increase storage capacity with high capacity baseboard

Not to hijack the thread but where/who supplies the high temp liner you mentioned.

ssfein said:

It would seem that you could increase the effective capacity of your storage by either raising the temp of storage to 190+ which would necesitate more expensive liners for thoes who have unpressurized tanks ( 4x4x8 at about $800) Or use high capacity baseboard to get more btu out of lower temp supply water. My house has slant fin 80 which is rated at 730 btu at 180F much lower at say 150F. The slant fin 95 is rated at 756 btu at 150F. Does anyone have experence with this issue? Any sources of slant fin 95 you know?
Thanks

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My advice to anyone planning a wood boiler is to put in more baseboard than you think you need. The more you have, the longer your storage will last. High output baseboard seems like a good idea, but more feet of standard might be cheaper to get the same result. Adding a radiant zone is another option for some.

It would seem that you could increase the effective capacity of your storage by either raising the temp of storage to 190+

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In my experience, this would be very difficult to do. The Tarm internal aquastat is set to shut the draft fan off at 190, back on at 180 (I think). When the draft fan shuts off, boiler temp will continue to rise to about 195 before starting to fall. In my setup an "off" cycle is about 15 minutes. Assuming the boiler continues to feed storage during the off cycle, and boiler cycles on at 180, actual boiler temp will drop to about 170 before the boiler temp starts increasing again. And as return temp rises above 150, cycling becomes more and more frequent, which increases inefficiency. I've never pushed my system to the max, but I think it would take a real effort to bring the 1000 gal storage to higher than 170 at the bottom, 180 at the top. I'm also using a plate hx, which at the top end will have a differential of about 3-5*.

In general I get no cycling as long as return temp is below about 140-150. Perhaps I could do better with higher flow rate.

In an ideal world, it would be desirable to modulate the burn and/or modulate the water flow to keep boiler temp just under maximum (190) so that it would not shut down.

With this thought in mind, has anyone experience with a variable speed pump that increases flow as temp rises? Or a draft fan controller that reduces draft as temp rises to slow the fire down? Does this make any sense? Would there be other problems?

I dont have to worry about a draft fan. I run my boiler straight out. As temp reaches 180-190 in the tank- my boiler temp will run 200 + . It does not seem to be a problem as the system pressure does not get high enough to activate the pop off... I try to load the boiler so I dont overheat the tank but sometimes I over do it Also, if it gets dangerous I lower the temp on the Samson and kill the combustion air to the boiler.

How do you know what the BTU rating on your baseboard is? In my cellar I have about 75 feet of copper-finned baseboard (this will be my dump zone for an overheat/power-still-on situation), but I also need to have 20K BTU of dump-zone for a gravity loop for the power-out situation. I have an extra 14 foot piece of superheavy cast-iron baseboard, plus 2 more 7 foot pieces to use. Hopefully one or both of these would work without a need to purchase something.

*edit off-subject*

MrEd said:

How do you know what the BTU rating on your baseboard is? In my cellar I have about 75 feet of copper-finned baseboard (this will be my dump zone for an overheat/power-still-on situation), but I also need to have 20K BTU of dump-zone for a gravity loop for the power-out situation. I have an extra 14 foot piece of superheavy cast-iron baseboard, plus 2 more 7 foot pieces to use. Hopefully one or both of these would work without a need to purchase something.

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The manufacturers website for any brand of BB will have output data for a corresponding temperature. You can roughly figure about 500btu per active foot of most brands at 180* water. High output will be 15% or so more.

As a general rule, it's always a good practice to design a BB system with excess capacity. It just gives you more flexibility in water temps you're able to utilize.

Handling lower water temps while still providing good output is a big advantage of a panel radiator system vs baseboard. You get radiant heat (long wave radiation) as well as convective air flow from a panel rad. The only, and I do mean only, advantage baseboard has is first cost. Baseboard always looks like heck within 5 years, it always falls apart and it's not nearly as comfortable as a panel rad system.

Now.......Cast iron BB is a whole 'nuther animal. It will give you a little radiant output somewhat like a panel rad will. Plus it will still be in one piece after a few years.