Triple Pass oil Boiler set up as cold start

jessedominick

I have a brand new boiler in a almost completed new home. It's the smallest Burnahm MPO IQ. I live in Southeast Alaska. It currently averages 20 degrees F. The plumber and electrician have wired this boiler to drop to room temp if there isn't a call for heat. Even when the outdoor temperature is very cold the boiler temperature will rarely get to 180°F. It's hard to tell how it will change when the indirect hot water heater is hooked up. Right now the hot water tank is installed on a zone valve but not wired in. There are three in floor radiant heating zones plus the indirect hot water heater. The first zone is a radiant slab for the downstairs. The second two heating zones are staple-up radiant in floor heating for the upstairs.
I know that many people on this forum will say that it is OK to have a triple pass boiler be set up as a cold start but it clearly states in the manual to avoid prolonged return water temperatures below 135°F because of the risk of condensate in the exhaust system. If these boilers are designed to be cold started then why would anybody ever hook up their outdoor reset card? The outdoor reset would be completely useless for me with the system set up as is right? My main concern is the build up of condensate in this boiler. most of this is all new to me but I come from a background in aviation where you always follow the manufacturers recommendations and you always go off of what the manual says. Please help clarify.
Thanks,
Jesse

STEVEusaPA

Your assessment is correct. It depends on how your boiler is piped. You should have a piping bypass installed to mix water leaving the boiler with the colder return water. This will keep condensing to a minimum, if at all.
Primary/secondary piping would help also, but the bypass is the solution.

jessedominick

It currently does not have a bypass. As you could imagine this plumber has me pretty disappointed. I could insist that he install a bypass but if he is not willing would you recommend re-wiring the boiler to run in a traditional manner, as in 160-180 F? I appreciate the input.
Jesse

Zman

The radiant heat running at 180 is a real problem, especially the slab. That is why it does not get to 180.
You can accomplish boiler condensate protection and outdoor reset by using a taco i-series mixing valve. Probably one for the slab and one for the staple up.
The house will be more comfortable with less overshooting as well.

DZoro

Jesse you need a bypass. You are correct and so is the manual. Your plumber needs to install it. Period. You need to protect your investment, you will ruin it with constant low water temps. Or he needs to provide proof that the boiler water return will stay at 145* or more. At the very least provide a return water temperature gauge at the boiler return line.

EBEBRATT-Ed

Both @Dennis & @Zman are correct. Your radiant temperature to the loops cannot exceed 120 supply and it is absolutely required that the piping and controls accomplish the following:

return temps stays above 130-140
supply to the slab is 120 or below
the boiler must be capable of at least 150 to get DHW out of the indirect.

This can be done with proper piping and mixing devices. Your plumber needs to do his homework. But, he probably won't. So provide him with a drawing. There is more than 1 way to do it. Look in the store on this site and by John Siegenthaler's book.

You need to get this right at the beginning or you will be very unhappy

jessedominick

Thank you guys so much for the input. I can maybe show this thread to my contract to relay to the plumber so he is aware of how far off the plumber really is. I'm glad the manual is right. What is "cold start" then? And why do so many people on these forums say that a triple pass boiler can be set up as cold start? Thanks again.
Jesse

Canucker

They can be set up as cold start but that assumes that it gets to operating temperature within a short period of time. Your radiant heat will keep the return temperature below the condensation point of the exhaust causing it to rot out the heat exchanger very quickly, which is why it needs a bypass

STEVEusaPA

Cold start simply means the boiler won't maintain temperature, when there is no call for heat.

lchmb

generally radiant will keep a pretty constant call on the boiler anyway. I would think (specially in Alaska) that once it get's cold your system wont cycle off much.. How about some pictures of how it's piped?

Gordy

It is very possible you will need a three temperature system ability.


One for the indirect.
One for the concrete slab radiant.
One for the staple up. Which will probably need higher supply water temperatures than the slab radiant. The only way to know is through the heat loss calculation for design.

Cold start, boilers with out bypass piping, or a boiler protection valve such as @zman mentioned the taco I series is the only way to insure boiler is protected from low return temps.

Otherwise it's a crap shoot. Maybe one cycle the boiler will shut down at 150. Another it may shutdown at 110. Depends where the boiler temp is at when setpoint is reached.

Key is to have boiler at above 135 at shut down, and get above that 135 as quickly as possible during operation to burn off the corrosive byproducts of the combustion process.

EBEBRATT-Ed

Cold start is ok if the boiler reaches operating temp fairly quickly. It's prolonged operation at below 135 will damage a boiler quickly

jessedominick

Supposedly the plumber isn't quite done with the installation. When they return to do the finish plumbing they will address some issues with the boiler. There are somewhere around 19 separate issues that I found with this system. My main question is; is the bypass routed through the DHW tank? It seems the DHW circulator is in the wrong place. I understand every plumber does things differently but I can't wrap my brain around some of this. Thanks,
Jesse

DZoro

Oh my, he has not a clue to what he is doing. You said you see 19 issues, you now have more of a clue than he does. There is no boiler protection what so ever. There is no bypass. Not even close to one. If your radiant mixing valve is set properly to 120* your boiler will be bringing in at the warmest 100*. When your domestic is on and set for 150* your boiler return will maybe be 130*. Both are wrong and will kill your boiler. That is just a tip of the ice burg. What's with the black iron in what looks like your make up water? He's a plumber? He shouldn't do HVAC either. Re pipe....with the manual instructions.

STEVEusaPA

Holy pro-press!

EBEBRATT-Ed

Maybe it's me but I don't see an expansion tank

DZoro

I don't either, but hoping it is on the right and at the ceiling. Looks like there is a pipe coming off the bottom of the air vent and goes to the ceiling.....

KC_Jones

> @EBEBRATT-Ed said:
> Maybe it's me but I don't see an expansion tank

On the heating or the domestic side. Not that it's always needed on domestic, but it would be worth adding it to the list for verification. The heating side surely needs it.

All the (now) wasted press fittings, so much money.