Appreciate the help. I like Tom Sawyers approach definitely over complicated. I had a plumber check it out and he agreed the temp down there is very comfortable. He said a 16 ft run on the long wall where the windows are will be plenty. I was going back and forth between just putting a pellet stove or doing the baseboard. I'm just waiting on the estimate.
I estimated the parts $150 for baseboards, $130 for zone valve, $75 for pex pipe, $50 for thermostat and wire run and then any little misc copper Ts to tie it in. It'll be interesting what the labor amounts to rough it, drain the boiler and tie it in to existing system. The estimate I get will decide if end up abandoning ship and throwing in the stove or rough the pex myself and tie it in down the road.
I'm going to side with Dana on this one. 16' is definitely way too short, since the math says that 50' itself is already too short.
Unless, of course, your goal is to fry your boiler and get the insurance company to pay for a new one. YMMV.
If we're settled that extreme short cycling is something to avoid, I see three viable options:
1. Run the basement baseboards off the same zone as the 1st floor. I'd put it in series, after the 1st floor, so the basement "sees" slightly cooler water. This will still almost certainly overheat the basement, but warm air rises and you'll get most of that back. Could make the basement uncomfortable, though. Alternately, you could plumb it in parallel and put a gate valve onto it to restrict flow, thus manually tweaking the balance.
2. Put 50' or so of baseboards in so that the basement zone is more like the others. Ideally, you should probably downsize the boiler next time you replace it, or maybe run an indirect water heater off it as well to make use of its excess capacity. The more perfectly the boiler is matched to the radiant (and indirect) load, the more time it will spend in its steady-state efficiency zone. The idea here is to make it run in short normal cycles, rather than short-cycling. The difference is in whether the room thermostat or the boiler's internal thermostat is making the shutoff decision.
3. Hang it all and just put independent electric baseboards down there.
For what it's worth, I don't see an overly warm basement as an entirely bad thing. It reduces the heat load above, and buys time when the power goes out before your pipes are at risk of freezing. Just so it's not so hot you can't go down there.
The math is going to cost him a couple grand that he doesn't need to spend. He said its always pretty comfortable down there without any heat at all. His existing heat pipes, domestic hot water pipes, washer and dryer all add heat to the zone. 20' of base will bump it up the few degrees he wants and I'll bet a whole lot that the cycle times are not materially different than he is already seeing on the rest of the house. I see this as the difference between engineers that spend their days at a computer and someone that has done so many similar installations that I can't even begin to count them. If he had a mod con down there I would probably side with you guys but not here. You are all over thinking this thing.
Originally Posted by moreira85
That's exactly why you DON'T just let a plumber be your hydronic heating designer!
If you run a parallel branch off the first floor zone and put a tweakable ball valve adjust the proportional flows between first floor/basment you can probably just drop in the 16-25' or whatever and get reasonable temperature without a zone valve and without a basement thermostat. It'll also lengthen the burn times on the first floor zone calls, which will improve the net efficiency slightly.
The napkin-math says even a 50' zone will be a comparative short-cycle at a 20F differential on the boiler controls. It's probably worth installing a heat purge economizer control (eg Becket AquaSmart, Intellicon 3250 HW+, Hydrstat 3200, all sub-$200 at internet pricing) to "exercise" the thermal mass of the system, maxing out the burn lengths, parking the boiler at a much lower temp during idle for lower standby loss. With sub-2 minute burns the thing is probably running about 75% efficiency instead of it's nameplate ~84% AFUE, but with a heat purging economizer control it can be pulled back north of 80%, saving maybe 10% on the overall fuel use.
Try turning down the thermostat by 5F on the existing zone with the greatest amount of baseboard, and bumping up the thermostat on the shorter baseboard zone by 5F, then time and count the burns for an hour. If the aquastat controls can be set up for a differential greater than 20F between the high and low limits, max it out, whatever it is (keep the low-limit above 130F though.)
Electric baseboard cost about 3x to heat with than 80% gas.
The output of even the smallest pellet stove will be RIDICULOUSLY oversized for the basement heat load- don't go there!
A pretty-good 3/4 ton mini-split (eg: Fujitsu AOU-9RLS2, Mitsubishi MSZ-FE09NA) would have an installed cost comparable to the pellet stove, and would be more appropriately sized, and it will modulate with load. It would cost about as much to operate as heating with 80% gas, and would be cheaper to run than a pellet stove. As a mostly-DIY you can get out for under 2 grand. Wth a pellet stove
If the math is going to cost a couple grand, I'm clearly in the wrong business, or not charging enough! :-)
Originally Posted by Tom Sawyer
As a mostly DIY site, if you give them enough of napkin level math, they can usually hit it close enough.
I'm not trying to slam anyone here and I'm just a guilty of overselling myself but sometimes a little light comes on and I stand back and look at the bigger picture. Sure, putting 20 feet of base is not the optimal thing to do but then again, his boiler is 20 plus years old and I'd bet money that the other zones are less than optimal in length too. It probably will short cycle a bit but no more than it probably already cycles.
Originally Posted by Dana
It's all true!
He says has 112' of baseboard cut up into 2 zones, so at least one of those zones is going to be pretty damned stubby for 85K of output, so if he is averaging better than 3 minutes of burn out of it I'd be surprised.
Which is why piggybacking the basement onto the first-floor zone by whatever means necessary is a marginal improvement, and a 20' stick by itself takes yet another step down the efficiency scale.
Definitely a candidate for a retrofit heat-purge control. If he can combine the basement & first floor with reasonable temperature balance and heat-purge the boiler at the beginning/end of calls for heat it'll cut down the number of cycles, lengthen the average burn, and crawl at least a bit out of the efficiency hole it's in.
At 85,000BTU/hr it's delivering about 200% of the actual 99% outside design heat load for the average MA house (according to utility site surveys) and about 300% the heat load of post-1980 2x6/R19 houses in MA. With the info at hand it's hard to say for sure what the whole house heat load is, but it isn't likely to be anywhere near 85,000 BTU/hr. He could probably heat his place just fine at 140F AWT, a temp at which the 112' of fin-tube is putting out ~35-36,000BTU/hr., and a boiler that delivers 40-50K would still have plenty of margin. But even a 40K output boiler will short-cycle on a 16-20' baseboard zone, yet would operate just fine on a 50' zone. Whatever he replaces it with should be right-sized for the heat load, but sizing the radiation on a new zone so that it will always short-cycle even with a right-sized boiler seems short-sighted.
A 20 year old short-cycling boiler is very likely to be replaced in under a decade. A $200 heat purge controller will likely pay off within 2 years. Spending the "extra" couple hundred in additional baseboard to ensure the next boiler doesn't get short-cycled seems "worth it" to me. YMMV.
It's 20 degrees out. My basement is 68 degrees without any heat.
That'll change when you replace that boiler with a newer high efficiency unit after it croaks from all the short cycling.
Originally Posted by moreira85
Really, no amount of insulation is *that* awesome, even at R9999999ZOMG999, heat leaks, albeit slowly. Obviously something is adding heat to the space, and if there's no deliberate radiation, what's left. The boiler, the water heater, and the pipes.
I'm thinking, if you're looking for simple, make the basement zone about the same size as the others, but then don't actually make it a zone. Either connect it in series with the 1st floor so the basement gets the "used" water from above that's cooled some or put a tweakable valve on it. Then, when you finally do replace the boiler, replumb the basement near-boiler piping to be its own zone.
Otherwise, set aside some extra $$ for adding more fin tube at the same time as the eventual boiler replacement.
How about some comments on roughing the pex tubing? If I have an 8 ft run of baseboard where would I want the beginning and end of the tubing to be roughed out of the drywall. If I also have 2 8 footers that I will have put together where should I start and end the pex out of the drywall?
That's really dependent on the particulars of the hardware you've got and how exactly they bolt to the wall and/or each other.
Just think of it as a jigsaw puzzle with the picture missing from the box.
That's due to the ridiculously high standby losses of your oversized boiler- it's like having an uncontrolled radiator parked in the corner of the basement.
Originally Posted by moreira85
If you ever replace it with something right-sized or more efficient you'll need enough intentional radiation to cover the load.