Selecting a new HVAC system for a renovation…
Our GC is about to start a gut renovation of our 2-family house that has a full-unfinished basement with one apartment on the 1st floor and the second apartment above on the 2nd floor, each floor is 1,200 sf. The roof is flat with no attic. The house was constructed in 1905 and is located in a suburb of New York City, region 5. Everything except the studs, windows and siding will be replaced due to age or needed upgrades. Heating is currently gas with radiators, no air conditioning.
When I found out the type of the proposed HVAC system I was a little concerned about the components used and cost of same, so I am looking for an unbiased second opinion. I have tried to ask a few HVAC consultants and contractors, but they do not call back or want to provide any advice if they cannot bid the job, which I understand. I was even willing to pay for advice if I found someone I could trust that would provide an independent opinion, but still could not find the right person to help me. I have asked many questions, only to have the answers add more questions…an endless cycle.
For now, our GC wants to only use the system specified and his HVAC subcontractor for the installation. The separate systems will be basically the same for both floors and includes the following for each floor:
• Navien Combi Natural Gas Boiler;
• Heat Flo (M#HF-40), 40 Gallon Hot Water Storage tank;
• Three (3) Ton Hydronic system with an Aspen, (M#AFM60), Variable Speed, R-410A, High Efficiency Air Handler;
• Luxaire, (M#CHD60S41S3), 3 Ton, up to 16 SEER, Single Stage Condensing unit. (Needs to be a horizontal discharge unit due to height restrictions that we have)
The only system difference is the 2nd floor will have 2 zones (the front rooms as one zone and the rear rooms as the 2nd zone. Pricing includes a digital zone panel, programmable thermostats and a static pressure relief damper, all necessary ductwork, refrigerant piping, condensate piping and heat piping.
While I have a general idea of how the proposed system works, I do not know if the proposed system is the most appropriate and efficient system for our house. We are looking for an above average system; it does not have to be top of the line. We previously ruled out the ductless mini-splits for aesthetic reasons and are okay with installing ducts on the 2nd floor, since we have 9 ft ceilings, no ducts are needed on the 1st floor, since they can be installed in basement/floor.
Does the proposed system have any significant advantages or disadvantages that I should be aware of? Is it above average in efficiency? Is the total proposed price of $46k for both systems reasonable for the scope of work? It appears high to me, but I never had ducts or a combi boilers installed before.
I am sure I have not listed all of the necessary details for the experts here to properly analyze, but if someone could point me in the right direction for advice it would be appreciated, since my biggest fear is missing the opportunity of installing the most appropriate system now when the opportunity to do so exists.
Any opinions or guidance would be appreciated, since I would like to sign the GC contract and start the project ASAP.
All the best, Bill
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Replies
Three tons of AC per floor is beyond ridiculous oversizing (by 2.5-3x, depending on windows).
A Navien combi-boiler's MINIMUM-fire output is probably greater than the heat load of a whole floor, let alone one zone of one floor. If your radation is cast-iron high-volume type it won't short cycle, but the higher-than-load firing rate of the unit means it'll never modulate. If you're abandoning the radiators and only heating with the (ridiculously oversized) hydro-air system it won't short cycle either.
If you have a combi boiler, there's no point to having the Heat-Flo indirect tank.
A typciall tightened up 2x4/R13 2- story house with typical window fractions and clear-glass storm windows (or clear-glass double-pan replacment windows from the 1980s) will come in at about 15 BTU/hr per square foot of conditioned space at 0F outdoor temps. Typical 99% outdside design temps in zone 5 Westchester county is about +10F give or take. eg: the 99% design temp for White Plains is +12F, Newburg's is +10F:
https://articles.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf
https://www.captiveaire.com/catalogcontent/fans/sup_mpu/doc/winter_summer_design_temps_us.pdf
So if you do a reasonable job on the insulation & air sealing the heat load of any one floor is likely to be UNDER 15 BTU/hr per square foot, but let's call it 15, pending a Manual-J heat load calculation. That's only 18,000 BTU/hr.
A 1.5 ton Fujitsu -18RLFCD mini-ducted mini-split can deliver about 20,000 BTU/hr @ +10F, and has more than sufficient cooling capacity for any given floor to boot. Throw in a couple of heat pump water heaters (preferred, since it dehumidifies the basement) or gas-fired tanks (could be cheaper up front) in the basement, the whole thing should be in the $15K range.
Hire an energy nerd to run a load calculation on the "after" picture of your air-sealing & insulation upgrades using AGGRESSIVE rather than conservative assumptions about air tightness. Only then will you be able to come up with reasonable HVAC solutions. But what has been proposed is out-of-the park CRAZY, unless you're planning to close it all up without insulation and add some extra air leakage.
FWIW: I went through this movie recently with a family in ~3000' house on Martha's Vineyard, MA, half of which was code-min new construction. The initial proposal they received was a modulating 4-5 ton heat pump with duct zoning plus a 1-ton mini-split, on a house that came in at about 30,000 BTU/hr @ +13F (their 99% outside design temp) for about $40K. What they ended up installing was a pair of 3-head multi-splits (since they couldn't find a contractor who would install an -18RLFCD in the basement for the new half). It's less than an ideal solution- the multi-split heads & 2-ton compressor is oversized for the loads on the newer part of the house, but not on the older half, so call it half-right. But it was $15K all-in (before getting $4K of rebate subsidy through state & utility programs) not $40K, and it'll be more efficient than what had been proposed. Total cash outlay for them was about $11K. It would have been about the same if they had installed the mini-duct solution in the attic (as had been proposed by one contractor), but punching holes in the brand new tight ceilings to put the ducts and cassette outside of conditioned space would have been less efficient than the oversized multi-split.
BTW: What are you planning to do for insulation & air sealing? What type of siding & sheathing? Is there any insulation in the ceiling joists upstairs, or any foam under the finish roofing above the roof deck? Type & condition of the windows...??
Stay away from the Navien combi units , although inexpensive and popular with a very good parts supply , there are reasons for all three of these , none of them good . Storing water in a tank after it has been heated by the Navien is a bad idea . Perfect breeding temp for Legionella bacteria is right in teh range where your contractors plumber will set it , guaranteed !
The low end as Dana eluded to will be far too much for your home also . What type heat emitters will he use ? Cast iron rads , baseboard ,? Has he or anyone for that matter conducted a proper room bty room heat loss ? This is imperative .
Unfortunately it seems as if you may be the unwilling recipient of the ," thats how we've always done it " syndrome . You not being able to find a consultant is not surprising . Contact Dominick from Abco , 917-509-5019 . Tell him I gave you his number . You could also contact 72*F consulting in NYC , John Cataneo .
If hot water heat is what you want it can be done properly and well . You'll want to ask the contractor's plumber what temp he plans on running to whatever heat emitters you will have , you'll also be interested that if he says 180* at design that he should run that at a 40* Delta T to allow the boiler to only not condense for a short part of the season while it is able to for better than 90% . If you are not returning water below 130* to the boiler your efficiencies drop below 90% and you will have wasted your money albeit , not much with the Navien . There are boilers now that fire down as low as 8,000 BTUh that do not require P/S piping and lots of other stuff necessary for that type of boiler .
Could not tell you if your price point is high or not , have no idea what the home requires , could be , maybe not .
What type building , detached , how many floors ? All these things make a difference but in the end remember , you don't get what you don't pay for . If comfort , true comfort matters , hot water cannot be beat . Mother Nature chose it as her perfect heat transfer medium long ago .
Dana asked most of the very pertinent questions , I think you should start asking these things yourself . Just because your architect or builder said it don't make it so .
Dana,
I am not surprised you believe the system is oversized. No one ever discussed calculations with me or the loads required. In reference to your question about siding and sheathing see my previous question on this site https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/45816/no-wall-insulation-now-what , which you also graciously responded to. For insulation we will either use foam or Roxul in the exterior walls, it will depend on what we find when we remove the lath and plaster. The new flat EPDM roof will have 3.5” of insulation on the roof deck. Can foam go in the unvented space below the roof deck? Not sure of the window type, but they were replaced about 5 years ago.
Based on your and Richard’s comments, I reached out to get the opinion of a well-known HVAC contractor in the area. He was able to come over this weekend (I was desperate) and low and behold he basically proposed the same system using Navien combi boilers, a 40 gallon storage tank and a hydronic air handler to provide heating/cooling and 3 ton condensers. Recommending the same system that was recommended by another vendor makes me think this must be the standard in the area. Both venders said the systems were direct vent which is better than having to vent to a chimney, which we now do.
I asked the HVAC contractor about the Fujitsu -18RLFCD going in the ceiling, but I was told they need 24” and would not work with 9ft ceilings. That seemed odd to me, since the unit measurements look a lot less than 24 inches. I’ll try to find someone that installs the Fujitsu systems.
Richard,
Thank you for the response. As I told Dana, another HVAC sub also recommended the Navien combi units. Is a better brand available? Possible Legionella in the storage tank is scary, why do they add a tank, if the combi boiler provides instantaneous hot water…at most only two people will occupy each 1,200sf apartment. I would never have thought our simple house would be that difficult to design a proper HVAC system when we are installing a new system.
Thank you for the referrals. It is very frustrating for a homeowner to find a knowledgeable HVAC person that will take the time to analyze your need and recommend an appropriate system. I shouldn’t have to always question and research the information received. I guess that is in my blood, but HVAC is not my expertise.
All the best, Bill
They added the tank I presume to hide or lessen the existence of cold water sandwiching which can and probably will occur with anything above 1.5 bath homes . Question is , how do they propose to keep that tank heated during long standby periods ? Better way to do this would be to install a right sized boiler and an indirect with plenty of insulation as a separate zone . That would eliminate alot of upsell stuff at a later date in an effort to make a poorly designed system work better . This also allows a higher storage temp north of 140* ( kills legionellosis) with the use of a mixing valve to temper DHW .
Most all of the combis also use a three way valve to switch from Space heating to DHW operation , these valves are problematic and often fail . Although it would be a warranty item within a certain time period , it is inconvenient and on most is labor intensive , you may also have to pay for labor since manufacturer warranty rarely if ever covers this . Something like the HTP EFTC140-F uses 2 separate circs to perform each operation , it also has a generous buffer inside the unit to store DHW , but as I have said , combis are sub optimal .
Low end modulation can also be problematic in a building like yours and you'll want to find something that readily accepts low flows through a good heat exchanger and does not require primary secondary piping like the Navien requires . Something South of 12,000 BTUh preferably . It is a hsame that more guys that have the knowledge to design for an efficient building are not more available . As long as training is done by the supply sector though that will not change . You did not mention what Navien was recommended but I will tell you the NHB is a very picky unit and if not done VERY WELL will give you problems . Watch what size model also , you don't wanna oversize to produce enough hot water and waste alot of energy because the thing short cycles on calls for space heating . Very good that you research , consider yourself at an advantage , most are victims .
The guy is clueless about those Fujitsus. The 18RLFCDs can be mounted vertically or horizontally, and does not need 24" (nor do the ducts). According to the manual a horizontal mount needs a minimum of 9-7/16" (less than 2.5"). See p.7
http://resource.gemaire.com/is/content/Watscocom/Gemaire/article_1365692188811_en_ii.pdf?fmt=pdf
Perhaps he was talking about width, between rafters or something? Mounting them below the ceilng in a closet or a hallway/stairwell soffit (that you'd have to build out) is pretty simple stuff. Depending on layout you may not even have to lower the ceiling or build duct soffits in the rooms it serves, but in a full-gut rehab there are plenty of ways to skin this cat.
The proposed ridiculously oversized 3 ton compressor per zone is likely driven by the similarly ridiculously oversized hydro air handlers.
With 3.5" of roofing polyiso above the roof deck (~R18, derated for climate), you can safely install up to R27 as fiber under the roof deck.
The operational cost of a well designed gas-fired hydro-air system might be somewhat less than with an 18RLFCD at your utility rates, but it's not clear it's worth the extra upfront cost. A non-modulating 3-ton condenser is the OPPOSITE of air conditioning comfort, since it won't run sufficient duty cycles to adequately dehumidify. A 2-ton Carrier GreenSpeed would be less oversized, and would also have more than sufficient heating capacity, but would be more expensive than than a Fujitsu solution.
If you're going with a gas-fired hydronic solution, real-radiation provides a lot more comfort & efficiency than an oversized hydro-air solution, and would allow you to size the air conditioning more appropriately. With a buffer tank on the hydronic heating system you can even micro-zone the place without risk of short-cycling the boiler to an early grave. There are several boilers out there that can modulated down to 7500-10,000 BTU/hr now, which would be much more appropriate for your loads.
BTW: With ~1200' of flat roof to work with, it's likely you have space for 10-15kw of rooftop PV. Divided into two 5kw+ systems net-metered solar would be able to cover the bulk of the space heating& cooling costs of a right-sized mini-split based system. (It would also directly lower the cooling load of the upper floor by shading the flat roof, reducing the roof temperature to something nearer the ambient air temp on hot sunny days.)
I'm not up to date on all of the NY state & local subsidies for PV, but the output of pocket cash for a mini-split + PV might not be much more expensive than a condensing gas hydro-air + oversized air conditioning solution, after factoring in subsidies, and would most likely have an overall lower operating cost if the solar power is net-metered.