Navien Combi Boiler with Hydronic Air Handler

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SeanTech

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First let me say, I am new to Combi-Boilers, so bare with me if I ask dumb questions.

I recently converted from Oil to Gas for many reasons (including getting a whole house generator). I went with a Navien NFC-200 175 Combi Boiler that is using my three existing First Co HBXB-HW Hydronic Air Handlers (one for each of the three zones in my 4BR house) and three new Taco ECM 007e Circulators. The system is using Cryo-Tek 100 Antifreeze (mixed with water) since two of the Air Handlers are in two differnt attics at different ends of the house. The three air handlers are used for both HEAT in the winter (location is New England) and Air Conditioning in the Summer. The conversion happened this week. So far the on-demand Domesic Hot Water (DHW) has worked great, having no problem keeping up with the Shower, dishwasher and washing machine needs for our home.

The question is I have is this. When there is a call for hot water, the system shuts off the three Taco Circulator pumps for the three heating zones (as I believe is normal for Combi-Boilers which prioritze DHW). If this happens when one of the zones is heating, the First Co Air Handler continues to run on that zone. Since there is no Taco circulation of hot water in that zone(s), the Air Handler quickly starts blowing COLD Air until the DHW request is completed. When someone is taking a shower this could be 20 minutes (Yeah, I know that is a long shower). I assume this is NOT correct? It seems to me that the Air Handler(s) should be SHUT OFF when the Combi Boiler has a request for Hot water since the Taco circulators are show off at this time. Also I assume in summer when there is a request for Hot Water I would NOT want to Air Handlers to shut off on a DHW request since they can contine providing cold Air from the Compressor.

Please let me know, it seems the system is not operating properly regarding the a call for HOT water while one (or all) of the Air Handlers is providing Heat to the three heating zones. I feel that the Navien Combi-boiler should send a signal to the air handlers to shut off during a DWH demand (when heating) - am I right on this?
 

John Gayewski

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First let me say, I am new to Combi-Boilers, so bare with me if I ask dumb questions.

I recently converted from Oil to Gas for many reasons (including getting a whole house generator). I went with a Navien NFC-200 175 Combi Boiler that is using my three existing First Co HBXB-HW Hydronic Air Handlers (one for each of the three zones in my 4BR house) and three new Taco ECM 007e Circulators. The system is using Cryo-Tek 100 Antifreeze (mixed with water) since two of the Air Handlers are in two differnt attics at different ends of the house. The three air handlers are used for both HEAT in the winter (location is New England) and Air Conditioning in the Summer. The conversion happened this week. So far the on-demand Domesic Hot Water (DHW) has worked great, having no problem keeping up with the Shower, dishwasher and washing machine needs for our home.

The question is I have is this. When there is a call for hot water, the system shuts off the three Taco Circulator pumps for the three heating zones (as I believe is normal for Combi-Boilers which prioritze DHW). If this happens when one of the zones is heating, the First Co Air Handler continues to run on that zone. Since there is no Taco circulation of hot water in that zone(s), the Air Handler quickly starts blowing COLD Air until the DHW request is completed. When someone is taking a shower this could be 20 minutes (Yeah, I know that is a long shower). I assume this is NOT correct? It seems to me that the Air Handler(s) should be SHUT OFF when the Combi Boiler has a request for Hot water since the Taco circulators are show off at this time. Also I assume in summer when there is a request for Hot Water I would NOT want to Air Handlers to shut off on a DHW request since they can contine providing cold Air from the Compressor.

Please let me know, it seems the system is not operating properly regarding the a call for HOT water while one (or all) of the Air Handlers is providing Heat to the three heating zones. I feel that the Navien Combi-boiler should send a signal to the air handlers to shut off during a DWH demand (when heating) - am I right on this?
What did the air handlers do prior to your new boiler? If they ran continuously then they will continue that until the controls are changed.

You are correct. It should relay off of the boiler somehow because you want them to stay running in the summer.

When you switch from heat to cool I would think there should be some logic for that, but you need a control person to sort it for you.

Probably should have been in the original price of install to sort this for you.
 

SeanTech

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Prior to the boiler conversation from Oil (traditional Boiler) to Gas (Combi Boiler) I didn't have this issue since I had a separate hot water Tank and the system could provide hot water and provide heat to all zones simultaneously. Bottom line - was no need to shut off air handlers when providing hot water in the past - so I agree, logic needs to change.
 

SeanTech

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Not sure this answers your questoin but...
The Navien defaults to DHW priority, when it sees a request for DHW, it automatically shuts off the Taco cirulators so it can dedicate itself to warming up hot water. When the request ends, it waits about 3 minutes (default) and then turns the circulators on again. This logic happens on the Navien.
 

Fitter30

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Trying to download the manual for wiring diagram to my tablet. Air handler wiring to keep them running do they terminate by boiler? How many sets of wires are there? How are the air handler running now? Wires twisted together? Brand and model of air handler thermostats?
 
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John Gayewski

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This guy wants the fans on the air handler to stop running when the circulators stop in the winter. Because they are blowing cold air.

In the summer the fans should run normally.

This is an out of the ordinary situation. Needs relays set up in a different way.
Not sure this answers your questoin but...
The Navien defaults to DHW priority, when it sees a request for DHW, it automatically shuts off the Taco cirulators so it can dedicate itself to warming up hot water. When the request ends, it waits about 3 minutes (default) and then turns the circulators on again. This logic happens on the Navien.
 

jadnashua

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Do any of the existing controls have end switches that you might use to control the air handlers? If the circulators have an end switch, you could run the low voltage control through that to control the signal to the air handlers to enable it to run when the circulator is operational, and it would turn off the air handler when the circulator was disabled by the boiler. Immediately turning the air handlers off would mean the air handlers might not be able to purge the latent heat out before shutting down, but that depends on the internal logic of the air handlers.

Or, you could use a new relay to control when the air handlers come on that would only be enabled when it's not in priority zone for the hot water supply. Lots of ways to fix this, but without knowing exactly what's there, and the logic in the boiler, hard to say what would be best and easiest. YOu might already have enough hardware to do this, and just need to rewire things a little.
 

SeanTech

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My system using the Navien Combi-boiler (Heat + OnDemand hot Water) to produce hot water the runs to three Air Handlers for (three zones in my house) to provide heat via warm air blown into the rooms.

The bottom line is that the Navien Combi-boiler can either be creating hot water on demand for shower/ sinks /Washing machine/ Dish washer (Domestic Hot Water or DHW) or producing hot water for the three heating zones to heat the house - but it can NOT do both at the same time. I belive this is "standard / typical" for any combi-boiler. The boiler automatically shuts off all of the zone circulators when it has a DHW request. If this doesn't happen, you will never get any DHW when any zone is heating part of the house.

I want the Air Handlers to stop running when the the Combi-boiler is providing hot water (DHW) and heat in the winter. Here is a an example scenario that demostrates the problem:
1) You are siting in your home office in the morning, you just turned up the heat on the thermostat and you can feel the hot air blowing on you from the air handlers - the room starts heaing up
2) Wife gets in the shower (DHW request) which shuts off all of the zone circulator pumps, but blower keeps running
3) Within minutes cold air is being blown on you since no hot water is circulating in the pipes inside the Air handlers, air just gets colder (especially since air handlers are in cold attic) until hot water / shower is shut off and circulators are automatically turned back on.
4) Your son get in the shower right after wife (DHW request) - more cold air blown on you, room hasn't heated up at all, in fact its getting colder due to cold air coming out of Air Handlers.

Solution: I need to shut off the Air Handlers in the zones when DHW request is on-going, better no heat vs cold air blowing on you.

Answers tp Fitter30 questions above:
- Air handler wiring to keep them running do they terminate by boiler? ==> NO. Signal comes only from Thermostat to turn on the Air handlers, that is the problem. I do need connection from the Navien to all 3 Air Handlers directly somehow to control this. I think I found a terminal to do this on the Navien schematic, but NOT sure how to this. Zone Circulators (Taco 007e) connected directly to the Navien NFC-175 (so it shuts them off during DHW request).
- The three Air Handlers are all First Co HBXB-HW (one model 30, the other two model 24's - same wiring no all three).

Below are the schematics:
1) Navien NCF-175 Combi Boiler
2) First Co HBXB-HW Air Handler
3) Messy diagram of how wired today.

Note: Looking at Navien Schematic, has a A/H terminal in the upper left. Manual states this interface can be used to stop the air handler operation when the boiler space heating function is not operating due to DHW supply demands. It stated the Air Handler contacts (A/H) "turn off" when the boiler is supplying DHW. I just have to figure out how to use this and connect it to all three of the Air handlers since I want them all to shut off when the Navien is in DHW (hot water demand).

Any suggestions?

I would like to avoid the expense of purchasing a separate Switch relay if possible - but I will do this if I have to.

Thanks to everyone for the advise !
 

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  • First CO Air Handler Wiring hbxb-hw321.pdf
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  • Today Diagram - Messy.pdf
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  • Navien NCF-175 Wiring Diagram.png
    Navien NCF-175 Wiring Diagram.png
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SeanTech

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Do any of the existing controls have end switches that you might use to control the air handlers? If the circulators have an end switch, you could run the low voltage control through that to control the signal to the air handlers to enable it to run when the circulator is operational, and it would turn off the air handler when the circulator was disabled by the boiler. Immediately turning the air handlers off would mean the air handlers might not be able to purge the latent heat out before shutting down, but that depends on the internal logic of the air handlers.

Or, you could use a new relay to control when the air handlers come on that would only be enabled when it's not in priority zone for the hot water supply. Lots of ways to fix this, but without knowing exactly what's there, and the logic in the boiler, hard to say what would be best and easiest. YOu might already have enough hardware to do this, and just need to rewire things a little.
Ok.. I checked into this, there is ONE relay available on the Navien motherboard the OPENS (breaks the circuit) when there is a DHW demand. I could feed the Green (24 V Fan control) from the themostat through this relay before it goes to the Air Handler Fan.. so wheneven there is a DHW request, the fan would shut off. There are a just a few issues with this:
1) Fan stops immediately: I disconnected the Green line from the thermostat while one zone was heating, the fan stoped immediately. As you stated, I would not be able to purge the latent heat in the air handler before shutting off. I would prefer a 30 sec to 1 min delay on shutting off the fan when the relay opens.
Note the Navien has a 3 min delay after the DHW request is completed before is closes this relay (and restats the zone circulators) - this makes sense or the fan would go on and off when anyone turns the hot water on and off when washing their hands. 3 mins is typically plenty of time for someone to wash their hands in a bathroom.
2) Need a separate relay for each of the three zones (air handler fans) - all controlled by this Navien DHW relay - I don't know what equipment can do this.
3) Summer Air Conditioning: I would want to disable this function in he summer as I don't want the fan stopping on a DHW request when the compressors are running. Seems like a simple bypass switch could work for this - I could manually switch this twice a year when transitioning between summer & winter.

Knowing very little about HVAC equipment, I have no idea where to find equipment to implement the logic above. I need the opening of one relay to drive opening three relays (and the same in reverse) - with a delay if possible. Any ideas on where to find equipment that can do this?

Thanks!
 

John Gayewski

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I think you just need to find a time delay relay of the right size. I'm not aware of a controls expert here. I'm certainly not. I'm more of a let 'er fly type. Which isn't good enough to give you specific advise.
 

Fitter30

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They make time delay relays with on and off delay for the ah blower. Time delay at start and delay when turning off. Like 30 seconds on and 45 seconds off. Would start the timing sequence with zone pump being energize thermostat. Condenser and ah blower would be enabled anytime zone pump wouldn't be running. G termial from thermostat gets energized when cooling is called or electric heat/ water. Gas furnace blower turns on by furnace temp or timer.
 
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