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My new home combi install

sonofaplumbersonofaplumber Posts: 52Member
edited August 19 in Radiant Heating
Hi All,

Its been 3 years since my last topic here.

My dad's house with the frozen steam system we talked about 4 years ago was foreclosed and repurchased and I am watching as they remove all that cast iron. Curious as to what changes are being done.

My home I got advice on 3 years ago about various convectors for and landed on a CI rad/radiant mix system with CI boiler and indirect will be on the market this week, as we've built a new home! I will miss those 110 year old rads. What a great system it's been.

On to something new. Over the last year my fiance and I (yes, we're engaged now) have been working on our new home. I had selected a combi mod/con boiler this time around and having only ever installed CI boilers in the past am enjoying the current century's trend for a change.

Consulting various people in the business I was turned away from HTP unit and to an unfamiliar Bradford White Brute FT boiler, a FTCW199. The salesmen claims these are a very solid built machine with very few reported defects and the installers really enjoy working with them. I did my own due diligence on the unit and agreed, plus it is a great value with everything that is included and integrated.

I went with the combi for cost and space requirement reasons over using an indirect or standalone water heater. The new home has a small attached garage which would serve double purpose as the utility room. I had the foresight to install osb on the walls and have the contractor sheet rock over it, so I could mount/hang things virtually anywhere.

The unit many are unfamiliar with but has a 199k input with 10:1 turn down. It has an stainless tube heat exchanged with aluminum finned tubes. Included is ODR, pump delay features, venting kit, LP conversion, overall a very complete package. It uses a 15-78 internal pump and was definitely designed to be easily maintained with great access to components like the control board and igniter.

The home is well insulated and will be heated primarily with six 300' loops of in slab radiant. 2 zones, 2 loops for the garage and 4 for the house. A 1500 sqft footprint with 2 stories. Supplemental heat will be provided in areas upstairs and in the main living area by daikin heat pumps.

I spent the weekend doing the majority of the install myself with no other help or input, and just wanted to post a picture for any constructive feedback or considerations. I will be finishing it up this coming weekend just need to install the vent lines, end switch wire and pressure test.

Edit: a photo of the new home with my old truck!






-Joel

Comments

  • JohnNYJohnNY Posts: 2,293Member
    Great truck!
    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
  • IronmanIronman Posts: 5,127Member
    That's nice, but it's the same boiler as an HTP UFT combi. Never believe everything a salesman tells you. Maybe I should say never believe ANYTHING they tell you.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • JakeCKJakeCK Posts: 88Member
    That house looks amazing. So the house is a 1500sq ft footprint and two floors so I'm guessing close to 3000sq ft total? 199btuh seems kind of high for a well insulated modern house?
  • sonofaplumbersonofaplumber Posts: 52Member
    edited August 19
    Ironman said:

    That's nice, but it's the same boiler as an HTP UFT combi. Never believe everything a salesman tells you. Maybe I should say never believe ANYTHING they tell you.

    Hey I'm a salesman!!! lol so I know how "true" that statement is, pun intended.

    That's interesting though. I'll have to go back over the specs and compare. It seemed to me when I was comparing them they had quite a few differences. Do you mean it is built by the same manufacture or literately the same?
    JakeCK said:

    That house looks amazing. So the house is a 1500sq ft footprint and two floors so I'm guessing close to 3000sq ft total? 199btuh seems kind of high for a well insulated modern house?

    Thank you for the kind words. 199 is way high. I don't expect to consume more than 20-40k btu/hr once the slab is stable. It was sized that way to have a higher capacity of DHW. It also has a higher turndown ratio so it can modulate at a lower min fire rate than the smaller 140 they offer or IRRC the HTP. That was something I picked up on right away and was also mentioned to me as a benefit for this unit.



    -Joel
  • sonofaplumbersonofaplumber Posts: 52Member
    To elaborate a little more, I didn't commit after a single sales guy's opinion, just trying to get to the point in the first post. I tasked my fiance's father with getting us a deal on a combi from his company. He's worked for one of the largest supply chains on the east coast (no name naming) but, for 35 years and is their cd driver for the state here and so visits every store and warehouse in the state throughout the week. He talked to and gathered opinions from various salespeople and installers along his route, and reported back to me what the general consensus was.

    The major thing he heard from a few people with the HTP was control board failures, and have not had a single reported failure yet on the Bradford White. It is a fairly new boiler to us in the area from what I had heard but so far, but maybe the HTP with a different name? over all, I'm pleased.

    -Joel
  • sonofaplumbersonofaplumber Posts: 52Member
    A quick google search reveals that the HTP and Bradford White units are in fact identical. I can't believe I missed that. didn't do enough homework but that's okay, still happy with the unit. We will see how it goes. I always liked HTP stuff anyway. It was a last minute decision change.
    -Joel
  • JakeCKJakeCK Posts: 88Member
    With you being so oversized just for DHW you'll never get the full benefit of the modcon. The thing will always be turned down to it's lowest fire rate even on the coldest days. I wonder if a smaller modcon with an indirect tank would have been more economic, unless space was a major concern?
  • hot_rodhot_rod Posts: 11,684Member
    the small combo 110-120 get you 3 gpm of dhw How much dhw do you require?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • sonofaplumbersonofaplumber Posts: 52Member
    I see this recommendation to go smaller and have an indirect on the forum a lot. I've given it some thought from both perspectives and i'll debate a little.

    I understand the original purpose of a modulating boiler is to vary the flame based on the heating load, not to switch between two widely different loads, big dhw and little closed loop. And having a max design day near the low end of the boilers fire rate leaves efficiency on the table.

    How low do they go? What is the lowest fire rate you've seen from different smaller mod/cons? The 140k unit has a 5:1 ratio, its min fire rate is 26k. Its a smaller boiler and you would all probably say "better sized" but it isn't. It only gives 4 gpm of dhw to the 199's 7gpm. With an even higher min fire rate. An even worse choice.

    How many btu does it take to raise 6+ gallons of water in the unit and near boiler piping just one degree. That's an easy calculation. At what point are you trying to heat this water not to mention a quarter million pounds of concrete with a candle? 5,000 btu is not a lot of energy, to be overshooting by that amount is 25% over sized around 20k (huge by design day/heat load calcs), and I could eat that much by opening an entry door for 11 seconds.

    Is being a little over sized on such a small heat load even noticed with such a big thermal mass? It's going to soak up the extra btus isn't it? Easily tweaked with pump speeds to get a bigger delta?. and will release this energy into the house over time, distancing the tstat calls apart, is it wasted energy? Isn't only the 5% that went out the vent a waste?. Same AFUE as a smaller boiler..


    I like indirects, and have one myself, in a basement well out of the beaten path. It is less than 5 years old and a very good quality one, but my oil burner cycles at least once a day usually late at night while im on the couch and its been 12 hours since the last DHW call. Always a full cycle to keep it up to temp just for standby losses. I think that one cycle (at a very high firing rate in ) would outweigh the wasted energy having a mod/con thats min rate is ~5k over the required input on a given day.

    -Joel
  • JakeCKJakeCK Posts: 88Member
    edited August 19
    You said your heat loss is between 20 and 40k btuh. That is a pretty big range for a heat loss at design temp. If its 40k they make modcons that small. I would size for the heat load and use a large indirect for hot water. Most conventional hotwater tanks are around 40k btuh anyways. With a priority zone controller you shouldn't have a problem. And if you guys do run out because of super long scorching hot showers there are heat recovery units that can be installed on the waste stack that can recover up to 80% of hot water from showers.

    The thing about large thermal masses like concrete is that they don't respond quick to changes to the set point. They're like giant flywheels, but at the end of the day the heat loss is what determines how much heat you boiler has to put out to maintain temp. So your assumption about it soaking up the btus is not really accurate. Yes it could soak up all that extra heat, and then you'll have hot concrete that will overheat your house. What will happen is that once the concrete is in equilibrum with the houses setpoint and heat loss it will only run for short durations to maintain temp at its lowest firing rate even in the dead of winter.
  • hot_rodhot_rod Posts: 11,684Member
    I suppose it comes down to you wanting or needing continuous 7 gpm, if so you have the correct unit

    Some brands have ramp delay and electronic derate down to 8000 so you can dial them in to small loads. Worse case you add a buffer tank.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • JakeCKJakeCK Posts: 88Member
    Another thing is cost of components. The difference in cost of a modcon at 200k btu vs 40btu is over 2k $ and thats just a standard modcon not a combi unit. That right there is the cost of a very large indirect and you save in fuel costs over its life. Also these modcon combi units are newer tech and less proven and very complicated devices which means more failures and earlier replacement. Spending 6 grand on one of these every 10 years is not my idea of a sound investment. An indirect I could see lasting 20+ years easily because of how little there is to them.

    And these prices are just the boiler not including install costs by a qualified installer.
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