Print

[dhymers]

Hi, to start, I am completely green to boiler systems so please bare with me..I recently bought a 150 year old house which has a wood doctor and indoor oil fired boiler system for hot water heating. The wood doctor is 12 years old and the boiler is a little older than that. 

I am having issues with getting heat to the boiler.  My wood doctor is set at 200 degree's and the return water is about 198 when I checked it the other day on the return line after the heat exchanger.  I can only get the boiler up to 140-150 if the heat is on. If I turn the heat completely off (Shut the return line valves) over night the boiler will come up to 190-195, and through the day if just using normal domestic hot water the boiler will maintain around 160-170. (again if the heat is completely shut off)  Today it was below freezing and had the heat on all day and the highest the boiler temp came up to was 145 degrees.  I have a Seces B180 heat exchanger (Believe this is 180,000 btu) and the circ pump on the heat exchanger is a Grundfos UPS 15-42. It is T'd of the supply side of the boiler and back into the return side below one of the circ pumps on the return of zone 1. It has a flow valve also in the loop.  The circ pump was set at low speed when I moved in and I had tried running it at both 2 and 3 with no change.  It sounds like there is water flow through the pump, I can hear a slight difference when I close the valve to the pump.  I am at a loss on what to do next.  Change the pump, the flow valve or maybe it should be piped differently than it is....any help is greatly appreciated.  I will post a couple pics of the set up too in hopes it helps or clarifies my explanation.

Again thanks in advance, and I do have to say this is a great site full of so much info

[RSI]

I tried looking up the heat exchanger and it looks like it is a pool heat exchanger rated at 180k but.

If that is what you really have it is way too small. On a boiler system you probably get about 1/4 the btu rating.

[dhymers]

Sorry I had missed the pics...hope this helps a little as well.  PIC's here: http://s48.photobucket.com/user/davidhymers/library/Wood%20doctor

Thanks for the info RSI, I will look into replacing it than. I was told to size the exchanger I should count the total feet of baseboard I have, multiply by 600 to get a BTU requirement.  Can someone confirm this or am I totally in left field?

[hondaracer2oo4]

Yes, baseboard puts out around 600 btu per foot at 180. You needs to buy an appropriate size flat plate hx.

[slimjim]

I agree on the heat exchanger, could you draw a diagram of the routing of your piping and post it?

[RSI]

I am kind of surprised it is working as well as it is. You can't use BTU ratings on a heat exchanger meant for a pool application on a heating system. The numbers are completely different.

If you need 180K btu and are running baseboard heat I would get a 60 or 80 plate 5x12 or 5x13" flat plate. You can probably get by with a couple sizes smaller but would keep it a little oversized with baseboard.

A 20 plate would probably work better than the existing heat exchanger.

[dhymers]

I will try to get a line diagram done tonight and post it...if the installer put a pool exchanger in I would really like to confirm nothing else is wrong.  I will also measure up the baseboards and rads and post so I can get the right info on proper size of heat exchanger. 

Thx

[dhymers]

I didn't get the line drawing completed tonight but I did measure up all the baseboard and radiators.

First floor 800sq ft with 47' baseboard and a 10 column radiator. I calculated this to be approx 32,000btu.
Second floor 1068 Sq ft with 59'baseboard and a 14 column radiator. I figured this to be about 42,000 btu.
I am also looking to drop in another cast iron radiator in the workshop soon.

Currently I have 2 zones, 1 up and 1 downstairs.

I will get the line diagram of the boiler system posted tomorrow.

[dhymers]

Slimjim, here is the line diagram of my system.  Let me know if something doesn't make sense or if there is something not right about the installation so I can get fixed when I replace the heat exchanger. 

I noticed on e-bay there is some 40 and 50 plate exchangers on there for around $250.00.  Would I be safe with one of these or worth spending double to purchase through our plumbing supply shop here?  Since I am spending the money now, what size of exchanger should I be going with.  I want to ensure I won't have to change it again down the road so going with a little oversized is no problem if recommended.

I added the line diagram here:

http://s48.photobucket.com/user/davidhymers/library/Wood%20doctor

[slimjim]

OK let's start with some obvious issues, first please tell me the domestic water line connected to the wood boiler supply is for water make up and not a lame way to heat your domestic water, second, why is there an expansion tank installed on the domestic cold water? Third the tube and shell heat exchanger is installed in reverse, the wood boiler water should be on the larger side ports, this is certainly not the right exchanger as RSI suggested but if you have to use it the wood boiler water should be on the outside ports and not the ends. Fourth, the wood boiler circ should be on the supply side of the loop and not the return after the heat exchanger

[RSI]

OK let's start with some obvious issues, first please tell me the domestic water line connected to the wood boiler supply is for water make up and not a lame way to heat your domestic water, second, why is there an expansion tank installed on the domestic cold water? Third the tube and shell heat exchanger is installed in reverse, the wood boiler water should be on the larger side ports, this is certainly not the right exchanger as RSI suggested but if you have to use it the wood boiler water should be on the outside ports and not the ends. Fourth, the wood boiler circ should be on the supply side of the loop and not the return after the heat exchanger

Pool heat exchangers normally run the boiler water through the ends and pool water through the sides. Either way it is not going to transfer enough heat. If you wanted to stay with a pool heater you would probably need one rated at a million btu or more to get enough heat transfer.

You can get a 40 plate but it is probably a little too small (I am talking about ~5x12", don't get a smaller size than that)
I would go with a 50 plate at the very minimum. It isn't that much more expensive to go up a few sizes more. A plate off ebay will work fine. Or you could buy from your local dealer for probably a lot less than a local supply house would charge.

[dhymers]

OK perfect, I will be replacing the exchanger as soon as I get one sourced. I will be pricing though the local dealer, and Crane. I am not sure the prices yet,but good to hear eBay ones are an option. I will go with a min 50 plate, but would it be worth my money to go larger and if so, how big would be ideal? I don't mind spending the money to make it right.

Sorry Slimjim, I did the drawing while at the office today and didn't draw in the expansion tank correct, it goes into the top of my boiler and has a cold water line connected to it to fill, and the cold water line that goes to the OSB line is just to top up the water in it. My DHW is heated through my boiler. I will also switch the circ pump around to the other line when I change the exchanger.  Can I ask why that would make a difference?

[slimjim]

Because the circ will have less resistance on it's supply side, they push water much better than pulling, there should be no restriction on the inlet side of the circ.

[dhymers]

Ok thanks for the info, so I should probably change the circ pump feeding the exchanger from my oil boiler as well so it is feeding the exchanger correct, or not as much of a concern where it is such a small loop?

[RSI]

They can be on the return on a pressurized system.