Added my low pressure gauge

ethicalpaul

OK well the direct relationship to that question is how oversized the boiler is. If the boiler is sized correctly with good main venting you can expect:
- During initial steam creation, prior to steam reaching main vents: basically zero PSI
- During steam filling radiators, prior to radiator vents closing: hopefully less than .1 psi
- After all radiator vents close (all radiators filled with steam). Still hopefully less than .5 psi, but almost everybody is a little oversized and steam pressure may raise during this phase

If you have .3 psi before all the radiators are completely steam hot, you are probably oversized, but not too bad. It would be way worse if you reached the cutout pressure during this phase.

Don_175

So I did a total of the EDR which I thought was accurate. Came up the 600 sf. But my boiler label says 546 sf. Would that make it undersized? 

I need to recalculate the EDR to make sure if it’s accurate. Most radiators are the tall column ones. We have one short one and a few of the cast iron cast rays. 

ethicalpaul

Based on your first post, this line:

> The gauge relatively quickly goes to 0.5 psi and after several minutes of steaming, it sits at about 0.8 psi.

I daresay there's no way you have 600sq ft of radiation with a 546 sf boiler.
Getting to .8 psi after several minutes of steaming tells me your boiler is oversized, period.

Edit: But there has been a lot of talk of a lot of gauges in this thread and later you said this:

> The new gauge reads less than 0.2 psi max after all main vents close.

With this reading it's probably pretty close. Does it ever climb? Anyway, you are way better off than oversized. I wouldn't worry about a thing.

I will say that mine is slightly oversized and my pressure doesn't rise until the radiators get fully steam hot.

ChrisJ

ethicalpaul said:

Based on your first post, this line: > The gauge relatively quickly goes to 0.5 psi and after several minutes of steaming, it sits at about 0.8 psi. I daresay there's no way you have 600sq ft of radiation with a 546 sf boiler. Getting to .8 psi after several minutes of steaming tells me your boiler is oversized, period.

Or the system is grossly under vented.

ethicalpaul

Sorry, I edited out from under you after reading back on the thread. He has a big mouth on each main and that reading is from his old gauge.

Don_175

So I remeasured all radiators and did calculations again. Still came up with 600 sf EDR. But my boiler says 546 sf steam. Isn’t the boiler sf usually more than EDR? We have no problems heating the house on the coldest days.

pedmec

Not really. If you are reading 546 as the net EDR then you are mostly likely not losing much heat thru the system piping arrangement. The manufacturers give you a gross EDR which is 1.33 times larger than the net, called a pick-up factor. this is the actual btu's that are leaving the boiler after combustion and transferred to the water. Standard practice in the industry is to assume that there will be about a 25% heat loss thru the piping. Its not an actual number but rather an approximation. Less pipe in your system, less heat loss. Well insulated pipe and fittings, less heat loss thru piping. so if your system is working fine don't worry about it being undersized. there is just less heat loss from other factors. you are probably getting a real EDR closer to 600

pedmec

Gross output is also referred to as the DOE heating capacity

Don_175

pedmec said:

Gross output is also referred to as the DOE heating capacity

Oh. OK. So if the net is 546 sf, with the pickup of 33%, it should be about 700sf? (546*1.33)?

pedmec

That is it. as long as the 546 is the net output your reading from the tag.

ethicalpaul

Well to be clear your sq ft of steam should match your radiation EDR, but 10% low is fine because as described above the manufacturer's build in that extra padding. You are fine.

Don_175

Thanks guys.