Help Me Design My Heating System

I'm picking up used AHS 260 boiler. I will be installing it in my detached garage, trenching it to my house.
We are restoring a 215+yr old farm house so everything is getting replumbed.
I currently have a propane hot water heater for DHW.
Cast iron radiators
I want to use the boiler for indirect DHW also.

I was thinking 5 or 6 zones
2 for the original stone part of the house (1st floor on one zone, 2nd floor and attic bedroom) Blaze King princess on 1st floor in fireplace.

3 for the addition (old addition is coming down, new addition which will be triple in size going up, zone for each floor, plus zone for the bathrooms) wife wants an old wood/coal cookstove in the kitchen addition.

Would like to use TRV'S, do I really need that many zones.

Possible heating of the garage, or at least part of it, plus heating garage bathroom, and DHW for bathroom. Garage is around 2000 sq ft, so I don't really want to try to heat the whole thing.

Boiler can't go in basement because of water table issues, during heavy rains, power goes out basement fills up with water.

Thanks,

Before I start making guesses, you should really consider getting a professional heat loss calculation and go from there.

That said, if you still like pure guesses:

If its old and drafty, and with poor insulation, I would go with 35 output BTU's per square foot. And perhaps double that for the section of the garage that you want to heat.

If you will be using standard hot water baseboards (such as the SlantFin Fineline 30 series) you will want no more than 52 feet of baseboard per zone.

At 50 feet of baseboard per zone and assuming 500 BTU's delivered per foot of baseboard, that will mean roughly 25,000 output BTU's per zone.

25,000 BTU's per zone divided by 35 BTU's per sq-ft = roughly 714 sq-ft per zone for the house. Half that for the garage.

Divide the home up into roughly 700 sq-ft sections and zone accordingly, using roughly one foot of baseboard for every 14 sq-ft of floor space. Don't forget to Include hallways and closets when factoring your sq-ft.

Your boiler should be capable of delivering about 184,000 output BTUH. 184,000 divided by 25,000 = 7 zones max at 50 ft of baseboard per zone.

7 zones x 50 ft of baseboard per zone x 500 BTUH per ft of baseboard = 175,000 output BTUH required.

To add DHW on a zone for an indirect HWT, allow for 34,000 output BTUH for that zone. That still leaves you with 150,000 output BTUH for the house and garage.

150,000 divided by 25,000 = 6 zones

There is enough boiler there for 6 zones of home/partial_garage heating and 1 zone for DHW.

But to be safe, assume that you will likely lose 1 zones worth of BTU's to the underground run plus to the boiler continually evolving away surface heat that is not going to go toward home heating, so that leaves 5 zones for home/partial_garage heating and 1 zone for DHW. I would insulate or jacket the boiler.

Your initial assumption of 5-6 zones, with one of those presumably for DHW appears to be quite sound.

If you want to use cast iron radiators, I believe they are typically rated at about 160 BTU's per sq-ft of surface area.

25,000 BTU's divided by 160 BTU's/sq-ft = 156 sq-ft of radiator surface area required per zone.

160 BTU's/sq-ft of surface area divided by 35 BTU's per sq-ft of floor space to be heated = roughly 1 sq-ft of radiator surface area needed for every 4-1/2 sq-ft of floor space.

Try out my simple design spreadsheet. It is attached here. To get 1 foot of baseboard for every 14 sq-ft of floor space you must set your local Heating Degree Days (HDD's) to 8100. I have done so for the attached. Your local HDD's are probably only in the range of 6,500 as a first guess, but due to the age of the home and the likelihood of poor insulation and high drafts I'm going for overkill in order to (hopefully, as after all this is guessing) end up on the safe side.

My spreadsheet program is for hot water baseboards. To convert it to radiators, multiply the feet of baseboard calculated for each room by 3-1/8 (3.125) to convert to the sq-ft of radiator surface area required per room.

If you enter the fractional sq-ft portion of the garage that you want to heat, it may be best to enter twice the sq-ft measured, so the program will be tricked into giving better results for the garage zone loop(s) requirements. The program is not intended to give correct results for garages or out-buildings, as it is intended only for residential home living space. If you end up with more than 150,000 BTUH as the calculated boiler output required for the job, then you will need to reduce (or abandon) the sq-ft of garage that you intend to heat. The whole garage thing may in the end prove to really confuse things.

No warranties or guarantees expressed or implied.

If you want to use TRV's, there is no need to have that many zones. The entire main house could be one zone as long as the radiators don't require a total flow rate greater than what a reasonably sized circulator can provide.

Plan on having the indirect water heater on its own zone, and pay attention to the pipe sizing between the boiler and the house. That AA260 won't be much good if it is piped to a large house with 1" pex.

The size of the home should determine the number of zones required (which may be only 2 or 3). The guidelines I've outlined are in keeping with the desire to experience only a roughly 20 degree temperature drop across each zone, as per classical design criteria for hydronic heating (excluding radiant). If you can tolerate a 30 degree (or more) drop you can easily get by with less zones. Perhaps with TRV's and continual circulation the drop across a zone is not nearly as much of a factor to consider. This would certainly be true if they are designed to have bypasses. Continual circulation may be an absolute must requirement for underground runs, but continual circulation comes with inherent heat loss inefficiencies that must be addressed through insulation.

lsayre wrote:The size of the home should determine the number of zones required (which may be only 2 or 3). The guidelines I've outlined are in keeping with the desire to experience only a roughly 20 degree temperature drop across each zone, as per classical design criteria for hydronic heating (excluding radiant). If you can tolerate a 30 degree (or more) drop you can easily get by with less zones. Perhaps with TRV's and continual circulation the drop across a zone is not nearly as much of a factor to consider. This would certainly be true if they are designed to have bypasses. Continual circulation may be an absolute must requirement for underground runs, but continual circulation comes with inherent heat loss inefficiencies that must be addressed through insulation.

Lots and lots of insulation and that insulation MUST remain bone-dry forever too.
No mater how much insulation...if it is soggy wet...it is useless.

Where is the OP?

Yes, I'm using cast iron radiators.
I definitely want to use TRV's.
I would like to keep the system as simple as possible.
The AHS 260 has a 1.5" outlet, so that's what I'm planning to use pex wise, or should adapt it to 2" pex?
When finished the walls of the stone side of the house will be r13, the roof will be r40+, currently repointing all of the stone on the inside before insulating, the draftiness will be cut down significantly.

I plan on running the pex through pipe, so that I can pull it and replace it if necessary, then I will spray foam the trench.

The stone part of the house's interior dimensions are roughly 21x24, so that's 504 sq ft times 3 floors.

Does it work better to run a zone to a manifold and feed each radiator individually?

jrv8984 wrote:Does it work better to run a zone to a manifold and feed each radiator individually?

I would think so, as parallel has room to room temperature uniformity advantages over series. And that way, if you add an automatic bypass valve (or DPTV) to each zone to maintain flow between that zones supply and return manifolds when all of the TRV's on said zone are closed, you will not need to purchase TRV's with bypasses in order to sustain series flow in the loop. It sounds like you are raising the complexity level of the install by considering this approach though.

It's more a matter of where I can run the piping. I have an exposed ceiling so I am restricted in how I connect my radiators.

About your heating needs, please invest in a copy of "Classic Hydronics" by
Dan Holohan. He writes his plumbing books for the layman and the plumber and
explains plumbing in the simplest terms for everyone.

If you invest in the $15.00 per foot Insulated PEX you will not have to foam the trench or lay any steel pipe.

Are you experiencing flooding from a neighbors property?? Why is it you are not concentrating on the basement repair? The damage you are describing from water ingress will lead to a foundation failure if it has not occurred in the past.

If you invested in a basement sump pump and catch basin you could put the boiler in the basement
on a slab that would also used for a coal bin and you would spend much less on plumbing and you could use a gravity hot water heating set up with your current radiators with one thermostat or manual thermostats mounted on each radiator.

Water ingress like you are describing is manageable with a sump pump or perimeter drainage and a sump pump.

From what you are describing your going to need an architect to design a drainage system for the home as well as a drainage piping system with a sump pump or two. It will be very hard to get a building permit with out any kind of soil tests for the architect to look at.

I technically live in a flood plain. During the rain storm in February, the water was 6 feet Below the surface of the ground, I have a hand dug well behind the house so I can measure. A new floor with drainage around the perimeter and a sump pit with dual pumps if planned in the very new future, but when you come home to find the power is out and your pumps aren't working, you can't do much about it.

I would prefer to be able to pull the pex, should a problem arise, than have to dig it up., that's why I am going to put it into pipe. I figure spray foaming a trench will be a far better way of insulating than buying the preinsulated pex.