Weil-McLain GV90+6 LP boiler vs Navien NCB-240 LP combi-boiler

srodster

I'm building a new brick ranch style home (Northwest IL), (2200 sq ft) and it has an unfinished basement. I'm at the decision point for heat and was pretty set on a W/M GV90+6 unit (91% AFUE) with a Aqua 2 series indirect water heater, model 85, when I was told to explore the Navien NCB-240 combi-boiler, (95% AFUE). I will be using LP. I intended to use base board heating (radiant fin registers) in a closed hot water system w/ maybe 3 to 4 zones and the TACO 6 control zone panel for potential future expansion in the basement. However, it was suggested I reconsider a couple items: 1) think about in floor heating for upstairs, (I will have hardwood floors), and 2) consider a Navien NCB-240 combi-boiler vs the W/M GV90 series.

I only have experience growing up with baseboard radiant heat. I am interested in understanding potential maintenance issues on either, and upfront costs of one vs the other. I know the boiler cost appears to favor the Navien unit, but I have no idea on baseboard heat vs infloor heat.......

And given the "same" conditions of domestic heated water, is one going to consume much more LP than the other when it comes to the hot water demand at the same setpoint.....

Thanks to those that have experience with these systems to share ideas, pros or cons, or best move ever, or regrets...., ha.....

EdTheHeaterMan

Not a fan of Combi heaters. Life expectancy is the main reason.

EdTheHeaterMan

If the basement floor is not poured yet, I would consider radiant tubing in the basement floor, even if you do not connect it right away. Tubing in an insulated concrete floor will be much better than any other heating system. Staple up tubing with hardwood floors are another more comfortable heating plan. You may enjoy the comfort at a lower temperature with floor heat. for example, if you set your thermostat at 68°F and that is comfortable with baseboard heating, you may be comfortable with 66° with radiant floor heat because there is more radiant heating you body and less convection currents heating your body. Convection means the air is moving, and moving air will tend to cool you off.

I would suggest that you add a secondary heating source in the event that your hardwood floors do not have the capacity to heat your home at design temperature (DT- aka: the coldest day of the year). I did a concrete slab addition in a South Jersey home with staple up to hardwood floor in the main home. Best thing I ever did. The addition was comfortable but since the original home was built in 1965, the insulation was not adequate and the floor as a radiator was not enough when the outdoor temperature got below 17°F. The existing gas furnace was my back up when the temps got too low for the few winter days that we need it.

kcopp

Never navien for me.

EBEBRATT-Ed

No don't buy a Navien.

Radiant heat is probably the best heat you can have, but it depends on how you live. Radiant need to run at a set setpoint no turning the heat up down or sideways. It brings the house up to set point slowly and then maintains a perfect temp and is efficient because you can run lower water temp in the boiler. Stay away from a combi and use an indirect.

Mod con boilers 15-20 years, Cast iron boilers maybe 30 years. Mod con more efficient but requires a real technician whereas a CI boiler most any decent tech can fix it

hot_rod

Consider radiant and panel radiators instead of fin tube
If so a mod con boiler for operating temperatures 140 or lower

combis are an option, it depends on your dhw useage

gyrfalcon

Also, how are these boilers being sized? 

Seems way too big of boiler for this size house. Especially a new build.  

JMWHVAC

@kcopp and @EBEBRATT-Ed May I ask why the negative opinion on Navien? We have installed dozens of various Navien models the last 6+ years and they have been near flawless (so far!). Are we doing the wrong thing?

SuperTech

JMWHVAC said:

@kcopp and @EBEBRATT-Ed May I ask why the negative opinion on Navien? We have installed dozens of various Navien models the last 6+ years and they have been near flawless (so far!). Are we doing the wrong thing?

I've seen two Naviens spraying water out of the heat exchangers at less than 6 months since they were installed.  They were both installed perfectly too. 

Anything but Navien is my thoughts as well. I see way too many problems with them. 

As far as the OPs question, I pretty much agree with everything said by @EBEBRATT-Ed above. 

Tom_133

I agree with no to the Navien, but it seems you should get some consulting help for the system that GV90 seems very over sized I just installed a 4 section in a 4000 sqft and it is happy, happy, happy.

kcopp

JMWHVAC said:

@kcopp and @EBEBRATT-Ed May I ask why the negative opinion on Navien? We have installed dozens of various Navien models the last 6+ years and they have been near flawless (so far!). Are we doing the wrong thing?

I think it is a poorly designed and low quality unit. I've seen to many issues.

Ironman

A 6 section boiler is way too big for that size house.

You need to start by doing a scientific Manual J heat loss calculation so that you know how much heat is actually needed in each room. That’s the foundation and starting point for designing any HVAC system.

I totally agree with what others have said about Naviens: they’re junk.

GGross

Whether you choose a cast iron, or a mod/con boiler, for me personally I would rather have a tank of hot water. I'm not a big fan of a combi with no storage for things like washing hands, standing with the faucet running for a minute plus to wait for hot water is not a good time, I did it for 10 years and swapped out for a tank and will never go back.

srodster

Thanks for the comments! I am going to stick with my GV90, but may go down to a 5, instead of the original 6. And likely to use the base board radiant fin heat. HVAC installer said the infloor heat would not make sense and be quite difficult.... Curious why some like the radiant and panel heat over the radiant fin heat. Appreciate it!

KC_Jones

srodster said:

Thanks for the comments! I am going to stick with my GV90, but may go down to a 5, instead of the original 6. And likely to use the base board radiant fin heat. HVAC installer said the infloor heat would not make sense and be quite difficult.... Curious why some like the radiant and panel heat over the radiant fin heat. Appreciate it!

A 5 is going to be ridiculously oversized as well, unless you are planning to skip all the insulation and windows.

2200 sq ft, modern construction, even if the basement is the same size, and your heating it all, most likely the 3 section will be enough, the 4 section at the absolute max.

It was stated above, you need to do the heat loss calculation for the building and size the equipment to that. Also, with zoning, sizing becomes even more critical. They can't even size the baseboard unless they have a heat loss for each room. Sure they could just throw some baseboard at it, but in reality they need to calculate how much is needed, heat loss is the only way to determine that.

I would speculate your installer just doesn't know how to do in floor, so they say it's bad. The truth is, it is by far the most comfortable way to heat a home there is. If you are set on that installer, I would avoid it as they aren't comfortable. If you want the best heat, find a new installer. It's your choice. I'd be a bit nervous if they are suggesting the boiler size they are, that is the first step and needs to be correct and if they aren't doing that right, what else will they get wrong.

Don't be one of the horror stories we read on here almost weekly.

As far as Navien, not sure what all it covers, but I believe they currently have a class action lawsuit going on so I'd probably avoid them for that reason alone.

srodster

Appreciate the comments KC. Heat loss calculation was actually close to 100,000, more like 96k, NW Illinois. I'll absolutely take a peek at the GV90+4 and discuss with HVAC man, don't want to be the horror story... He's been doing it for 30 years, so hopefully he knows the best options for the given situation.

KC_Jones

srodster said:

Appreciate the comments KC. Heat loss calculation was actually close to 100,000, more like 96k, NW Illinois. I'll absolutely take a peek at the GV90+4 and discuss with HVAC man, don't want to be the horror story... He's been doing it for 30 years, so hopefully he knows the best options for the given situation.

Was that 96k including the basement?

Actually, even if it is that seems high for new construction. I guess if there is enough glass and cathedral ceilings. Would need more details for it to make sense.

Hot_water_fan

Seems really high for a new house. Double check that. They are notoriously inaccurate. 

Ironman

100k btus for a 2250 square foot house?? Ridiculous! That’s over 44 btus per square foot.
I’ve been doing load calculations for 45 years and I’ve never seen even the most leaky old farm house need anywhere near that much.

The energy code requires that a new house be constructed to be under 25 btus per square foot. Most come in at 15-20.

If your contractor told you that you need that much, you need to find someone else.

GGross

Yesterday i did a load calc for a new house in northern michigan, high ceilings, wall to wall windows on one side, huge windows on the entire first floor, and a completely glass walkway connecting 2 wings of the house. Even if I take the basement out of the equation entirely the load for the upper 2 levels is at 22 BTU/sqft, and thats only when it is -10f out.

I would have your people revisit your load calc

srodster

Hey KC, ya that load did include the basement too.

KC_Jones

srodster said:

Hey KC, ya that load did include the basement too.

Would need more information on the building, but if it's of a fairly standard design, normal size windows, ceiling height, etc. then that number seems high. Basements typically have a relatively low heat loss and shouldn't add dramatically to the number.

The actual calculations aren't really done by sq ft., we just discuss it like that for ball park purposes to see if it makes sense. The real calculations take into account windows, insulation value, doors, basically all construction details and develop a heat loss for the building from that.

As said above you should not be above 25 per sq ft, and in this day and age it should not be hard or even a stretch to get down to 15-20, the basement being even less.

Lets say you get the main floor to 20, that would be 44,000, the basement would be say half that, you'd be a total of 66,000. The 3 section boiler in the product line you are looking at is rated for 65,000, so it would be a perfect fit. The 4 section would be oversized, 5 would be crazy and a 6, total insanity.

Again, if you have some crazy architecture, high ceilings, huge and numerous windows, then it may go higher, but an example of that was given and even it is only 22 per sq ft.

Also keep in mind, that rating is only on the coldest day of the year, all the other days it is lower, and most days it will be significantly lower.