Less hotwater than expected from Koil

23T model HilKoil




I have one of these in my Poccono, its not making as much hot water as i expected. I have it hooked to a 40gal tempering tank then it feeds my electric HWH. With a coil that size i figured i would be making to much hot water so i installed a kickspace heater dumpzone, i cant really even open up the dump zone because its just making enough water for our normal houshold use. Its not real cold out yet but figured i could get more hot water when the stove is at idel than it is doing now. Would it be ok to add a second coil infront of this one and lower (closer) to the burner then pass the water thru both. Any ideas?

I've been playing around with a single 24" loop from Hilkoil, and also passed it through a 40 gallon tempering tank and got similar low hot water output at an idle fire. Even with a full fire, I think that two, three, or even four, Hilkoils installed in the stove, would allow me to use a dump space heater, a small section of radiant floor heating, or a hot water to air heat exchanger, in the duct work.

I did cycle my one 24" loop, that went to the 40 gallon tempering tank, through a 22" x 22" water to air heat exchanger, and was quite surprised how well it did work, but with one coil, it couldn't keep up with the demand.

My tank temperatures would stay around 150 degrees when I didn't use any water or cycle it through the exchanger, but soon as I cycled the water through the heat exchanger, the temperature dropped to 75 degrees. When I used hot water, the tank would drop to 95 degrees. It would also take about 12 hours to reach 150 degrees.

So, all of this experimenting around leads me to the conclusion that more Hilkoils installed into the stove would provide the needed heat output I need. Go ahead and put another one in and see how much it improves. You do have to remember, at idle fire, it still may not give you the results you need until the stove is cranking some.

I put a hilkoil in my Harman SF250 and hooked it to my oil boiler "on the boiler side" but couldn't get the water temp up much past 140*. So i made my own coil the hiokoil was 57" long and the one i made was 120" and it still wasn't enough . I could get the water to 170* but couldn't maintain it to long. Now i install the 57" hilkoil in as well, it was a tite fit but i got it in there and hooked it in sequel for total of 15ft. Now i can heat the boiler and use the domestic hot water coil as well i can maintain between 160* and 180* the only time the oil burner will kickin is if there are back to back showers and it will only run for 2 minutes or so. I have Taco 007 running with a ball valve to slow the water down. You don't get much heat out of it when the stove is just idleing you have to keep the stove temp up to be any good.

I have a Hilkoil in my old Alaska Kodiak. I use my 50 gal. Elec. water heater (elec. turned off) as the storage tank and run a Grundfos pump constantly. I also have a kick heater installed in the family room to dump excess heat when needed. This setup provides all of my hot water once the stove is started for the season. This setup has worked well for 3 of us living in the house, however you must plan your hot water usage accordingly. The system isn't quick recovery, so multiple back to back showers, etc. will pull too much hot water at once.

I see one major difference between your setup and mine which is the height of the coil. My coil is directly over the grate and is adjustable to keep the coil over the fire. I have been using this setup for over 10 years. Another thing I have myself trained to do is clean the ash off of the coil everytime I empty the pan. I do this using a "hot glove" and simply wiping the ash off of the coil. The first year I had the coil I didn't clean it while the stove was running and it developed a thick layer of baked on ash that no doubt inhibited some heat transfer and made cleaning the coil a real chore.

Here are some pics of my setup:

I have two 21T's installed in my stove, in series. Before I continue, you might be interested in this read: My HW coils are looking rough after summer in damp basement

I have them connected to my boiler. My install: The project has begun: Harman Mark III heating coil install - Yes, the fire has to be going pretty good in order to produce any heat. Basically it takes a looong time to heat the boiler up with these, so if I have the heat turned on by thermostat upstairs, these will just supplement the oil burner. In warmer weather with little or no heat demand from the boiler, I have got the water temp up to 264*!! This is one of the reasons I'm waiting until Dec. 1st to light up. But when the boiler temp is that hot, I need to be careful with the DHW -- SCALDING hot!!

& yes, keep them clean. I believe this was part of my problem that lead to what you saw in that first link.

stokerstove wrote:
I see one major difference between your setup and mine which is the height of the coil. My coil is directly over the grate and is adjustable to keep the coil over the fire. I have been using this setup for over 10 years. Another thing I have myself trained to do is clean the ash off of the coil everytime I empty the pan. I do this using a "hot glove" and simply wiping the ash off of the coil. The first year I had the coil I didn't clean it while the stove was running and it developed a thick layer of baked on ash that no doubt inhibited some heat transfer and made cleaning the coil a real chore.

Here are some pics of my setup:

After my intall and watching the fire it does seem the coil is to far back and to high above the fire. I see you are right over the flame. I think i will just get a additional coil and place this one lower and to the front so it is over the fire, and just tie them togher.

I think if your just heating DHW, you should be good with the coil you have. I see your from Maryland and your temps are in the 50's daytime and 30's night. The stove just isn't running hard enough yet to really heat the water. You are saving money still by having preheated water. Once the daytime temps drop into the low 40's and 20's @ night you should see a big difference. Keep in mind the recovery time using a coil of this type in a stoker stove is going to be much longer than a traditonal HW heater or boiler. I'm only running a single loop coil and have found it works well. Just needs to get colder.

Jeff

Few things i could do that would help. My tempering tank in only 40 gallon and that water does get pretty hot when the stove gets running above 50%. But one shower or a load of laundry and the temp drops back quick. I have a kickspace heater that i install that feeds a utility/mud room that has no heat and know way to run air duct, so i was really hopeing i could run this heater more. It will only run a few hours and it will drop the 170* water down to below 120*. I was thinking if icould install the second coil i could run this heater more and it will help move some heat into a room that doesnt get the radiant heat from the stove. Also i think i will look for a 80 gallon tank to use and store up some heat when the stove cranks up.

i knew this was going to be a trial and error project. I will wait and see how it run when it gets cold. then decide what type of reworking i will to do the system come spring.

So far for the limted budget i have been working with i am rather impressed. Just under $3000 for the entire project including the chimney, stove, coil, pump and plumbing.

TdiDave, are you using a pump or thermosiphon? I'm using thermosiphon and found that if the bottom of the tank is not at least even with the inlet of the coil where it goes into the stove, I wasn't getting the whole tank up to temp. I raised the tank so the outlet (where the drain is) of the tank was at the same level as the inlet (on the stove). This made a big difference in the amount of water I got. Don't ask me why, but it did help. Just something to look at. Good luck.

Jeff

The outlet of my tank is even with the inlet of the coil. I do have a pump but have a aquastat. Have been playing around with using the pump & just letting in thermosiphon. It seems that the thermosiphon works better when at low fire, i think the pump moves the water to fast. I do se a nice 20* difference from inlet to outlet on the coil using thermosiphon. But if coil intel temps drop to 60 it will only be around 100 after about 8 hours.

I like your setup. I was going to make some changes to mine this summer but never got around to it. Now I'm glad I didn't. I like the temp. guages on the inlet and outlet so you can see the difference in temp. As I said before, once the temps drop and stay there, you will see much more hot water than you are seeing right now. I was concerned at first with the temps I was getting and was told to be patient, that it will work out for me once the temps drop, which it did. Also as I said, last year I had it tied directly into my HW lines and it supplied enough water so I cold shut the NG heater right off. I just found that to be kind of a pain when the temps were a litle higher in the spring and fall. I had to relight the water heater and switch the valves so I had HW. At that point I ran my coil tank to my NG tank and used it as a preheater. When its cold out the only time the NG tank fires is to maintain temp. When we use HW the NG doesn't usually even fire. And i'm only using a single loop coil.

Jeff