Water Coil or Stand by Tank

In summer what is more efficient the water coil in a VF-3000 coal boiler or a separate circuit (zone valve; one circ pump on the system). I have not received my boiler yet and I am not sure how it works. I was thinking my present DHW stand-by tank may cause it to ramp up every time the water tank calls for heat. Would a water coil cause it to ramp up too or would it handle the occasional shower etc. in idle mode? Thanks -Steve

Using the coil in the boiler won't make it ramp up...because it stays up! It is more efficient to have an indirect water heater tank and let it ramp up and cool off than it is to keep it up to temp all the time. Also, it's nice to have the back up of the tank. Using just the coil if you happen to ask it for hot water jussssst as it is at low temp, you might have some cool water until it gets stoked up.

Hello Steve

My opinion FWIW is that the a seperate hotwater tank, like a boilermate, won't save you much if anything over the boiler installed coil. The reason is that the Harman boiler will be running 24/7 albeit in pilot mode, and will be idling with a water temp of about 140 to 150 degrees or so which is fine for making hot water. It won't matter if the coil is installed in the boiler or if you have a seperate tank, the boiler will still be loosing heat to the surroundings, and burning the same amount of coal. The VF3K has about 50 gallons of water so reserve capacity is very good also.

If it were a gas or oil fired system, where the burner came on just long enough to supply the heat demand, then yes the tank is the way to go.

You can buy the boiler coil for around $200 or so or spend upwards of $1000 for the tank with coil.

Pardon my confusion - it doesn't take much, but will the VF3k produce enough hot water in idle for say a shower with and flow restricting shower head without ramping up. With a 50 gallon reserve at 140-150 it would seem it would? Freddy I don't understand what you mean that it stays up. In summer the boiler would be on a low fire and a long as there is no demand for hot water how is it going to be running more than idle? I already have the boiler mate hot water on
a zone valve so I thought I would keep it that way until I wondered about the t-stat in the water tank maybe making the boiler stoke itself more than it would with the boiler coil option (which I ordered but was considering cancelling). Thanks for all you thoughts. Steve

Depending on how big a fire you have in pilot mode, and what your aquastat is set for, you should be able to get a shower in without the boiler ramping up. One shower will drop my boiler about 5 to 10 degrees. If its idling around 150 then the single shower would bring it down to around 140, may or may not get it to stoke.

I burn about 10 to 12# per day to make hotwater, not too bad given what other fuels cost these days.

I've found that boiler water at 140 will produce plenty of domestic hot water. If you had oil, you might make out by having the indirect, but with coal, you'd still have to maintain some heat in your boiler. Ramping up and down probably won't save much money.

Indirects are great for large water demand and scaling/lime problems.