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Old 12-17-2019, 02:59 PM
 
636 posts, read 268,207 times
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We got a new 95% efficiency combi gas boiler/hot water heater with indirect storage tank, 3 heating zones and 2,000SF house with insulation and new windows. It was 60 degrees in the house and we set the temp to 70. In two hours the temp only only moved up to 61, 62 and 65. I also don't notice a difference in how long it takes to get hot water upstairs. Is this normal?

I just installed Nest E thermostats so I'm wondering if that's the problem. I had a schedule for 60 degrees at bedtime, then 68 at 6am. I checked at 1am and it had already started preheating - what's the point of turning down the temp then?

With our old boiler, it would heat from 65 to 72 by the time my son's bath was over. Our first heating bill this winter was nearly $500 so that probably explains why. I'm hoping our gas bill goes way down with the new combi.

In our first house, we had a high efficiency gas furnace and would schedule 60 degrees at bedtime and 68 at 6am and it would only take 75 min or so. It was 1270SF with one heating zone.

Last edited by matrix5k; 12-17-2019 at 03:22 PM..
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Old 12-17-2019, 03:47 PM
 
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Depends on house layout. If you have a split ranch(open basement, open floor plan) or a place with very high ceilings ( large volume)
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Old 12-17-2019, 04:02 PM
 
Location: Massachusetts
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Yes, this is normal. Your heating contractor should have explained it to you. A high efficiency boiler usually only raises the temperature about one degree per hour. There is an outdoor thermometer connected to it so this is consistent year-round (i.e. the warmer it is outside, the lower the boiler water temp will reach). You should set your thermostats to never lower more than two or three degrees overnight or while you're at work. It seems counter-intuitive to have heat you don't need but it's more efficient that way. Otherwise, it runs constantly for eight+ hours just to catch up.
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Old 12-17-2019, 05:27 PM
 
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2500 sf, three zones, old 90s boiler tech with Nest thermostats. Night time temp is 63 degrees and I set it to 69 degrees for 7am. Usuallly takes 2 hours to get to temp when ida around 30 degrees ambient outdoors. This months heating bill was $250

Of course, I realize there are a lot of variables in play here so it’s not an apples to apples comparison.
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Old 12-17-2019, 06:14 PM
 
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Quote:
Originally Posted by mondu View Post
Yes, this is normal. Your heating contractor should have explained it to you. A high efficiency boiler usually only raises the temperature about one degree per hour. There is an outdoor thermometer connected to it so this is consistent year-round (i.e. the warmer it is outside, the lower the boiler water temp will reach). You should set your thermostats to never lower more than two or three degrees overnight or while you're at work. It seems counter-intuitive to have heat you don't need but it's more efficient that way. Otherwise, it runs constantly for eight+ hours just to catch up.
I will try this thank you. I'll set temp to 69 while home and 66 at night and away. Do you recommend a temperature for the boiler? The plumber set it to 140 by default. I raised it to 150, not sure if that will help or not. Really hope my gas bill goes down.

Last edited by matrix5k; 12-17-2019 at 06:24 PM..
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Old 12-17-2019, 08:42 PM
 
Location: Massachusetts
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Quote:
Originally Posted by matrix5k View Post
I will try this thank you. I'll set temp to 69 while home and 66 at night and away. Do you recommend a temperature for the boiler? The plumber set it to 140 by default. I raised it to 150, not sure if that will help or not. Really hope my gas bill goes down.
I assumed, maybe incorrectly, that all new high-efficiency boilers have an outdoor reset control that automatically sets the boiler temp based on the outside temp. This lowers your energy costs in milder conditions. See here for more info:

https://www.bobvila.com/articles/out...iler-controls/

If your unit only has a manual control, maybe you should raise the temp even higher for this time of year. You really should talk with your installer though, as they'll know the equipment and your heating needs to help find the ideal setting.
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Old 12-17-2019, 09:06 PM
 
Location: Needham, MA
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My house is a bit bigger than yours (about 2400 sq feet) and my heating system works at about the same rate as yours. I installed a high efficiency gas boiler about 5 years ago and honestly I don't recall the previous standard efficiency boiler heating any faster. Furnaces definitely can change the air temp much faster than boilers so you're able to really cut the temp and then heat it back up at night or if the house is empty while you're at work. With a boiler as others have already said, you don't want a ton of variation in the temperature schedule. Just a few degrees is really all you want it to vary.
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Old 12-18-2019, 04:50 AM
 
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The recovery time is mostly related to the square inches of radiator, not the boiler. The radiators are sized to hold temperature in subzero. If you make them bigger, the temperature in the room will oscillate hot-cold. You get to pick between fast recovery time and stable temperature.

Both my places have Peerless boilers with forced hot water baseboard radiators. I have radiant heat in the floor of one bathroom. One boiler is from 1987. The other is 2010. The newer one is electric ignition so no pilot light and about 1% more efficient. I could swap in a high efficiency boiler and I doubt that the recovery time would change. All boilers heat water to the same temperature.
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Old 12-18-2019, 08:37 AM
 
Location: Needham, MA
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Quote:
Originally Posted by GeoffD View Post
The recovery time is mostly related to the square inches of radiator, not the boiler. The radiators are sized to hold temperature in subzero. If you make them bigger, the temperature in the room will oscillate hot-cold. You get to pick between fast recovery time and stable temperature.

Both my places have Peerless boilers with forced hot water baseboard radiators. I have radiant heat in the floor of one bathroom. One boiler is from 1987. The other is 2010. The newer one is electric ignition so no pilot light and about 1% more efficient. I could swap in a high efficiency boiler and I doubt that the recovery time would change. All boilers heat water to the same temperature.
That makes sense. The speed at which the room heats is limited by the speed at which air travels over the radiators. So, increase the surface area of the radiators and the room will heat faster. This is why a "forced hot air" system (a/k/a a furnace) changes the temperature so much faster. It's actively pushing air over the heating coil and pulling heat into the room. A radiator is more of a passive system and relies on the natural rise/fall of air as it heats and cools.

I recently renovated my kitchen and because all of the walls now have cabinetry I had to get rid of all the passive radiators in there. I thought about doing a radiant floor in there but at the recommendation of my contractor ended up with a toe kick heater under the cabinet. While the heater's fan is definitely loud, that room noticeably heats up faster than the rest of the house because the fan is actively pulling the heat from the hot water pipes.
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Old 12-18-2019, 09:32 AM
 
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Lots of variables here....

What size was your previous boiler (btu) and what size is the new one? The older ones were typically oversized at 2X needs.

Also, do you have cast iron radiators or baseboard - heat response time is mostly driven by the volume you have to heat. Hopefully they sized the boiler and pumps accordingly.

With 3 zones and a new system, it will take some time and trial and error to get it right and comfortable for your needs - you may need to rebalance some zones - call the guy who installed it.

I'm not a fan of the 'learning' mode for nest for hydronic, especially for cast iron radiators. I would set it to come on sufficiently ahead of time such that it is at temp. when you get up.

As other have said, hydronic is better when you don't have big temp. swings but it is a far more comfortable heat than a furnace.

How much did the changeover cost? - what/when do you estimate break-even point?
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