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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 21527
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have 2 story fully attached brick row house with basement

Customer Question

I have 2 story fully attached brick row house with basement 4 ft above ground. 1000sq ft per floor, I am doing gut renovation new marvin integrity windows with 1.5 inch spray foam insulation on each cold wall front which is 20ft wide front and back of house with insulating sheetrock. I have 9.5 ft high ceilings on 1st and 2nd floors and 8 ft in bsmt. I am going to put radiant floor heating in basement 7 large old style cast iron radiators on 1st and 2nd floors. I will also be putting r30 in 2nd floor ceiling. What size hot water condensing boiler do I need in NYC.
Submitted: 2 years ago.
Category: HVAC
Expert:  Rick replied 2 years ago.

I need to know the total glass area of all the windows. I'm assuming 2 exterior insulated doors?

Customer: replied 2 years ago.
windows glass size
7 27x72
5 29x72
2 25x34
1 27x34
2 29x34
2 exterior glass marvin integrity patio doors
36 x96
36x 80
1 insulated 36x80 door
i uninsulated exterior door that leads to insulated weather stripped foyer
Expert:  Rick replied 2 years ago.

Ok, I'll get back to you in a bit once I do the calcs

Expert:  Rick replied 2 years ago.

I get a heat loss based on these specs of 54,500 BTUh. Since you're using hot water radiators I would upsize the boiler output a minimum of 30% to 50% to accommodate the large water content of the system. If you don't it could take forever for the radiators to warm up from a cold start. Since most condensing boilers modulate burner output according to system demand upsizing the boiler has no downside. In fact an even higher output capacity has no downside if the boiler modulates burner output.

Customer: replied 2 years ago.
I had my plumbing heating guy say 180k btu. So what do you think of prestige trimax 110? According to your calculations that should be more than enough, according to him I will be way underpowered.
Expert:  Rick replied 2 years ago.

No way the heat loss is anything near 180. That said you will be dealing with this guy (I assume) after the install and I can virtually guarantee that he will point to the smaller boiler (than he recommended) as the cause. The Prestige series will modulate down to as low as 25% of the max output so 25% of the 175k model is ~44k. Probably more than what you want for optimal efficiency but not terrible either. The other consideration is DHW. If you are using an indirect fired water heater (it is the best option) and you have a lot of hot water demand then the 180k boiler output would be beneficial and is even required to achieve rated DHW tank output in some cases. If you don't have any other options for a second opinion from another plumber and you have a decent relationship with your plumber (he isn't likely to be offended by your shopping for my opinion) then mention my calcs to him. The thing is that low water volume condensing boilers were not designed for high water volume systems so bigger isn't necessarily a bad thing.

Expert:  Rick replied 2 years ago.

Also Triangle Tube is a good product.

Customer: replied 2 years ago.
We already installed new water heater so boiler would be used just for heating. He is recommending navien but i haven't heard great things, what brand do you recommend?
Expert:  Rick replied 2 years ago.

Not a huge fan of Navien. We actually prefer Buderus but Triangle is also a good option. I'd get a second opinion if you can

Customer: replied 1 year ago.
What do you think of slant fin boilers?
Expert:  Rick replied 1 year ago.

Slant fin makes great baseboard their boilers are ok but I have no experience with Slant Fin condensing boilers.

I'd appreciate a favorable rating