Help me choose system for midsize new england house

[Rekonn]

Hello, which of these two systems would you choose? I have a 2100 sqft 2 floor house built in 1928 with attic and basement in Arlington MA. I've had two contractors do manual J calculations, both came up with ~66k heating btu load. I plan to finish the basement (~900sqft) in the next year or two. Both options are very similar in price, so that's not really a factor.

System 1: AC + hydro air
First floor:
2.5 ton Carrier FV4CNF002 fan coil with ECM motor AHRI #3657139 and hot water coil in basement
Second floor:
2 ton Carrier FV4CNF002 fan coil with ECM motor AHRI #3657138 and hot water coil in attic
Two condensing units installed outside on plastic pad, Carrier 24ACC630A and Carrier 24ACC624A
Buderus GB142-30 condensing gas boiler, 96% AFUE
reuse existing indirect water heater
save cast iron baseray baseboards currently on first floor for when basement eventually finished


System 2: AC + furnace
First Floor:
80,000 BTU Trane XV95 Variable speed Furnace, XB14 3 ton Trane condenser, Trane 3 ton coil
Second Floor:
60,000 BTU Trane XV95 Variable Speed Furnace, XB14 2 ton Trane condenser, Trane 2 ton coil ( Furnace boxed in attic to keep insulated )
2410 April Air Filter
Model 400 April Air humidifier ( basement only)
Furnace sized for future basement zone
new 50 gal gas hot water heater

[dan sw fl]

Hello, which of these two systems would you choose? I have a 2100 sqft 2 floor house built in 1928 with attic and basement in Arlington MA. I've had two contractors do manual J calculations, both came up with ~66k heating btu load.

How does that compare to your current heating usage?

How did the contractors know what to use for infiltration and wall insulation in the Manual J calc?

[Rekonn]

The house currently has a mix of steam radiators and cast iron baseray baseboards, powered by an oil boiler. I moved into the house at the beginning of May, and it worked well for the days that got down to the 40's. We requested a year's worth of oil bills from the previous owners of the house, but did not get it.

I gave both contractors a floorplan of the house, and they measured every window in every room, noting which were single pane vs double.They both asked me about wall insulation, and I told them whole house has plaster/lath walls and brick exterior. I guessed that the exterior walls have no insulation. I don't know what was used for infiltration.

[motoguy128]

If an oil boiler, keep the radiant heat, but use a heat pump for mile weather above about 30F.
You might want to just use the smallest size of electric strips for the aux upstairs, and a hot water coil downstairs, but again, undersize the aux and still use your radiant heat, to minimize drafts and air movement, reduce duct size and costs.

WIth the furnaces, those furnace sizes are massively oversized for your climate unless you leave a couple windows open all winter. 40k, 60k should be plenty if not still oversized. For AC, I'd thinking more like 1.5-2 tons on each floor depending again on some construction details.


IS this a stone or stick frame construction? Does it maintain indoor humidity levels when there's a sudden drop in temperature in winter? I' trying ot determine is it's a fairly tight home. IF you turn off the heat in the morning on say a 30F day, does it cool off by only 2-4F all afternoon or by 5-6F. New construction would cool off by 5-6F, but a older stone or brick home will usually only lose 2-4F. Does it have a lot of shade and deep overhangs. Some 1920's homes have deep overhangs for natural shading since.


IF it's a stucco, stone or brick and if you have all the original plaster walls inside and thick hardwood floors, it won't need nearly as large of a heating and cooling system. But for cooling, shading make a big difference.


1920's construction can vary significantly. In most cases, if it's stucco outside and plaster insude, it's probably tighter construction than many new homes, if you have good storm windows and the prime windows have been restored/reglazed. Repalcement widnows more than 8-10 years old probably leak more than wood windows with good storms.

You really are best having a home energy audit done first ot see how you home performs. For a comparison, my 3200sqft 1925 home is a much more diverse climate (both a lot hotter and colder) in Iowa only actually needs about 60k BTU for heating and 3 tons of cooling for the whole house. In reality, due to equipment sized available, I have a 60k furnace on both floors, and a two 2 ton AC's. I have a LOT of widnows, but very, very, very deep overhangs for natural shading.

[Rekonn]

Ok, looks like I have more research to do as I definitely don't want to buy an oversized system. If anything, I'd prefer to go slightly undersized as I plan to improve insulation and eliminate leaks.

It's stick frame construction. Based on some fireblocking I've seen so far, it may be balloon framed. I don't know about the ability to maintain temp and humidity, I just haven't monitored it closely yet. I'll check floor thickness later tonight.

Should I get a blower door test done? From what I've read so far, it seems relatively inexpensive way to get real quantitative data on infiltration. Is a blower door test something that's included in an energy audit?

Keeping the radiators isn't an option. My wife doesn't want them on the first or second floors. We are converting to natural gas, and just had a new gas line run to the house. The oil boiler will be replaced.

[Rekonn]

Here's a pic if it helps answer any questions. The front of the house faces west.

[neheating]

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[motoguy128]

With the shade, window area and brick you might be able to cool that entire house with 3 tons or less on a humid 87F day (warmer parts of MA are only 87F design temp) or less easily.

Sorry, I misread the oil. reread your quotes. I'd go with the boiler and hydronic air handler on both floors. Be use ot use outdoor reset. Then the unit should be running almost continously. Heating airflow might end up being higher upstairs, but I'd oversize the coil so you can use lower water temps most of the time.

[Rekonn]

National Grid a/k/a Keyspan a/k/a Boston Gas will do an energy audit for you in Arlington MA for free. It is paid for by the energy conservation line item in your National Grid gas and NSTAR electricity bills. I would sign up immediately, there is a shorter wait time in the summer than in the fall. They should be able to do a blower door test and lots of other interesting stuff. Also expect to get a lot of coupons for energy efficient appliances, shower heads, boiler efficiency analysis, etc. They don't advertise this but is available upon request. I believe they contract with Honeywell for the audits.

I had a free energy audit arranged through Masssave. They told me they don't do blower tests in older homes due to risk of stirring up asbestos. At the time I didn't think much of it, didn't know that I would really want that. The asbestos thing seems like a lame excuse, or probably they're trying to be super careful in avoiding lawsuits. In any case, I'm going to see if a private company will do one for me. Otherwise I got some new light bulbs, and they changed changed shower heads and stuff. The main benefit is I'm now eligible for the 7 year 0% loan and rebates on new equipment.

[Rekonn]

With the shade, window area and brick you might be able to cool that entire house with 3 tons or less on a humid 87F day (warmer parts of MA are only 87F design temp) or less easily.

Sorry, I misread the oil. reread your quotes. I'd go with the boiler and hydronic air handler on both floors. Be use ot use outdoor reset. Then the unit should be running almost continously. Heating airflow might end up being higher upstairs, but I'd oversize the coil so you can use lower water temps most of the time.

Good to know, thx!

I just remembered that the home inspector said the fireplace was missing a damper. Maybe that's the reason for the high btu load estimates? I'm thinking about getting an air tight chimney cap/damper to fix that.

[motoguy128]

I'd just take the fireplace out of service and install a direct vent fireplace later. Yes, you're probably losing some heat out of it, but not 60k BTU worth. In summer, it would leak air mostly in reverse, if at all.

FYI - if you actually needed 140k BTU's to heat your home, even with HE furances you'd have a $600+ gas bill in the coldest 2 months. I doubt you're over $300. A perfectly sized systme runs almost continously for several hours in design conditions. Which again, is about 87F and 6-10F where your at.

[neheating]

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[Rekonn]

Neheating, yup, you're right, but please edit your post to remove my street address. How do you know the house? Did you service the boiler? The insulation on the steam pipes looks newer, and the inspector said it wasn't asbestos, so I should be good there. What do you mean by sink sump? And, ugh, the wallpaper is special, lol. So are the hardwood floors, only the edges not covered by the previous owner's large rugs are finished! The house needs work, but I'm happy with it, thx!

[beenthere]

neheating, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here.

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[Rekonn]

Heating airflow might end up being higher upstairs, but I'd oversize the coil so you can use lower water temps most of the time.

Was rereading this, makes sense, more surface area makes using lower temps possible, getting most efficient use out of condensing boiler. Could you tell me how to know if the coil is properly oversized? Do hot water coils have some kind of metric I should look for? Do I ask my contractor for a hot water coil model number, and then google that?

[motoguy128]

All water coils will all have data table showing capacity for airflow, water flow rate and water temperature... usually with correction values for differnt return temps.

Yes, get the model number then do some searching. SOmetimes hydpic air handler will have multiple coil sizes for the same size blwoer. Other times you have to use a different blower size.

Keep in mind, that with modulating boilers, usually return water temp cannot be higher than 150-160F, and to be effcient, you need return temps under 140F. Ideally under 120F.