New Boiler with indirect

3zht

Good morning all, I've been reading as much information online such as this website and getting great information. My situation is a little different as I have a 1978 tri-level house that has a furnace on the second floor only so we can remove that from the equation, I believe. I know how many therms I used per month but it's difficult for me to guess if the therm's are being used by the boiler or my gas furnace (see my dilemma?).

The first floor (1st zone) (900sq ft with 1 bed, 1 bath, and a living room. 100 feet of baseboard)
Third floor (2nd zone) (900 sq ft with 3 bed, 2 baths. 80 feet of baseboard)
Garage (3rd zone) 2.5 car with 45k btu modine hydronic heater running off boiler (heated to 45-50F only)

Gas bill was over $500 in January so I insulated the attic (previously had R19 in attic) and now it's R39. All windows and doors have been replaced with updated efficient models. My current boiler is original to the house and is 200k BTU input, 160k BTU output which seems VERY overkill. If I'm not mistaken I have my house needing just under 80k BTU to heat.

I have had a few contractors come in and they all seem to want to install the Navien 240E combi. After doing all my research and calculations I'm looking more at a mod con boiler with a direct fired 50 gal as we have two small children who need baths.

I was looking at the Lochinvar knight boilers and didn't know if the wall mount/floor mount made a difference. Also I'm thinking the 110N may be better than the 80N because the 110N has a net BTU of 89. Am on I base to make the correct decision here? I'd hate to have a boiler that can't warm my house during these -10 nights.

Intplm.

The contractors that you have had over and have made suggestions? Gave you their expert advice? Are they the same people who will be servicing your system. If so, and I hope that they are.
Keep in mind that you are buying a product and service that goes along with that product. The company, and product that they install should be integral with each other.

EBEBRATT-Ed

@3zht
#1 you need an accurate heat loss...no guessing or measuring baseboard heaters that doesn't work. You can down load the Slantfin app and do it yourself if need be. Then you will have the right size boiler.

200k input is way too large to heat two floors

Zman

You want to be focusing on the minimum turndown, not the maximum. After all, it is the typical days consumption that will save you money.
Your house has plenty of radiation so a mod con will be able to run at low temps and efficiently. The 80 is obviously plenty for your load. It has a very similar minimum to the smaller models, so no harm if you over size it a bit.

3zht

Thank you all very much for the time and the expertise. I downloaded that slantfin app and it was wonderful. I believe I filled it all out properly and I'm showing a heat loss of just under 50k. The lochinvar knight 110 goes down to 10,450btu while the 85 goes down to 8,075k btu.

My issue is this. Contractor wanted to install 150 which is way oversized obviously. I had to talk them into the 110 because they refused the 80k btu model. Now, if I convince them to install the 80k model I can easily see something going wrong in the future and them saying "This is why we wanted to install the 110". Is the small amount of extra BTU's worth that argument or should I just go for the 110?

EBEBRATT-Ed

@3zht ,
This is like bypass surgery. If your contractor won't cooperate get a second opinion.

How your contractor selects the size of the boiler tells a LOT about his qualifications. A heat loss is the only way ...for hot water heat.

Basing the size on the old boiler wrong!
on square footage wrong!
on measuring baseboard wrong!

3zht

I'm at least leaning toward the 80k btu model now. Thank you! I'll stay up to date with how it goes.

Zman

The 110 is oversized but not grossly oversized. I don't think you will have any issues going with it. The 80 would be the correct choice.

CrawlerHero

The Lochinvar Noble Combi 199 could be a great solution for you. Depending on the ground temperature of water where you're at, it will handle the domestic HW load no problem and is more than enough for heating. 10:1 turndown.

STEVEusaPA

CrawlerHero said:

The Lochinvar Noble Combi 199 could be a great solution for you. Depending on the ground temperature of water where you're at, it will handle the domestic HW load no problem and is more than enough for heating. 10:1 turndown.

Why almost 3x oversized? Just for domestic? Are they filling a 4 person hot tub every night?
And what does ground water temp have to do with it?

Jellis

@STEVEusaPA
The original post states they have baseboard and a modine heater so no it would not just be for domestic water.
Ground water temp would affect the amount of GPM of hot water that can be produced, and the OP mentioned having children that took baths. Certainly a valid thought.

3zht

I do have baseboard in the house and a Modine in the garage. I was trying to stay clear of a combi unit but I appreciate the mention of the noble. I live in NE and the incoming water temps get a little low during the winter. We have children taking baths etc so I figured the indirect would make sure we never had a worry.

hot_rod

I agree the indirect is a better choice for your case. More wiggle room in an indirect to boost drawdown. With a Combi you are limited to the specific GPM at the water temperatures they indicate, no cheating the DHW output

If you do expect a large DHW use now or in the future, the 110 will recover it a bit more quickly.

3zht

I was looking at the 110 as I stated before but I'm not sure if the efficiency is worth giving up just to have faster recovery of hot water. I figure how often does everyone shower at once? As long as they give 5 minutes or so and don't take 20 min shower we should be good with the 85. Plus that will give us the efficiency all winter as well. Am I correct in this thinking?

hot_rod

The efficiency will be the same with either size. What can happen with and over sized boiler is short cycling. However that 80 had a low turn down 10,540 but/ hr. so without knowing your smallest load and how often it calls it is hard to predict how often it will cycle with low loads on mild days.

These boilers do have have way to limit heating output, put delay on firing, ramp delay so the 110 should be able to accommodate your application and give you the extra DHW horse power.

Keeping in mind you are replacing a 200K boiler that may have been cycling it's brains out

3zht

I would assume the garage will be the smallest load as it's set to 50F and only runs certain times of the year. The other two zones are pretty equal in size (fin baseboard length wise) so I'm not entirely sure how to find the smallest load.

hot_rod

So 1800 sq feet of home with fin tube comes up to 50K? Seems a bit high. Or does the garage show up in the 50K load calc?

What size is the Modine in the garage? it could take up all the output, unless you balance or limit it's needs.

Given all that you have shared, I would go with an 80- 85K.

3zht

It's a 2600 sq ft tri level but the second floor has it's own furnace in it. I'm only heating 1800 sq ft of the house with the boiler plus my garage. The heater is the garage is set low (45-50F) unless I plan on being out there and then I'll raise it to 65 or so.