Honeywell Evohome (British smart TRV/thermostat) in US one-pipe system?

david_and_heather

I have one-pipe steam with a newish Burnham boiler in a 1923 Colonial-style home in NJ. I was reading yesterday about the Honeywell Evohome. This is a smart thermostat system that has smart thermostatic valves: in addition to turning your boiler on and off, it will turn individual radiators on and off, essentially creating a zoned system with one zone per room. Amazing.

This thing is only sold in the UK. When I contacted Honeywell, they told me that they don't recommend using it in the US because it's designed for the UK. Not helpful--what, exactly, is the incompatible part?

I found a discussion on Stack Exchange that dealt with this question. They said that you can't use such a system in the US because the radiators are connected in series. I'm not a plumber, but I don't see how one pipe can be a series: every radiator terminates a pipe. I guess they are all connected to the same main, but that still seems parallel to me.

Is there anything technical stopping this product from being sold in the US? If it ever is sold in the US, is there any reason why it wouldn't be compatible with a one-pipe system like mine? Is there anything, from a technical sense, that would stop someone bold and/or foolhardy (not me, I promise) from buying one of these guys in the UK and installing it on a US system?

Fred

This sounds like it is problematic on a conventional one pipe system. There are TRV's available that can be installed on a few radiators on a system that will prevent air from escaping the radiator and consequently pretty much prevent the radiator from getting hot. They are designed for areas that overheat and where adjusting the vent size isn't sufficient.
The problems I see with this system on a one pipe steam system are:
- Steam boilers are sized for the total connected EDR (Radiation). Many are already over-sized. With every radiator you shut off, the boiler becomes more and more over-sized. That will cause the boiler to short cycle, probably on most if not all heating cycles. Short cycling on pressure is not fuel efficient and adds additional wear and tear on gas valves/other control devices on the boiler.
- If any single zone (room) calls for heat, the entire boiler will run to heat that one room. Remember the boiler was designed to heat the entire house. Why would you want to run a boiler full out to heat individuals rooms, one at a time? You can't just use one tenth or one quarter or one half of the boiler.
- I would envision the boiler running (and short cycling) almost all season because one room or another calls for heat.

On one pipe systems, radiator vents are designed in various sizes and even adjustable to allow more or less steam into a radiator. What exactly are you trying to accomplish with the system you are considering? Fuel efficiency? Not going to happen, Different temperatures for each room? Why would your comfort requirements change from room to room?
Spend your money improving and maintaining your steam system. Make sure you have great main venting so you can balance your radiators, make sure the boiler/burners are clean and working like it should, replace any leaking radiator vents, correct any leaks in piping and radiator inlet valves. Let the system work for you.

Jamie Hall

Connected in series? On steam? Never. Neither one pipe nor two pipe. Whoever wrote that was clearly clueless about steam.

That said, @Fred 's comments are right on the mark. It is possible to use a few TRVs on the vents of a one pipe system and not cause really significant problems. The emphasis is on "few" -- by which I mean less than 10% of the installed radiation. Anything more than that and the evils Fred mentioned will happen.

Follow his last paragraph.

KC_Jones

Couple of points even more basic than above. First if it's designed for U.K. they don't use NPT threads they use BSP which are straight none tapered threads, so they wouldn't hook to your rads. There are probably adapters I'm just not a fan (personal opinion alert). Second as far as I know U.K. doesn't use steam heat in residential applications so this isn't designed for steam only hot water. Also as has been said on one pipe the TRV goes on the vent not the supply pipe. Supply piping is to be fully open at all times on one pipe steam.

david_and_heather

Thank you all!

i07nyc

I was thinking about ordering this system from the UK. I have hot water with cast iron radiators. I think if I put danfoss valves on my radiators the evohome controllers should fit. My only concern is if the Wi-Fi is compatible. Anyone else see any other problems?

Ironman

You'll get better response by starting a new thread.

Jamie Hall

Ironman said:

You'll get better response by starting a new thread.

True enough, @Ironman -- but for the benefit of @i07nyc , the unit was probably designed for 50 hz 240 volt power. That we do not have. Why not choose something designed for what we do have?

i07nyc

Jamie, no company sells anything remotely similar in the u.s. I can tear open walls and replumb the whole house to zone everything or try this system. Good point though on new thread

Ironman

Another thing to consider: what type of boiler do you have and how is the system piped?

Zoning up a low mass boiler is bad idea and some piping methods don't allow zoning individual rad's.

If your boiler and piping arrangement will allow it, TRVs would probably be a more practical solution.

i07nyc

Just for anyone else in the U.S. thinking about trying this system, the main problem is the thermostat voltage. I'm pretty sure I can get everything else to work but the voltage differences are a problem.

Ironman

I think it's more than just voltage. Honeywell could very easily make it for US voltage. There's obviously a reason they don't.

In Europe, hydronic systems are installed and maintained by certified techs who are well versed. Homeowners are required by law to have one these techs come out annually and inspect and maintained the system.

In America, this is not the case. In fact, just the opposite is true: most "plumbers"or "techs" are pretty much clueless about hydronics. That's why this site exists. Plus, we have a lot of DIYs that attempt repairs or modifications, but lack proper knowledge of how things really work.

Honeywell is aware of this and of the different piping methods that have been frequently employed here that won't allow for individual zoning. Knowing the different circumstances here, and the issues that would frequently arise from them, they're not gonna sell that product in this market.

It's simple: when the product is mis-applied and doesn't work, the product is what gets the blame, not the knucklehead that installed it.

That's why I asked before and will again: how is your system piped? If the piping method won't allow individual zoning, it won't work.

i07nyc

I know what your saying. My house ( 3 story 1904 built) actually has each radiator on its own loop except for 1 radiator on the 3rd floor which we don't use the room anyway. For my situation I'd be a good candidate but I know many people whose houses are not plumbed the same way where evohome would not work.

Ironman

I'll think you'll find that TRVs are you're best option if you're really sold on going this route. They'll work well with any type of boiler in that old system as long as it's pumped and not gravity flow anymore. Of course, they won't call the boiler on, so you'll have to have your stat location to be optimal.

LJPurvis

I, too,have thought of purchasing the Honeywell Evohome system. I live in an area with Geothermal. The water is pumped into our house at a constant pressure like city water. It comes in at 165 deg. It is an open system. Once we use it we dump it into a creek behind the house.

Each room gets its own supply. Some rooms have a single radiator and some have two. All the “return” lines of each room feed to a master return. This master is what feeds outside for dumping. The whole house is currently controlled via a single thermostat on the main floor which controls a valve the controls the main dump line outside.

I would like to take the whole house control to individual room control. Honeywell’s Evohome looks like the perfect solution. Reading this thread I am rethinking that thought. Maybe Nest with wireless relay switches.

Any thoughts on this?

ChrisJ

I'm curious to see what these are. I highly doubt the system runs on 230v and I doubt it cares about line frequency. More likely it runs on 5-12v DC or close using a small power supply.. I assume the TRVs use batteries.
Few things care about line frequency. Some clocks do most electronics do not.

I don't know if it'd work out of the box but I bet it could with minor work.

nicholas bonham-carter

LJP- It seems you have a hot water system, which may be more like the systems for which the Evohome was designed to control, however, there are various means of improving your heating comfort which are designed for US domestic systems, which work well, and are able to be serviced by your local professional hydronic expert.
Are you having heating comfort problems which lead you to consider this unusual, (for us), route? Don’t forget to start a new thread.—NBC

LJPurvis

I have started a new thread. We are having a few comfort problems; mostly due to the fact that the thermostat that controls the return shutoff valve for the whole house is in the dining room. This can create a very warm upstairs and cold spots in the main floor.

50ketchcourt

I live in Canada and have an evohome installed on a hot water radiator system with 6 x HR92 trv’s.
Bought it all in the uk and installed myself as there was nothing available over here.
For power I use a 110/230 transformer but will be wiring direct to the 220v breaker.
It works amazingly well and now have zone control of all my bedrooms.
No idea why Honeywell won’t sell this in North America.

Jamie Hall

"No idea why Honeywell won’t sell this in North America"

You don't? It's designed and intended to run on 220 volt 50 hz single phase current, to European standards. It's not designed or intended to be run on 120/240 volt 60 hz North American current. It's not listed for it, and -- with so many other Honeywell products which are designed to UL and CSA standards and listed -- it's not worth the time and effort.

You can use it -- but you're on your own if it causes a problem. Your insurance won't go near it.

PC7060

I really like the EVoHome setup myself.  Not sold in US because the size of our radiator conversion market isn’t large enough to warrant the design updates. 

And really, how hard is it to walk in room and twist a standard TRV knob?  Course I don’t see a lot of those being installed in Virginia either. This more a remove and replace area.