperStor are awesome, don't hear the oil burner kick in too much during the summer. But with the price of oil I might as well open the door & throw $$ out! I have seen a couple threads mention efficiency & that some people weigh their wood prior to burning. Is all the efficiency stuff complicated? I guess right now to have a good system in at a reasonable price will be better than paying for oil. The payback is getting shorter & shorter. Kevin