a little perplexed

ElderGreen

My brother has a tarm wood boiler in series with his weil mclain boiler. recently done. weil mclain boiler also weas used for hot water via the tankless coil. now he uses the wood boiler as the primary source of heat. the oil burner on tghe weil mclain has been shut ott manually. so there is no fire in the weil mclain at any time, and firomatic is closed going to it. but he still gets hot water out of the tankless coil even though there is nothing firing it.  i checked the water temp coming out of the wood boiler going to the non-fired oil boiler and the temp was 250 deg f. I'm thinking just the heat of the heating water circulating through the unit is heating the tankless coil.  Is this possible?

Tom_133

Series...

If it is piped in series than sure the wood is maintaining the temp in the weil mclain, I don't believe series is the best or most efficient way to pipe it but it will keep temp. 250f seems about 60-70 degrees too high though!

icesailor

250 degrees"

I never trust gauges for accuracy.

That said, if the gauge is within 10% of accuracy, the system is a steam bomb, waiting to expand.

How else were you going to get hot water if not from the tankless on the boiler?

ElderGreen

not my work

this is not my work, but something my brother had done. He was under the impression that the tankless coil was in series with the rest of the boiler water until I told him that's not how it works. When I was there looking at it I asked him how he was getting hot water since the weil mclain was not being fired. He said "Well, the other one is pumping through the coil" which it is clearly not. I explained to him that the tankless coil is a seperate circuit of water isolated from the hydronic circuit.  So i'm thinking that since the cutout temp is at 250 degrees on the wood boiler the hot water coming from it is so hot that it is radiating through the tankless coil keeping it hot. Unless the tankless has a horiific leak and is sharing water with the hydronic system. Anyone ever seen a setup like this? The temp cutout should be more like 200 right?

Jamie Hall

That tankless coil

in the Weil McClain doesn't care what's making the water hot on the outside of it, just so long as it is.  In this case, it would appear that the hot water from the wood furnace is keeping the water in the Weil warm enough so that you get nice hot water just as you usually would -- except that you don't have any control on it.  In the warmer parts of the year, when he is using the wood boiler less, he may find that he doesn't get the hot water he would like.



And as ice says, if that thing really is running anywhere near 250, it's a bomb waiting to go off.  It was my impression -- correct me if I'm wrong -- that on a hot water system there should be a pressure/temperature relief valve which should open at not more than 210.  If there isn't, you might consider one... before you go into orbit... and reset whatever is controllng that wood furnace to hold the water temperature below 200 or so.

ElderGreen

valve

pressure relief valve is on there but obviously not functioning properly. He's got some work to do

Jamie Hall

Not just pressure

The relief valve must open on temperature as well, at below 212.  Otherwise if, God forbid, the pressure valve opens when the temp is above 212 he's likely to get the whole thing flashing into steam and, quite literally, exploding.



That puppy is just plain dangerous until he gets the proper safeties on it, and I wouldn't want to be within a city block of it when it's running.

ElderGreen

gonna fix tonight

I called him and told him we need to change that today. Pressure relief valve change and control the size of the fires in the unit. There is no heat dump zone for the unit so I guess controlling the fire is paramount. Will also have to come up with another way to heat domestic water

SWEI

buffer tank

Is simpler than a dump zone.  A standard (tank-type) electric water heater will do this at the lowest cost.  Don't hook up the elements.  You need to pump enough water to keep the temps under 160F and it needs its own relief valve.

ElderGreen

so the water will

cool off enough just going through the hot water heater that;s not powered? If so then that sounds pretty good! 80 gallon enough?

zacmobile

storage

Tarm boilers & indeed any other gasification wood boiler worth their mettle usually employ large amounts of water storage (buffer tank) to extend burn times & burn efficiency.

Paul48

Not Potable!

Please........That water is heating system water only!

SWEI

water won't cool off

until you pump it out into the distribution loop.  The point of the tank is to let the boiler burn the whole load of wood without overheating or needing to be choked off.



How many pounds of wood does the boiler firebox hold?

icesailor

Bomb Making:

Your brother has a future in Bomb Making. Like the one on Mythbusters with the electric water heater and the plugged relief valve.

ElderGreen

I realize this is not potable water.....

this was a used tarm given to him that someone installed pretty ridiculously.

ElderGreen

i see,

increase the volume of water through a buffer tank to maximize cool down through more water

ElderGreen

thanks for reinforcing the

fact that the relief valve needs to ALSO go off on high temperature. My brother was arguing with me about it saying  only a pressure valve for 30 psi.

ElderGreen

T&p valve must open

below 212 degrees, what psi should it open at, 30? Do they make such a combination?

SWEI

buffer tank

just holds BTUs.  The more gallons of water in the boiler and buffer tank, the longer the boiler can run without blowing the relief valve or being choked off.  You want the boiler to run until the wood is consumed, without having to choke it off.  The nominal boiler output (e.g. 102,000 BTU/hr for the Tarm Solo Innova 30) tells you how many GPM to push through the boiler and what size pipe and pump to use on the boiler loop. The weight of wood in the firebox tells you how many BTUs will be produced by that load.



The best way to handle the distribution side is to use a motorized mixing valve with an outdoor reset controller.  If you don't understand what this all means, you might want to consider hiring someone to design this system for you.  The increased comfort level in the house alone will be worth it.

icesailor

You know,

You know, if you take an 80 gallon electric water heater and connect it to the tankless like I do on "normal" jobs, you could get the best of both worlds. You get a T & Pr relief valve on the tank, and the indirect (tankless) coil in the boiler will act as a heat remover. It takes a lot of nuts to heat the water in a water tank of 80 gallon size. AND, as the fire goes down, the fire side can remove heat from the domestic side. You can shut off the burner and not need hot water. If the fire side is cool from the end of a burn and you want hot water, turn on the burner.  The water heater works both ways.

There's a better way to do this, You just have figure out how to do it.

ElderGreen

I looked into taco mixing

valves and outdoor reset controller. So I take it to put in the proper t&p valve we need to calculate the btu rating

icesailor

Opening Pressure:

The opening pressure for a T & Pr relief valve is supposed to be some percentage above the tank working pressure. I can't remember what it is. I could look it up. Its all in MGL Chap. 142.

ElderGreen

30 psi for pressure

and 210 for temp. do you know if they make such a valve?

ElderGreen

30 psi for pressure

and 210 for temp. do you know if they make such a valve?

icesailor

No,

I doubt that they do. 30# potable water systems are few and far between and the blow off pressure must be a percentage above the working pressure.

SWEI

BTU rating

You need to know is the total for a full load.



Icesailor also suggested another option below, assuming the boiler has a tankless coil installed.



Edit: PRV would be sized to the maximum output rate of the boiler.  Allow a bit of headroom on a wood gasifier as they can really crank out the BTUs at peak burn.  With a residential gasifier you can use a 500k BTU PRV, which can be had for under $20.

pipeking

BOILERS DO NOT HAVE TEMP RELEIF!!!

  releif valves for boiler r presure only.  they r based on btu/h.