Always a fly in the ointment!

Tom_133

Hello All,

So I am quoting a job for a local company that needs a boiler. It should be a simple chop and swap, but no.

The old boiler is a condensing NTI that is 18 years old, and has more than 100k hours on it. It has been terrific. The system is very poorly piped and really should never have worked but it's been going strong. Here is a quick diagram so we can all see how forgiving hydronics are.

The question I have for all is that when I install the new TFTN boiler I cant leave the putrid piping the same, I want to fix it. The problem is the budget is quite tight and was curious if anyone has used the DHW circuit as a zone of heat and just set the boiler settings to see it as a high temp zone and give it priority for 30 mins, then swap back over to low temp for the slab in the rest of the building. The slab actually doesnt call often due to the heat pumps, and the ambient room temps because this is a bakery. I hate the idea of this but they dont want to pay to do a full repipe, I am open to ideas. I could leave the injection the way it is and just make a true primary secondary, but I like the idea of the boiler condensing as much as possible and using the high temp only occasionally

pecmsg

Is that allowed by the boiler manufacturer, or the Local Authorities having Jurisdiction?

Then NO.

Tom_133

I apologize if thats not even allowed! I had no idea. Was just a thought.

pecmsg

I’m not sure either. Here I don’t think the inspector would approve. But that’s here.

Contact your local building department

Contact the manufacturer

Tom_133

The manufacturer shows a couple different uses, one interesting one I didnt think of was a buffer tank. If there was room and funds were available, I could put a tank in, and feed that zone.

Jamie Hall

If I were still your AHJ, @Tom_133 , I'd take a close look at what the boiler literature had to say — and maybe talk to their rep. — and then I'd say go for it. But I'm not your AHJ any more…

But I can't see a good reason why it wouldn't work just fine.

hot_rod

nany if the mod cons gave multi temperature zone ability built into the control, what model are you considering?

EdTheHeaterMan

In order to be more clear, Does your piping look llki this for the DHW and the Baseboard zone?

Otherwise I can't see how the DHW or the Baseboard are getting any heat. Is the expansion tank connected to the Spirovent?

If on a budget, then you leave the DHW and the System Circ pumps in place. exclude them from your warranty on materials and workmanship. Use the mixing station to provide the lower temperature and exclude that from your warranty for material and workmanship.

In order to provide high temp heat from the DHW circuit on the boiler will be problematic. The boiler does not have the capability to operate at low temperature and high temperature at the same time. Allowing only high temperature from the DHW circ to the high temperature space heat zones for a 30 minute max time may be insufficient when you get close to design temperature. (what will you do to fix that when that time comes and you are neck deep in emergency calls due to the cold weather?)

Finally, it appears that you have 2 circ pumps on the low temperature circuit. Is that correct?

Looking foreword to your response

Sincerely

Mr.Ed

Tom_133

https://forum.heatinghelp.com/discussion/comment/1809240#Comment_1809240

Hey Hot rod,

I was hoping we could as a group chat about how that works, I am pretty sure the NTI TFTN boiler that I plan on using can do that. Not sure exactly how that works on the boiler/piping side.

Tom_133

Ed,

The DHW is being done away with, I have that one small baseboard zone, and there are probably 5 pumps on the injection side. The 5 zones are all concrete radiant zones. I really wanted the boiler to do the thinking and handle the outdoor reset. It's annoying the baseboard loop exists but I gotta make it work.

hot_rod

As I recall all temperature zones are piped into one header. The boiler changes output temperature as various zones call. It does have some overlap however.

If you want two temperatures at the same time, you will need a mixing device.

If you only have one low temperature zone, a manual mix valve works well. Boiler runs on ODR for the high temperature, the low temperature "floats" with that reset temperature.

Tom_133

thanks Hot Rod,

Thats how I saw it happening as well. The guys who put that baseboard zone in years ago got cheap on the baseboard and it runs alot. The radiant is in concrete so it has pretty long run times as well. It's a bummer, I wanted the boiler to run at 110 or less whenever possible. He doesn't want to spend the money to fix the baseboard zone either… I tried.

mattmia2

I think some could be set to run 2 different ODR curves depending on which zone is calling so if only the radiant is calling it fires at a lower temp based on outside temp. If the baseboard is calling then the radiant gets whatever the mixing device is set to, if only the radiant is calling the boiler only heats it to the odr curve for the radiant and the mixing device uses all boiler supply water.

mattmia2

But you want to do cadillac work and they are willing to pay for a focus.

Tom_133

If you have never been to Vermont thats the slogan, Champagne taste on a beer budget!

Anyone want to suggest a mixing valve? Man as you jump up to 11/4" it gets pricey! Each zone has a taco 007 on it, and there are 5 zones, of varying sizes and amount of tubes.

Man it bugs me I cant just make this work, but that one zone of high temp is a pain. I do also have a 20 gallon buffer tank I thought about tying in to the DHW call since the boiler can be adapted to a buffer tank or DHW. Then I could pull the zone off that, and that would be simple, and the tank may help.

EdTheHeaterMan

Eliminate the high temperature zone completely….

Then the boiler will do the temperature modulating and operate at the best efficiency with all that low temperature water.

If the baseboard zone can operate off of the replacement water heater with a heat exchanger, or perhaps a dedicated small electric boiler. or a separate gas boiler that also makes DHW using an indirect, or a combi boiler/DHW thing.

Or just let you mother-in-law live in the baseboard heated area with no heat… That'll get her to move to the retirement home sooner!