Pressurized outdoor wood boiler with backup propane combi boilerCombi

Sasquatch

Pressurized outdoor wood boiler with backup propane combi boiler. Having issues with overheating. Should i add a strap on aqustat. Or a thermal plate? Changing all 4 relief valves and a door seal on the stove. But what can i do to prevent overheating? Is there an alarm available to know when to snuff the stove?

Jamie Hall

Wood boilers -- or coal -- are very much subject to overheating. What controls the inlet draught damper? Even with good control on the draught, they will overheat -- it's the nature of the beast. You need a dump tank with a separate pump and aquastat.

The aquastat can also activate an alarm, if you wanted.

hot_rod

Build a smaller fire!  There needs to be some air entering the firebox or else the fire smolders, smokes and goes out. Even small amounts of air or occasional bursts of the fan can cause overheating on low or no demand conditions 

So either load it lightly, in mild weather, or add a buffer that could absorb a burn cycle, or a dump zone. They can take more fire tending on low load days then fill out design days. Adjusting the burn to the load is part of solid fuel burners.

GroundUp

What model wood boiler? Is it set up as a constant circ system with 24/7 flow through the water jacket?

Sasquatch

Looks homade its in my workshop yes 24 hour flow

Sasquatch

Looks like a some kind of thermal valve. Shuts the damper down after 15 mins of running

Jamie Hall

Unlikely to be adequate. 15 minutes of burn, if the thing is really going, is going to be a lot of heat. You really need an aquastat to activate a dump zone. That should be a tank which is large enough to absorb all the heat from a single, full load fire without overheating, starting at some reasonable temperature for the system as a whole -- perhaps around 110 F or so.

Properly set up wood (or coal) burning systems should, in my humble opinion, be able to close the draught essentially completely in the event of over pressure or over temperature -- either of the water or the area around the boiler) and, as a backup, have a big enough dump tank to handle a full load of fuel at any damper setting.

And they should be able to do all that when the electricity fails, without operator intervention. This takes some thought -- but it is preferable to burning the place to the ground.

hot_rod

A low water cutoff is a good idea also. If they over heat an pop the relief, you could dry fire

The cutoff switch need to close off air 100% as Jamie mentioned.

wood burning for heat is an interactive hobby.

Sasquatch

Going to separate the combi from woodstove, and put a few fan style heaters in the basement. Keep the two loops seperate. Anyone have an install diagran for a a pressure wood stove install?

hot_rod

What is your goal with separating the two heaters?
Your first post was regarding over-heating?

In this Journal you will see some common piping and wiring ideas. The cover pic is the most common. that buffer tank could be a hydraulic separator if you don't want to add a tank?

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10_0.pdf

Also a pic of an excellent text book Heating with Renewable Energy on all sorts of wood and pellet systems.

A pic of one method to pipe an overheat loop. The one pictured is for protecting from overheating in a power outage. It could also be triggered by a high temperature condition, dual protection.

If the systems are combined you could use one of the heating zones you already have for over heat protection. A garage is a good dump zone, instead of over heating a living space. At least the excess heat is in a place you might want it.

leonz

Sasquatch said:

Pressurized outdoor wood boiler with backup propane combi boiler. Having issues with overheating. Should i add a strap on aqustat. Or a thermal plate? Changing all 4 relief valves and a door seal on the stove. But what can i do to prevent overheating? Is there an alarm available to know when to snuff the stove?

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If you would like some friendly advice from someone who burned wood and coal in a hand fed boiler for over three decades remove this boiler and invest in a new one.
A homemade boiler will not pass a plumbing inspection nor will your insurance cover a fire loss.

You need a properly designed indoor wood boiler that is UL and CSA listed, has a firebrick lining, at least one low water cut off and mechanical aquastat controls.