Tarm HS4.0 boiler is too big I think

A couple of gut reactions. From your picture showing 12 firetubes, I too would estimate that this is a 200kbtu boiler. My Tarm Solo Plus 40 has eight firetubes and is rated at 140kbtu.

As to using more pellet fuel than is needed, that is somewhat problematical. The heat has to go somewhere, so unless you had windows and doors open, the btu's were going into your house or being wasted someplace else. Pellets at 7055 btu/lb net heating value, at 1 ton/week, are 0.85 cords/week at 16,600,000 btu/cord (a rough estimate for heating value of seasoned cord wood of mixed species). That might not be excessive for a house your size in particularly cold weather. You probably could benefit from an energy audit and heat loss calculation which could tell you what your heat loss is. Keep in mind that same volume of pellets is roughly equivalent to 122 gallons of fuel oil (115,370 btu/gal net heating value). Based on local prices, what are the equivalent economics of pellets vs fuel oil?

In other words, your spending a mortgage simply could be the cost of heating your home. For my wife and me, heating/utility costs were a major factor in our decision as to what size and type of house we wanted to own. Our house is 1500 sq ft with full basement, and our seasonal wood use in the cold northern Minnesota climate is 4 cords of aspen plus 1 aspen cord equivalent of supplemental electric heat. That's equivalent to about 3.5 cords of oak.

I know nothing about your Tarm pellet boiler. To what extent is it able to modulate its burn rate? The more able it is to do that, the less you might be able to benefit from a buffer tank or a larger small storage tank. The purpose of a tank would be to absorb short term excess btu's to maintain an efficient burn rate, and then to use those excess btu's when you needed more heat than the boiler was producing (or was "off").

Using chestnut on top of radiant floor heat, or any other wood floor, has more to do with the temperature at which you are maintaining the floor than the use of a wood floor. Others can tell you safe temperatures for a wood floor. All that I know for sure is that I use water at 100F for the concrete slab in my shop.

Thought you were talking about a wood boiler at first.

What is its minimum output? Which is the modulation aspect of the above post.

I also emphatically second getting an energy audit done - heat has to be going somewhere. Are you new to this house? Do you know how much of what fuel it used in past winters before the Tarm?

Going back to the winter thread, brrrr, https://www.hearth.com/talk/threads/help-with-my-biomass-boiler-tarm-hs-4-0.139337/ :

-Are the pipes in the basement still uninsulated? That would make a nice summer project, lol, especially if it's cool down there.
-The heat has to be going somewhere (maybe some to the outside through the basement via the uninsulated stuff)
-I would think that with a big boiler that turns on and off a lot, there'd be losses out the stack during startup while it comes up to temp, therefore, I bet a buffer tank would help, but it'd probably be on the large size, and have you priced any lately????
-I'm totally no expert, but is there insulation under the pex tubing in the basement under the radiant wood floor?

Are these the right manuals for your unit?
http://woodboilers.com/media/wysiwyg/Downloads/Product_Brochures/Multi_Heat_Brochure.pdf
http://woodboilers.com/media/wysiwyg/Downloads/Product_Manuals/Multi_Heat_Manual.pdf

While no doubt a big boiler, it does seem to modulate down to 30%, but then it goes into Standby since it doesn't have electric ignition.

Does it operate on Standby a lot? That's not good for creosote.

How is your boiler setup with respect to the manual? I'm thinking Table 4.1. Maybe you could set it up for low heat, if that's indicated.

I'd bet you are losing a ton of heat up through the ceiling/attic & roof. Air sealing there would help immensely.

(Nobody around here puts a heating unit in the attic - that part kind of boggles my mind, might be the unfamiliarity with the concept though...)

Any state efficiency programs you can hop on?

Your radiators and radiant floor should be running on outdoor reset to the design temperature dictated by the room-by-room heat loss (Manual 'J').

The only cure for an over-sized boiler is a buffer tank. In your case more accurately, an insulated storage tank, 500-1000 gallons.

It appears your system is only half done.

Define .....INCREDIBLE...... 7 tons? 10 tons? 14 Tons? per season....

American solar tech is an option for a. Storage tank.

heaterman said:

Define .....INCREDIBLE...... 7 tons? 10 tons? 14 Tons? per season....

Click to expand...

I read a ton a week.

I thought my ceiling and attic were insulated well. Should have been two layers of r-19. Was in most places. But not all. Had a pro tighten up ceiling. Then blow a foot of insulation in. Big noticeable difference.

a buffer tank is NOT a good solution for the Multi-Heat. Because the boiler does not have automatic/electric ignition, it cannot turn itself on and off. Buffer is only appropriate for a batch firing boiler like a wood boiler or something that can turn itself off when the buffer tank is satisfied. A buffer with the Multi-Heat would produce long idle times which is to be avoided. I think the best solution is to run it in low output mode as you have been. The dump zone in the garage is also a good idea. Two questions: what triggers the dump zone and how much fuel are you burning for the whole heating season (I know one ton per week peak)?