Combi-boiler, cold rooms and two types of radiators

aw273

Thanks Ironman - I'm not disagreeing with you, I'm just relaying what I was told. It was also a warranty replacement, so this Tech would not have changed the tank size, anyway.

Ironman

I know you're not. I just amazes me how a parts changer with no real hydronic knowledge will spout of something like that without even checking to see if it's true.

I just ran it on Amtrol's sizing tool and using the quick residential calculator it recommended an SXV 30 floor tank which has an acceptance volume of 11.3 gal. Your EX 30 tank has an acceptance volume of 2.5 gal. Can you see the difference? You need a tank that's almost 5 X the size you now have.

Their commercial calculator called for an AX40V which also has an acceptance of 11.3 gal.

aw273

I know this tech isn't the best (everyone I've spoken to on this board or in real life dismissed the idea of cleaning out the radiators as the solution), but I would have thought the installer 6 years ago was capable.

I have them coming out on Tuesday and I'll specifically ask about a bigger tank.

I just double checked the pipe diameters and they are 2.5" and 2" in the laundry room, and then scale down in the first 8-10' to 1.5" and 1" pipes. It is a mess of old iron and then copper, where past home owners have renovated.

aw273

Ironman, out of curiosity, I went to the Amtrol calculator and at the max BTU for my boiler from the Navien site*, it told me the EX 30 if I select finned baseboards and EX 60 if I select Cast Iron.

Most of my system is on the finned ones (10/12 radiators).

And the 30 and 60 have a 2.4 G and 2.5 G acceptance volume, respectively. is that a big difference? and what should I adjust to get the recommendation you got for a larger tank (i.e. what am I doing wrong)?

*(I read max for my combi is 120,000 btu and I put 125,000 in the calculator).

Ironman

Here's' a copy of Amtrol's residential sizing chart. You need to insist that they follow this, not their opinions.

Jamie Hall

And there isn't any need to switch out the brass radiators. With some thought and intelligent work, honestly pretty much any radiator can be balanced with any other. Don't let them do it.

So far you've had some good advice from the good folks above -- and some not so good (if quite understandable) advice from someone local. Where is this project? It may be that we know someone nearby who might be able to swing by and take a look -- and whom we could vouch for.

aw273

Hi Jamie,

We're in Toronto.

Ironman, what's the difference between the SX series and the EX? the SX seem like higher volume for the same BTU's on their website.

thanks,

aron

Jamie Hall

Oh dear. Toronto. Nice city... if you like cities. But I don't think we have folks up that way (there's a good man in Montreal, but that's way too far!).

That being the case, do the best you can with your "techs" -- and tell them to listen to @Ironman -- he really does know what he's doing.

aw273

Thanks Jamie,

My understanding is that the boiler has a max temperature of 180F which is about the minimum for the brass radiators and then they have no thermal mass once the boiler stops running, which are both contributing to the discomfort in the house.

Believe me, I don't want to change anything if I can help it. That's one of the reasons why I'm here.

I really appreciate the advice from Ironman and you and everyone here. It is helping me learn a lot. I need enough context to have an intelligent conversation with the local "experts," otherwise they can just jargon me into whatever they're recommending. So the more I understand the more empowered I can be.

and of course, on this forum, the only advice people can give me is based off my own poor descriptions and semi-understood information, so I might be causing my own confusion

aron

Ironman

aw273 said:

Ironman, out of curiosity, I went to the Amtrol calculator and at the max BTU for my boiler from the Navien site*, it told me the EX 30 if I select finned baseboards and EX 60 if I select Cast Iron.

Most of my system is on the finned ones (10/12 radiators).

And the 30 and 60 have a 2.4 G and 2.5 G acceptance volume, respectively. is that a big difference? and what should I adjust to get the recommendation you got for a larger tank (i.e. what am I doing wrong)?

*(I read max for my combi is 120,000 btu and I put 125,000 in the calculator).

You're correct about the 120k btus instead of the 200k. But this is why I said that it needed to be calculated with the commercial calculator because of the water volume in your large pipes. The residential calculator doesn't factor that extra volume in, it just uses a generalized factor based upon btus. The commercial is a scientific one that doesn't use btus, but water volume and the amount of degrees it's heated. You also have two cast iron rad's that factor in. Covering them with blankets doesn't change that.

The commercial calculator called for an AX 40V which is a commercial tank that has the same acceptance as the SX 30V which is a residential version.

You cannot over-size an expansion tank (within reason), but you most certainly can under-size one as you're experiencing. The cost of the SX30 is not significantly that much more. Go with that one and the problem will be gone.

Isn't that what you want?

aw273

Absolutely!

And appreciate the added couple of points:

1) you can’t really oversize an expansion tank, and
2) the difference is the extra water in the bigger pipes

That gives me a lot more ability to pushback if they try and tell me a larger tank isn’t needed.

Jamie Hall

OK -- you have the tank to fix now! Pity we don't have someone nearby to play, as there is a way -- indeed, a rather simple way (if you know what you are doing, that is) to handle the low mass brass radiators. That is, moderate the water temperature from the boiler to match the heat demand, and keep the water circulating all the time. You may have read about outdoor reset -- and that is the principle behind it. In your situation you might have one zone for your two cast iron radiators and another for the brass (although that might not be needed). The controls would be a little more complicated than just a thermostat!

Another approach might be to play with the thermostat, either the anticipator or the cycles per hour setting. Having the boiler coming on more often, but not for as long a time each time, might even things out more, too.

neilc

@Jamie Hall said:

Oh dear. Toronto. Nice city... if you like cities. But I don't think we have folks up that way (there's a good man in Montreal, but that's way too far!).

That being the case, do the best you can with your "techs" -- and tell them to listen to @Ironman -- he really does know what he's doing.

maybe the good guy in Montreal knows of a good guy in Toronto ?

Jamie Hall

Well, he might... it's @Henry

hot_rod

There are plenty of qualified hydronic companies in the Toronto area. Where about are you located?

The wholesalers often know which contractors are the most knowledgeable, so do manufacturer reps.
If you call a wholesaler ask for the hydronics department.

Equipco is the Caleffi rep for that area, at least one of them has been a contractor and would know who to call. Let me know if you need a contact.

aw273

Sure Hot_Rod a contact would be appreciated

mikeg2015

The pressure reading on the display is on the discharge of the internal pump not the outlet. It reads a bit 5psi high. 20-25 is normal for these boilers when running m. I think it fills to 17-18 static. That parameter can be lowered.

Why the mixing valve on the domestic? The system has a minimum flow and it’s even more touchy in the combis I’ve found and will cycle on and off and may not play nice combined with the check valves in the mixing valve. I’d ditch it altogether and just set it to 120 or 125.

That expansion tank is too small if you have larger steel pipe in the system and are running higher temps.

The upstairs nearing issues could be air locked or a balancing problem with how he piped it. Should have reduced to 1” for each some if each floor can be isolated and used separate pumps for each Zone. Maybe I missed that in another post.

mikeg2015

Just demand the bigger tank. There isn’t a huge price difference. He’s lost 2x that in call backs already. Too big is not a problem either. About EVERY commercial “engineered” system I’ve seen has an undersized expansion tank because they used the wrong data somewhere in their calculations.

mikeg2015

One more note. If you are running higher water Supply temps, you may need to slow down the internal pump to reduce return water temps so the return on the secondary loop matches the primary. That internal pump is I think around 5-7GPM from low to high from the estimates I’ve run Thats with glycol so maybe a little higher with water.

The opposite can happen. You supply 180 but secondary flow rate is higher than the internal pump so the radiators only get 170-175.

hot_rod

You can also add an additional exp tank instead of replacing the one if it is too small.

hot_rod

aw273 said:

Sure Hot_Rod a contact would be appreciated

I'll get some names to you today

hot_rod

I'll send you a private message with 3 names and contact info. You should have a mailbox at the top right of the header here. if not send me an e-mail bob.rohr@caleffi.com

aw273

found them, thanks!