Air conditioner replacement
Current A/C has a leak (Trane XR15 – series model 4TTR5061E, 5.0 ton air cooled condensing unit, with a matching 4TEE3F66A Air Handler) that we installed in 2011 (with PSEG Long Island rebates) and were told can’t be repaired.
Also interested in heat pumps given the environmental benefits and PSEG Long Island NY rebates/federal tax credits. Have gotten estimates for Mitsubishi and Bosch systems, but having difficulty deciding. Both proposals say they will get rebates based on manual-J and meeting 90% or more of our heat requirements.
Our current heating is an oil furnace with 4 baseboard zones and 4 radiant zones. We don’t have A/C in the basement (baseboard heat) nor 4 bathrooms (3 radiant, one baseboard). Above grade square feet: 3,400; basement: 1305
- Mitsubishi MXZSM60NAM-U1 5 Ton Smart Multi Heat Pump
- Mitsubishi SVZ-KP36NA 3 ton Multi position air handler for 2nd floor
- Mitsubishi SVZ-KP30NA 2.5 Ton Multi Position Air Handler for 1st floor
- Mitsubishi MUFZKJ15NAHZ-U1 15k BTU High heat heatpump for Den (our den has a small A/C vent near a vaulted ceiling to the roof and is over our garage and has baseboard heat)
Proposal 2:
Two new Bosch 3 ton 20 seer IDS Heat pump systems. The new BOVA36 condensing units will be placed in the same location as the existing units on elevated slabs. We will replace the copper refrigeration lines. The new BVA36 air handlers will be hung from the roof rafters giving the new condensate drain lines optimum pitch to the gutter system. Under the air handler will be a new auxiliary drain pans. Aprilaire merv 13 Media air cleaners will be installed into the return ducting for added filtration. We will be replacing all of the duct work in the attic. The duct work will consist of a sheet metal trunk line, air tight damper collars and r-8 flexible ducts. We will be adding another return duct to the 2nd floor hallway. All duct work will be air sealed and balanced upon completion. Both thermostats will be replaced with Honeywell Dual Fuel pro IAQ models. The disconnect switches & whips will be replaced.
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Replies
Keep in mind that the "multi-split" units like the Mitsubishi smart-multi do not modulate as well as the 1-to-1 ratio mini splits. Around here, the experts (I'm not an expert) tend to recommend against the multi-split setups, although a few posters have had success. There are many posts of people unhappy with those setups, though.
Also, the Mitsubishi proposal sounds like it is almost 7 tons of capacity for 4700 sq ft? That sounds oversized.
As for Bosch, keep in mind that they are not communicating, so they supposedly do not control the indoor fan speed based on how hard the compressor is running. This often leads to humidity complaints because the units don't do a great job dehumidifying.
Hi aunsafe2015, thanks for your reply!
We are leaning towards the Bosch option and met with a nice company that was helping to guide us a bit more. They felt we could start with the Bosch 5 ton 20 SEER and avoid ductwork. The brochure (attached or https://www.bosch-homecomfort.com/us/en/ocs/residential/inverter-ducted-split-family-ids--18527266-p/) has some info about "enhanced humidity control". Does it sound like those controls would address the humidity concerns despite not having communication between indoor and outdoor? We were considering an Aprilaire 8920w (https://www.aprilaire.com/whole-house-products/thermostats/wifi-thermostat/model-8920w) - not sure if that helps with humidity as well?
They are offering a Fujitsu 25 SEER mini-split option (ASUG15LZAS, AOUG15LZAH1, 15LZASH1) for our Den which is 20*20 with vaulted ceiling. The den currently has it's own baseboard heat but shares A/C with the one zone. If we do the mini-split now, it would be part of a whole home rebate from PSEG resulting in ($5000+electrical work to add a circuit outside). If we wait, it will only have a partial discount ($7600 + electrical work).
Any further guidance is greatly appreciated.
That's still 6+ tons of capacity for ~4700 sq ft. Still sounds high to me. You should search this forum for how to do a load calculation.
Also, I don't necessarily think the Bosch is a bad unit, but I personally would not get one. If I wanted a traditional split system I would get a Trane XV18 or XV20. I know from experience that those do an excellent job dehumidifying even when operating at their lowest capacities.
If I wanted something from Mitsubishi, I'd consider the SVZ series you listed in your original post, but I would match them 1-1 with outdoor units rather than doing a multisplit.
If you only want 1 unit instead of two, something like the 48-ton Fujitsu units would probably be adequate capacity: https://www.fujitsugeneral.com/us/products/split/mp-ah-unit/index.html.
But 1 unit serving 3 stories will inevitably have some pretty significant temperature differences from story to story...
Thanks again Aunsafe2015!
Good to hear that we don't need the extra capacity. We actually don't have A/C in our basement currently and would not be adding it- so it's 3400sq ft that we are directly cooling.
The uneven temps are a bit annoying. How do you feel about a damper system? We were told we could add that after the fact for about $10k less than duplicating the indoor/outdoor units + duct work. Or, any opinion on smart vents like this one from Flair which in theory would be an even less costly way to modulate temps across floors/rooms? https://flair.co/pages/central-systems-smart-vents?gad=1&gclid=CjwKCAjwpayjBhAnEiwA-7enaxBHBsqlu63DSi0w91ALYfPltiyAM-9k0j1QOcZ3utcAjavvFmSX0hoC8bUQAvD_BwE
I'm a bit sour on Trane since our current system had a fan issue and a leak in 12 years. Also, would like to find a way to make the heat pump work given the ongoing savings.
Is humidity the main concern with the Bosch 20 SEER 5 ton outdoor condenser Model # BOVA60-M20 (Variable speed also modulates up and down for demand) and Bosch 20 SEER 5 ton Air Handler 220V Model # BVA60-M20 (2 speeds)?
"Good to hear that we don't need the extra capacity. We actually don't have A/C in our basement currently and would not be adding it- so it's 3400sq ft that we are directly cooling."
Clarification: I'm not saying that you do not need the extra capacity. I don't know if you do or not. You should really do some searches on this website and read up on it. Search for "load calculation" or "manual j" or something along those lines.
I'm saying that it's highly unlikely that you need 6-7 tons, especially now that you've mentioned your basement isn't included. Only a competent load calculation can tell you for sure whether or not you need the extra capacity. And no, the HVAC companies will almost certainly not be doing a "competent" load calculation. They typically use rules of thumb. "Oh, 4000 sq ft? 6 tons sounds about right" -- that's about the extent of what most HVAC companies will do.
Yeah, the dehumidification would be my main concern with Bosch, and I noticed you posted something that said they now have a 2-speed blower. I think the blower used to be only a single speed. A two speed blower will help, but it's still not as good as a fully variable-speed modulating blower like you get on for example the Trane XV18 or XV20.
Thanks again @aunsafe2015- the outdoor condenser Model # BOVA60-M20 is Variable speed, but I'm not sure if that helps. The air handler is 2 speed. Load calculations were done after measuring each room and considering insulation, but to your point, I don't know exactly how they did it.
Make sure you look at the manual J numbers for cooling.
When you install more than 1.5 times the manual J the units will not run long enough to dehumidify in the summer. The classic symptom is the house is cold and clammy. You are forced to select a lower than desired set point in an effort to get any moisture removal.
If 1.5 times your cooling load fails to meet 90% of your heating load consider adding the required insulation or skipping the rebate.
In my opinion putting HVAC equipment in any attic is a very bad idea and a total act of desperation. I will restrain myself and reframe from saying anything more insulting about this bad idea.
FYI the recipe for a bad heat pump install is any compressor connected to multiple heads and 200% oversized.
Walta
Thanks @Walta100. The ductwork has been in the attic for 20+ years (by the prior owners). I don't think I can afford to move it all to another location- not even sure where it would go.
I'm not clear on your recommendation to skip the (~$5000) rebate- are you saying that the minimum requirements for rebate are greater than what's needed for my home?
What I am saying is read your manual J if 1.5 X the cooling load is more than 90% of the heating load change the inputs to the manual J by adding insulation.
Understand if you are unwilling to consider improving your building envelope and you buy oversized equipment to get the rebate the oversized equipment will not remove enough moisture the house maybe uncomfortable in the summer.
The fact that someone else made the poor choice does change the fact that it was and continues to be a poor choice. The fact is you bought the poor choice your now own the poor choice you are now paying for the wasted energy as the results from the poor choice. Until you can see this error and find a way to undo it 20 -50% of the energy you are paying for is lost in your attic. The smart move is to get the HVAC out of the attic.
Walta
"The smart move is to get the HVAC out of the attic."
Or, make the attic part of the encapsulated, conditioned living space.