Dear kind folks at Heating Help,
We recently bought a 100 year old two-family house in NJ, gutted it, and are re-insulating it. We're finishing the second floor small apartment first so that we can move in asap, and will finish the larger apartment next year (leaving it with bare studs for now) and the basement a few years later.
We prefer a hot water boiler with baseboard and indirect hot water tank.
Zones will be as follows:
(numbers are rounded)
Zone 1: Second floor separate apartment
400 sq-ft 10,000 BTU 20' BB
Zone 2: First floor
860 sq-ft 31,000 BTU 55' BB
Zone 3: Second floor master bedroom/bath
210 sq-ft 5,500 BTU 10.5' BB
Zone 4: Basement
600 sq-ft 30,000 BTU 51.5' BB
Optional Zone 5: Attic-closet
500 sq-ft 9,000 BTU 15' BB
Total without attic: ~ 77,000 BTU
with attic: 86,000 BTU
We decided not to go with a separate boiler for the 400 sq-ft apartment (Zone 1) because of the added cost and also so that we won't have to bother with separate gas service for that apartment. So for the first heating season, the boiler will be used for only this small space, and the rest comes later.
Our plumber asked his normal supplier what they would suggest, keeping in mind ease of service and getting parts, and they said Navien NHB 150 (with 15:1 TD) or a WM 140K CI, either one with a WM AquaPlus 55 indirect.
It would appear that they over-sized, which I understand is the "norm" and I would need to address this with them especially if I go the CI route.
He took rough measurements of the room and windows, but did not do a formal heat loss. The heat loss and baseboard lengths listed above are my best layman's attempt using the Slant Fin heat loss application.
My questions are as follows:
1. When it comes to baseboard installation (from scratch), there's limited wall-space and budget. The slant-fin app is giving lengths based on 180 degree WT. I understand it's best to oversize to reduce this temperature, but if we don't, or only do so by say, 20%, will that be enough to make a Mod Con worthwhile?
2. Given the size of the zones, would either boiler be likely to short cycle.
a. The attic will be well-insulated, but we weren't necessarily planning on heating it. However, I thought of adding some baseboard up there just to make the 5500btu zone bigger (keeping the thermostat in the bedroom). Does this help? Is it necessary?
b. During the first year using only 10,000 btu plus DHW, will even the mod con short-cycle, as even this zone will require less than this on non-design days.
c. Would using longer lengths of baseboard in the smaller zones help with short cycling or make it worse since SWT would be lower in that case?
3. Is the WM AquaPlus 55 indirect water tank a good choice for the price? The rep at WM said that this is a revised model as of this year that addresses an issue with the prior one. Not sure I like to buy a product when it's first released, but I understand that WM is a reputable company generally and it's the brand that this supplier deals with.
Anything I haven't thought of?