heat loss in direct vent boiler out flue

Joe Brix

Don't take this the wrong way, but I don't understand why you went to the expense of buying an Ergomax for a buffer tank and then didn't want to go through the trouble of piping it correctly.

First, you had an indirect already so the Lochnivar tank with 3 large tappings would have been a better buffer and cheaper I assume.

You also ignore the best pri/sec piping scheme. Yes it would require another circulator, but it's the only way to isolate the boiler from the buffer properly.

You can't mix the supply and returns of the boiler and heating loads with out conflicting flows or requiring the boiler and zone pumps be on at the same time (cancelling some of the buffer's benefits).

I think you can still re-pipe the Ergo using the T&P and prsssure gauge ports as talked about in the other thread that would allow the zones circs run without the boiler circ. But there would probably be some ghost flow through the boiler when several heating zone circs where on at the same time, but this would be better then having the boiler circ always on.

Dave_61

heat loss in direct vent boiler out flue

I'm sorry to rehash this, but I'm trying to figure out if we should do some repiping or not.
We have a direct vent gas fired copper tube boiler to which we hooked up a buffer tank to stop shortcycling.
Our supply header and return header are piped via closely spaced tees into the boiler return from the tank.
This means that we need the boiler pump to run as long as any pump on the supply header is running.
The boiler, as I said, is direct vent. The flue rises vertically out of the top of the boiler for about 5 feet and then makes a 90 degree bend and travels horizontally about 4 feet before terminating in the sidewall.
There is an intake fan in the boiler that pulls fresh combustion air in from outside. As far as I can tell, there is no damper in either the intake or the exhaust flue.
When the burners are not on, but the water is travelling through the HX, will there be enough heat loss to warrant repiping the system so the boiler pump will only run when the burners are on?
Thanks.
Dave

Dave_61

Joe,

The Ergomax tank was actually cheaper than the Lochinvar, and with it I figured we would be able to make DHW as well.
As you know from the boiler room forum, I asked many many questions and thought it was all figured out how to pipe it. I was told to tee the supply to tank as well as house supply together. We then had all of the zones overheating as the boiler pump was pushing water through all the zones even with the individual pumps off.
The Ergomax rep then told me to repipe it as we have it, which i am not crazy about because the boiler pump must run constantly.
If we did pipe the 1.5" return header to the T&P and Temp ports (which are both 3/4"), would those 2 inlets provide the equivalent flow of the 1.5" header? What would we do....place a tee at each port and then put the T&P valve at the top of one tee and the temp gauge on top of the other tee?

Joe Brix

Yes

it would work, but the zones would not get the hotest water in the tank, since the zone circs are pulling off the return. But if you have that now and it works, then you should be OK. Pipe the Ergo's coil into the PhaseIII since the Ergo's coil wil pre-heat the inlet water, reducing the amount of time the Phase III will call for heat.

I would build a header pipe between the 2 3/4" tappings and yes put some Tee's in there to mount the T&P and guage on.

Dave_61

Thanks Joe,

everything seems to be working well with the supply out of the bottom of the tank, but we could just as easily remove the supply header from the bottom of the tank and move it to the 2 3/4" tappings on the top of the tank (as it is currently right next to the return header). Would that make more sense? Since it would not be teed directly into the boiler loop as before, we won't have any problem with ghost flow through the supply zones as before, right?
We will also be doing as you say and piping the DHW connections to preheat the water for the Phase III.

Joe Brix

Think about flow

You also have a flow check on the boiler supply to the Ergo? I would not put the zone supply on the 3/4" tappings because if you left the zone return on the boiler return, water would try to flow from zone to the boiler bypassing the tank. Also when both boiler and zone circs are running, the boiler supply pressure would cross over the top of the tank and get sucked up by the zone circs. The zone return would get pushed towards the boiler return.

Dave_61

You're right

Joe. The flow would shortcircuit around the tank. The only checkvalve the boiler circuit has is a swingcheck in the boiler supply to tank. Would we need any others?

Joe Brix

I would

think about a flow check on the zone return before it ties into the Ergo return. Don't want ghost flow back up into the heating zones when the boiler circ is on.

Dave_61

Yes,

we were going to also add that. Nothing else in boiler loop besides swingcheck in boiler supply to tank, though?
Dave

Joe Brix

Boiler supply

drops into the tank from the top tapping , so hot water in the tank would try to migrate back up the boiler supply piping, but a check valve should stop migration back to the boiler. Your picture links are no longr available, but that supply piping is a good heat trap since it drops down before going to the boiler, hot water doesn't want to travel downward. You might get a small amount of flow back to the boiler if multile 007's were running, since the zone supply still shared the return port with the boiler. But this won't be anywhere as bad as having to run the boiler circ pump all the time.

Dave_61

Joe,

one other question....when we tie the return header (1.5") to the 2 ports (each 3/4"), I was thinking we would do as follows...

At each port, have a brass tee (3/4" x 3/4" x 3/4"). On the top of each tee would be T&P valve and Temp gauge respectively.

The 1.5" return header would split into 2 1.5" pipes at a 1.5" x 1.5" x 1.5" tee and each leg of the 1.5" pipe would be brought as close as possible to the inlet pipes before being reduced to 3/4" via a 1.5"-3/4" copper reducer at the 3/4" tees. Does that sound like the best way to pipe it?

Also, currently, the return header terminates in the boiler return far below the top of the Ergomax. When we disconnect it from the boiler return, would it make sense to leave it with a loop below the top of the tank as another heat trap to prevent ghost flow? It is currently about 4 feet below the top of the tank. So would it make sense to then leave it low like that and then bring the 1.5" pipe up to the top of the Ergomax to make the connections on top of the tank (so the water returning from house zones would travel down about 4 feet below tank and then back up to top of tank?

Joe Brix

Sure

Bring the 1.5" across the top of the tank like a manifold and Tee off reducers down to the 3/4"'s. (Maybe you're describing the same thing.)

The return piping drop should be OK. Maybe put another auto air vent on the pipe drop like you had on the supply.

Does the Ergo have an air vent on it?

Dave_61

The air vent

on the tank is teed into the inlet of the Ergomax where the boiler supply enters.
For the air relief valve on the return header, I'd assume I would put it where the return header turns 90 degrees from vertical to horizontal above the Ergomax?

Joe Brix

Yes

I'd just put one in to aid filling the lines and avoiding air pockets but it's not a show stopper since you do have one on the supply pipe/tank.