Viewing a single comment thread. View all comments

yesimon t1_jdwjkv3 wrote

You don't want an HVAC engineer (people who prototype HVAC equipment to be made in factories), and as you correctly surmised most contractors won't put in much effort on system design either.

Given this is a condo in Cambridge, it likely is a very old building. This means even Manual J calculations by "diligent HVAC contractors" are probably very inaccurate. The best way to size a system would be to use your historical fuel consumption from past years https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler. This will be the most accurate way to determine your empirical heat loss, which would determine sizing, the most important design factor in a heat pump.

Further details about system design and selecting equipment will depend on your specific needs and considerations.

4

Murky_Ocelot_6737 OP t1_jdwm2qp wrote

It's actually fairly recent (2008) but the furnace is nearing end of life.

Who should I get in touch with to get that done for me? I'm only managing the unit, not owning it, but both the owner and I would like to get it done correctly.

1

yesimon t1_jdwnjao wrote

For calculating historical heat loss that is for you to do. Outside contractors don’t have your historical fuel bills.

Since you have central ducting, system design is easy - any HVAC contractor can install a appropriately sized central heat pump to replace a furnace.

Final note is that the operating cost of a heat pump in Cambridge is currently more expensive than a natural gas furnace.

2

andrewsinclair t1_jdxjmu9 wrote

I replaced two furnaces with a heat pump and two air handlers, and my experience is that operating costs are higher, particularly in Feb. It drives me crazy that almost every article about heat pumps pivots to comparing them to electric resistance heat in the second paragraph and implies they’re cheaper to operate than gas.

Anyway, I have no regrets and I like the heat pump, I don’t want a consumer backlash against them due to the media setting unrealistic cost saving expectations.

3

Murky_Ocelot_6737 OP t1_jdyznl9 wrote

Thanks for sharing this. I have found others with similar experiences. When did you switch? Do you mind sharing the brand and model that you have?

‘’I’m trying to figure out if the latest ones, that are rated for even lower temperatures might overcome this problem.

1

andrewsinclair t1_jdzjj4c wrote

It has been three years I think. I have a Mitsubishi. The Mitsubishi seems to be everywhere.

I should also mention that operating costs of course depend on electricity rates. I have the Cambridge municipal 100% renewable plan. My rate with delivery is $0.30/kWh. That’s another annoyance with news articles; they often assume a much lower rate. I think they omit delivery charges, but I guess there are places in the US where electricity really costs half of that.

2

dyqik t1_jdx7thv wrote

That expense will depend on the ambient temperature. The efficiency of heat pumps is a lot better at 50F ambient than 35F - like double or more.

My home's crossover on a third party supplier electric tariff is currently around 40F.

1