Advice for HVAC renovation in Eastern MA
joe_fb
| Posted in General Questions on
We are adding a small addition to our house (c1960) and hoping to upgrade our heating system as part of the process. We are about 20 miles west of Boston.
We currently have a FHW baseboard by oil-fired boiler setup. It’s a Burnham V7 (c1998) with a coil in the boiler for DHW. We use about 950 gallons of oil a year for a two-story, 1750sqft house. After the addition we’ll be at about 2000sqft. We use window A/Cs now and I hate them. I’d like to move to central AC as part of this.
I was considering moving to a ducted air-to-air heat pump system to lower our footprint and take advantage of the state rebates ($7k-$10k) . I had planned to use the boiler as the backup and for domestic HW for a few more years, but my understanding is the boiler is on borrowed time already. I don’t want a heat pump system without a backup.
No gas on the street. A few contractors have pushed moving to a propane furnace and central air system – no heat pumps, no rebates, not much of a carbon footprint reduction. Not ideal.
So basically we are starting over on an HVAC system and need DHW included. What kind of setup should we be looking at that is green-er and gets us AC in the process?
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Replies
Given that central AC is wanted and emissions matter to you, at minimum you should install a heat pump. So your decision is actually easy! Backup can be: electric resistance (expensive to run, cheap to install), furnace (propane or oil, both expensive to run, moderate to install) or another boiler (same efficiency as the furnace, more expensive installation usually). The backup source is for peace of mind and won’t be required to do much actual heating. The best option might just be to keep the existing boiler as backup - boilers can last a very long time.
Going with just a propane furnace and no heat pump isn’t a good sign - get them on board or find new contractors. Propane is expensive and the price delta between new AC and new HP of the same quality is minor.
Around me (zone 5) heating with fuel oil is more expansive than resistance electric heat and heating with propane is about the same cost. A properly sized cold climate heat pump in our climate can hit an average COP of 3, so a heat pump would be about 1/3 of the cost of propane and even less than that if using oil. So anybody that is trying to tell you that heat pump is not the right solution doesn't know what they are talking about.
If the state is offering you that high of an incentive for a heat pump, than a heat pump is a no brainer. Cheaper to install and WAY cheaper to run.
You'll have to do a bit of homework to figure out what your heating load will be including the new addition and size from there. This a good resource you can quickly modeling your house that is pretty simple to use (does require your email but free from there):
https://betterbuiltnw.com/hvac-sizing-tool
Once you know roughly your heating load, you can search through here for equipment:
https://ashp.neep.org/#!/
My guess is you are looking at about a 2.5 ton heat pump for the existing house and depending on build quality and insulation a 1.5 to 2 ton for the new construction.
Akos, 250 sqft addition would require 1.5 to 2 tons? Or did you read the post as an additional 2,000 sqft?
What happens when you speed read, I misread it thinking it is a 2000 sqft addition. 250sqft of new construction will barely budge the heat loss for the old house, maybe a 1/4 ton larger unit.
Very helpful.. Thank you for the links. Sounds like a the heat pumps are an obvious choice.
In this scenario what do you use for backup heat and DHW? Feels like a new boiler is a must even if we go with a heat pump.
An oil boiler can last for like…40+ years. I wouldn’t replace it. If you do have to replace it, then just get a furnace and abandon the baseboard in place. Much easier to integrate with a heat pump.
What is the backup for your oil boiler right now? I don't see why a properly sized heat pump would be different. I'm heating places in colder climate than yours with heat pumps with no backup heat of any kind.
A right sized cold climate hyper heat unit can carry your place without issues even without strip heaters. If you really must have a backup, install strip heaters. The oil burner and rads can stay or you can take them out and reclaim the floor space.
Any ductwork that can properly cool your house will be able to fully heat the place as well, so you are not adding a lot of cost to go off the oil heat. Register location is a bit more important in older houses for heating comfort but that is not a big change. The key to good efficiency and comfort is to avoid the equipment and ducting in unconditioned attic as this seems to be a hard fight with HVAC installers south of the 49th parallel. If you really can't do ducting elsewhere, at least don't have the air handler in the attic.
As for DHW, I would keep the system as is until something breaks. Heating hot water with oil is more expensive than resistance tank especially in the summer time. Once something dies, you can make a choice to go for a simple electric tank or a heat pump water heater, both options should be cheaper to run.
You could also see if Dandelion Energy operates in your area. They are trying to make ground source heat pumps more mainstream and cost effective. It would be a good comparison for air source heat pump quotes.
If you've got room to have ducts installed, I'd suggest looking at a ducted mitsubishi system. We've had a 2 zone (2 air handler) system installed for a few years now and really like it. You could install heat strips as a backup in case the heat pump itself failed.
What electric utility are you on? Any chance you're on a town-owned utility or in a town that has negotiated long term contracts ( https://www.masspowerchoice.com/ ) ?
We used Boucher Energy Systems for our project and they were great. I'd highly suggest talking to them for a project like this: https://boucherenergy.com/
Lastly, remember that starting in 2023 you're eligible for 30% of the project as a tax rebate (up to $2k).
I didn't know about the tax rebate in 2023. I'd only been looking at what MassSave was offering. Thanks for tip on an installer. The few I've talked to who suggest the heat pump also say we need two separate systems - one per floor. Sounds like that's the setup you have. What do you use for DHW?
We are on Eversource for electric. No muni option. How often are you using your backup heat?
We had a natural gas high-efficiency boiler for heat (via hydro coils in the air handlers) and for DHW, so we kept that as our backup. At our electric/gas pricing our economic balance point is around 5F.
We did have to use 'emergency' heat once right after the system was installed because the outdoor unit has a failure in the refrigerant piping :-(
When you talk to contractors, consider pricing on 2 separate outdoor units vs one large multi-zone outdoor unit. It would give you redundancy (and maybe let you skip a backup source) and better turn-down ratios. Knowing what we know now, I wish we had considered that option.
Can you do solar to offset your electric?
@jwasilko - How are you calculating the economic balance point for heat @ 5 degrees with a high efficiency boiler as your backup? Some of the calcs I've attempted to do with the Eversource electric and gas rates get it closer 30 degrees. I ask because I am looking into similar options as you and brianjf in the metrowest area of MA. The monthly cost to run the system is a big consideration for me and I am debating if I should keep, replace or ditch my 40 year old gas boiler when I add heat pumps soon.
I have Boucher coming out next week so I am excited to speak with them.
@brianjf there are also additional heat pump rebates coming next year as part of the Biden inflation reduction act. Up to $8k depending on your income
I'm using this spreadsheet I found online: https://www.dropbox.com/s/mlfbpamdoo7pta8/HP_Balance_Point_Worksheet.xls?dl=0
We've got a town power utility and solar, so our electric rates are under $0.11 kWh (all-in), so that's why our economic balance point is so low. Natural gas peaked over $2/therm but our electric rates have been pretty stable for years.
Boucher is back here next week too for a quote on the other half of our house!
This article shows how to use your historical fuel usage to size a replacement system:
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
brianjf,
Have you considered replacing the boiler with an air to water heat pump and keeping the piping and also using the heat pump to heat your domestic hot water?
Things to consider:
1. Are the piping and radiators in good condition?
2. Is there a rebate for this type of system?
3. This type of system would not have a backup unless you install an electric resistance type heater in perhaps a water storage buffer tank that could be part of the system or perhaps another method. Electric resistance could also be used as a backup for the domestic hot water.
4. Can your existing radiators be used as air conditioners to cool the space as well? Do they have a method for collecting and disposing of condensate or can that be added? Do they have fans that will circulate the hot/cold air around them?
5. One item to also consider, is your electrical service and panel large enough to add an electrically powered HVAC system without an upgrade?
Best of luck.
Josh