Replacement boiler for baseboard heat
I am in CT Zone 5a, with Runtal hydronic baseboard radiators, and would like to install a Viessman Vitodens 222-F for DHW and the space heat. I think the radiators are a smidge undersized (according to the Man J from 2019). Can I get a second look and some advice? The contractors have all given conflicting advice.
The Total Heating Required is 33,755, 1414 sq. ft house, 1 story ranch. (The numbers below represent: per room BTUH Needed/Runtal Baseboard BTUH.)
Room 1- 3093/3050
2- 6969/6840
3- 3734/3420
4- 6133/4560
5- 2490/2280
The Runtal numbers are based on size with AWT at 160-degrees (max temp for space heating from the 222-F is 165-degrees, they advise counting on 158-degrees). Since the Manual J in 2019, we have added attic insulation and basement sill insulation, if that makes a difference.
Will the existing radiators work?
*Edited to add: This is not a full list of rooms and radiators, as there are a few rads I still need to purchase. Those will be properly sized.
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Replies
Manual Js are often low quality. Have you run a fuel usage heat loss?
This was done by a certified HERS rater and was a part of a much larger assessment. I trust it! And, unfortunately, I haven't used any fuel to heat my home in 5 years, so I can't run the usage heat loss.
Can you wait 1 year? I’d see if any of the rooms are actually cold first before spending. It’d also let you dial in the fuel loss. You cannot trust software heat loss calcs, way too much guessing goes into them.
Since we have no heat outside of our wood insert, I will be buying a boiler sooner rather than later!
I meant buying the boiler, then waiting to see if you need more baseboard than you currently have.
Ah, got it.
Room #3 is particularly concerning. If you have zoning that room won't be warm on the coldest days, if you don't have zoning it will be cold all the time.
Generally you want the radiators slightly oversized rather than undersized as you have them. The insulation improvements you've made may be enough to tip the balance for the other rooms.
You may be referring to room 4 (not 3), and I agree. Moving this one to another room and purchasing a rad that will be slightly oversized for that room might be necessary. We can feel a difference in the home since the insulation improvements, so I am hopeful that the other rads will be in line with the current heat requirements of those rooms. Thank you!
Yes, 4 not 3.
Is the current boiler operational?
Assuming it is it would be ungreen to replace operational equipment do so force new equipment to be manufactured needlessly and is wasteful. Replacing equipment unnecessarily make no economic sense any new equipment is only slightly more efficient than the old equipment.
Reduce, reuse only then do you recycle.
Manual J calculations are a great tool but they are ruff estimates at best and almost always wildly wrong when done free of charge by someone preposing new equipment.
Walta
TO make such a judgement one would have to know what the old boiler was. IS it near end of life? Is it an oversized[now] atmospheric vented boiler that will be performing well below its rated AFUE?
Judging by the size of the house it sure sounds like a 60s ranch that could have a 50+ year old boiler.
I would ask the OP what their gas usage was now and what the comfort level of the rooms is now. Then one can judge whether replacing the boiler is 'green' or not
The Viessman seems to run slightly colder than classic water temps, so if you have a cold room now it will be worse in the future.
Since the radiators are sized for design temp, one would think having increased the insulation level and dropped teh water temps slightly may be a wash
I currently have no heating in my home, other than a wood insert that is sufficient for all but the coldest days. The Man J was a part of a larger assessment done by an independent HERS rater.
Ahh, so it is hard to say.
The other variable is distance from the thermostat.
A room with higher loss close to the thermostat will make the other rooms run warmer where as a room with higher loss far from the thermostat will run cool
A great point - it’s not an exact science. Say one room runs cool - you could double the baseboard and be well oversized while the room remains the exact same temp.
The radiators are individually controlled at the unit. Won't that make a difference?
In that case yes! TRVs are great. But will you or they even notice if a room is a degree under setpoint? Probably not, we’re humans not robots.
Usually the way TRV's are plumbed is that one radiator doesn't have a TRV. Ideally that one is closest to the thermostat and the smallest radiator relative to the load of its room. In other words, the radiator that should be on the most. So that radiator is on whenever the thermostat calls for heat. The other radiators turn on whenever the thermostat is calling and their TRV is also open.
What you want to avoid is a situation where a room with a TRV is cold but the room with the thermostat is warm, so even though the TRV in the cold room is open the thermostat isn't running the circulator so you're not getting any heat.
I plan to put the thermostat in the hallway where there are no rads, a good distance from the wood burning insert (it is always fairly temperate, but not warm). The towel bar rad in the bathroom will have no TRV. Low load (1006 btuh), but it would be nice to always be warm in that room!