Fasten your seat belts...

Jamie Hall

I just read that the DOE has put out a recommendation for people to use 7 to 10 degree (F) setbacks when they are not in their houses. Better begin thinking about what you are going to say…

LRCCBJ

Nothing wrong with a 7-10F setback IF you have the capability to recover in a reasonable amount of time. Most of the time, FHW radiation will NOT allow a reasonable amount of time. Of course, you can use a programmable 'stat to achieve a setback in an unreasonable amount of time, however, that unreasonable amount of time is not fixed. You might need 4 hours to recover when the ambient is 30F. You might need 10 hours to recover when the ambient is 0F.

Additionally, with a mod-con, this approach is directly contrary to fuel efficiency and savings. At the end of the day, you're probably even on cost when the modcon must recover at 84% efficiency rather than greater than 90% if there is no setback.

This large setback approach is generally quite frustrating for most homeowners with FHW to understand and implement.

I will state that I can do a 10F setback on a FHA system and deliver 70K to the space. The recovery is less than two hours. One of the benefits of FHA. I might suggest that the DOE was thinking of FHA systems with they suggested such an approach.

It is also likely that steam systems can typically recover 10F in two hours, under most conditions, due to the elevated supply temperatures and the generally oversized radiation that is typical in steam systems.

So, YMMV and it is strictly dependent on the capability of the radiation.

ethicalpaul

Do you have a link to this? I assume people will react the same way they did when Carter suggested people put on a sweater.

ChrisJ

I can easily do a 10f setback without issue.

I won't but I can.

SlamDunk

If energy prices spike, people would do that without being told to.

EBEBRATT-Ed

The set back you can do depends on the OA temp as well. IMHO 7degrees is a bit much at design conditions. 4-5 is probably OK.

But a set back in some buildings with some heating system will not save any money. You have to re heat the walls, floors, ceilings furniture etc etc. Not much savings and may cost you more.

ChrisJ

https://forum.heatinghelp.com/discussion/comment/1819361#Comment_1819361

Reheating doesn't make sense. Yes you need to bring the mass back up to temp but that heat is never lost, you get it all back when the room cools. The objects simply store it.

The cooler the space the less heat loss. A manual j shows this. If the system isn't broke I don't think it's possible to cost more to do a setback.

GGross

https://forum.heatinghelp.com/discussion/comment/1819233#Comment_1819233

It's pretty thorough as far as recommendations go. They even mention heat pump users, and those in severe climates are poor candidates for setbacks. The steam and radiant floor advice was not my favorite lol

https://www.energy.gov/energysaver/programmable-thermostats#:~:text=You%20can%20save%20as%20much,those%20in%20more%20severe%20climates.

ethicalpaul

Thanks for the link, @GGross! That struck me as a well-written, useful guide. Where's the bad part, Jamie?

What was the part about steam and radiant floors that you didn't like, @GGross ? It seemed reasonable to me

ethicalpaul

https://forum.heatinghelp.com/discussion/comment/1819246#Comment_1819246

Reduction of waste is good even if energy prices don't spike.

GGross

https://forum.heatinghelp.com/discussion/comment/1819421#Comment_1819421

Reasonable for sure I just don't like how vague this was.

"However, some manufacturers now offer thermostats that track the performance of your heating system to determine when to turn it on in order to achieve comfortable temperatures at your programmed time."

It sort of feels like its added in there with a little less weight, followed up by suggesting a programmable thermostat and using guesswork. I think the radiant floor setback discussion specifically could be a whole report for itself, it may be more helpful for the average homeowner. But then again they will end up here if the guesswork gives them trouble lol. Who am I kidding, nobody is really going to read this, just some headline on facebook or the like.

Sal Santamaura

Interesting comments, but I expect the entire thread will be irrelevant two and a half months from now.