Converting FHW heat to Forced Air Heating/Cooling with a Navien NCB-240

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KW2

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Hello,

This forum is great, and while I've read some very useful information, I'm posting to get more specific advice for my situation. Thanks so much in advance.

The home is an 1880s home in MA that is heated with gas FHW radiators:
*2,300 sq ft on 3 floors
--- 950 sqft on 1st with 0 beds and 0.5 baths
--- 900 sqft on 2nd with 4 beds and 1.0 baths (plans to convert this floor to 3 beds and 2.0 baths within 1-2 years)
--- 450 sqft on 3rd with 2 beds and 0.0 baths
*Completely uninsulated (plan to insulate 1st/2nd fl walls, 3rd fl(attic) TBD as spray foam may be needed)
*Will have a dishwasher, laundry, and the aforementioned bathrooms
*The current gas boiler vents through a chimney that we removed; thus it needs to be power-vented, is 12y.o. and only 80% efficient. We understand this is a $2k+ 'fix' and power-vents are not very reliable.

The project:
Our goal is to convert the FHW radiators to forced air heating and cooling to get A/C and eliminate the radiator footprints. We are targeting 2 zones, and due to the old house have limited duct work options, so we are leaning towards a unit in the basement to heat/cool the 1st floor and a unit in the 3rd floor to heat/cool the 2nd and 3rd floors. Right now we have a 12 y.o. gas Burnham furnace rated at 80.0% efficiency. We've had a few proposals for gas furnace forced air heating/cooling, hydro air, and atankless Navien NCB-240 hydro air option.

Recommendations?
We've had reps from authorized outlets from Trane / Carrier / Lennox come out, but we've also gotten quotes from contractors/plumbers. Our plumber recommended the Navien 240 hydro air option, which seems to be somewhat cheaper than the more traditional 2x furnace/cooling unit options. He also recommended adding a 20gal indirect tank to help address the lag from needing hot water to actually getting it from the Navien. The combi boiler is a new concept to me, and I'm wondering if someone here with more professional expertise can affirm / deny that this type of setup and boiler would (could?) be appropriate for my home.

Thanks so much in advance...

KW
 
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BadgerBoilerMN

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You will miss your hydronic heating. We almost never take it out, but install radiant heating every day. We do all HVAC and plumbing but people with hot water heat are spoiled.

If you want to stay cool a mini-split heat pump would be in order but some good design with a proper ACCA Manual 'J' room-by-room heat load is the first order of business.
 

KW2

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BadgerBoilerMN: Thanks for your feedback. We have heard that hydronic heating is indeed best, for the type of comfortable slow heat it provides. But to get central / ducted A/C, it seems we have to install duct work anyway (ductless mini splits not an option due to appearance). Combined with the need to power-vent the current boiler, it seemed to make sense to just convert to forced air heat as well. A bit of a bind.

Tom Sawyer: Going this route would be forced air for cooling and heat as well? Do you view the mini split setup as superior to a combi boiler + 2 air handlers and a/c compressors?
 

Dana

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Mini-ducted mini-splits work, (and can offer auxilliary heat as well) and you don't have to hack in vertical duct chases to get the cooling to all floors. The mini-duct air handler can be fit between joists with short duct runs to multiple nearby rooms.

For a 3-floor house with ~600' of conditioned space per floor either a 3-zone 1.5 ton compressor with three 3/4 ton mini-duct cassettes or three separate single-zone units (more efficient, easier to install, but may be more expensive.) The Fujitsu 9RFLCD dedicated single-zone mini-duct cassette is super efficient in both heating & cooling mode (HSPF 12.2/ SEER 21.5) , and still puts out a decent amount of heat even at -4F (if you needed or wanted to heat with it.) Mitsubishi has a similar series of mini-ducted units, but they fall short on both efficiency and capacity at low temps, making them less than ideal for much of MA. (The Mitsubishi wall-blob mini-splits are pretty good though, especially the FHxxNA series.) A typical 1880s house in MA does not have a huge window/floor ratio to drive air conditioning loads with, and you're almost certain to come in with a cooling load under 1 ton/1000' of conditioned space, which is why I'm suggesting the 3/4 ton units, but if a careful load calculation tells you the AC loads are higher than that on a given floor, there are 1-ton and 1.5 ton versions too. If you insulate and air seal the heat loads would probably be fully met with the 3/4 ton units as well, but you really have to run the numbers, as BadgerBoilerMN suggests.

Zone balancing (either heating or cooling) with ducts is a pain, and the air-flows required for good cooling season balance differ dramatically from the flows for heating season. With one mini-duct cassette per floor the zoning is a given.

High mass hydronic radiators are more efficient and more comfortable than central ducted hot air. Pumps use less power per delivered BTU than air handlers, and air handlers impose room-to-room pressure differences that increases outdoor air infiltration (and thus the actual heating/cooling load.) The mini-duct cassettes have some of the infiltration drive aspects of a fully centralized zoned duct system, but it's a tiny fraction thereof.

A condensing boiler and a hydro-air handler with an AC coil in it could get you there, but it's still an expensive solution that provides less comfort (trust me, I have a hydro-air solution as my "hail Mary" second stage on one of my zones when the radiant can't keep up, that also serves as the central AC air handler, and it pretty much sucks for comfort at both.) Unless you REALLY want to get rid of the high mass radiators for space reasons, you might just replace the old P20(x) with a cheap right-sized (for the whole house load) Burnham ESC series direct-vented ~85% efficiency cast iron and add ducted mini-splits for cooling + auxilliary heat. Then if gas prices spike you can let utility prices determine which you heat with, if you like.

The notion that a combi boiler needs an indirect to deal with it's ignition lag issues is a bit pathetic. I thought Navien had fixed some of their more egregious ignition lag issues, but apparently the installer thinks otherwise(?). If you're going to install an indirect, there is no point to using a combi-boiler, and makes it more likely that you'd be able to right-size a modulating condensing to the load.

Spending the money on building efficiency air sealing an insulation almost always buys more comfort than higher efficiency mechanicals, with the exception of fully right-sized and tweaked in modulating systems. Hooking up a mod-con to an air handler means you're stuck with whatever the air-handler delivers. While there are modulating air handlers too, it ends up being an expensive kludgy mess of a system with many design risks & flaws. But either a right sized mod-con boiler under outdoor reset control with high-mass radiators, or mini-duct mini-splits both modulate over a significant output range, and are quite a bit more comfortable (and quiet) to live with.
 

MIKE KC

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stay away from navien ncb combi units. I HAVE SOLD SEVERAL- AND WILL NOT SELL 1 MORE OF THE -------- JUNK- ALWAYS WORKING ON THEM-THEY SEND PARTS FAST AND TALK ALLDAY LONG. I AM TRYING TO MAKE MONEY-I HAD TO PULL A UNIT AND INSTALL NEW ONE ON A SAT. TO HELP COSTOMER-WORKED ON OTHER UNIT MANY TIMES AND ASKED FOR NEW REPLACEMENT UNIT. WHEN I DID THAT THEY HAVE TOLD ME ITS MY PROBLEM AND HAVE NOT RECEIVED ANY CREDIT ON THE OLD ONE. AND NOW HAVE PROBLEMS WITH OTHER NEW UNITS---JUNK
 

MIKE KC

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Hello,

This forum is great, and while I've read some very useful information, I'm posting to get more specific advice for my situation. Thanks so much in advance.

The home is an 1880s home in MA that is heated with gas FHW radiators:
*2,300 sq ft on 3 floors
--- 950 sqft on 1st with 0 beds and 0.5 baths
--- 900 sqft on 2nd with 4 beds and 1.0 baths (plans to convert this floor to 3 beds and 2.0 baths within 1-2 years)
--- 450 sqft on 3rd with 2 beds and 0.0 baths
*Completely uninsulated (plan to insulate 1st/2nd fl walls, 3rd fl(attic) TBD as spray foam may be needed)
*Will have a dishwasher, laundry, and the aforementioned bathrooms
*The current gas boiler vents through a chimney that we removed; thus it needs to be power-vented, is 12y.o. and only 80% efficient. We understand this is a $2k+ 'fix' and power-vents are not very reliable.

The project:
Our goal is to convert the FHW radiators to forced air heating and cooling to get A/C and eliminate the radiator footprints. We are targeting 2 zones, and due to the old house have limited duct work options, so we are leaning towards a unit in the basement to heat/cool the 1st floor and a unit in the 3rd floor to heat/cool the 2nd and 3rd floors. Right now we have a 12 y.o. gas Burnham furnace rated at 80.0% efficiency. We've had a few proposals for gas furnace forced air heating/cooling, hydro air, and atankless Navien NCB-240 hydro air option.

Recommendations?
We've had reps from authorized outlets from Trane / Carrier / Lennox come out, but we've also gotten quotes from contractors/plumbers. Our plumber recommended the Navien 240 hydro air option, which seems to be somewhat cheaper than the more traditional 2x furnace/cooling unit options. He also recommended adding a 20gal indirect tank to help address the lag from needing hot water to actually getting it from the Navien. The combi boiler is a new concept to me, and I'm wondering if someone here with more professional expertise can affirm / deny that this type of setup and boiler would (could?) be appropriate for my home.

Thanks so much in advance...

KW
DONT USE NCB BOILER-JUNK JUNK JUNK- SOMETHING IS WRONG WITH THEM-ERROR ERROR. I USED TO SELL THEM. IF U LIKE COMMING BACK TO THE SAME PLACE ITS FINE, HAVE INSTALLED A LOT OF EQUIPMENT. SOME HAVE PROBLEMS BUT THESE TAKE THE CAKE
 

MIKE KC

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Hello,

This forum is great, and while I've read some very useful information, I'm posting to get more specific advice for my situation. Thanks so much in advance.

The home is an 1880s home in MA that is heated with gas FHW radiators:
*2,300 sq ft on 3 floors
--- 950 sqft on 1st with 0 beds and 0.5 baths
--- 900 sqft on 2nd with 4 beds and 1.0 baths (plans to convert this floor to 3 beds and 2.0 baths within 1-2 years)
--- 450 sqft on 3rd with 2 beds and 0.0 baths
*Completely uninsulated (plan to insulate 1st/2nd fl walls, 3rd fl(attic) TBD as spray foam may be needed)
*Will have a dishwasher, laundry, and the aforementioned bathrooms
*The current gas boiler vents through a chimney that we removed; thus it needs to be power-vented, is 12y.o. and only 80% efficient. We understand this is a $2k+ 'fix' and power-vents are not very reliable.

The project:
Our goal is to convert the FHW radiators to forced air heating and cooling to get A/C and eliminate the radiator footprints. We are targeting 2 zones, and due to the old house have limited duct work options, so we are leaning towards a unit in the basement to heat/cool the 1st floor and a unit in the 3rd floor to heat/cool the 2nd and 3rd floors. Right now we have a 12 y.o. gas Burnham furnace rated at 80.0% efficiency. We've had a few proposals for gas furnace forced air heating/cooling, hydro air, and atankless Navien NCB-240 hydro air option.

Recommendations?
We've had reps from authorized outlets from Trane / Carrier / Lennox come out, but we've also gotten quotes from contractors/plumbers. Our plumber recommended the Navien 240 hydro air option, which seems to be somewhat cheaper than the more traditional 2x furnace/cooling unit options. He also recommended adding a 20gal indirect tank to help address the lag from needing hot water to actually getting it from the Navien. The combi boiler is a new concept to me, and I'm wondering if someone here with more professional expertise can affirm / deny that this type of setup and boiler would (could?) be appropriate for my home.

Thanks so much in advance...

KW
NCB PROBLEM CHILD-PUT NAVIEN ON SPEED DIAL
 
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